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imist

NIST Special Publication 887

Composite Materials for Offshore Operations:

Proceedings of the First International Workshop

Houston, Texas

October 26-28, 1993

Edited by

S.S. Wang

D.W. Fitting
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NIST Special Publication 887

Composite Materials for Offshore Operations:

Proceedings of the First International Workshop

Houston, Texas

October 26-28, 1993

Edited by

S.S. Wang, University of Houston

D.W. Fitting, National Institute of Standards and Technology

Materials Reliability Division

Materials Science and Engineering Laboratory

National Institute of Standards and Technology

Boulder, Colorado 80303-3328

Sponsored by

Minerals Management Service, U.S. Department of the Interior National Institute of Standards and Technology, U.S. Department of Commerce

University of Houston

Co-sponsored by

U.S. DEPARTMENT OF COMMERCE, Ronald H. Brown, Secretary

TECHNOLOGY ADMINISTRATION, Mary L. Good, Under Secretary for Technology

NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY, Arati Prabhakar, Director

Ameron, API, Amoco, Brunswick, CNEB, Conoco, DuPont,

Exxon, Hercules, Shell, TCSUH, U.S. Navy

August 1995
National Institute of Standards

and Technology

Special Publication 887

Natl. Inst. Stand. Technol.

Spec. Publ. 887

396 pages (Aug. 1995)

CODEN: NSPUE2

U.S. Government Printing Office

Washington: 1995

For sale by the Superintendent

of Documents

U.S. Government Printing Office

Washington, DC 20402
Abstract

The First International Workshop on Composite Materials for Offshore Operations was held on

October 26-28, 1993, at the University of Houston, Houston, Texas. This international workshop

provided a forum for attendees to review the current state of practice and to assess the current state of the art in using composite materials for offshore petroleum exploration and production operations.

It also addressed research issues which might mitigate the gaps between the current practice and the

state of composite technology to allow economic and enabling utilization of composites by the

petroleum industry. The issues addressed in keynote presentations and working group discussions

spanned a broad spectrum of scientific and engineering concerns, including: materials systems;

fabrication and construction; material performance; long-term durability and environmental effects;

structural design, testing, and reliability; nondestructive evaluation and condition monitoring;

flammability and fire safety; nonstructural applications; advanced applications; regulatory concerns; and certification issues. There were over 225 participants in the workshop representing the petroleum

industry, manufacturers, design engineers, certification organizations, and academic institutions. This

proceedings of the workshop contains 35 invited lectures and papers, discussions, summaries, and

recommendations of the 8 working groups, as well as critical assessments and recommendations of

needed research and development on advanced composites for deep-water offshore exploration and

production operations.

Key Words: advanced materials, certification, composites, construction, damage tolerance,

environmental degradation, fabrication, flammability, fire safety, FRP, GRP, maintenance, NDE,

nondestructive testing, inspection, offshore platforms, structural design

Except where attributed to NIST or MMS authors, the content of individual sections of this volume has not been reviewed or edited by the National Institute of Standards and Technology or the Minerals Management Service. NIST and MMS therefore accept no

responsibility for comments or recommendations therein. The mention of trade names in this volume is in no sense an endorsement

or recommendation of the National Institute of Standards and Technology or the Minerals Management Service.

iii
IV
Contents

Page

Executive Summary 1

Summary and Recommendations 5

"Advanced Composites Offshore: Current Status andA Proposed R and DProgram" 7

B.W. Cole, Amoco Corporation, Naperville, Illinois K.H. Lo, Shell Development Company, Houston, Texas

J.G. Williams, Conoco, Inc., Ponca City, Oklahoma

S.S. Wang, University of Houston, Houston, Texas

1. Introduction 19

2. Workshop Program and International Steering Committee 23

3. Invited Presentations—Government and Industrial 29

3.1 "U.S. Minerals Management Service's Perspective on Compositesfor 31

Offshore Operations and Safety Management,

H.G. Bartholomew, Minerals Management Service, U.S. Department of the

Interior, Herndon, Virginia

3.2 "Approach ofNational Energy Board on the Use ofComposites in the 35

Petroleum Industry" G.R. Yungblut, National Energy Board, Calgary, Canada

3.3 "UK Governmental Perspective" 39

M. Bishopp, Health and Safety Executive, Liverpool, United Kingdom

3.4 "Norwegian Authorities' Perspectives on Composite Materials for 43

Offshore Operations" T.G. Dahle, Norwegian Petroleum Directorate,

Stavanger, Norway

3.5 "An Engineering Documentation Schemefor GRP in the Oil Industry," 47

C.J. Houghton, Phillips Petroleum Company United Kingdom Ltd.,

Surrey, United Kingdom

V
Page

3.6 "OLF's Involvement in the GRP Industry," 65

J. H. Jenssen, Conoco Norway, Inc., Stavanger, Norway

4. Keynote Addresses 69

4. 1 "Petroleum E&P Industry Perspective on the Use ofComposites in 71

Offshore Operations," B.W. Cole, Amoco, Corporation, Naperville, Illinois

4.2 "Petroleum Industry Applications ofComposites in E&P Operations," 77

J.G. Williams, Conoco, Inc., Ponca City, Oklahoma

4.3 "Composite Materials for Offshore Operations, Industry Perspective," 83

G.G. Robertson, Ameron, Inc., Pasadena, California

4.4 "Marine Composites—The U.S. Navy Experience, Lessons Learned Along 91

the Way," IX. Caplan, U.S. Naval Surface Warfare Center, Annapolis, Maryland

4.5 "Advanced Composites: Shaping Tomorrow," 115

J.M. Bowman, DuPont Advanced Materials Systems, Newark, Delaware

4.6 "Studies Relating to the Use ofFibre Reinforced Composites in the 117

Offshore Industry,"A.G. Gibson, Centre for Composite Materials Engineering,

University ofNewcastle upon Tyne, Newcastle upon Tyne, United Kingdom

5. Working Group Papers 129

5 . 1 "Materials Developmentfor Cost Effective Fabrication," 131

D. Wilson, Fibers and Materials, BP Chemicals (Hitco), Santa Ana, California

5.2 "Polymer Composites Program in the Polymer Division atNIST," 139

RS. Parnas, G.B. McKenna, and D.L. Hunston, Polymer Division,

National Institute of Standards and Technology, Gaithersburg, Maryland

5.3 "Polymer Composite Materials Performance Criteriafor Offshore 149

Petroleum Production: An Overview," J.P. Dismukes and M.J. Luton,

Exxon Research Engineering Company, Annandale, New Jersey

5.4 "Characterization ofComposite Materials," 161

G. Hansen, Hercules Materials Company, Magna, Utah

5.5 "Some Perspectives on the Use ofCompositesfor Offshore Operations" 171

S.S. Sternstein, Rensslaer Polytechnic Institute, Troy, New York

vi

J
Page

5.6 "Material Performance: Micromechanical Modeling ofComposite Fracture," 175

J.A. Nairn, Material Science and Engineering Department, University ofUtah,

Salt Lake City, Utah

5 . 7 "Impact Damage Tolerance ofFRP Composites in Offshore Applications," 185

F.S. Uralil, Shell Development Company, Houston, Texas

5 . 8

"The Effect ofSeawater on Polymeric Composite Materials," 1 93

W.L. Bradley, P.L. Chiou, and T.S. Grant, Offshore Technology Research

Center and Mechanical Engineering Department, Texas A&M University,

College Station, Texas

5.9 "Influence ofSeawater on Transverse Tensile Properties ofPMC," 203

L.A. Carlsson and F. Pomies, Department of Mechanical Engineering,

Florida Atlantic University, Boca Raton, Florida

5.10 "Assessing the Glass Epoxy Interface after Environmental Exposure" 213

H.D. Wagner, A. Lustiger, and S. Ling, Exxon Research and Engineering

Company, Annandale, New Jersey

5.11 "Analysis-Based Design Toolsfor Offshore Application," 227

S.W. Tsai, Stanford Composites Design Center, Department of Aeronautics

and Astronautics, Stanford University, Stanford, California

5.12 "Composite Applications in Offshore Operations," 233

K.H. Lo, Shell Development Company,

Westhollow Research Center, Houston, Texas

5.13 "Flammability and Fire Safety ofComposite Materialsfor Offshore 24

1

Operations," T. Kashiwagi and T.G. Geary, Building and Fire Research

Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland

5.14 "Fire, Smoke, and Toxicity Research with Composite Pipe," 253

K. Schmidt, Specialty Plastics, Inc., Baton Rouge, Louisiana

5.15 "Twenty Year History ofSuccessful Applications ofComposite Pipe in 26

1

Sea Water Service," RH. Lea and K. Schmidt, Specialty Plastics, Inc., Baton Rouge, Louisiana

5.16 "Advanced Compositesfor the Offshore Industry: Applications and 269

Challenges," M.M. Salama, Conoco Inc., Ponca City, Oklahoma

5. 17 "Using Composite Materials to Protect Vulnerable Equipment Against 289

Jet Fires," L.C. Shirvill, Shell Research Limited, Thornton Research Centre,

Chester, England

vii
Page

5.18 "A Course ofAction for Introducing Composites into Offshore Operations " 295

F.J. Fischer, Shell Development Company, Houston, Texas

5.19 "Flammability and Fire Safety ofComposite Materials," 309

U. Sorathia, Carderock Division, U.S. Naval Surface Warfare Center,

Annapolis, Maryland

5.20 "Safety Philosophyfor the Use ofComposite Materials Offshore" 319

S.W. Ciaraldi, Amoco Norway Oil Company, Stavanger, Norway

6. Working Groups and Discussion Summary Reports 327

7. List of Workshop Participants 363

8. Author Index 385

viii
Executive Summary

Executive Summary

With ever-increasing challenges in developing deep-water offshore structures for petroleum exploration and production, composite materials technology is expected to play a more

important role in meeting the stringent requirements of cost-effective operations and enabling the

capability of petroleum technology and its supporting industries. Composite materials offer

substantial weight reduction, superior corrosion resistance, long fatigue life, outstanding

vibrational damping and energy absorption, and the unlimited potential of innovative material and

structural tailoring to meet desired performance requirements. Along with low maintenance, low

total-life-cycle costs, and ease of fabrication, construction, and installation, composite materials

and structure are ideally suited for immediate and future deep-water challenges. They offer high

potential payoffs that are just beginning to be explored and represent a large potential opportunity

for U.S. and world industry. Realizing this great potential will require understanding the existing

technology and future development of composites, the specific requirements and economic

restraints of deep-water offshore applications, and certification and other regulations.

To provide an open forum for leading experts from industry, government, and academia

throughout the world to address these issues, the First International Workshop on Composite

Materials for Offshore Operations was held 26-28 October 1993 at the University of Houston in

Houston, Texas under the joint sponsorship of U.S. Minerals Management Service, the National

Institute of Standards and Technology of the U.S. Department of Commerce, and the University

of Houston. Other sponsors included American Petroleum Institute, Ameron, Amoco, Brunswick,

Canadian National Energy Board, Conoco, DuPont, Exxon, Hercules, Shell, Texas Center for

Superconductivity at the University of Houston, and the U.S. Navy. The enthusiasm of the

participants (211 from many nations) resulted in a productive meeting.

The goals of the conference were (1) to review the current stat of the art and assess

current practice in utilizing composites for offshore operations; (2) to identify gaps between the

state of the art and the state of practice; (3) to determine and prioritize research initiatives that

might mitigate these gaps and enable safe and economical use of composites by the oil industry;

(4) to bring new opportunities to the oil and gas industry through proper and innovative

applications of composites; and (5) to provide guidance to petroleum and engineering-service

industries for certification of composite offshore structures and components.

The workshop, which lasted two and a half days, consisted of eight working-group

sessions and one summary session. More than 45 papers were presented, including 6 invited

presentations on the perspectives of government and industry and 6 keynote addresses delivered

by world leaders in their respective technical areas. The presentations provided a comprehensive

overview of the current status of composites applications in the offshore industry, the state of the

art in various areas of petroleum composites technology, and the certification and regulatory

agencies' perspectives on the utilization of composites in offshore exploration and production

operations.

3
The eight working group sessions focused on topics selected by the international steering

committee of the workshop: (1) fabrication, construction, maintenance, and repair; (2) material

performance, damage tolerance, durability, and environmental degradation; (3) structural design,

optimization, testing, and reliability; (4) nondestructive evaluation; condition monitoring and

inspection; (5) flammability and fire retardation; (6) facilities and secondary structural applications; (7) advanced applications; and (8) certification issues and policy concerns. In each group,

leading experts, invited by the steering committee, made presentations and guided and stimulated

the discussions.

In the concluding session, the chairmen of the working groups summarized the discussions

and reported the recommendations of their respective groups. Representatives of the international

steering committee —B. W. Cole of Amoco, K. H. Lo of Shell, J. G. Williams of Conoco, and S.

S. Wang of the University ofHouston — provided a document that summarized the current status and recommended a comprehensive R and D program for advanced composites offshore.

This proceedings describes the scope, the organization, and the program of the workshop.

It contains a summary, recommendations reported by the steering committee representatives,

invited lectures, keynote addresses, and most of the papers presented in the working-group

sessions. Also included are a list of working-group chairs and panelists and their discussion

summaries. A list of registered workshop participants is given at the end of this volume.

S. S. Wang

Workshop Chairman and Coeditor

4
Summary and Recommendations
6
SUMMARY AND RECOMMENDATIONS

ADVANCED COMPOSITES OFFSHORE: CURRENT STATUS AND A

PROPOSED RESEARCH AND DEVELOPMENT PROGRAM

by

B.W. Cole, Amoco Corporation

K.H. Lo, Shell Development Company

J.G. Williams, Conoco, Inc. S .S. Wang, University ofHouston

1 . INTRODUCTION

The petroleum industry is gradually building increased acceptance of fiberglass reinforced plastic

(FRP)materials. Some companies make extensive use of FRP pipe for onshore hydrocarbon

gathering and transmission lines. A few companies have used FRP downhole tubing products.

In offshore applications there is limited use of FRP products in secondary structure such as cable

trays, walkways, railing and grating. Recent developments in the North Sea area have resulted in

projected increased usage of FRP pipe for various types of low pressure water service offshore.

Industry acceptance of advanced composites, however, is still in the early stages of development.

Feasibility work on production risers constructed of carbon/glass fiber laminates was started in

1980. The results of that work have been positive, yet there are no advanced composite systems in

service offshore today nor are there any commercial products available.

Studies have shown that some offshore advanced composite applications could greatly reduce

capital requirements, decrease maintenance costs or enable operations that are technically or

financially infeasible with state of the art materials. The petroleum industry has great interest in

these products. However, many are primary structural systems or high pressure hydrocarbon

piping systems, the consequence of failure in these systems is very high, involving safety risks,

environmental risks, and the financial risk of losing infrastructure.

The investment required to develop reliable commercial products for high risk applications is very

large - more than suppliers can afford. The investment is also more than any one petroleum

company is likely to commit to at this time. Each offshore platform represents an investment in excess of one billion dollars. The use of new materials systems such as advanced composites in

critical systems would be a huge risk - a risk that petroleum companies are not likely to take until it aligns with a strong industry need, offers clearly demonstrated benefits, and is based on

technology that is well characterized, and understood.

The need for alternative materials is developing quickly in the petroleum industry. The pressure is growing to reduce the cost of exploration and production and there is strong evidence that

advanced composites could reduce costs. There is increased interest in developing deep water

leases in the Gulf of Mexico to increase US reserves and advanced composites could be utilized to reduce the cost of deep water facilities. Many undeveloped fields in the Gulf of Mexico and in the

North Sea are small. Development of those fields will be feasible only with the development of

7
as well. But advanced composites will be used in these applications only if the work is initiated soon to develop the technology base that is needed to gain industry acceptance.

2. PROPOSED FOCUS AREA

There is a large advanced composites technology base in this country that has been developed to address the materials needs of the defense, aerospace and commercial aircraft industries. A similar

technology base must be developed to use advanced composites products successfully in offshore

applications. Some of the needed technology can be transferred from the existing base and adapted

to the offshore environment. But a major investment in an expanded technology base is needed to use these materials on a commercial basis.

A large focused program is proposed to assist with this effort. The program could be described as follows:

"Development of the reliability data base, the design methodology and software, the manufacturing

technology, the construction technology, and the smart structure sensor technology needed to

utilize advanced fiber composites in critical offshore exploration and production (E&P)

operations ".

3 . PROGRAM OBJECTIVES

The technical objective of the proposed program is to identify and resolve each of the barriers that

limit the acceptance of advanced composites for critical applications by the petroleum industry.

This effort would start with a survey to access in detail the needs of the petroleum companies and

engineering firms that design and specify offshore structural systems. Technology development

programs would be formulated to address each of the critical needs that limit the acceptance of

advanced composite materials for critical systems. The programs will involve multi-disciplinary/

multi-industry teams that include all parties needed for commercialization.

The business objective of the proposed program is to develop a path to commercialization by

involving key companies in the development programs from each element of the supply chain and

from a broad spectrum of user engineering groups. The development programs would include

economic analysis at key junctures to assure that technology development is strategically aligned

with industry business needs. Further, market potential will be defined and updated frequently so

that companies on the supply side have accurate information. It will be critical that all parties

involved have current business opportunity information to maintain a sense of urgency and to minimize the cycle time required to develop each technology element.

The U.S. Air Force sponsored programs in the 60' s were successful in developing aircraft

applications for advanced composites because they focused on the needs of the engineering groups

that design and specify structure. The same strategy is proposed for this program. We intend to build acceptance by first developing applications that are low risk, moderate payoff and can be

implemented near term (1995-200) while developing the technology base for high risk, high payoff

applications that will be implemented long term (2000 and beyond). Table 1 shows some

preliminary projections for usage of composite components over the next ten years. Spoolable

pipe for water injection would be an example of a low risk application that can be developed early

in the program to develop the experience needed for acceptance of high risk applications, such as hydrocarbon pipelines, late in the program.

8
4. TECHNICAL BARRIERS

Five technology issues are defined at this time as barriers to utilization. As stated above most

applications are in critical systems. The consequence of failure in these systems is very high. The

safety of the production platform is at risk should failure occur in a tether and there is environmental and financial risk should failure occur in a riser. So the most important technical

barrier is reliability. The design of critical components must be based on statistical materials data

bases and probabilistic design methodology must be developed to satisfy rigorous risk assessment

analysis.

The second barrier is the absence of manufacturing technology needed to produce cost effective

offshore structure. For example, most offshore applications require tubular structural elements.

Batch process filament winding manufacturers are limited to lengths ranging from 30 to 75 feet, so

frequent connections are required. Connections increase the probability of failure and add

substantially to the cost of the installation. The proposed program would focus on the

development of a continuous process for manufacture of long composite tubular profiles. This

program will include the development of robust resin cure technology and the use of sensors and

process control techniques (intelligent processing) to assure quality and to minimize product

variability.

The third barrier that is anticipated is design methodology and composite structure design software

that is user friendly. The design software that is available is fragmented and not user friendly in the sense of modern software packages. The capability to design complex composites systems lies in the hands of a few experts and the comprehensive software packages are privately owned. It is proposed that funds be used to develop a comprehensive design software package applicable to offshore structural systems. This is a large task that requires characterization work on material

systems conditioned in offshore environments and extensive development of design/analysis

methodology applicable to offshore types of structures. The objective of this task is to make it relatively easy for knowledgeable structural engineers to design composite structures.

The fourth barrier is the lack of construction techniques, equipment and experience with

composites in offshore operations. The proposed program would focus on industry needs for

construction with continuous composite tubulars. All aspects of offshore construction will be

addressed including storage, transport, submersion and installation of continuous tubular goods.

Innovative construction techniques will be sought to minimize installation costs which is a large

portion of total costs with state-of-the-art carbon steel construction. So it is very important to include installation in the effort to develop positive economics for alternative materials.

The fifth technical barrier relates to the reliability of composite offshore systems during service.

Imbedded sensor technology will be developed for real time monitoring of offshore composite

structures to assure that critical systems are not compromised by unanticipated service conditions.

5. PROPOSED R&D PROGRAMS; SCOPE & FOCUS

To overcome the major technical barriers aforementioned in Section 2, the scope of the proposed

program will focus on cutting-edge advanced composites technology R&D with a high degree of

technical risk, but would offer significant opportunities to leverage major advances for petroleum E

& P operations with high payoff of billions of dollars for several groups or sectors of industries.

The proposed program embraces a number of interrelated projects and new critical industrial

capabilities. These high-risk, high-payoff projects are critical to successful development of

9
market-driven offshore products and their commercialization, such as composite platform tethers,

composite production risers, various composite subsea pipe lines and spoolable composite pipes,

for deep sea E & P operations. These interlocking R&D projects will complement each other and

provide the synergy that will have the greatest impact not only on the petroleum energy E & P and

its supporting technologies but also on the economy of a number of sectors of industries. Also,

included in this section are some of the major potential participants from various sectors of relevant

industries, national and governmental laboratories, and academic institutions, which can be

organized to form a proper team for each of the projects.

5.1 Reliability

The composites offshore reliability technology development will address the most critical technical

barrier that prevents the petroleum E & P industry from large-scale utilization of the radically new

and different material systems to realizing their fullest potential. The objectives of this project are

to establish innovative technology bases for understanding, characterizing and controlling

materials, manufacturing and structural reliability of offshore composites and to conduct the proper

risk assessment to meet the requirement of regulatory agencies.

a) Material Reliability

Large-scale system studies need to be conducted to determine various optimal

combinations of resin and fiber systems suitable for different offshore components and

structures. Distinct damage mechanisms and failure modes need to be identified and

formulated into material system tailoring and reliability design. The effects of marine

environments on mechanical properties of different polymer composites should be

determined and documented. The issue of long-term creep and durability of fiber

composites on the integrity and safety of offshore components and structures is of critical concern. Model development and a statistical data base are essential to ensure proper

evaluation of long-term material performance and associated size effects.

b) Manufacturing Reliability

Offshore composites product variability is governed by manufacturing reliability. Quality assurance is most critical in ensuring the manufacturing reliability. Effects of

manufacturing parameters on the product variability should be determined by proper

processing modeling of offshore composites. Associated measurement techniques need

to be developed, and a data base on the offshore composites manufacturing reliability

should be established to provide quantitative information on this issue. Development of

proper methodologies and associated techniques to effectively control and optimize

offshore composites product variability should be made to ensure the manufacturing

reliability.

c) Structural Reliability

Development of acceptable methods (or tools) is needed for performing system reliability

analysis of complex or novel composite offshore structural systems. Establishment of

analytical methods is required to describe/analyze the joint occurrence of environmental

variables and loads in a probabilistic domain to form input to system risk/reliability

analysis of composite offshore systems. Research is also needed to quantify the

probability of detection and sizing of structural defects and their effects on composite

10
offshore structural failure. Modeling and experimentation should be conducted on crack

initiation and growth in complex components, e.g., offshore composite joints and

fittings. Of particular interest is development of probability-based analytical methodology

to relate the composite offshore component reliability to the overall system reliability.

5.2 Continuous Process for Manufacture of Long Composite Tubulars

Nearly all the major offshore components targeted for advance composites are tubular with thick

walls. Significant economical benefits and production advantages can be realized if an automated

continuous manufacturing technology can be developed for this class of advanced composite

products. The emphasis of this project should be on high-speed intelligent manufacturing

technology development, especially for very long length composite tubulars. the development of

high-speed continuous processing technology for advanced offshore composites should include the

following:

a) Manufacturing processes: filament winding, pultrusion, resin transfer molding, braiding,

combined filament wind and pultrusion, other innovative methods

b) Material forms: dry fibers, hybrid fibers, wet winding, prepreg tape winding, woven

fabrics, preforms, other reinforcement forms

c) Intelligent process control: curing monitoring and control, fiber placement tension,

compaction/consolidation, embedded sensor technology, instrumentation development,

process modeling

d) Product variability: quality assurance, product variability evaluation & control, effect of

product variability on material properties

e) Manufacturing economics

5.3 Design Methodology and Composite Structure Design Software

The objectives of this project are to develop analytical methodologies and associated advanced

design capabilities for construction of advanced offshore composite components, and establish

critical material and component performance criteria for modeling, design and validation.

Successful developments of these methods and design capabilities will accelerate large-scale

utilization and rapid commercialization of advanced offshore composite products in petroleum E &

P, maritime and advanced materials industries. The broad range efforts planned in this project

should include:

a) Advanced Analytic Methodology Development: Composite lamination theory/analysis

for thick-wall cylindric shells, multiaxial failure (strength) for thick wall composite

tubular, multiaxial cyclic fatigue degradation and failure, long-term creep and its effect on

leakage, life prediction for long-term performance and failure, optimization for material

selection, lamination tailoring and structural performance, transportation and installation

induced stress and damage, dynamic, environmental and probabilistic loading based

reliability analyses.

b) Integrated computer-aided design tool development and artificial intelligence:

11
Based on the above advanced analytic methodology development, an integrated

computer-aided design tool or software package development program should be

attempted. This effort should include: material system models, multiaxial failure

(functional or structural) modes and criteria, environmental effects assessment and

probability modeling of damage tolerance and residual properties, 3-D effects involving

transverse deformation and bending and torsion economic/cost, analyses and modeling

reliability-based design with performance goals and acceptability criteria, design norms

and life-cycle optimization.

c) Associated Critical Performance Characteristics Evaluation:

The purpose of this effort is to establish critical performance data bases for modeling,

design and final validation of offshore composite components in actual service

environments. A large-scale, system effort is needed to establish the following critical material and structural performance data bases for design and evaluation.

- damage evolution and tolerance

- multiaxial failure modes and failure criteria

- environmental degradation and failure

- long-term creep and creep failure criteria

- cyclic fatigue and degradation under multiaxial fatigue

- local instability and compressive failure

5.4 Offshore Composite Construction and Installation

The construction project would be used to develop offshore technology for construction with

composite components. The proposed program would focus on needs associated with

construction with continuous or very long composite tubulars. All aspects of offshore construction

will be addressed including storage, transport, submersion and installation of continuous tubular

goods. Innovative construction techniques will be sought which will minimize installation costs, a

large portion of total costs with state-of-the-art carbon steel construction. An example would be

the deployment of a composite tether from a spool.

5.5 Smart Composite Materials and Intelligent Offshore Composite Structures

The objective of this project is to develop offshore composite materials and structures with

embedded sensor technologies for real-time interrogation of material damage and degradation in the

marine environment and for on-line monitoring of composite offshore structural performance

during service. The development of this technology will provide major advances in the industry

capability of improving safety of the critical composite systems and expediting commercialization

of offshore composite E & P utilization.

Advanced composite materials and structures integrated with embedded optical fiber or other sensors represent new and exciting technologies that may revolutionize the development, design

and operations of offshore composite structures and related machineries and equipment. They will

lead to future offshore systems that are safer and easier to maintain and monitor their integrity, and

can sense and correct their structural and environmental anomalies. More advanced intelligent

offshore composite structures may be able to control their stiffness, dynamic configuration,

orientation, rotation and acceleration, etc. In this project, the following areas of research and

technology developments should be considered:

12
a) Fiber optics and other sensor technology development, including

Optical fibers sensors, including intensity based, polarization and various interferometric sensors

Optical time and frequency optical domain reflectometries

Demodulation techniques for fiber optical sensors Other sensor and instruments, such as miniature GC.

b) Smart material technology development

Advanced fiber composites with built-in fiber optic monitoring system (e.g., acoustic

emission, opto-acoustic sounding, etc.)

Material integrity monitoring with optic fiber sensors (e.g., damage growth evaluation)

Potential opto-control systems for offshore composite damage

c) Intelligent offshore composite structure development

Offshore composite structural measurements with fiber optic sensors, including

deformation and vibration and motion, and control.

Active dynamic control of large composite tubulars, including benefits of

embedded/bounded sensors and actuators. Piezoelectric dynamic control application

Mechanical modeling of piezoelectric substructure coupling

Impedance matching of actuators for various functions and offshore composite structural

systems

Active offshore composite structural acoustic control with induced strain actuation

6. ECONOMIC IMPACT

Domestic oil reserves are declining and without further discoveries and development, proven U.S.

reserves at current rates of production will last only another 10 years. Approximately 65% of

United States energy needs are supplied by petroleum while at the same time U.S. oil production in

1993 was the lowest in 35 years. The United States will import approximately 3.1 billion barrels

of oil in 1993, 49.2% of consumption and 53% of the negative balance in international trade.

One promising source for new petroleum production is from deep water (over 2000-feet) in the

Gulf of Mexico. Composite materials could provide a very important contribution to the

development of deep water reserves in the Gulf of Mexico as well as in other parts of the world

such as the North Sea and the west coast of Africa. If composite components are developed and

built by U.S. companies; they could be used to support oil industry needs worldwide, help make

U.S. oil and service companies more competitive in international exploration and production

services and provide significant improvements in the balance of payments.

Some of the potential offshore composite applications are shown in Table 1. Estimates are included for worldwide usage over the next 10 years in terms of product length, material usage in

total pounds, and cost of manufactured components. It should be recognized in this scenario that the development cycle for an offshore platform takes at least five years. So the applications

associated with deep water platforms would not occur before year 2000. The projections in Table

1 assume just 6 floating platforms with composite tethers and risers from year 2000 to 2005, a

conservative estimate considering there are more than 10 deep water platforms under study for the

Gulf alone that could go into production during that time period.

13
The 184-million pounds of composite weight utilization forecast in Table 1 includes composites

constructed of carbon, aramid and glass fibers. Stiffness constraints which govern the design of

some of the components such as the tether drive the design toward the use of carbon fiber while

other components having less demanding requirements normally use glass fiber or hybrids of glass

and carbon. If one assumes that half the projected weight is for fiber and half the fiber weight is carbon, the carbon fiber consumption in the 10-year period would be 41 million pounds. This

would indicate an $8.2 MM annual market for carbon by year 2005 assuming linear development

of the market. The $2.7 billion value forecast in Table 1 for composite components is based on

offshore needs including subsea, but does not include additional expected onshore utilization of

new composites technology.

This is the estimated value of manufactured components and does not include the cost of

installation. Offshore installation costs can be very high ranging from 2 to 8 times the cost of

material in the case of steel construction. We have not tried to estimate installed costs here because

new construction techniques are expected to reduce the cost of composite parts as compared to that of in the installation of steel.

To summarize, we anticipate positive economic effects throughout the supply sector, the utilization

sector, and the entire US economy. The supply sector gains a new market that will replace the loss

of projected defense and aircraft sales. The US offshore engineering firms, the construction

companies and the service companies will develop capabilities with a new technology that will

greatly improve their competitiveness in the world market for petroleum services. The petroleum

companies will reduce the cost of E&P operations generally. More specifically, they can reduce

the investment needed to develop the deep water reserves in the Gulf. As indicated above we badly

need new US reserves. This is an issue that impacts many economic factors, cost of energy,

international trade balance, etc.

7. INDUSTRY COMMITMENT

The petroleum E&P industry uses new technology routinely and generally has high commitment to technologies that meet industry needs. The E&P industry has shown interest in composites as

alternatives to metals to solve several different materials needs. As mentioned in the introduction,

the acceptance of FRP piping for offshore service has increased dramatically over the last two

years in the North Sea area. There are several active joint industry research programs in Norway

and in the UKOOA formed by the petroleum industry to develop the technology base for utilization

of FRP composites on the topside of offshore platforms. Those programs are very active now and

they receive extensive government support. The North Sea programs help, however, they do not

address the use of advanced composites for offshore operations.

The technology base for advanced composites resides primarily in the US. The first US joint

industry program involving the application of advanced composites to petroleum operations was

initiated this year. Several petroleum companies and supporting industries are supporting Hydril in the development of coiled tubing. This is a demanding but noncritical application where

carbon/glass hybrid composites hold promise for extending the capability and the life of small

diameter tubing utilized in downhole operations.

A core group of representatives from the petroleum industry announced at the workshop that they

plan to form a consortia of petroleum companies and supporting industries for the purpose of

developing composite material applications for petroleum E&P operations. The response and the

enthusiasm resulting from the announcement have been very encouraging. The consortia will

corroborate with the formation of the Composites Engineering and Applications Center (CEAC) at

14
the University of Houston. The CEAC is expected to start operation 3/1/94. The first task is to administrate a survey and design study to better define the materials needs of the industry and the

markets for alternative materials.

The activities described above all point to a strong interest and commitment by the industry to pursue the development of alternative materials. The petroleum companies have also shown a

strong commitment in recent years to joint industry development of new technology that benefits

the industry as a whole. That commitment extends to cooperative efforts that involve government

laboratories and government agencies.

The materials suppliers and the manufactures are also quite interested in cooperative programs that will result in new markets. Markets for advanced composites are depressed and the development

of new markets is essential for the survival for many companies. The petroleum E&P industry

may represent one of the few remaining market opportunities for the advanced composites supply

industry.

The development of good information on industry needs and time based markets for alternative

materials will be essential. Current activities on the design of platforms for deep water reserves in

the Gulf of Mexico will be very useful in the development of accurate forecasts. We do not

anticipate a problem in finding participants for projects requiring matching funds.

8. IMPORTANCE OF THE PROGRAM

The DOD has funded the development of advanced composites technology applicable to thin panel

structure used in aircraft. Design methodology, manufacturing technology, materials

characterization and reliability have been addressed as required for aircraft structure. However,

that technology is not applicable to the thick wall cylindrical structure and the environments that are typical of offshore applications.

The summary below compares the existing DOD manufacturing technology to that proposed for

offshore components.

Manufacturing Technology

DOD/Aircraft Skins

Materials Carbon/epoxy

Geometry

Process

Quantities

Size

Cost

Mfg

Structure

Thin panels

Autoclave

2000 lb/AV-8B Plane

12' x 20"

200-750 $/lb

DOD/Missile

Carbon/epoxy

Kevlar/epoxy

Thin wall tubulars

Filament Wind

(batch)

8'D x 20'L x 0.100'T

50-150 $/lb

Offshore

Hybrids

Carbon/Glass/aramide/epoxy

Thick wall tubulars

Filament Wind/Pultrude

(continuous)

2.5MM lb/platform

12"D x 0.75"T x continuous

15-25 $/lb

15
The aircraft skin technology is included because it constitutes most of the DOD inventory. That

technology does not translate at all to the needs for offshore structure. Rocket motor

case/missile/launch tube technology is tubular, but those structures had totally different

performance criteria: light weight/low stress/single mission vs. thick wall/long life/sustained

loading. So, very little of that technology will meet the requirements of offshore structure. In manufacturing technology, the key difference is cost. Industry studies show that composites start to offer significant systems cost savings at 25$/lb. Manufactures contend they are close to that figure with 75 feet batch processing of hybrid fiber composite production risers. Hybrid structures of glass, aramide, and carbon fiber are used to reduce the material costs as much as possible.

The timing is ideal for an industry-government cooperative initiative in this area. As mentioned in the introduction, the use of FRP composites offshore has received a great deal of attention in the

last two years. We expect to see very significant increases in the use of FRP materials offshore in the near future, including piping systems for the upcoming TLP's for deep-water GOM

production. The FRP experience will provide the basis for acceptance of advanced composites

offshore when the technology base is available.

Deep water production in the Gulf will start with the Auger platform in 1994. The Mars platform

and the Ram Powell platforms are scheduled to go into production in '96 and '98, respectively.

These platforms will not use advanced composites because of the technology barriers described

above. The initiative would provide the technology needed for the use of advanced composites on

the deep water platforms projected for year 2000 and beyond. Industry experts have projected that six deep water platforms will be constructed from 2000 to 2010.

Federal funding could make the difference. The supply industry has little capital to invest in new

product development. Experts project significant cost savings in deepwater platforms by using

advanced composites, but reliability is a concern and the technology base is not in place. A very

large investment would be required to develop that technology base. So the industry is proceeding

with metals technology. Advanced composites offshore represents an opportunity that may go

unfilled unless a major initiative is developed to address it. A federal program would provide the means for that initiative.

16
Table 1 - Offshore Oil Industry Composite Applications, Estimated Potential Usage

and Earliest Application over the next Ten Years.

Composite

Component

Quantity Composite

Weight, Million lb Component

Cost, MIIIIon$

Earliest

Application

Tether Six TLP's

in 3000-ft water

16 tethers, 40 risers per TLP

1 5 430 2000

Riser 9 1 80 1 998

Tubing Inside Riser 6 90 1 998

Spoolable Pipe 20-million ft 1"-4" 20 300 1996

Drill Pids 0 5 million ft 5 1 25 11 996 w a v

Drilling Riser 0.1 million ft 1 25 1995

Subsea Structure 5 70 1995

Subsea Pipe Line 3000 mile 50 800 1996 1

2000 z

Mooring Rope 12 Floating Production

Storage Facilities

3 60 1996

GRP Facilities 20 200 1993

Platform Structure 50 600 1998

TOTAL 184 2880

1 Water Injection flowlines

2 Hydrocarbon flowlines

17
18
1. Introduction

19
20
1. INTRODUCTION

Composite materials are increasingly being considered for use in offshore petroleum production

engineering operations. This is particularly true for deep-water offshore platform and drilling

technologies. Composite materials are recognized to offer substantial weight reduction, superior

fatigue and corrosion resistance, outstanding acoustic, vibration damping and energy absorption, and

unlimited potential of innovative material and structural tailoring to desired stiffness and strength.

Coupled with low maintenance and low total life-cycle costs and ease of fabrication and construction,

composite materials are an enabling technology ideally suited for both immediate and future deepwater challenges and offer the highest payoffpotential in the offshore operations. Success in realizing

this great potential will require understanding the existing composites technology base and its future

development, unique structural requirements of deep-water offshore operations, and economic and

reliability constraints in the use of composites.

1.1 Workshop Objectives

To review the current state of the art in composite materials for offshore use, and to assess the

current state of practice for offshore operations;

To identify gaps between the state of the art and state of practice;

To determine and prioritize research initiatives which might mitigate these gaps to allow safe and

economical utilization of composites by the oil industry;

To bring out new opportunities to oil and gas industries through using composite materials and

structures; and

To provide guidance to petroleum and related industries for certification of offshore composite

structures and components.

1.2 Issues Addressed and the Program

The topics covered in the workshop will focus on offshore structural, nonstructural and advanced

applications, including: structural components, mooring systems, risers and tubing, platform (water

and oil) piping, coiled tubing, drilling equipment, completion equipment, and logging and MWD

tools. The issues to be addressed will span a broad spectrum of scientific and engineering concerns,

including: material systems, fabrication and construction; material performance, long-term durability

and environmental effects; structural design, testing and reliability; NDE and condition

monitoring/inspection; flammability and fire safety; GRP applications; advanced applications;

regulatory concerns and certification issues.

21
The workshop was conducted with a two and one-half day program. The first day's program

consisted of a series of invited lectures given by internationally recognized experts. Working group

sessions followed the invited lectures and continued to the second day. Findings from each working

group were presented and discussed in the third day sessions.

1.3 Working Group

Each working group was led by a chairperson and a co-chair, with the assistance of a recording

secretary to facilitate and document the discussions. Working group chairs, co-chairs, recording

secretaries, and panelists are listed in Section 6 (Working Groups and Discussion Summary Reports).

Attendees of the workshop participated in the discussion sessions, in one of the following eight

working groups:

I. Fabrication, Construction, Maintenance and Repair

2. Material Performance, Damage Tolerance, Durability and Environmental Degradation

3. Structural Design, Optimization, Testing and Reliability

4 NDE and Condition Monitoring/Inspection

5. Flammability and Fire Safety

6. GRP Applications

7. Advanced Applications

8. Policy Concerns and Certification Issues

22
2. Workshop Program and

International Steering Committee

23
24
2.1 WORKSHOP PROGRAM

Tuesday, 26 October 1993

7:30 a.m. Registration opens

8:30 a.m. Welcome and Introduction —S.S. Wang, University of Houston

1. GOVERNMENTAL and INDUSTRIAL PERSPECTIVES

8:40 a.m. Minerals Management Service (USA) —KG. Bartholomew

8:50 a.m. National Energy Board (Canada) — G. Yunblut

9:00 a.m. Health & Safety Executive (U.K.) —M. Bishop

9:10 a.m. Norwegian Petroleum Directorate (Norway) —Per Endresen

9:20 a.m. UKOOA (U.K.) — C. Houghton

9:35 a.m. OLF (Norway) —J. Helge Jenssen

9:50 a.m. Coffee Break

2. CRITICAL ISSUES, EXPERIENCE LEARNED, AND FORECAST

10:05 a.m. Keynote Address #1 — Oil and Gas Industry Perspective

B.W. Cole, AMOCO

10:35 a.m. Keynote Address #2 — Oil and Gas Industry Perspective

J.G. Williams, CONOCO

10:05 a.m. Keynote Address #3 — Composites Industry Perspective

G. Robertson, Ameron

1 1 :35 a.m. Keynote Address #3 —U.S. Navy Experience

/. Caplan, U.S. Navy DTRC

Noon Lunch

1:30 p.m. Introduction to the Working Group Format

for Discussions —S.S. Wang

1 :45 p.m. Move to Working Group Meeting Rooms

2:00p.m. Presentations by Working Group Chairmen

3 : 15 p.m. Coffee Break

25
3:30 p.m. Working Group Sessions

5:00 p.m. Adjourn

6:00 p.m. Reception and Texas Barbecue

Wednesday, 27 October 1993

8:00 a.m. Registration opens

4. CRITICAL ISSUES, EXPERIENCE LEARNED AND FORECAST

8:30 a.m. Keynote Address #5 — Challenges and the Future

J.M. Bowman, Du Pont

5. WORKING GROUP DISCUSSIONS

9:00 a.m. Working Group Sessions

10:15 a.m. Coffee Break

10:45 a.m. Working Group Sessions

Noon Lunch

1:30 p.m. Working Group Sessions

3 :00 p.m. Coffee Break

3:30 p.m. Working Group Sessions

5:00 p.m. Adjourn

Thursday, 28 October 1993

6. WORKING GROUP PRESENTATIONS AND DISCUSSION

8:30 a.m. Presentations by Working Groups # 1-4 and General Discussion

10:00 a.m. Coffee Break

10:20 a.m. Presentations by Working Groups #5-8 and General Discussion

1 1 :50 a.m. Concluding Remarks —S.S. Wang and C.S. Smith

12:10 Workshop Adjourns

26
2.2 WORKSHOP CHAIRMAN, SECRETARY, AND INTERNATIONAL

STEERING COMMITTEE

Workshop Chairman

Su Su Wang, University of Houston

Secretary

Dale W. Fitting, National Institute of Standards and Technology

International Steering Committee

U.S. Minerals Management Service Charles E. Smith and Maurice Stewart

Canadian National Energy Board Ibrahim Konuk

U.K. Health and Safety Executive M. Bishopp

Norweigian Petroeleum Directorate K. Nilsson

National Institute of Standards and Tech. Dale W. Fitting

U.S. Navy Rembert F. Jones, Jr.

U.S. Coast Guard Paul Cojeen

ABS Americas J.S. Spencer

American Petroleum Institute George G. Huntoon

Major Oil and Gas Companies

Amoco Bill Cole

BP

Chevron

Conoco

Exxon

Philips Petroleum

Shell

H.J. Choi

Steve Tumipseed

Jerry G. Williams

Jemei Chang

Alex Lou

W.G. Gottenburg

27
International Steering Committee (cont'd)

Composite Materials Industry

DuPont

Brunswick

Hercules

Ameron

AMAT

SpyroTech

M. Monib

Douglas Johnson

Mark Courtney

Ram Ananthataman

Tore Lundh

Chris Lundberg

Machinery, Tool, and Equipment Industry

Schlumberger

Halliburton

Bart Thomeer Don Hushbeck

Energy Engineering Service Company

McDermott Richard Lopushansky

Academic Institutions

University of Houston Su Su Wang

28
3. Invited Presentations —

Government and Industrial

29
30
U. S. MINERALS MANAGEMENTS SERVICE'S PERSPECTIVE

ON

COMPOSITES FOR OFFSHORE OPERATIONS

AND SAFETY MANAGEMENT

By

H.G. Bartholomew

Deputy Associate Director

Offshore Operations & Safety Management

U.S. Minerals Management Service

Herndon, VA 22070

Introduction and Welcome

On behalf of the U.S. Minerals Management Service, I want to add my welcome to all of you to

this first international workshop on composite materials for offshore operations.

I want to extend a special welcome to our colleagues from Canada, Norway, the United Kingdom,

and elsewhere outside the United States, whose participation truly makes this an international event. A number of Thank You 's also are in order:

• First, thanks to the organizers and co-sponsors of the workshop, Dr. Su Su Wang, University

of Houston, and Dr. Dale Fitting, National Institute of Standards and Technology.

• Also, thanks to the University of Houston for hosting this event and for the generous use of

their facilities. • And special thanks to the members of the joint government-industry steering committee for

preparing the workshop program.

• And lastly, a special word of appreciation to the many other co-sponsors, whose names you'll

find listed on the front of the workshop program.

The Minerals Management Service

As most of you may know, my agency, the Minerals Management Service, or MMS, regulates oil and gas exploration, development, and production in the offshore waters of the United States.

Not as well known is that MMS also collects lease bonuses, rents, and royalties due to the U.S.

Government for minerals production from Federal and Indian lands, both offshore and onshore.

Last year, MMS collected more than $2 billion, making us the second or third largest revenue

collecting agency in the U.S. Government.

And of course MMS conducts a technology assessment and research program aimed at promoting

the use of the best and safest technologies in offshore operations.

31
Workshop Objectives

It is in furtherance of this mission that we are pleased to join with NIST, the University of

Houston, and the dozen other government agencies and companies who have made this workshop

possible.

Our purpose in co-sponsoring this workshop is to facilitate an exchange of information on

composite materials for offshore applications among regulatory agencies, oil companies, material

suppliers, composite manufacturers, certification organizations, design engineers, and academic

institutions worldwide.

This workshop should also serve to:

• First, review the current state-of-the-art in composite materials for offshore use; • Second, assess the current state-of-practice for offshore operations; • Third, identify gaps between the state-of-the-art and state-of-practice, and to suggest and

prioritize research initiatives that might mitigate these gaps to allow safe and economical use of

composites by the offshore industry; • Fourth, identify new opportunities for the use of composite materials; and

• Fifth, to provide guidance to industry and regulatory agencies on the use of composite

materials offshore.

Importance of Composites

At the outset, I want to stipulate that, while I have an engineering background, I am not an expert

in either structural engineering or the use of composites. In these areas, I rely on experts such as Charles Smith, who manages MMS's safety technology program, and Felix Dyhrkopp, the

manager of our platform verification program.

The experts tell me that composites are characterized by high stregth-to-weight ratios and resistance

to corrosion and fatigue.

These characteristics allow offshore facilities designers to tailor structural and mechanical

responses to a degree unachievable with conventional materials. In turn, this will produce safer

structures and lower maintenance costs.

Technical and Regulatory Issues

Before the full potential for composites can be realized, however, we need to address a number of

technical and regulatory issues. To this end, we need an organized effort to identify critical issues

and to assess those actions that will enable the use of composite materials in the offshore

environment. Which brings us to this workshop.

Before closing, I'd like to pose some issues for consideration by you, the experts:

• First, MMS's interests regarding the use of composites are wide-ranging and go from

installation, maintenance, repair, testing, inspection, and certification issues to concerns over

fire safety, durability, damage tolerance, and environmental degradation. • Next, while API RP-14G addresses the relative merits of reinforced fiberglass plastics (RFPs)

in deluge and firewater systems and other API documents address the use of RFPS in storage

32
tanks, MMS has no regulations that address acceptance or inspection of composite materials in offshore applications.

I'm told that we would consider the results of performance tests in reviewing applications for

the use of composites~for example, flame, toxicity, and smoke tests—provided that such tests are conducted in an environment that closely resembles offshore conditions.

• Moreover, MMS has no regulations on the use of composite materials offshore, although

requests to use composites have been considered and approved by MMS on a case-by-case

basis.

For example, based on proven long term use in the North Sea, coflex, which is flexible pipe

fabricated from sheets of steel molded into a rubber jacket, has been approved in the U.S. for

deep water risers and pipeline segments in mudslide areas.

RFPs and other non-traditional materials have been approved for use in offshore galleys, living

quarters, open atmospheric drain systems, and produced water systems. In addition, RFPs have

been approved for chemical and non-hydrocarbon storage tanks.

Conclusion

In closing, I again want to thank Dr. Wang and Dr. Fitting for organizing this workshop and the

steering committee and co-sponsors for their support. And I thank all of you for participating in

this important undertaking.

33
34
Approach of National Energy Board on the Use of Composites in Petroleum Industry

Glenn R. Yungblut

Engineering Branch

National Energy Board

Calgary, Alberta T2P 3H2

Canada

Introduction

Innuit (Eskimos) living in the Canadian Arctic make ingenious use of a "composite" material in constructing their dwellings[1]. The most readily available material in their environment is naturally ice which is a crystalline material. We know from our research programs that ice is typically a brittle material. The cracks in an ice sheet can sometimes propagate miles. Inuit has

found that by freezing moss into a block of ice, one can obtain a quite a different material that

is comparatively ductile. We know that there are many other examples of earlier use of

composite materials going back as early as 1500BC such as armour plates, Samurai swords.

There are also many examples of composites in nature such as wood which is a cohesive

combination of cellulose fibers and lignin and bone which is composed of compact tissues and

slender fibers made from cancellous tissue[2].

Although modern composites are also based on the same principle of mixing different materials

to obtain a material that possesses the best qualities of the individual constituents, they are

usually designed and developed to obtain a precise set of properties. I am sure that during the

workshop, we will be exposed to various types of composites: fibrous (plastic reinforced with

glass fibre or carbon fibre or metals reinforced with boron fibre), laminated (cladded metals,

laminated glass, plastic-impregnated cloths), and particulate (concrete, ceramics, acrylonitrile

butadiene styrene (ABS) polymers). The purpose of this presentation is to describe, in general,

how we are handling the approval and certification of these materials and also to describe our

research and development efforts in this area rather than providing a survey of such materials or their applications.

Regulatory Responsibilities of the National Energy Board

The National Energy Board (NEB) has regulatory responsibility for all oil and gas exploration,

drilling and production facilities, and activities, in the Northern Territories including offshore

Arctic Ocean. NEB is also responsible for regulating the construction and operation of pipelines

that cross provincial or international borders.

The principle objective in regulating exploration, drilling, development, and production

activities is:

(a) To ensure the safety of the workers on the site or facility;

(b) To ensure that all reasonable steps are taken to protect the environment; and,

35
(c) To ensure that the production practices do not result in the oil and gas resources being

lost or wasted.

These objectives are achieved through ensuring that proper design and operating criteria are used. In fulfilling its responsibilities, NEB develops, administers and enforces a number of sets of regulations which establish the approval process and prescribes standards that must be met

in order to obtain an approval. Generally, these standards are selected or developed in consultation with technical experts in the oil companies.

NEB also cooperates with industry in the development of new design codes and standards

which may be referred in the regulations.

NEB also manages an extensive research program to develop new design and analysis methods

to improve effectiveness of the regulation to make the Canadian oil and gas project cost

effective. We also sponsor research to develop new materials and structures and new

construction techniques to keep the Canadian industry competitive.

Acceptance and Certification Procedures

Before any approval is given, a careful study is made of the equipment, materials and

procedures that will be used to determine if the regulations are being met and if the

environment will be adequately protected at the particular site or area.

During the approval of drilling and production systems approvals, most of this study role can be delegated to recognized certifying authorities. However, in the case that a new material is being proposed that is not clearly covered by the regulations and the standards referred in the

regulations, the company would be expected to demonstrate that the use of new materials

would provide a level of safety higher or equivalent to engineering performance specifications

that are the prescribed or intended by the regulations.

This can be accomplished by presenting documentation and data on the performance of the

new materials obtained in a laboratory environment or during the application of the material

under similar conditions. We know that there are continuing efforts to rationalize and

standardize this process in various countries. One of the major efforts in this area is taking place

in Europe under the term of "Performance Based Materials Selection" (PBMS)[3]. In NEB, we

are keeping an open mind towards such developments and would consider including references

to these standards in our regulations or may decide to sponsor the development of Canadian

standards to cover the unique conditions in Canada.

Research and Development

We have a number of unique problems in Canadian offshore. The main challenge in designing

structures is to overcome high loads induced by ice-structure interactions. NEB has sponsored

research and testing program to develop high strength composite steel-concrete-steel sandwich

walls.

36
Other problems related to ice stems from the low temperature properties of conventional

materials such as carbon steel. Canadian government is sponsoring research towards the

development of high toughness alloys.

In pipeline area, we have been experiencing problems since the mid 1980's due to a phenomena called stress corrosion cracking (SCC). The term SCC is used to describe a crack

initiation and propagation process which results from the interaction of tensile stress and

corrosion. In pipelines, SCC cracks are usually initiated at locations where the coating is separated from the pipe and bare metal contacts a corrosive fluid.

Composite materials have been proposed to address these kinds of problems. Recent literature

contains many such developments[4,5,6]. However, as discussed in [3], the use of composites

in offshore is not always economical or straightforward. We also have to understand the longterm behaviour of composites and overcome some of the difficulties associated with the longterm behaviour of these materials under given environmental and thermal conditions[7].

At NEB, we are prepared to work with industry to develop standards for design, fabrication and

selection of the composites. We would also welcome opportunity to join research efforts in this area initiated in other countries.

References

[1] The New Materials, D. Fishlock, John Murray Publishers, London, 1967.

[2] Fundamentals of Engineering Materials, P. A. Thornton, V.J. Colangelo, Prentice Hall,

lnc.,Englewood Cliffs, New Jersey 07632, 1985.

[3] An Engineering Documentation Scheme for GRP in the Oil Industry, C.J. Houghton,

OMAE Proceedings, 1993.

[4] Composite Materials Volume 3: Engineering Applications of Composites, ed. by B.R.

Noton, Academic Press, New York, new York, 1974.

[5] Rebuilding the World with Composites, L. Kempfer, Materials Engineering January 1 991

.

[6] Carbon Fibre, Poised to Dominate: Canadarm, T. Stevens, Materials Engineering, August

1990.

[7] Long-Term Behaviour of Composites, ed. by T.K. O'Brien, ASTM Publication Code

Number (PCN) 04-813000-33, Philadelphia, Pa., 1982

37
38
UK GOVERNMENTAL PERSPECTIVE

Mark Bishopp

Head - Fire Engineering

Offshore Safety Division

Health and Safety Executive

Liverpool, England

The UK legislative regime for the offshore industry is currently in the process of being

reformed. This reform is a consequence of the Cullen Report into the Piper Alpha disaster which

made a number of criticisms of the old legislative regime. The major criticisms were that the

Regulations were too prescriptive, were not in line with modern thinking on safety legislation and were constraining technological development. The Cullen Report made a number of wide ranging

recommendations for reform, all of which were accepted by the UK Government, the Health and

Safety Executive (HSE) is in the process of turning these recommendations into legislation.

The old system, much of which has yet to be reformed, consists of a number of Acts and

Regulations which are prescriptive in nature. These Regulations make requirements that certain

precautions be provided, regardless of whether there was a need for them, and often the standard to which they would be provided is specified regardless of the actual situation. The Regulations were

backed up by formal guidance, perhaps the best known of which is the guidance to the Construction

and Survey Regulations, usually called the Green Book or the 4th. Edition Guidance. This guidance

is primarily targeted at designers and the Certifying Authorities and, had, partly due to the lack of

anything better, become regarded as equivalent to the Regulations themselves.

This prescriptive style has certain advantages, for the designer it gives a clear set of rules

which must be complied with, and does not require the provision to be based on the results of a risk or hazard analysis. For the Regulator the advantages are that it is easy to demonstrate fairness in the

treatment of all operators because the rules are exactly the same, and at the enforcement stage these

same prescriptive rules give a clear go/no go decision.

The downside is of course that there is no connection between the actual hazards present and

the precautions required by the Regulations. This inhibits innovation and the development of

alternative methods of ensuring safety as there is no mechanism to provide a credit for such a developments.

The inflexibility of this legislation was also shown by the need to grant around 400 requests a year for exemptions from certain provisions of the legislation.

The first element of the reform process is now in place, with the Safety Case Regulations,

which came into force on the 31 May 1993. In essence these require that for existing installations

the operator must submit a "Safety Case" to the Health and Safety Executive (HSE) by the end of

November this year. This Safety Case must identify the hazards and show how these hazards will be

managed and controlled throughout the lifetime of the installation, and demonstrate that the risks to personnel have been reduced to "As low as reasonably practicable" (ALARP). These precautions

will be a combination of a installed precautions such as active and passive fire protection, and a

Safety Management System They emphasise the need to design out the hazard ie inherent safety

and prevention rather than control and mitigation

39
The next phase is the review and reform of offshore legislation. The first of the new

regulations will be the Prevention of Fire and Explosions, and Emergency Response Regulations,

(PFEER Regulations), the consultative draft of which has recently been published for formal public

consultation, There has already been substantial informal consultation with all parties in the

industry on these draft Regulations. The consultation phase will close on 3rd December and it is intended to have these Regulations in place by the Summer of 1 994. These Regulations will be

accompanied by an Approved Code of Practice (ACoP) which will be issued by the HSE. We also see the need for technical guidance on Fire and Explosion Hazard management and on Emergency

Response, one way of taking this forward would be for guidance in specific areas to be prepared by

the Industry Associations. The hierarchy of this is that the Regulations are at the top of the tree,

then comes the Approved Code of Practice which gives practical guidance on the ways in which the

safety goals set by the Regulations can be met, below this is the Technical Guidance and the various

Standards that can be adopted, International, National, Industry (eg API standards) and internal

company standards.

The Regulations make a number of requirements:-

Regulation 5 (1) (a) The duty holder shall perform, and so far as is reasonably practicable,

complete, and repeat as often as may be appropriate, a sufficient fire and explosion analysis in relation to the installation.

Regulation 5 (3) In this regulation "fire and explosion analysis" means a process consisting of -

(a) identification of the various events which could give rise to a major accident involving a

fire or explosion;

(b) evaluation of the likelihood and consequences of such events;

(c) the identification of suitable arrangements to prevent, detect, control and mitigate the

effect of major accidents referred to in (a), other than arrangements for evacuation escape and

rescue of persons; and

(d) establishment of suitable and sufficient performance standards in relation to such

arrangements and the structures and plant they involve.

Regulation 9(1) The duty holder shall make suitable and sufficient arrangements to prevent fire and explosion, including such arrangements to -

(a) minimise quantities of hydrocarbons on the installation;

(b) prevent the uncontrolled release of hydrocarbons;

(c) prevent the accumulations of explosive atmospheres; and

(d) prevent the leakage of flammable liquids;

and to prevent their ignition.

The Regulations emphasise the need for an integrated approach to fire and explosion hazard

management, with the priority being given to eliminating hazards by design, ie inherent safety, then

prevention, minimisation, control and mitigation. The recommended approach in the Regulations is derived from the Safety Lifecycle approach developed for programmable electronic systems,

whereby the overall safety requirements are determined as a result of the hazard and risk analysis,

these requirements are allocated to the various safety systems. The performance standards for the

various systems are therefore set by the hazard analysis.

Following the PFEER Regulations there will be the Management and Administration

regulations, which it is planned to have in place by late 1994, and the Design and Construction

Regulations which it is intended to have in place by Summer 1995. These Regulations will reform a

40
large number of the existing prescriptive requirements which will be revoked. This will achieve a

simplification and rationalisation of the existing legislation, and will complement the Safety Case

Regulations by setting minimum standards applicable to all installations.

Application to Composites

The current Construction and Survey Regulations says very little about the use of composite

materials. Part VI which deals with materials states: in paragraph 1 "....All such material, so far as

is consistent with its Junction, shall be incombustible. ", Paragraph 3 of this Section indicates that

steel, concrete and aluminium should be selected from grades conforming to a recognised standard.

For other structural materials it simply states that they should be suitable for use in a marine

environment.

The guidance to these Regulations indicates for example that A and H rated fire walls should

be constructed of steel or other equivalent material, and that all materials should be

non-combustible. The guidance had extensive sections on steel, but virtually nothing on composite

materials. With many composite materials failing the standard tests for combustibility, designers

had the option therefore of going the safe conventional route and using steel based materials or preparing a fairly detailed justification for the use of composites, often with few generally

acceptable standards to use as a basis and accepting the possibility that this justification would not

be acceptable to the Regulator. With the tight timescale of many offshore projects it is not

surprising that few designers were prepared to take that risk. One of the criticisms of the Cullen Report of the old legislation was that it inhibited

technological development. As a consequence, one of the objectives of the new legislation is to remove such artificial barriers to development, and I therefore believe that many new applications

for alternative materials such as composites will be proposed in the future. UKOOA has developed

a series of guidance documents on the use of composite materials offshore which will give potential users the basis for demonstrating that their proposed use is acceptable, I am sure that Chris

Houghton who is speaking shortly will expand on this subject. I welcome such industry initiatives.

41
42
Norwegian Authorities' Perspectives on Composite Materials for Offshore Operations

Thor G. Dahle

Norwegian Petroleum Directorate

P.O. Box 600

N-4001 Stavanger, Norway

Introduction

The Norwegian Petroleum Directorate (NPD) is the governmental agency vested with the task to supervise the offshore licensees' performance regards regulatory compliance. The scope of the

NPD supervision comprise the licensees' performance regards safety and working environment, as well as the management of the petroleum resources.

The petroleum activity offshore Norway started in the mid 60'ies, and fairly quickly a number of

major oil and gas discoveries were made. The development in the 70-ies and 80-ies was characterised by huge, integrated installations, including the development and use of gravity base structures.

Towards the end of 1993, a total of approx. 5 billion tons oil equivalents (toe) has been produced,

are being produced, or is decided to be produced. Future discoveries are combined with a relatively

high uncertainty, with scenarios ranging from 3 to 12 billions toe additional discoveries for the

entire Norwegian Continental Shelf. There is also a potential for enhanced recovery from existing

or planned developments which may add approx. 0,5 billion toe to the above figures.

Future development scenarios are characterised by a high number of relatively small fields. The

scenarios indicates as many as 200 - 300 developments within the next decades, against around 40

per today. This means that the majority of future developments will consist of relatively small

fields with a marginal profitability. Based on today's technology, many of these field will not be

profitable, unless there will be a significant increase in the oil price.

Norwegian offshore safety regime

Norwegian petroleum legislation emphasises the sharing of roles; the licensed companies to be

fully responsible for prudent activities, and the authorities to supervise that the licensees comply

with the given framework. The NPD has been greatly concerned that the regulations and the

supervisory functions should fully reflect this basic principle. Hence, the NPD has gradually

changed the profile of the supervisory function towards an increased focus on the internal control

systems in the licensees' organisations.

The Norwegian offshore safety regime rests on the principle of self-regulation (Norwegian:

"Internkontroll"). The main feature of this regime is the requirement for a systematic organisation

of the internal management systems that shall ensure compliance with rules and regulations. It also

43
implies that the NPD does not issue any kind of approvals concerning installations, equipment,

components, personnel etc., neither directly, nor by delegation to a certifying body. The basic

philosophy behind, is the perception that approvals imply a transfer of responsibility from the

licensees to the authorities.

Safety regulations

The NPD has recently completed a major restructuring of the safety regulations pertaining to the

offshore activities. The revision was deemed necessary mainly because the legislation during the

initial period of the offshore petroleum activity had gradually developed into comprehensive,

detailed instructions related to technical solutions, procedures etc. In view of the change in supervisory profile to approach the control systems rather than undertaking detailed inspections etc., the

specific requirements in the regulations were an obvious anachronism. Besides appearing as a hindrance to the industry's need and wish to be innovative, it implied a transfer of responsibilities

from the licensees to the authorities, thus conflicting with the basic principle in the regulatory

regime.

The new regulations are, as far as practicable, expressed in terms of goal-setting requirements, i.e. they state the purpose of the requirement rather than specifying the technical solution. One significant effect of this type of regulations, is the freedom it offers the licensees to choose solutions

which are optimal to the specific projects and compatible with corporate philosophies. In addition

it promotes the search for new and cost-effective solutions.

Supervisory strategies

The NPD has paid great attention to the development of supervisory strategies and methodologies

which reflect the basic principles in a regime based on self-regulation. The initial approach based on detailed inspection, approval of procedures, drawings and documents, etc., had the contrary

effect, in the sense that it resulted in a transfer of responsibilities from the operator to the authorities.

The current strategy implies that the operators' self-regulation systems are evaluated by means of

system audits and verifications. System audits are well planned and systematic examinations of the

self-regulation systems in order to ensure that these have been established, complied with and

maintained as specified. Verifications are spot checks which aim to ensure that the systems actually give the expected output.

This approach implies that the NPD does not give safety related approvals to the operating companies, neither for plans, nor for the use of installations, equipment or components. Again, the rea- son is that approval implies a transfer of responsibility. As a further consequence, the NPD's

supervision does not make use of a certifying body, as such arrangements can be seen as a kind of

delegation of approval authority.

44
A central tool in the NPD supervisory activities is the consent system. In brief, this system requires

the operators to apply for an NPD consent prior to starting the activity at certain pre-defined milestones throughout the various phases in the field development, production phase and removal.

Application for a consent shall contain a self declaration as to the status of the relevant parts of the

self-regulation system, identified deviations between the planned activity and the pertaining legislation, the safety impact of such deviations, and a plan for the removal of or compensation for such

deviation.

Based on this declaration, and with a view to previous experience with the company in question,

the NPD will initiate the actions that are deemed necessary in order to remain confident with the

company's capability of carrying out the activity in a satisfactory manner. A consent is activity

oriented, i.e. it is concerned with the activity to be executed, hence not implying any kind of

approval of installations, equipment etc.

The consent milestones have been carefully chosen as appropriate for the operators to review their

accumulated experience with the project so far, and to assess the plans for the planned activity.

Also, these milestones provide the authorities with the opportunity to have an impact on crucial

decisions in the project development.

The potential for composite materials

From a Norwegian point of view, a continuous search for more cost-effective solutions are therefore highly needed. Use of composite materials for various applications may prove to be one

important contribution to such a development. Substitution of steel with composite materials may

have positive effects both with respect to investments and to operational costs. Concerning the

investments, there is a close connection between the total weight and the cost of an offshore

installation. Any contribution to weight reduction will therefore have an impact on the total investments. In the operational phase, the cost saving potential is obviously tied to the volume of

maintenance.

There is, however, all reason to have a cautious attitude to the introduction of composite materials on offshore petroleum installations, both for technical and for safety reasons. In all human enterprise, technological improvements have been achieved by some degree of trial and error. The offshore industry, however, is to sensitive to serve as a experimental scene. Norwegian experience

indicates that an typical offshore modification, e.g. changing of a piping system, can cost as much

as ten times more than a similar operation in an onshore plant. In addition, the lay-out characteristics of an offshore installation imply certain accidental scenarios which can not be tolerated. Great concern must therefoiebe paid to the methods and systems that shall assure the quality of composite materials for offshore application with regards to the physical properties. These include technical strength and durability as well as fire properties.

A great challenge is connected with testing and inspection. As conventional methods do not apply

to composite materials, new methods will probably have to be developed. However, there will also

45
be a need to change of attitudes towards reliance in quality assurance activities that ensure that product will meet the required standard.

REFERENCE:

1 Acts, Regulations and Provisions for the Petroleum Activity. Volume I and II. The Norwegian Petroleum Directorate, Stavanger, Norway. Updated 1 1 1993

Print!)

82" 7257"369"

5782"7257"370"9" (IndividuaI Rations also available as separate

46
An Engineering Documentation Scheme for GRP in the Oil Industry

by

C. J. Houghton, Phillips Petroleum Company United Kingdom Ltd

(Chairman UKOOA FRP Workgroup)

Presented at OMAE, June 1993, Glasgow, Scotland

ABSTRACT

The absence of adequate engineering documentation has been a major inhibition to the use of GRP in offshore oil industry projects. Increasing dialogue with Regulatory and

Certifying Authorities has emphasised the importance of thorough performance based

documentation in gaining their approval. This paper describes the work of the UKOOA

FRP Workgroup (with collaboration from other industry groups) in developing a framework for common industry documents for the use of FRP materials offshore,

initially focusing on piping applications. It is intended that these documents be submitted

to ISO for future adoption as international standards. (A short postscript has been added

at the end of the paper, to describe the progress since this paper was originally

presented)

BACKGROUND

The use of glass reinforced plastics (GRP) on offshore installations in the UK Sector of

the North Sea, requires that any documentation scheme must address the existing

legislative requirements. Due account must be taken of the Offshore Installations

(Construction and Survey) Regulations 1974 and of any guidance issued by the relevant

Government Departments in support of the Regulations. In respect of materials of

construction, the Regulations (Ref 1) stipulate that:

"Every part of an offshore installation shall be composed of material which is suitable having regard to the nature of the forces and the environmental factors

to which that part may be forseeably subjected. All material, so far as is consistent

with its function, shall be incombustible.'

1

In 1986, the Government supported Offshore Energy Technology Board, identified

weight and cost savings as one of the priority areas for study. To this end they identified

the use of lightweight materials (GRP and aluminium alloys) as a possible way of

achieving substantial savings. As a result, a conceptual study was commissioned by the

Offshore Supply Office of the U.K. Department of Energy. This study, published in 1987,

supported the perception that the introduction of lightweight materials into the offshore

oil industry could generate significant weight and cost savings, at a time when the advent

of lower oil prices necessitated cost-effective engineering. More importantly, however,

the Piper Alpha disaster in July 1988 demanded that safe engineering was a paramount

requirement.

47
The offshore use of a combustible material such as GRP, need not conflict with the

objectives of safe and cost effective engineering provided that relevant factors are taken

into account when its use is proposed. This was recognised by the Department of Energy

in 1988, when they wrote to industry bodies and the Certifying Authorities advising of

their intent "to develop guidance on performance requirements for composite materials",

emphasising the importance of fire safety. They also proposed the establishment of an

ad-hoc working group of interested parties to provide input to the preparation of such

guidance. This proactive stance was further reflected in the issue of the Fourth Edition

of their Guidance Notes on Offshore Installation: Guidance of Design, Construction and

Certification. Section 24 of the Notes covering "Materials other than steel or concrete",

states that "non-combustible materials should be used except where any required

property or use of a material precludes non-combustibility". Specific factors that need to

be taken into account, when the use of GRP was proposed, were listed as follows:-

Fire risk in the location of use and likely fire exposure (intensity and duration);

Consequences of failure in fire (e.g. for pipes or tanks containing combustible

liquids or gases, or structures supporting such);

Fire endurance to provide the necessary fire integrity of the structure or piping

system;

Combustibility;

Ignitability;

Surface spread of flame;

Emission of smoke and toxic combustion products, especially for applications

within enclosed spaces likely to be occupied by personnel.

A UKOOA (United Kingdom Offshore Operators Association) Workgroup was formed

in 1989, whose objective was to further the use of GRP materials offshore, especially in

seawater piping applications. Against the above background, a meeting was convened,

in London, in early 1992 by the UKOOA FRP (Fibre Reinforced Plastics) Workgroup.

The selection of FRP rather than GRP in the Workgroup title, is to signify recognition

that fibres of different types other than glass may be used where appropriate. This

meeting was part of a continuing liaison between UKOOA and the Health and Safety

Executive (HSE), who had taken over responsibilities for offshore safety matters from

the Department of Energy. The meeting addressed:

a) the current level of industry knowledge on GRP piping applications and in

particular a recent project in the Norwegian sector of the North Sea, where a

successful programme of system development and testing had resulted in approval

for the retrofit of GRE piping with a fire protective coating, as firewater system

deluge piping, in place of carbon steel (Ref 2);

b) an action plan building on the Norwegian work,to permit wider approval of GRP

use in the UK sector.

It was suggested that the use of "performance based materials selection" (PBMS) against

appropriate application performance requirements reflected the goal-setting objective

approach within safety assessments as recommended by the Cullen report, after the Piper

Alpha disaster. This approach could permit exemption from SI 289, pending the

48
introduction of new legislation recommended by Cullen. The meeting agreed that a workgroup forum comprising HSE, Certifying Authorities (C.A's) and UKOOA should

be established to pursue action plans. These plans included the listing of concerns and

definition of documentation requirements for proposed applications, eg. a Code of

Practice (later to be re-named, Guidelines).

What follows in this paper should be viewed in context of the above "background".

THE BENEFITS OF FRP OFFSHORE

The motivation within the North Sea offshore industry to obtain wider approval for the

useof GRP materials, in particular piping, is linked to the historical problems that have

been encountered with metallic materials in seawater service and the need to improve

safety and cost efficiency in both existing producing fields and new projects.

The first generation of North Sea platforms used carbon steel, either bare, galvanised or

internally lined with concrete for the range of seawater piping services from utility to

cooling water and firewater systems. Although there are some cases of reasonable

lifetime performance of carbon steel, the majority of experience has been that major

maintenance costs have been incurred as a result of corrosion, mostly internal. In

particular, firewater deluge systems have been prone to plugging of the deluge nozzles

from corrosion product scales, often rendering these critical systems ineffective.

During the late 70's and early 80's, there was a major shift away from carbon steels to

copper-nickel alloys (90/10 Cu-Ni) for seawater and other water service piping. On the

whole this material has performed reasonably due to its inherent seawater corrosion

resistance. However, over a number of years several limitations became apparent which

in total have caused many operators to move towards high alloy stainless steels as an

alternate. These were, velocity Umitations, which necessitated the use of larger diameter

piping sizes in design (with the associated weight and cost penalties), a history of

localised erosion failures in continuous flowing service, despite the best efforts of

designers to limit velocities below 3m/s in design, corrosion failures when used in

produced water service and exposed to hot slightly acidic fluids often containing

sulphides and a general susceptibility to mechanical damage during installation and in

operation.

The mid 80's saw a move towards high alloy stainless steels, 22% Cr duplex, 25% Cr

super-duplex and super austenitic 6% Mo grades. These materials, despite their

significant cost and early availability problems have been used extensively throughout the

North Sea. Their main advantage over copper-nickel is their high strength and

effectively unlimited erosion resistance, which has permitted designers to reduce pipe

diameters while retaining thin wall thicknesses (typically schedule 10S). However, these

materials have also shown some limitations in use. One problem area has been the

fabrication controls for welding of thin walled piping and another has been the recently

reported crevice corrosion failures in threaded and flanged connections of 6% Mo

grades, at service temperatures between 10-45 C, in as short a period as 8 months from

the Norwegian Sector (Ref 3).

49
Many of the benefits of GRP are obvious in the context of the above background, i.e. a natural corrosion resistance to seawater and to a wide range of typically used chemicals

offshore, over a temperature range which adequately covers that normally found offshore,

with the possible exception of produced water systems.

The fabrication related benefits of light weight (i.e. ease of handling) and use of adhesive

bonding instead of welding, thus minimizing "hot work", are especially important in the case of retrofit projects to existing offshore installations, where the offshore labour costs are usually the major project cost component

Further less obvious benefits include, an erosion resistance high enough (typically in the

range 5-10 m/s) to ensure equivalent pipe sizing with stainless steels, when taking

account of overall process design limitations of pump sizing and acceptable system

pressure losses, etc. (in the author's opinion there is still considerable conservatism in

this area. Reliable flow loop testing and field experience indicates that velocities of 10

m/s and higher should cause no problem with due design consideration of cavitation and

water hammer effects). Essentially "maintenance free" life-cycle operation should be

achievable if properly designed, installed and with due care for its limited physical

robustness in service.

All of the above benefits are in addition to the often cited material cost benefits. This

aspect should be treated with caution for a number of reasons. Although GRP piping is unquestionably cheaper by a significant margin (from 0.5 to 0.2 times that of stainless

steels and copper nickel, the larger the pipe diameter the bigger the saving), for complex

piping systems offshore with large numbers of fittings, i.e. bends, elbows, tees and flanges

etc, the overall installed cost benefit ratio is often reduced to a range of 0.5 to equivalent

cost, again dependant on the system pipe sizes. For example, a cost comparison exercise

for a piping system covering 1" to 3" diameters will show little to no cost saving over

stainless steels, or even as recently reported from Norway, against titanium.

One would expect to show large fabrication manhour savings for GRP systems over all metals, however, with increasing use of cold bending technology, the cost advantage in

small diameter ranges is also marginal. For size ranges above 3-4" diameter, significant

savings can be expected, of the order of 50%, although this has not been well

documented for any large North Sea projects to date. Other factors influencing

fabrication cost savings will be the location (i.e. whether carried out on or offshore) and

the degree of spool pre-fabrication possible to minimize site bonding.

A paper from J.D.Winkel of Phillips Petroleum Company Norway (Ref 4), also being

presented at this conference, provides a detailed economic review of several GRP retrofit

projects in the Ekofisk field over the last 4 years. One conclusion was that the project

engineering design costs were too high due to lack of training, poor product

standardization and a general lack of experience feedback from completed projects.

Another unfortunate trend in recent major North Sea projects, is that of design

conservatism, two examples being the use of "heavy duty" flanges throughout and the use

of electrically conductive piping for seawater systems, both of which reduce the economic

benefits to the project. Although at this stage in the use of GRP offshore in the North

Sea, a conservative design approach is understandable, the author hopes that the PBMS

approach within the document suite under preparation, will allow designers to aim more

confidently for "fitness-for- purpose".

50
All of the above comments regarding costs have been based upon the use of bare GRP

piping. For critical applications, where extended fire endurance is a performance

requirement (i.e. deluge systems), the use of GRP in conjunction with fire retardant

coatings, such as intumescents, must be considered. It has been demonstrated under

normal hydrocarbon and full scale jet fire tests (Ref 5), that this combination can provide a technically viable material alternative to metallic piping systems. In fact, it should be

stated that some of the commonly used metallic materials for deluge systems have not

been subjected to these rigorous proving tests, their performance capability has been

"assumed". However, in relation to cost-effectiveness, the use of currently available fire

retardant coatings with GRP has the effect of approximately doubling the material cost

and therefore making the economics of a direct comparison on materials marginal for

new projects. This area of application should continue to be attractive for offshore

retrofits and promising industry sponsored research in Norway, evaluating "thin film"

intumescents could result in improved "system" cost-effectiveness in the future.

In summary, significant cost benefits can be achieved with GRP piping systems, in both

new development projects and particularly with offshore retrofit projects. However, it is not wise to generalise on the level of installed cost saving as this will vary with, location

of installation (on or offshore), the degree of spool prefabrication, system complexity,

system pipe sizes, the comparative metallic materials and current market costs and the

level of design completeness and conservatism. Therefore, until the use of the material

becomes more widespread, project specific lifecycle cost evaluations are recommended.

REVIEW OF CODES AND STANDARDS

The following is a brief review of the principal codes and Standards, currently in use, related to GRP piping applications in the marine, petrochemical and offshore industries.

The three public domain Codes and Standards documents of most use in providing

guidance for the use of GRP piping offshore are: OLF Recommended Guidelines on Specifications for Composite Piping

Offshore, November 1991.

IMO Guidelines for the Application of Plastic Pipes on Ships, Dec 1992.

* ASME B 31.3 Chemical Plant and Petroleum Refinery Piping.

(OLF is the Norwegian counterpart to UKOOA, and has had an established GRP

Workgroup since the late 1980's).

The OLF document was written specifically for GRP piping applications on offshore

platforms and represents an important first step in providing standardised engineering

guidance for the use of GRP offshore. There are four main sections:

Qualification Testing and Manufacturing Requirements

Design of Piping Systems

Handling, Storage and Installation

Inspection, Maintenance and Repair

51
On the face of it this should provide sufficient guidance to meet the needs of the

offshore oil industry. However, it was felt that the OLF document structure did not lend

itself readily to adoption into an internationally accepted standards format, i.e. API or ISO, allowing ease of future revisions, nor did it use a performance based methodology

allowing the user to demonstrate "fitness-for-purpose" to the Certifying Authorities. It was

also considered that the important aspect of fire safety was inadequately covered.

Despite the above comments, it was widely accepted and agreed that this document

would be a major reference for the required suite of industry standard documents sought.

The IMO (International Maritime Organisation) document, aimed at shipboard

applications, gives good guidance on the issues and concerns which need to be addressed

but provides only limited detailed information about GRP piping design, procurement

and installation. Most significantly it prescribes fire endurance requirements and means

of demonstrating performance against three standard test procedures of increasing

severity. These provide a necessary basis but may require modification before being

applied to offshore structures.

The ASME Code, being written predominantly for metals, places the requirements for

GRP (and other non-metallics) into a separate Chapter VII, thereby allowing exceptions

to the corresponding paragraphs of the base code given in the previous chapters. The

main areas addressed by the Code are the consideration of the different material

properties, pressure design rules and bonding requirements. While the Code identifies

many of the important issues and concerns there is little supportive guidance.

All the above documents make reference to National Standards/Specifications which

provide the means of defining acceptance criteria, most of which cover component

specifications. Significant references include:

API Spec 15LR Specifications for Low Pressure Fibreglass Line Pipe.

ASTM D 1599 Standard Test Method for Short Time Hydraulic Failure Pressure of

Plastic Pipe, Tubing and Fittings.

ASTM D 2992 Standard practice for Obtaining Hydrostatic or Pressure Design Basis for

"Fiberglass" (Glass-Fiber Reinforced Thermo-setting Resin) Pipe and Fittings.

ASTM D 2563 Standard Practice for Classifying Visual Defects in Glass-Reinforced

Thermo-Setting Resin Pipe and Tube.

BS 5958 Control of Undesirable Static Electricity

ISO DP 5658 Reaction to Fire Test - Spread of Flame Test

One area not well addressed in the OLF, IMO and ASME documents is material

anisotropy and its effect on stress analysis. A standard which provides a much greater

depth of information about system design is BS 7159 "Design and Construction of Glass

Reinforced Plastics (GRP) Piping Systems for Individual Plants or Sites". Of particular

note are recommendations given for flexibility and stress analyses factors. As it stands

BS 7159 is not immediately applicable for use within the offshore industry because it was

written primarily for the chemical industry for applications up to 10 bar and where

greater emphasis is placed on corrosion resistance than structural efficiency. Also the

design qualification procedure is different to that in ASTM D2992, usually referenced

by manufacturers supplying to the oil industry.

52
None of the above documents is sufficiently complete to meet the needs of the oil

industry within their own right. All have some facet of information which is missing and

very often redress must be made to more than one document. This introduces potential

for conflict. For example the ASME bonding qualification tests requires that the test assembly should be subjected to a hydrostatic test pressure of four times the design

pressure for not less than one hour with no leakage or separation ofjoints. This conflicts

with some of the manufacturers' products which have been qualified according to API

15LR to meet the long term design basis requirement but which will leak at less than

four times the design pressure (this has recently been drawn to the attention of the B31.3

review committee, and a revision is anticipated).

There are gaps still to be filled which are not well covered by the above documents. The

most important are perceived to be:

(i) Lack of procurement specification of sufficient rigor to ensure all components and variants meet a defined specification.

(ii) Lack of guidelines for fire performance.

(iii) Uncertainties in definition of appropriate limits for less tangible

design parameters such as erosion limits and water hammer effects.

PERFORMANCE BASED MATERIALS SELECTION

It is not the intention within this paper to repeat the content of another paper being

presented at this conference (Ref 6). Rather, the intention here is to outline the concept

of the PBMS approach within a total documentation framework and to demonstrate that

this approach is compatible with the safe use of GRP (piping) offshore.

The documentation framework proposes three tiers of documents. Tier 1 is the

Guidelines that has been drafted by the UKOOA FRP Workgroup in consultation with

the Regulatory and Certifying Authorities. The scope of the Guidelines covers

identification of factors that have to be addressed when engineering with FRP materials,

while also defining what constitutes FRP. The Tier 2 documents are Specifications and

Recommended Practices covering system performance requirements and their

achievement through all project phases from design, procurement and construction,

through to operations and maintenance to decommissioning. Tier 3 documents define

standards and procedures for specific test methods.

The hierarchy of the documentation framework is illustrated in Figure 1, hence, the Tier

1 document, ie the Guidelines, is essentially philosophical in nature. It is the " what

issues must be addressed" document. Tier 2 documents are application-specific and

address "what performance is required and how do we get it?". The Tier 3 documents

underpin the Tier 2 documents via the definition of standards and procedures by which

attainment of the required performance is confirmed.

53
PBMS is at the heart of the documentation framework. This affords a common

methodology in which material selection reflects true functional needs and keeps abreast

of technological advances. Prescriptive approaches cannot keep pace with such advances,

and designing with FRP by seeking "equivalence" to traditional (steel) options is technically ill-founded. The PBMS concept, described below, provides a means of

establishing common performance bases from which technically equivalent competitor

materials and designs may be assessed for safety and cost effectiveness.

The PBMS Concept

In the PBMS approach, acceptance of a material depends on demonstration that it (or

the system constructed of it) complies with a performance specification, the requirements

of which are based on an assessment of the functional requirements of the system but

are material-independent. The aim of introducing the PBMS approach is not to promote

GRP per se but to base selection on a material's technical merits and to avoid excluding

fully satisfactory materials for arbitrary reasons.

The price of PBMS is better upfront definition of what is expected from systems - i.e. performance requirements - than may have been customary or necessary when material

options were more limited. The prize, however, is improved quality or material

performance arising from a quantified, standardised and auditable approach.

There are four key steps in implementing PBMS:

i) Identify and document kev functional needs

These should be based on an assessment of all key aspects of a system's

desired function during all operational phases. For example, for an offshore firewater piping system both standby and emergency situations

should be considered. In the emergency case, the fire exposure survival

duration required should reflect the firefighting and abandonment

philosophies of the installation, its layout, firewater system design and

control, and the nature of credible fire insults (fire type, heat flux and

duration).

ii) Develop performance requirements to meet functional needs

Performance requirements should provide a workable means of assessing

whether a material or system is capable of achieving its intended function,

the assessment may be made by test/measurement or, where adequate

predictive analyses exist, by calculation.

Requirements for any particular performance feature may differ for

different operational phases of the system under consideration. For

example, firewater piping may be required to be leaktight during standby,

but during emergency operation minor leakage is unimportant so long as design water delivery rates can be achieved.

54
The use of defined performance requirements will avoid the problem of

carrying over into designs in new materials any feature of traditional

designs which are incidental or arbitrary rather than functionally necessary.

iii) Screen candidate materials for technical acceptability

Simplification in screening methods should be sought so far as rigour is not

compromised. For example, although predictive models are being

developed for the fire response of even quite complex materials, at present

performance requirements for fire resistance often still require testing,

although in some cases samples may be substituted for full structures. In

other examples compliance with a functional requirement may be

demonstrated by a simplified material characterisation test, e.g. heat gain

limitations to a structure may be assessed by thermal conductivity

measurements on samples of fire protection materials and appropriate

analysis. For established technologies sufficient data is often available to

demonstrate compliance with defined performance requirements.

(iv) Make final selection from technically acceptable options based on other

criteria e.g. cost, availability

Completion of steps i/ to iii/ above will ensure that final selection can be made based

on commercial criteria from a short list of technically acceptable solutions.

To summarise, PBMS uses standardised acceptance tests or performance predictions to

vet all candidate materials against performance requirements derived from an assessment

of functional needs. The approach gives, and is seen to give, a "level playing field" for

competitor options and improves the quality of the material selection and design

processes, at the cost of improved design definition in a project's early stages. By

contrast, traditional prescriptive approaches specify materials but do not necessarily ensure satisfactory performance.

From the foregoing it is argued that the PBMS approach is compatible with the

Regulatory objective that the engineering design will comprise materials of construction

that are consistent with their function.

THE UKOOA WORKGROUP APPROACH AND TIMETABLE

As a result of the meeting in February 1992 with the HSE and CA's, the UKOOA FRP

Workgroup focused its resources on two main objectives, the preparation of Guidelines

covering all offshore FRP applications and a piping specific suite of documents in the

form of Specifications and Recommended Practices, underpinned by existing standard

test methods. The latter objective also involved the consideration of a fire testing

requirements for GRP piping. Underlying the whole activity was a "performance based

material selection" approach that is compatible with a legislative regime that presumes

the use of any material to be consistent with its function.

55
It was clearly understood from the beginning that any guidance documentation, either

Specifications or Recommended Practices, to come out from the Workgroup would be

submitted to an appropriate internationally recognized standards body for incorporation.

This would ensure the widest possible use and value for any documents. Because of the

strong links with API 15 Committee for Plastic Pipe through some of the active

Workgroup member companies, this was considered initially, to be the most suitable

body. However, further debate on this subject, including discussion with API 15

Committee representatives, concluded that ISO standards would be the preferred final

format to ensure the widest use and acceptance.

The Guidelines

After some early debate it was decided to write the Guidelines to cover all FRP

applications offshore, rather than restrict it to GRP materials or specific applications. It was also agreed that it was essential to gain a wider technical review and input than was

available within the Workgroup members (who comprise materials engineers,

composites specialists, piping engineers and general offshore project engineers).

A small sub-group was established to write an initial draft. Major source documents were

the OLF Guidelines document, the IMO document (both referenced above), and a draft

guidelines document (specific to piping) that had been prepared under contract for the

Dept of Energy in late 1990, and made available to the Workgroup.

The Table of Contents is shown in Figure 2 and one of two appended summary guidance

tables, modelled from the IMO document, in Figure 3. From the preface, "The Guidelines identify factors which should be addressed when

considering the application of FRP materials on offshore oil and gas facilities. The

document is intended to be a common check list for design engineers, end users and

approval authorities, to ensure that all relevant factors relating to specific applications

of FRP in the offshore environment have been considered".

It is worth making the point that, following the PBMS approach, a large part of the

Guidelines will be applicable to ALL materials evaluation, not just composites and

therefore is of wider value to design engineers.

The initial timetable was to complete the Guidelines by 1st April, 1993. This timescale

permitted more time for input from key industry groups such as the OLF GRP

Workgroup, API 15 Committee and the Industry Advisory Group (LAG), established for

the preparation of the piping related documentation suite (see below), as well as the

Certifying Authorities and the HSE.

The 4th draft (14th April, 1993) was formally submitted to the HSE for their final review

and endorsement in May, with the intention being to submit it to ISO along with the

piping specific documentation suite in September 1993.

Industry Standard Documentation for GRP Piping Use Offshore

The second objective for the Workgroup was the preparation of industry standard

documentation for piping. Although numerous specifications and other engineering

documents have been developed for GRP piping, the development has been rather adhoc resulting in overlap and inconsistencies between documents.

The UKOOA members increasingly recognize the benefit of using industry standard

56
documents, thus minimizing their own in-house requirements and providing a common

basis for the supply industry. GRP piping applications, predominantly for low to medium

pressure seawater, cooling water and firewater services had been identified as an area where significant benefits could be obtained, working from the large body of information

already in existence.

It was decided that the preparation of a suite of documents, which would address design,

procurement, fabrication, operation and maintenance and could be adopted by an

international standards body was the goal.

The planned approach involved the following stages:-

Preparing an outline document structure and a preliminary bid document.

Pre-qualify potential contractors to carry out the work and obtain budget

quotations.

Submit a request for funds and obtain UKOOA Council approval for the work.

Obtain bids from pre-qualified companies and devise an auditable technical

evaluation process.

Establish a steering group from the UKOOA FRP Workgroup.

Establish an Industry Advisory Group, comprising representatives from

manufacturers, engineering design companies, GRP fabricators, Regulatory

Authorities, Certifying Authorities and key researchers.

Award a contract and complete the work on schedule and within budget.

The above process was commenced in July 1992, and in mid-November a contract was

placed covering a project duration of eight months, commencing December 1992. To aid

project control, the scope of work was divided into eight principal CTR's (the project

schedule is shown in Figure 4).

The LAG established has 24 members and will meet three times at key stages in the

project to provide technical input to and comments on the documents under preparation.

At present, the work is proceeding to schedule with the first draft of the documentation

suite issued for comment.

The document suite structure is following that proposed by the Workgroup, with five

sections (intended to be stand alone documents) comprising:-

* Philosophy and Scope

* Procurement Specification

* Recommended Practice for Design

* Recommended Practice for Fabrication and Installation

* Recommended Practice for Operations and Maintenance

A third area that the Workgroup has been addressing over the last year, is that of fire

testing requirements for FRP materials. Aperformance based strategy document is under

development to provide guidance on the fire endurance properties that may be required

dependant on the material application, its criticality to the facility and safety of personnel

onboard, its location and the consequences of failure. The current version of the

"decision flow chart" is shown in Figure 5. The strategy may, after a full industry wide review, propose a number of standard fire tests (similar to the IMO approach) to allow qualification testing of components or systems against differing levels of hydrocarbon fire severity, up to and including jet fires.

57
THE FUTURE M1

The use of GRP or FRP has many other potential beneficial application areas besides

low pressure piping. Some of the more important of these include:

* Fire and Blast Protection Panels and Enclosures

* Module Panels, i.e. living quarters

* Downhole Tubing

* Low Pressure Tanks and Vessels

* Caissons and Deep Water Risers

* Secondary structural applications, i.e walkways, ladders, access platforms

and cable trays

The use of composites for fire and blast protection has attracted much attention in recent

years and is fast becoming an accepted and often preferred material for this application.

Ease of handling and its lightweight compared to metal based alternatives are the main

reasons for this success. Most structures have been qualified for service by full scale

testing. This is expensive and time consuming and further work is needed to quality

design procedures. This shortcoming is not specific to FRP, it also applies to metal based

structures. Joint Industry Programmes such as Marinetech North West ("The Cost

Effective Use of Fibre Reinforced Composites Offshore, Phases 1 and 2, 1988 - 93) and

the Steel Construction Institute ("Blast and Fire Engineering Project for Topsides

Structures, May 1990 and ongoing), can provide valuable input here.

A recently completed joint industry study managed by ODE and BMT ("Development

of Guidelines for the Application of Fibre Reinforced Plastic Materials to Topsides and

Superstructures in a Marine Environment, 1989 - 92") demonstrated how a complete

module in GRP (on a portal steel frame) could be designed and built to meet previously

prescribed load and fire performance criteria. This culminated in the issue of design

guide engineering documentation. Although quite different in application, similar

technology is being developed for use as subsea protection structures.

GRP downhole tubing has provided cost effective service for many years in North

America and the Middle East as an alternative to corrosion resistant alloys. While it is reported to have been used offshore in the Gulf of Mexico its use offshore is restricted

by the high design pressure and temperature usually encountered and high deviation

angles at which there is no operational experience of GRP. Nevertheless there are

opportunities where the reservoir shut-in pressure is or has diminished below about 3000

psi which makes the use of GRP tubing technically feasible. The challenge is to upgrade

the technology to meet the higher temperature requirements likely to be more frequently

encountered in the future. New developments taking place in Norway and USA is enabling thermoplastic line FRP tubing to be produced in a continuous length for use

as subsea umbilicals and coiled tubing. This raises the possibility that similar technology,

when applied to downhole production/injection tubing, could provide the benefit of

reduced drag and increased reliability, particularly of value in extended reach drilling.

Recent trials in the USA are reported to have demonstrated the capability of flexible

drillpipe made from composites to drill small radius bends for re-entrant drilling

applications.

58
GRP tanks have been in use for many years offshore but problems still arise. This is often due to poor identification of all design loads (eg lifting) and failure to

identify/comply with a suitable design code. The use of BS4994:1987 ("Design and

Construction of Vessels and Tanks in Reinforced Plastics") should ensure a sound basis

for the design of tanks and vessels. One area of increasing interest, especially in Norway,

is the proposed use of GRP for hydrocarbon separators.

GRP walkways, cable trays and access platforms have been used offshore particularly in

the Gulf of Mexico. There are niche applications where the benefits of ease of handling,

lightweight, low installation cost and corrosion resistance make the use of these attractive

despite the material cost being more expensive than galvanised carbon steel. The main

concern is fire and tests suggest that this material should not be used on primary escape

routes where there is risk from hydrocarbon fire engulfment. A recent British Standard,

BS 4592 Part 4, 1992, addresses the use of GRP's for flooring, walkways and stair treads.

One area of particular benefit would be access walkways below steel jacket cellar deck

levels, often exposed to storm wave action.

Looking much further ahead a potentially very attractive use of composites is as a production riser of a Deep Water Facility particularly at depths beyond 1500 m. Here

the benefit is derived from the material's lightweight and high fatigue strain.

The above list is not exhaustive and work is in progress on other applications including

subsea flowlines and topside process piping. However, the widespread use of many of

these applications will be inhibited by a lack of structured industry standard design and

fabrication documentation. We hope that the approach taken by the UKOOA FRP

Workgroup will provide a "blueprint" that can be used to minimize the time frame

required to develop the necessary documentation to permit future composite applications

offshore.

POSTCRIPT

Since the content of this paper was reviewed at the 1st International Conference on the

Use of Composites Offshore, in Houston, the following progress has been made.

In March 1994, at a special meeting in Aberdeen, Scotland, the Tier 1 Guidelines

document and the Tier 2 piping specific documentation suite were formally issued to

industry under the UKOOA cover. Also, the Fire Testing Strategy document was

released for wider industry comment. Further, in September of 1994, the ISO TC67/SC6

Committee approved a new work programme to take the UKOOA "Specification and

Recommneded Practices for GRP Piping Use Offshore" documentation suite and API

15LR and develop an ISO standard for GRP piping for use offshore. The target date for

completion being December 1997.

(Note, figures 1,2,3 and 5 have been updated from the original paper).

59
ACKNOWLEDGEMENTS

The author acknowledges permission to publish this paper from Phillips Petroleum

Company United Kingdom Ltd.

In particular, the author would like to acknowledge the direct contributions to the paper

from his fellow UKOOA Workgroup members, Dr R.A.Connell of Shell UK Exploration

& Production and Dr P.A.C.Medlicott of BP Engineering & Research.

Also the significant contributions to the Workgroup efforts in the last year of the

following, J.Alkire and W.Cole of Amoco, Dr P.Boothby of British Gas, R.Watson of

Chevron, I.Wattie and G.Walker of Conoco, J.Winkel of Phillips Petroleum Norway,

J.Milnes of Shell and last but not least E.Provost of SIPM.

REFERENCES

1. Offshore Installations (Construction and Survey) Regulations 1974 (SI 1974/289)

2. "Fiberglass Firewater Systems for Offshore Platforms", S.W.Ciraldi, J.D.Alkire and

G.G.Huntoon, OTC Paper 6926, 1992

3. "Super Stainless Steels: Review of Norwegian Offshore Practice", P.Lovland, OTC

Paper 7315, 1993.

4. "Maintenance and Cost Performance of Glass Fiber Reinforced Plastic (GRP)

Piping at Ekofisk", J.D.Winkel, OMAE 93, Paper 93-894S.

5. "Jet Fire Testing of Topside Pipework", PJ.Boothby, OMAE 93, Paper 93-892M.

6. "A Performance-Based Purchase Specification for GRP Pipes and Fittings (Based

on API-15HR/API-15LR)", E.Provost, OMAE 93.

60
FIGURE 1 o

u.

LUOz<Q

LUOX

(/)

LL

LLo

LU

(0

CC

LL

Hi2

LUXo

CC

LU

«0zozs3OoQ

CDzE

LU

LUZ5z

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61
FIGURE 2

GUIDANCE FOR

FRP USE OFFSHORE

• CONTENTS

- Scope

- Purpose

- Philosophy - Component/system performance factors - Risk assessment

- Component/system design

- Manufacture and quality control - Handling, storage and transportation - Installation and testing - Operational requirements

- Health and safety - Three tier engineering documentation scheme

- FRP performance (structures/piping) - Fire testing logic diagram

- Glossary

FIGURE 3

FRP Performance Parameters - Piping

Performance Service parameter (a) rt» ic) (d) le) if) (gl (h) (i) (j)

Pressure - internal Y Y Y Y Y Y P P Y Y

Pressure - external Y Y N Y P Y N N Y Y

Impact 1

1

P P ? P ? P P P P P Thermal loads N Y s, Y Y Y N N P Y

Blast overpressure P Y N Y Y Y N N Y P Creep P Y P P Y Y P P P P Bending loads Y Y Y Y Y Y Y Y Y Y

Axial leads Y Y Y Y Y Y Y Y Y Y Budding P P P Y Y Y P P P Y

Water hammer Y Y P Y P N N P Y Faogue Y Y N Y N P N N Y N

Erosion Y Y N Y P Y N N N P Cavitation Y Y S

v P Y N N P Y Abrasion P P ? p ? P ? P ? P Temperature P Y N ? p Y P P P N

Chemical resistance Y Y p ? Y Y Y Y ?

Pet meanon Y Y Y Y S Y Y Y Y Y Environment Y Y N Y Y Y Y Y Y r

Fire endurance P Y N Y Y Y N N P P

- beat release Y Y Y P P Y Y Y Y p Surface spread of flame P P Y P P P P P P P Smoke - viability Y Y Y Y Y Y Y Y Y Y

- toxicity Y Y Y Y Y Y Y Y Y Y

Electrical conductivity Y Y P Y Y Y P P P Y

The above Table is only a guide. Performance parameters should be determined for

all applications on i case by case basis.

Notes : (a) Service water (0

(b) Cooling fluids (g)

(c) Potable water (h) (d) Firewater - wet systems (i) (e) Firewater • dry systems (j) Y - Yes N - No

P - Possible

Produced water Grey water (non-hazardous waste) Son-hazardous drains Chemical injection

Ballast water

(1) Impact to be considered if locanon/rouong does not preclude impact. C) Water Research Council ceraficanon required 62
FIGURE 5 FIRE TESTING STRATEGY FOR FRP MATERIALS

(DECISION FLOW CHART)

kaT?

APPLICATION

CRITICALITY OF SERVICE LOCATION OF SYSTEM

NO TESTNG

REQUIRED

OENTIFY PERFORMANCE PARAMETERS FLOW

PRESSURE ENDURANCE I

QUALIFY THREAT

OVERPRESSURE

FIRE TYPE i.t JET or HYDROCARBON

CENT!FY PERFORMANCE PARAMETERS!

SET PERFORMANCE

STANDARDS (QUANTIFY)

VISBUTY

TOXICITY SPREAD Of FLAME

HEAT RELEASE

SET PERFORMANCE

STANDARDS (QUANTIFY)

SELECT SYSTEM

FIRECOOE

SELECT

FIRE TEST PROCEDURES

SELECT RRE TEST PROCEDURES

I [ TEST

06TAJN PERFORMANCE

RESULTS

TEST I

~1

OBTAM PERFORMANCE

RESULTS

YES SEEK ALTERNATIVE DESIGN

63
64
OLF'S INVOLVEMENT IN THE 6RP INDUSTRY

Jens Helge Jenssen

Conoco Norway Inc.

P.O. Box 488

4001 Stavanger

Norway

Tlx. 33145 conor n, Telefax +51 41 05 55

Introduction

OLF is the Norwegian Oil Industry Association. 22 oil companies,

drilling companies and catering companies are members in this

industry association which is the main negotiating party towards

the authorities, unions and the rest of the society.

6RP Work Group

In 1990 a GRP work group was established under the Operations and

Engineering committee in the OLF organization. The reason for

establishing the work group was to propose a new GRP specification,

because the existing Norwegian Standard was outdated.

Representatives were nominated from Conoco, Elf, Hydro, Phillips,

Saga, Shell and Statoil. All of these companies have major

operations in Norway, and some are taking advantage of resources in

the mother companies.

The Specification was completed in 1991, and normally a work group

in the OLF organization should be discontinued when the job was

done, however, several important issues had been raised during this

period, and we were encouraged to continue the work. It was at a

point of time considered if the work group should be upgraded to a

sub-committee

.

Following are some details on the most important issues which the

work group has been involved in:

OLF GRP Specification

In some offshore petroleum projects undertaken in Norway, it had

been necessary to undertake parallel detail engineering on the most

competitive GRP pipe suppliers. This had been done in order to

keep the competition until the contract was signed for the

installation. In addition, the existing Norwegian Standard for GRP

pipe and fittings was outdated, and needed to be updated. The work

group drafted a scope of work, approval was made from OLF for

spending some money, and the composite technology contractor AMAT

A/S was awarded the contract for drafting The OLF Recommended

Guidelines on Specification for Composite Piping Offshore. The GRP

work group acted as a steering committee for the work.

65
The main objective of this document was to provide the member

companies with guidelines for qualification testing, manufacturing,

piping system design, installation, handling, storage and

commissioning of glassfibre reinforced thermosetting plastic piping

systems. The document was designed such that the chapters were

independent. This would allow the producer, the designer, the

fitter and the inspector/maintainer to concentrate on one chapter

each. During the development of the document, the suppliers were

informed about OLF's activity.

The document is being distributed free of charge on request upon

contact to OLF, po. box 547, 4001 Stavanger, Norway, telephone +51

56 30 00, telefax +51 56 21 05 or telex 84 00 144.

Recently UKOOA established a document entitled "Specification and

Recommended Practice for Use of GRP Piping Offshore". The

document, which has used the OLF specification as one of the

building blocks, will be recommended adopted by ISO and possibly

API.

Training of GRP Fitters

In a study performed by Veritec and Veritas Research in 1992, it

was found that unqualified GRP fitters have approximately 5 times

more leakages per installed length of installed GRP systems as

properly trained fitters. Because of the results of this analysis,

OLF decided to upgrade the existing training for GRP system which

is available in Norway. In light of this, OLF awarded a study to

TI (The Norwegian Institute of Technology) in 1992 for improving

their own training manual. TI is the organization which is

undertaking most training of GRP fitters in Norway.

The work has been completed, and presently an improved training

program is available to the industry.

Certification of GRP Fitters

In order to ensure a good quality in installed GRP systems, the

requirement for a certification system for GRP fitters had been

identified quite early. The work group has seen this as a natural

follow-up after completion of the improvement of the GRP training

program. Because TI is the main training institute in Norway, and

also because of their involvement in certification of welders, a

proposal was requested for establishment of a certification system

for GRP fitters.

The GRP work group has made a request to the OLF management for

funding the development of a certification system for GRP fitters

on the budget for 1994.

66
Databank for GRP Installations

The GRP work group has proposed that a project for establishment of

a database for installations on the Norwegian part of the North sea

should be covered on the budget for 1994. The background for

proposing the establishment of this database are several:

*for improvement of safety

*for avoiding same mistakes are experienced at several

locations

*for improvement of technology transfer

*for accelerating incorporation of GRP components /systems

*for providing a status of what is going on in this area

Two potential contractors have submitted project proposals. In

order to have a bigger population, the databank may be expanded to

incorporate all of the North Sea.

Future Activities

The OLF work group is continuously evaluating other issues which

may benefit the member companies. Some of the issues which are

assumed to be covered in the future are:

common inspection routines

guidelines/specification for tanks and/or pressurized vessels

adoption of the UKOOA specification

*more active cooperation with UKOOA

Conclusion

OLF's GRP work group has so far been involved in developing a GRPspecif ication and improved training for GRP fitters. It is our

ambition to continue solving problems and concerns which prevent

the incorporation of GRP systems safely and efficiently in the

Norwegian offshore industry.

Acknowledgement

I wish to thank the OLF companies for sponsoring the work, and AMAT

and TI for undertaking the projects in a professional manner.

Finally I wish to thank R. Aarnes (Elf) , J. Malmo/B. Moursund

(Hydro) , F. Thorstensen/J. Winkel (Phillips, H. Thon (Saga) , H.

Buvik (Shell) and E. Oren/B. Melve (Statoil) for participating in

the work group.

67
68 i
4. Keynote Addresses

69
70
PETROLEUM E&P INDUSTRY PERSPECTIVE

ON THE USE OF COMPOSITES IN OFFSHORE OPERATIONS

Bill W. Cole

Amoco Corporation

Post Office Box 3011

Naperville, IL 60566-7011

Introduction

Carbon steel is the backbone of the offshore industry. The petroleum exploration and production

(E&P) industry makes a large investment each year in steel structure, steel tubulars, steel pipe,

steel vessels and many other steel products. However, carbon steel is susceptible to corrosion, a

constant problem in the offshore environment. As a result, the E&P industry puts a great deal

of effort into corrosion control. Large sums of money are spent for cathodic protection systems,

for corrosion inhibitor systems, for inspection and for maintenance programs. Corrosion

resistant alloys (CRA) are available for considerably higher initial costs and they are used in

critical applications where corrosion cannot be tolerated. Corrosion control and CRA materials are active research areas supported by the E&P industry. Altogether, these corrosion related

programs become a major factor in the cost of E&P operations.

Carbon steel is also a very heavy material of construction. The weight of steel piping and

vessels, for example, are factors in the high costs associated with offshore construction. The

weight of steel can be a limiting factor in the design of platforms for deep water operations.

There is little doubt that carbon steel will continue to be the back bone of offshore construction.

However, the added costs related to corrosion and the limitations cited above indicate that there are opportunities for alternative materials. CRA materials will satisfy some of the needs, but

installed stainless steel can cost 4 to 10 times more than carbon steel. So there is an economic

incentive to seek alternatives.

In recent years the E&P industry has started to use composite materials on offshore platforms.

FRP piping has been shown to be cost-effective and to have the performance characteristics

needed for water service. FRP has also been used for secondary structure such as cable trays,

walkways, railing and grating. FRP fire and blast resistant panels are becoming popular for new

construction in the North Sea area.

The advanced composites industry has evaluated the feasibility of using high modulus fibers in

several offshore applications with positive results. Feasibility work on advanced composite

production risers, for example, has been in progress in France since 1980, and the results have

been positive. Yet there are no advanced composite products in service today offshore, with the

possible exception of a few prototypes that are still being evaluated.

71
The E&P industry certainly has interest in composites as alternative materials, yet the industry

has been slow to accept them. This paper examines that acceptance issue and offers some

suggestions for gaining improved acceptance in the future.

Industry Acceptance Of FRP Pipe for E&P Operations

The acceptance of composite materials by the E&P industry is best characterized if the

technology is first divided into the following four categories: FRP line pipe, FRP downhole

tubing, FRP process pipe and other applications for offshore platforms, and advanced composite

products. Line pipe and downhole tubing are not offshore products, but the industry has a large

experience base with those products that impacts the acceptance of composites for offshore

applications.

FRP Line Pipe

The petroleum industry clearly has a need for corrosion resistant line pipe materials. Amoco has

been using FRP line pipe for hydrocarbon gathering and transmission lines since 1983. Some of

the other petroleum companies also make extensive use of FRP line pipe. FRP is normally used

when the service conditions are corrosive and FRP is considered to be lower in cost over the life of the project than carbon steel or carbon steel with a corrosion inhibitor system.

At Amoco, we believe production costs can be reduced with the selective use of FRP and we

continue to use these products. We believe, however, there are opportunities to improve

industry acceptance of FRP line pipe in the following areas: (1) compliance with API

specifications, (2) manufacturer's pressure ratings, (3) product quality, (4) quality of

installations, and (5) long term reliability.

Amoco has been conducting long term strength tests (ASTM 2992) since 1985 to establish

pressure ratings for commercial pipe products. The American Petroleum Institute (API) now

provides purchase specifications (API 15HR & API 15LR) with standardized methods for

establishing product pressure ratings, but some of the commercial products are not yet

qualified to those standards. Some petroleum companies establish pressure ratings

independent of the manufacturer's recommendations. Some companies continue to express concern for the long term reliability of FRP line pipe and use little of it, but Amoco

continues to have confidence in these products.

FRP Downhole Tubing

Some of the most demanding corrosive environments are in downhole applications. In those

environments, there is a clear need for corrosion resistant tubing materials such as FRP.

Commercial FRP tubing products are available, and a few companies have used them

successfully for years. Most companies, however, do not use FRP tubing extensively. The

primary industry concerns are with difficulties in make-up/break-out, temperature resistance,

long term strength with combined loading and long term reliability. FRP lined steel is a

72
related product that eliminates some of the concerns and has been used in the oil patch for

many years. API is currently working on the development of API 15TR, a purchase

specification for FRP tubing.

Industry Acceptance of FRP Offshore

FRP Firewater Pipe

In 1989, Amoco Norway Oil Company (ANOC) started work on an operations problem with

the deluge firewater system on its offshore platform Valhall. 1 Deluge firewater systems are used for fire protection on the wellhead and process areas of offshore platforms. Most of

the piping in these systems is dry with open spray nozzles and sprinkler heads. Several

miles of 2" to 8" carbon steel pipe are used for these systems on a typical platform. Deluge

systems are tested periodically. Residual seawater from system tests and the hostile offshore

environment causes internal corrosion of the carbon steel pipe and subsequent blocking of the

spray nozzles and sprinkler heads. An extensive maintenance program was instituted for

system clean-outs to keep the Valhall system operational.

ANOC facility engineers considered several options for restoring the Valhall system

including more extensive maintenance programs, replacement with corrosion resistant alloys

(CRA), or replacement with titanium. Alloy steels have been used for deluge systems on newer platforms. 2 Because of the Amoco experience base with FRP line pipe, the ANOC

facility engineers also considered using insulated FRP pipe. A preliminary life-cycle cost

analysis showed FRP to be an attractive option.

At that time the Norwegian Petroleum Directorate (NPD) regulations restricted the use of

non-metallic materials in offshore safety systems. ANOC solicited the advice of AMAT, a Norwegian engineering firm having experience both with composite materials and offshore

operations. Together they met with NPD in January 1990 to explore the use of FRP in the

Valhall firewater system. Based on that dialogue the following requirements were identified

to demonstrate the safety of FRP in firewater systems: a risk assessment study to establish

acceptance criteria, fire survivability tests of insulated FRP to demonstrate performance,

detailed specifications to define product requirements and a quality control program to assure compliance.

A project team was organized and a plan was generated to address each of the tasks. ANOC

sponsored the early work. Technica did the risk assessment study. AMAT undertook the

, product development work, the pool fire tests and the development of a specification.

SINTEF did the jet fire tests. Various insulation systems were evaluated with commercial

FRP pipe products. The NPD was consulted and informed of the progress throughout the

program. Early results were promising and other operators expressed interest in the project.

Conoco Norway, Norske Shell and Statoil joined the program as co-sponsors. The project

team completed all the tasks in less than two years. An extensive test program demonstrated

that insulated FRP pipe can function in an environment of explosions, hydrocarbon pool fires

and jet fires. The program was concluded with a 300 meter pilot installation on Valhall that was completed in December 1991.

73
FRP Process Pipe and Other Applications

The Valhall program has been a catalyst for several additional activities in 1993 related to the use of FRP pipe on offshore platforms. Amoco installed FRP firewater systems on two

new platforms, one in the Netherlands sector and one off Trinidad. Amoco has also installed

FRP piping on Valhall for a filtration system and for a drainage system. Other operators are

also installing or are planning to install FRP piping systems on their platforms.

There are many active research programs in Norway and the UK that are developing the

technology needed for further use of composites offshore. SINTEF SI and Marinetech

Research, for example, both have large programs working on topics related to composites

offshore. There is little doubt that industry acceptance of composites is developing quickly

in the North Sea area. UKOOA is working with HSE to gain approval for FRP pipe systems on platforms in the UK sector. The UKOOA GRP work group initiated work with

ODE/AEA to draft a specification for FRP process pipe offshore in January 1993. That

specification has been completed and will issue in November 1993.

Industry Acceptance of Advanced Composites

The offshore E&P industry is complex and it has depended on innovations in many different

technical areas to achieve the offshore capabilities that exist today. The E&P industry has

interest in advanced composites materials as well. There are needs for alternative materials

that are high strength, light weight and corrosion resistant. Advanced composites, those

systems that use high modulus fibers such as carbon or aramid, have been considered for

production risers (and tethers) for floating platforms, coiled tubing, drill pipe and subsea

flowlines. Note that these are all primary systems with demanding performance criteria and

the consequence of failure is very high for some of them.

IFP/Aerospatiale started development work on production risers nearly 15 years ago.

3 Composite tubes with carbon and glass fiber have been evaluated in offshore environments

with positive results. However, very little has happened with composite production risers in

recent years. Brunswick Composites attempted this year to organize a JIP for further

development of composite production risers, but they have not yet found a sufficient number

of subscribers. There is substantial interest in the coiled tubing application. The team of

Hydril and MMFG was successful in organizing a JIP for the development of composite

coiled tubing using carbon and S2 glass fibers. Conoco is also actively working on a composite coiled tubing product. Conoco has evaluated several advanced composite

applications for offshore operations. 4 Still, there are no advanced composites products in

service offshore nor are there any commercial products available as we approach the end of

1993.

74
Building Industry Acceptance of FRP and Advanced Composites

So what is needed to build industry acceptance of these materials? We need to be sensitive to current trends in technology management, we need to understand the key elements in the success of the Valhall firewater program, and we need to follow the example of successful

efforts in the North Sea area.

E&P companies are starting to put more effort into the management of the technology

development and application process. The focus of E&P industry technology programs is changing from technical discipline to business need. There is more emphasis today on

determining the value of new technology elements. In the future, technology programs will

be prioritized for funding on the basis of potential value to the business units.

Composites development efforts need to focus first on industry needs to identify the real

opportunities for composites. Then, opportunities need to be quantified so the value of the

technology is established for specific applications. As champions of the technology we

believe that composites can reduce the cost of production. Too often, though, we don't

really know to what extent composites can reduce the cost of production. Our focus has

been on the technology and the value of that technology for specific applications has not yet

been determined. If high value is demonstrated, then the priority for composites projects

will also be high and industry acceptance will occur naturally as product performance is demonstrated during the technology development and delivery process.

The Valhall program demonstrated the importance of approaching the development of

composites applications with a team. A key element in the success of that program was the

involvement of the regulatory agency, the offshore engineering community, the

manufacturers and several of the petroleum companies. Also, Valhall was far more than a technology demonstration or a product development program. All of the following important

issues were addressed during that short program: life-cycle economics, safety, environmental

impact, performance criteria, performance verification, source of supply, purchase

specifications, quality assurance programs (manufacturing and installation), consent by NPD

and a pilot installation. So the work scopes for applications development programs need to be broad as well as being thorough in the development of the supporting technology. The

Valhall program also demonstrates the advantages of performance based specifications for

products and materials as opposed to prescriptive based specifications. 5

Perhaps the most important lesson to be learned from recent events in the North Sea area is the importance of having operator's organizations. The productivity of the OLF and

UKOOA organizations together with supporting research from organizations such as Marinetech Research and SINTEF SI are very impressive. The US operators need to find a way to organize their efforts in similar fashion.

75
Summary

The US petroleum companies must assess needs and opportunities on an industry wide basis.

Some of the product development programs will be costly yet they will benefit the industry

as a whole. It is best to conduct these programs on a joint industry basis. Technology gaps

will be identified. The subsequent R&D programs need to be coordinated and funded on a

JIP basis. Finally, the regulatory agencies need to be involved and we need a mechanism

for on-going communication with MMS and the Coast Guard.

We need to form an organization that can pull together an alliance of the E&P and

supporting industries, the composites industries, the research community and government

agencies that are affected by offshore operations. We need that organization to facilitate and

provide momentum, focus and direction to JIP programs. And, we need to focus on the

development of composites applications that will meet industry needs.

References

[1] S. W. Ciaraldi, J. D. Alkire, and G. G. Huntoon, "Fiberglass Firewater Systems for

Offshore Platforms," OTC Paper 6926, 1992.

[2] C. J. Houghton, "An Engineering Documentation Scheme for GRP in the Oil

Industry," OMAE, 1993.

[3] C. Sparks, P. Odrn, G. Metevand, and M. Auberon, "Composite Risers for

Deepwater Applications," Proceedings of the 4th EC Symposium, Berlin, November

3-5, 1992.

[4] J. G. Williams, "Developments in Composite Structures for the Offshore Oil

Industry," Proceedings of the Offshore Technology Conference, Houston, 1991.

[5] E. Provost, "A Performance-Based Purchase Specification for GRP Pipes and Fittings

(Based on API-15HR/API-15LR)," OMAE, 1993.

76
PETROLEUM INDUSTRY APPLICATIONS OF COMPOSITES IN E&P OPERATIONS

Jerry G. Williams

Production Technology

Conoco Inc.

INTRODUCTION

The use of composite materials in the petroleum industry offers many attractive opportunities to reduce cost and improve performance while maintaining or even improving safety and

environmental standards. Production from deep water (over 2000-feet) petroleum reservoirs in the

North Sea, west coast of Africa and Gulf of Mexico is expected to become an important source for

new development in the twenty-first century. Composite components could help accelerate

production from deep water by providing solutions which are both practical and economical.

Production in deep water is significantly more difficult and expensive than production onshore or from shallow waters closer to shore and system weight and performance become more important

factors. Although weight savings and corrosion resistance are the primary drivers to use

composites, the most important factor to encourage wide spread use of composites in the oil industry

will be establishment of a clear economic advantage of employing composites versus using traditional

materials.

Historically, composite products constructed of glass fiber reinforced plastic (GRP) have been used

in onshore oil and gas operations for over 30-years (ref. 1). Early applications included storage

tanks and low pressure pipes requiring very little sophisticated technology. In recent years, onshore

applications have grown and GRP is used extensively for flow lines, water injection lines, and tubing

(ref. 2). Fiberglass product manufacturers have used advanced materials and design methods

developed for aerospace and industrial applications to improve their products. As a consequence,

the performance and reliability of fiberglass based components have improved significantly and a

host of new applications have emerged including high pressure pipes and advanced couplings.

Recent advancements in understanding of fire safety issues (ref. 3) and development of detailed

design specifications (ref. 4) have overcome barriers to the use of GRP components on offshore

platforms. Consequently, there is high interest in using GRP in new offshore projects and in

refurbishment of old facilities. Most recent offshore applications have focused on using GRP pipe

for the transport of low pressure water including cooling water, injection water, produced water

and for fire water systems.

The expanded interest in the use of composites for offshore operations began around 1986 with a

joint industry program focused on fiberglass applications conducted by Center for Industrial

Research (ref. 5) and another joint industry program on composite risers conducted by Institut

Francais du Petrole and Aerospatiale (ref. 6). In recent years, most major oil companies have hired or reassigned personnel to guide the development of composites for oil industry applications. In

addition, major oil companies have sponsored R&D programs investigating composite applications

and several workshops on composites with offshore focus have been held including those listed below.

77
WORKSHOPS FOCUSED ON COMPOSITE APPLICATIONS FOR OIL INDUSTRY

(si AMAT/NPD, Norway - 1989, 1990, 1992

National Research Counsel, Washington - 1990

o

o MIT Sea Grant, Cambridge - 1991

Marine Composites, London - 1991

o

o Maritime/Offshore Uses, New Castle - 1992

University Of Houston - 1991, 1993

The oil industry represents a significant untapped market for composite applications and the

advantages and opportunities are just beginning to be recognized within the oil and composites

industries. The support by government funds in the United States and Europe has done much to accelerate the pace of development and significant benefits can be expected in the future.

COMPOSITE MATERIAL ADVANTAGES IN PETROLEUM APPLICATIONS

The primary motivation to use composite products by the petroleum industry is to reduce

maintenance costs in production operations and to improve the capability to economically drill and produce oil and gas, particularly from the difficult challenges of deep water (ref. 7). The

assets of composite materials which are particularly attractive for oil industry applications

include corrosion resistance, reduced-weight, long fatigue life, and the ability to tailor properties

to meet unique design requirements.

The corrosion resistance of composites is the primary reason for the rapid growth of GRP pipe

and other composite components in recent years. In addition, GRP can provide a positive

environmental impact by reducing the need for chemical corrosion inhibitors. High performance

requirements demonstrated in fire safety tests and backed by rigid standards has also permitted

GRP to be used in safety critical applications such as fire water delivery pipe.

The weight savings potential using composites can be significant since the density ratio of steel to composites is approximately five. Most applications can easily show a direct 50 percent weight

savings. As was found for aerospace applications, the maximum benefits of using composites,

however, will only be achieved when the weight savings are synergistically additive, not on a

direct replacement basis. For example, the weight saved in using a composite riser on a Tension

Leg Platform (TLP) reduces the weight of hull needed to provide buoyancy which in turn reduces

the size of the tendon needed, etc. If the platform already exists, the only benefit of replacing

the riser with composites would be increased payload to counter the weight of unexpected

production and equipment upgrades.

For high performance applications, particularly offshore, advanced composite materials including

carbon and Kevlar® fibers are being given serious consideration. The higher cost of these

materials compared to steel, however, makes the benefit/cost ratio more difficult to justify.

Technologically, advanced composites can be shown to have high promise for deep water offshore

platform applications where reducing weight is important and for downhole components where

composite property tailoring provides enabling capabilities unavailable using metal designs. For

example, coiled tubing has very demanding requirements in which steel products are being

extended to the limit of performance capability while composites promise to extend the needed

operating parameters to operate at higher pressures and to extend further into extended reach

well bore holes (ref. 8).

78
COMPOSITES TECHNOLOGY DEVELOPMENT NEEDED

As noted above, the primary motivating factors to use composites in the oil industry are to save

cost and provide new enabling capability. In most cases the cost and performance comparison is with steel for which there is a long established experience base including readily available

material suppliers and fabricators, detailed materials data base, refined design guidelines and

standards, design experience, and operator familiarity. A similar state of readiness must be

established before composites will be fully embraced by the industry on a purely 'Tit for purpose"

economically competitive basis.

Several technology deficiencies were identified at the "National Conference On The Use of

Composite Materials in Load Bearing Marine Structures" sponsored by the National Research

Council (ref. 9). One of the recommendations from the conference was that a collaborative

marine-aerospace-automotive industry effort be launched to address specific analysis and design

issues peculiar to the marine application of composite structure. Better understanding of

structural mechanics issues, it was felt, would help provide greater confidence to use composites

and encourage future commitments to promising application opportunities. Important materials

and composite structural mechanics issues recommended for development to support marine and

offshore applications included: development of design procedures specific to marine and offshore

application requirements, basic material performance in the marine and oil production

environment, improved tubular join design, damage tolerance criteria, Non Destructive Test

(NDT) methods to assure quality and assess damage, repair procedures, analysis of thick-walled

structures, understanding of large deformation responses, improved analysis and test methods to predict failure, and innovative design concepts to provide cost-effective solutions to marine

environment problems.

Specific components such as a riser, tether or drill pipe have primarily been developed by

aerospace companies seeking to explore new business opportunities. In some cases such R&D

efforts have been conducted over long periods of time (as long as a decade) without resulting in

actual field implementation. The slow pace of progress from R&D into field service for high-tech

applications such as a composite riser discourages commitment to new development. At current

oil prices, oil companies are hesitant to make major commitments to production in deep water

which means the market for beneficial composite products is uncertain. Another significant reason for the slow pace of applying promising new composites technology is a lack of experience

in composite materials by project engineers in the oil companies and by design engineers in the

oil service companies. Design tools and training focused on the oil industry are needed to bridge

the gap and make the transition to a "fit for purpose" design philosophy in which all materials

including steel and composites are evaluated on the basis of performance and cost.

Although a strong foundation in composites has been developed for aerospace and automotive

applications, it can not be assumed that this technology is sufficient in all cases to meet the needs

of oil industry applications. The application of composites in the oil industry provides

significant opportunity for the development of challenging new technology, while at the same

time sufficient technology is currently available for near term applications to be on a firm

foundation.

OPPORTUNITIES TO USE COMPOSITES

Applications for composites in the offshore oil industry may be listed under four broad

categories: (1) Facilities, (2) Platform Structures, (3) Pipe Lines and Subsea Equipment, and

79
(4) Downhole.

Facilities include the equipment needed on the platform to support the production of oil and gas

including the equipment used to separate the produced fluids and gas and treat and remove

water. Facilities thus includes pipes and tanks, and in a broader sense also includes the

supporting elements of the platform from the fire protection system to walkways and living

quarters. The platform structure includes the deck and columns and structural elements which

tie the platform to the sea bed. For a Tension Leg Platform (TLP), the platform structure would

include the tethers and foundation template.

Circular pipe is the most common structural form used in the petroleum industry. Steel pipe is used extensively in exploration and production operations to carry oil, gas, and water and as a

structural form for actual construction of the platform. Specific applications include flow lines,

water injection lines, tubing, casing, subsea control lines, drill pipe and many other uses. Welding and threaded joints are the two primary methods of joining steel pipes. Pipe has very

demanding performance requirements including high pressure and the associated need for

reliability to protect personnel, equipment, and the environment.

Composite materials are also receiving attention in the oil and marine industries for their

nonstructural assets including enhanced safety and reduced environmental impact. For example,

from a safety perspective, firewater piping has been widely accepted as equivalent or better than

steel products. The difficulty of using steel is that the products of corrosion may clog the deluge

nozzles which makes necessary frequent operational safety checks. Numerous fire resistant

materials have been made available in recent years (many as spin off from aerospace programs)

including advanced phenolic resins and intumescent coating. Comprehensive testing in the U.S.,

U.K. and Norway in recent years has done much to advance the understanding of the fire safety

of composite materials and to develop safety standards. OLF (Norway) and UKOOA (United

Kingdom Oil Operators Association) have made major contributions to the development of

standards for composite applications (ref. 4) and the technology being developed is rapidly

extending across international boundaries including into the United States. The environment

may also benefit from the use of composite pipes in offshore operations by reducing the need for

corrosion inhibitors and paints applied to protect steel components. Much work, however, still needs to be done in the important area of safety and environmental impact.

A white paper describing the need for the development of composites technology for oil industry

application was recently submitted to the National Institute of Standards and Technology

(ref. 10). Table 1 taken from this paper describes a rough estimate of the quantity and market

value of projected utilization of selected composite components during the next ten years. It should be recognized in this scenario that the development cycle for an offshore platform takes at

least five to ten years from discovery to first oil. Some of the primary structure components

such as the composite tether will thus not be used in quantity until the out years of this period.

The long lead time, in fact, is part of the risk factor which inhibits oil companies from

committing to composites and is a primary reason for the need for industry supported

development and demonstration programs.

The 184-million pounds of composite weight utilization forecast in Table 1 includes composites

constructed of carbon, Kevlar® and glass fibers. Stiffness constraints which govern the design of

some of the components such as the tether drive the design toward the use of carbon fiber while

other components such as facilities which have less demanding structural requirements normally

use glass fibers based on lower cost. If one assumes that half the projected weight is for fiber

80
and half the fiber weight is carbon, the carbon Tiber consumption in the 10-year period would be

46-million pounds. Compared with the current carbon fiber annual production rate of

approximately 18-miIIion pounds, this is a significant quantity. As indicated above, the demand

for advanced composite components will be greater at the end of ten years than at the beginning

while fiberglass components will show an earlier growth history. The $2.9 billion value forecast

in Table 1 for composite components is based on offshore needs including subsea, but does not

include additional expected onshore utilization of new composites technology.

Before the forecasts of Table 1 become reality, the oil industry must be convinced that a similar or greater level of cost benefit would occur in E&P operations by adopting composites

technology. Although it is a conservative industry, the oil industry rapidly adopts new

technology when it is clearly profitable to do so.

REFERENCES

1. Williams, Jerry G.: Oil Industry Experience With Fiberglass Components. Offshore

Technology Conference. Houston, TX. Paper 5380. April 27-30, 1987. pp. 211-220.

2. Huntoon, G.G.: and Alkire, J.D.: Design and Performance Properties of Oil Field

Fiberglass Tubulars. SPE. San Antonio, TX. Paper 19728. Nov. 14-17, 1989.

3. Ciraldi, S. W.: Fiberglass Firewater Systems For Offshore Platforms. Offshore

Technology /Conference Paper 6926. May 4-7, 1992.

4. Specification and Recommended Practice For The Use of GRP Piping Offshore.

UKOOA. March 1994.

5. Stokke, Reidar: Glass Fiber Reinforced Plastics (GRP) Offshore. Center For Industrial

Research. Oslo Norway. Summary of JIP - March 1986 to December 1988.

6. Sparks, C. P.; and Schmitt, J.: Optimized Composite Tubes For Riser Applications.

OMAE. Houston, TX. 1990. Volume III - Part A, pp. 1-8.

7. Williams, Jerry G.: Offshore Experience - Opportunities For Composites In The

Offshore Oil Industry. Proceedings of the Use of Composite Materials In Load Bearing

Marine Structures. National Conference convened by the National Research Council's

Marine Board. Washington, C.C. September 25-26, 1990.

8. Sas-Jaworsky, Alexander; and Williams, Jerry G.: Development of Composite Coiled

Tubing for Oil Field Services. SPE. Houston, TX. October 3-6, 1993.

9. National Conference On The Use of Composite Materials In Load-Bearing Marine

Structures. Volume I: Summary Report. Volume II: Conference Proceedings. Meetings

in Arlington, VA on Sept. 25-26, 1990 sponsored by the Ship Structures Committee,

Marine Board, National Research Council. National Academy Press. 1991.

10. Cole, B. W.; Lo, H. K.; Williams, J. G.; and Wang, S. S.: A Focus Program On

Advanced Composites Offshore. White Paper submitted to National Institute of

Standards and Technology. January 6, 1994.

81
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82
COMPOSITE MATERIALS FOR OFFSHORE OPERATIONS

INDUSTRY PERSPECTIVE

Gordon G. Robertson

Ameron, Inc. 245 South Los Robles Avenue

Pasadena, CA 91101-2894

October 26, 1993

Introduction

Composite materials based on fiber-reinforced resins are not new. Applications abound where high

strength, light weight and corrosion resistance are needed in the products we use. Examples from

familiar industries listed below range from commonplace to exotic:

• Oilfield (Line pipe, Downhole Tubing, Sucker Rods)

• Industrial (Pipe, Tanks, Stacks, Process Equipment)

• Marine (Boat Hulls, Masts, Pipe) • Automotive (Drive Shafts, Springs, Body Panels) • Aerospace (Aircraft Floor Panels, Cargo Liners, Spacecraft, Voyager Aircraft) • Armaments (Rocket Motor Cases) • Transportation (Passenger Rail Cars, Trailers) • Construction (Structural Shapes, Poles, Grating) • Medical (Artificial Limbs, Braces) • Recreation (Golf Clubs, Tennis Racquets, Fishing Poles, Skis, Canoes)

• Consumer (Furniture, Appliances, Computer Cases)

These applications developed during the past 40 years. There is every reason to expect that new services

will be found in the future. Ameron's fiberglass pipe business has grown at a 15 percent compound rate for the past 30 years, and the future still looks bright.

Offshore oil operations can benefit greatly from use of composites. Elimination of corrosion and weight

reduction are primary advantages. Life cycle costs can be substantially lower than competing materials,

as illustrated below. Those of us representing the Composites industry must demonstrate that our

products are predictable and reliable. The Oil and Gas industry must be willing to embrace new

technology. And, together we must work with the regulatory agencies to ensure fire safety.

Materials

At risk of oversimplifying, the properties of any composite can be characterized in terms of a resin

matrix that imparts corrosion resistance, and one or more reinforcing materials, usually in fiber form,

that provide strength and stiffness.

Setting aside for now the possible future use of thermoplastic composites, the primary resin systems

currently in use fall into one of three categories, as shown in Table 1. All are thermosets, meaning they

crosslink during polymerization and do not melt at elevated temperature.

83
TABLE 1 - TYPICAL RESIN PROPERTIES

Tensile

Strength

(ksi)

Tensile

Modulus

(psi/106 )

Elongation

at Rupture

(%)

Degeneration

Temperature

(oF)

Epoxy 12 .5 5 500

Polyester 10 .4 5 400

Phenolic 7 .8 2 1000

It should be noted that within each category, there are wide variations in properties depending on

specific polymer and cure system. Chemical resistance also varies widely; but, generally, polyesters are best in acids, epoxies are best in bases, and phenolics are best in solvents. Resin system cost is generally

as tabulated from epoxies as most expensive to phenolics as least expensive; but again, there are

variations within each category.

Typical properties of common fibers are listed in Table 2.

TABLE 2 - TYPICAL FIBER PROPERTIES

Tensile Tensile Elongation

Strength Modulus at Rupture

(ksi) (psi/106

) (%)

E Glass 500 10.5 4.8

S Glass 665 12.4 5.7

High Strength Carbon 560 33 1.6

High Modulus Carbon 420 52 0.8

Aramid (Kevlar 49) 525 12 4.4

An optimum structure generally results when the least cost fiber per unit of tensile modulus is selected.

For commercial composites, E Glass is by far the most common. Only where weight savings are exceedingly valuable can other, more expensive, fibers be justified. It should be noted, however, that

the cost of carbon fiber is falling with increasing use; and, its conductive nature is indispensable in some

applications. Fibers can be supplied as continuous roving, or in a variety of mats and cloths depending on the processing needs of the fabrication.

Advantages

Even for one resin/fiber combination, there exists a wide range of final properties depending on fiber

orientation in each layer of the composite. This defines an important advantage, in that material

properties can be tailored to fit the individual needs of the application. For the composite product

manufacturer and user, this implies a duty to understand application conditions, and to carefully control

each step in fabrication of the finished item. A thorough qualification test procedure on prototype

products, agreed to in advance between supplier and user, is essential.

84
Most composite materials which are reinforced with glass fibers (as opposed to carbon or other high

modulus fibers) are somewhat more flexible than the metallic materials they replace. Careful design can

turn this to advantage. For example, steel pipe subject to temperature variations in

service must be provided with expansion joints or loops to relieve internal stresses. Fiberglass pipe, on the other hand, can be locked into supports. The lower modulus of

elasticity prevents excessive axial loads due to temperature changes and results in much lower pressure

surges on deluge pump startup.

Weight savings in excess of 50% can be realized using glass-reinforced composites. Larger savings are

possible with carbon fiber. Advantages of composites are summarized in Table 3.

TABLE 3 - PERFORMANCE ADVANTAGES OF

COMPOSITE MATERIALS

• Tailored Material Properties

• Weight Reduction

• Corrosion Resistance

• High Strength

• Improved Fatigue Resistance

These advantages can result in major cost savings.

Cost Comparison

Installed cost data for offshore piping systems have been published recently. The cost comparison of

Table 4 represents a fire water system on an Elf Aquitaine platform in the Congo.1

TABLE 4 - INSTALLED COST RATIOS

FOR REPLACEMENT OK OFFSHORE

FIRE SERVICE PIPING SYSTEM

Material Cost Ratio

Carbon Steel 1.00

Epoxy GRP 1.10

Stainless Steel 1.55

Cu/Ni 90-10 1.80

High Moly Alloy 3.70

85
Table 5, also taken from Reference 1 gives cost comparisons from real case situations in the North Sea.

TABLE 5 - NORTH SEA PLATFORM PIPING

Case

Reduction in

Installed Cost

8" produced water, Carbon steel replaced

with GRP

60%

30" sea water pipeline, Carbon steel replaced with GRP

65%

10-24" filter package for water injection

High Moly stainless compared to GRP

85%

TABLE 6 -.INSTALLED COST RATIOS' FOR PIPE

IN CORROSIVE SERVICE

Cost Ratio

4" Diameter 12" Diameter

Polyester GRP 1.00 1.00

Type 304L Stainless 1.41 1.24

Type 316L Stainless 1.58 1.38

The installed cost ratios of Table 6 are taken from Reference 2. They represent conditions typically

found in corrosive services within the chemical process industry.

Figure 1 shows installed cost in dollars per foot for several alternate materials proposed for yard

installation of a fire service system destined for the Gulf of Mexico (Amoco Immortelle Platform). The

interesting item here relates to costs for application of intumescent coating for enhanced fire resistance.

Tables 4, 5, 6 and Figure 1 suggest the following conclusions regarding costs:

o Composite materials compete even more favorably in offshore structures than in land based

installations. This is particularly true in cases where replacement is required on an operating

platform.

° Harsh working conditions, as in the North Sea, further enhance the cost benefits of composites

because of light weight and easier joining methods.

c Even when fire protective coatings are required on composites, the installed cost can be less than

metallic materials of equal corrosion resistance.

86

So far, only material and installation costs have been considered. This is appropriate for selection

between composites and corrosion resistant metallic alloys. However, between composites and carbon

steel, the significant benefits on a life cycle basis must be considered. Even if the installed cost of carbon

steel is 10 percent lower than a composite product (see Table 4), a single replacement of the system due

to corrosion during its service life will produce a strong life cycle benefit for the composite product: (1.0 + 1.0)/1.1 = 1.82 Cost Ratio. In seawater piping systems, two replacements of carbon steel are often

required during the service life. In addition, the steel system will require intensive corrosion monitoring

and perhaps temporary repairs, the costs of which were not included above.(1> Nor are the benefits of

weight savings which approximate 60 percent included.

Challenges

Fire performance of composite materials must be carefully evaluated when used offshore. Uniform

standards are needed for:

• flame spread • smoke density • gas toxicity • fire endurance time

including jet fires

The fire performance of composites has been studied extensively; but, it is beyond the scope of this paper to comment on the literature. However, it should be pointed out that regulatory criteria which

require "fire performance equivalent to steel" are not very helpful. Any fire endurance time, for

example, can be obtained at increased cost by insulation of the composite material. Likewise, flame

spread ratings can be reduced by application of appropriate coatings. The final product may still be

lower in cost than alternates of equal corrosion resistance, as demonstrated above.

The ability to tailor properties to specific conditions of use (an important advantage mentioned

previously) may present the user with a bewildering array of choices and alternatives, none of which have

a history of successful application offshore. This "job-shop" approach to fabrication leads to a lack of

reliable design data. Often the user's response is to simply stick to traditional materials. A more

sensible approach involves prior agreement between users and suppliers on the broad range of required

performance criteria. This allows the manufacturer to produce a well-defined standard product which

can be subjected to the appropriate performance tests in advance of order placement. In this case, the user can design confidently, knowing that standard products are available.

Mutual education and technology transfer between the offshore industry and composite producers will focus on composite material advantages and limitations.

Offshore applications

Composites are being used or contemplated for use in the following offshore applications:

Vertical pump column (or caisson) piping

Topside seawater system piping

Deluge systems, dry and wet

Chlorination systems

Subsea flowlines

Column or caisson wrappers

88
• Gratings, Railings and I beams

• Living accommodation modules

• Lifeboats • Pipe hangers and supports

Other applications may prove feasible in the future.

Case Histories

Amoco Trinidad Immortelle Platform - This is a deluge fire service system with factory-applied Pittchar

coating on epoxy pipe and fittings. The platform was designed by Brown & Root and fabricated at their

Greens Bayou yard on the Houston Ship Channel. It was shipped by barge this year and launched near

the coast of Trinidad. Two Amoco platforms at that location will tap 500 million cubic feet of natural

gas to supply the energy needs of Trinidad and Tobago. Other platforms in this area have used

composite pipe for nearly 30 years. Pipe with fire protective coating has also been shipped recently to Singapore for fabrication prior to installation on an Arco platform intended for the coast of China.

Phillips Platform in North Sea. Norway Sector - Six and 8-inch diameter vertical column piping has

become a stock item for Phillips and Statoil in Norway since 1990, as well as Maersk Oil and Gas in Denmark. Column piping normally contains a submersible pump and is used for lifting sea water up to the platform decks.

Statoil Gullfaks A Platform in North Sea - This is a produced water system installed by Kvaerner

Installasjon in July 1991. The epoxy pipe ranges from 1-inch to 24-inch diameter. Almost all materials were delivered as prefabricated pipe spools.

Ameron presently has an order to supply the following pipe systems to Phillips' Judy and Joanne

Platform, in the UK Sector of the North Sea.

• Seawater supply and return • Firewater - wet system only • Sodium hypochlorite seawater injection systems • Cooling medium supply and return

The pressure rating is 20 bars.

89
References:

1. Thon, H. et al, Use of Glass Fiber Reinforced Plastic (GRP) Pipes in the Fire Water System

Offshore, Senter of Industriforskning, Oslo, Norway, ASME Materials Engineering, Vol. III-B,

1991.

2. Britt, F., Stainless Steel vs. Fiberglass Pipe Costs, Chemical Engineering, Feb. 1990, McGraw

Hill, Inc.

90
MARINE COMPOSITES - THE U.S. NAVY EXPERIENCE

LESSONS LEARNED ALONG THE WAY

Ivan L. Caplan

Carderock Division, Naval Surface Warfare Center

Annapolis Detachment

Annapolis, MD 21402

INTRODUCTION

Current seaborne applications of composite materials in the U.S. Navy have been limited. For

submarines, these applications include sonar domes and windows, towed array fairings, and prototype

diving plane bearings and control surfaces. The focus for surface ships has been for coastal

minehunter (MHC-51) hulls 1

. Over the past ten years, however, there has been a growing interest in the development and application of composites for both primary and secondary load-bearing structures (such as lightweight foundations, deckhouses and hulls), machinery components (such as composite

piping, valves, centrifugal pumps and heat exchangers), and auxiliary or support items (such as

gratings, stanchions, ventilation ducts and screens, etc). This renewed interest in composite materials

is a result of the U.S. Navy's need for greater weight savings, reduced maintenance and life cycle costs and enhanced signature control. In many cases, these benefits may be achieved by replacing and

redesigning metallic components and structures with composites.

As might be expected, the naval and offshore communities share common interests in the use of composites for their respective applications. These include reduced structural weight, reduced

corrosion/erosion effects of seawater, improved fatigue performance, dimensional stability, domestic

availability, ease of fabrication, and tailorable properties

2

. At the same time, a number of concerns

also are shared by both communities; these include: acquisition costs, damage tolerance (structural

resistance to service/impact/shock/ out-of-plane loads), moisture resistance, joint integrity, thick

laminate processing and reproducibility, quality assurance and inspection, failure behavior and design

criteria and fire performance (flammability, smoke, toxicity and residual strength).

The high specific strength of fiber reinforced composites make them very attractive candidates

for pressure hulls for deep submergence vehicles. Composite pressure hulls can have weight-to--

displacement ratios which are significantly lower than metal hulls, giving them a greater payload

capability. Pressure hulls of glass and graphite reinforced epoxy have been built and tested in a

variety of configurations up to 4 foot diameter. Figure 1 shows a typical composite pressure hull

configuration being evaluated. Composites also are attractive candidates for a variety of secondary

structures for submergence vehicles, such as pressure flasks, tanks, fairings and control surfaces.

Figure 2 shows a composite control surface for a deep submergence vehicle. Significant reductions in maintenance costs can be achieved for these structures due to excellent corrosion resistance of

composites, and low acquisition costs due to hydrodynamic shaping during fabrication.

Technical issues for composite underwater applications that are being explored in Navy

research programs include reduced cost fabrication processes for thick composite structures, methods

for increasing tolerance for fabrication defects such as ply waveness, increasing resistance to impact

damage, developing design concepts for structurally efficient joints and penetrations, and improving

stress and buckling analysis methods and failure models for thick composite laminates under biaxial

compression.

91
• Operating depth potential of

3-4 times steel hulls • Fiberglass shell layup:

2:1 circumferential to longitudinal • Integrally wound stiffeners • Designed /fabricated /tested in 1986

Figure 1. Composite Pressure Hull Prototype (1/22 - Scale)

• Approximately 40% reduced weight • Improved corrosion resistance • Reduced magnetic signature • Potential for reduced maintenance costs

VACUUM BAG/OVENCURE

FABRICATIONMOLDED SYNTACTIC FOAM TAILPIECE

GLASS/EPOXY

SKIN

SYNTACTIC FOAM

CORE

- GRAPHITSEPOXY BOX SPAR

MOLDED SYNTACTIC FOAM NOSEPIECE

STAINLESS STEEL LEADING EDGE PROTECTOR

(NOT SHOWN)

METAL SHAFT INSERT

Figure 2. Composite Control Surface (1/4 - Scale Prototype)

92
TECHNICAL ISSUES

Marine structures tend to be thick and large when compared to aircraft or space composite

structures which tend to be thin, stiff and loaded primarily in tension. This has necessitated an

extensive development program within the U.S. Navy to address these "seaborne" concerns. Unlike

the aerospace composite community, which is large, "high tech" and consists of many defense

contractors, the marine composite community primarily includes a myriad of small "low tech" boat

builders that rely on "hand lay-up" to produce their boats and craft. The large U.S. shipbuilders, of

course, are set-up solely for metal (steel) fabrication and their labor force is trained accordingly.

The use of composite materials in the marine environment offers significant technical

challenges. The most important of these issues include: the long term effects of seawater immersion

on fiber/matrix adhesion; fire performance, integrity and fire hardening of composite materials; low

void, affordable processing of thick section structures; and improved design procedures, test methods,

scaling laws, and failure criteria for primary structures. The progress achieved by the Navy in several

of these areas will be discussed below.

THE EFFECT OF WATER IMMERSION

In an extensive study sponsored by the Office of Naval Research (ONR) conducted over the

past three years, the Carderock Division, Naval Surface Warfare Center (CDNSWC) investigated the

effect of long term water immersion on fiber/matrix adhesion by measuring interface dominated

mechanical properties of all four major classes of continuous fiber composites (glass/thermoset,

carbon/thermoset, glass/thermoplastic, and carbon/ thermoplastic) before and after immersion in 50°C

distilled water3

. The goal was to determine the degree of degradation of the fiber/matrix bond and

quantify the effect on mechanical performance.

Thermosets

The glass/thermosets evaluated included vinyl esters (8084, Derakane 51 OA), and epoxies (SP

365, Tactix 123). All had excellent retention of adhesion following immersion; electron microscopy

before and after immersion did not indicate a loss in adhesion. The technology of glass roving sizes

and glass fabric finishes is mature. There are effective coupling agents for most (if not all) thermosets

used as composite matrix resins, so achieving adequate, hydrolytically stable bonds between resin and

glass is generally not a problem if proper processing procedures are followed.

Carbon/vinyl ester compatibility was evaluated with AS4w, XASg, and T300 UC309. Carbon

fabric reinforced vinyl esters were found to have poor adhesion as shown in Figure 3. In all cases, electron microscopy shows almost bare fibers in the vinyl ester matrix composites. It appears that

carbon fiber sizes are compatible with epoxies, but these treatments are not chemically compatible with

vinyl esters.

Thermoplastics

Property retention data and microscopic inspection of the transverse flexure failures for five

glass/thermoplastic materials evaluated (E/PPS, E/J2, S-2/PEEK, S-2/PEKK, and S-2/Vectra), indicate a substantial loss in fiber/matrix adhesion. This is shown in Figure 4 for E/PPS. As-fabricated

materials appeared well-bonded and had good properties, but water apparently rapidly hydrolyzed the

fiber/matrix bonds, reducing adhesion and resulting in low flexure strength. Interestingly,

93
120

DRY 72 HR BOIL 5 MONTH 50C 5 MONTH RT

VINYL ESTER (8084) HI EPOXY (EPON 9405)

Figure 3. Effect of Water of Flexural Strength of Carbon/Vinyl Ester vs. Carbon/Epoxy

glass-reinforced thermoplastic molding grades (E/PPS and fibers are relatively short in molding grades)

fiber/matrix bond strength is less critical in these materials than in continuous fiber composites.

Carbon/thermoplastics evaluated included AS4/PPS, AS4/J-2, AS4/PEEK, and AS4/PEKK. All

four carbon/thermoplastics tested had excellent fiber/matrix adhesion, both dry and after water

conditioning. Slight matrix-dominated property reductions of AS4/J-2 can be attributed to matrix

plasticization since properties return upon desiccation.

FIRE - THE CONSTANT THREAT

Fire aboard a ship or submarine threatens the crew and platform itself and must be fought

independently with limited on-board resources. In the fall of 1985, the Chief Engineer of the Navy,

VADM Webber, stated that quantified fire performance requirements must be established for

composites to be used aboard U.S. Navy submarines. Subsequently, these requirements were

developed and the usage of composites inside Navy submarines is now covered by MIL-STD-2031

(SH). Two guiding principles4 were established for the use of composite systems aboard submarines.

First, the composite system will not be the fire source, i.e., it will be sufficiently fire resistant not to be a source of spontaneous combustion. Second, secondary ignition of the composite material must

be delayed until the crew can respond to the primary fire source, i.e., the composite system will not

result in rapid spreading of the fire. It should noted that the Navy currently has no general fire standard for composites used aboard surface ships. The flammability requirements for surface ships

are different than those for submarines and vary with location within the ship. Instead of survivability

94
EFFECT OF WATER IMMERSION ON E/PPS

PHILLIPS LG40-70

PERCENT RETENTION

70 j ~

SBS 90 FLEX STR

DRY 3 MONTHS IMMERSION

Figure 4. Property Retention and 90° Flexural Surfaces of E/PPS, Both Dry (Left) and After

Three Months Immersion at 50°C.

95
measured in minutes, as it is in submarine fires, the critical issue in surface ship fires is the residual

strength of structures at elevated temperatures for a period of 30-60 minutes.

Under OMR and Naval Sea Systems Command (NAVSEA) sponsorship, CDNSWC has been

evaluating composites fire related issues for the past several years in collaboration with industry,

universities, research institutions and other government agencies. This comprehensive effort includes

work on fire performance and test method development 5

, thermal and fire barriers to protect the

composite structures against fire damage, effects of combustion by-products on toxicity and electronics

corrosion, and residual load bearing strength and structural degradation of composites during fire

6

.

Fire Performance of Composite Materials

A broad spectrum of thermcset and thermoplastic glass and graphite fiber reinforced composite

materials have been evaluated. These include fire retardant vinyl ester (VE), epoxies (EP), cyanate

esters (CE), bismaleimides (BMI), phenolics (PH), polyimides (PI), polyphenylene sulfide (PPS),

polyether sulfone (PES), polyaryl sulfone (PAS), polyether ether ketone (PEEK), and polyether ketone

ketone (PEKK). The flammability characteristics evaluated in this study included flame spread index

(ASTM E-162), specific optical smoke density (ASTM E-662), combustion gas generation, residual

flexural strength (ASTM D-790), heat release and ignitability as measured by cone calorimetry (ASTM

E-1354).

With the exception of vinyl ester, all glass or graphite reinforced composite materials met the

requirements of flame spread index (maximum 20). Also, with the exception of fire retardant vinyl

ester and thermoplastic J-2, all glass or graphite reinforced composite systems met the requirements

of specific optical density at 300 seconds (maximum 100) and maximum smoke density of 200 as per

MIL-STD-2031.

The rate of heat release, especially the peak, is the primary characteristic determining the size,

growth, and suppression requirements of a fire environment. MIL-STD 2031 requirements for peak

heat release (ASTM 1354) at 75 and 100 kW/m2 are 100 and 150 kW/m2 respectively. Glass or

graphite reinforced phenolic, polyimides, and many of the thermoplastics composites met this requirement as shown in Figure 5. MIL-STD-2031 (SH) requires the ignitability of organic matrix

based composites to be greater than 60 and 90 seconds at radiant heat fluxes of 100 and 75 kW/m2

respectively. All unprotected composite materials evaluated in this study failed to meet the ignitability

requirements of this submarine specification.

Thermoset composite materials, in general, have higher heat release rates than thermoplastics,

but have higher (better) ignitability resistance. Of all the composite materials evaluated, glass/vinyl

ester composites were the least desirable from the fire point of view but most desirable from the

affordability point of view. Phenolic based composite materials provided the optimum balance of fire resistance and affordability, however, their mechanical performance for primary structures is generally

poor. Advanced thermoplastics, for the most part, have lower heat release rates, but are also

accompanied by lower ignitability resistance and lower glass transitions temperatures. It is in this area of ignitability, however, where fire barrier treatments provide the most benefit by delaying the onset

of spontaneous ignition by providing a significantly greater time interval for the fire fighters to control

the fire.

Fire Barriers (Fire Hardening)

The main conclusion from the fire testing conducted by CDNSWC is that unprotected

composite systems cannot fully meet the stringent fire requirements specified for interior spaces of

U.S. Navy ships or submarines. Military vessels must perform their mission even when damaged, and

96
350 — GL/VE(2) — GL/EP(3) | -*-GL/BMI(10) — GL/PH(19B) | ^GL/PMR(23M)

+ GL/PPS(24)

-^-GR/PEEK(26)

^GR/PEKK(29)

-^GR/PAS(27)

-^GR/PES(28)

^GR/PPS(25)

25 50 75 100

Flux, kW/m2

Figure 5. PHR vs. Flux for Selected Composite Materials

must survive the fire for sufficient periods of time to effect rescue missions. To enhance the fire endurance and survivability of composite structures, incorporation of fire barrier treatments is necessary. These treatments function either by virtue of their ability to reflect the radiant heat back

towards the heat source or delay heat penetration by their insulative, ablative, or endothermic

properties. This delays the heat-up rate and reduces the overall temperature on the back side of, for

example, a structural bulkhead. It is important to note, that fire hardened composite compartments can

actually serve as an excellent containment area which can prevent, or significantly delay, flashover in adjacent compartments.

In a recent study by U.S. Navy7

, several fire barrier treatments were evaluated including

ceramic fabric, a ceramic coating, an intumescent coating, hybrid of ceramic and intumescent coatings,

silicone foam, phenolic skin, thermoplastic coatings, APM (ablative protective material), Interam

endothermic mat E-IOA, and Interam intumescelt mat I-IOA. The composite systems evaluated with

these thermal barrier treatments included glass/vinyl ester, glass/epoxy and graphite/epoxy. Test results show that the intumescent coating, the ablative protective material, and Interam endothermic and

intumescent mats were the most effective composite fire barriers. With any of these fire barrier

treatments, all composite systems evaluated met the ignitability requirements of 90 and 60 seconds at 75 and 100 kw/m 2 respectively. This is illustrated in Figure 6, which shows peak heat release rates for the bare glass/epoxy panel [1003], glass/epoxy/ APM (0.125" thick) [1004], glass/epoxy/ I-10A

(0.125"thick) [1041], glass/epoxy/ I-10A (0.250"thick) [1044], glass/epoxy/ E-10A (0.20"thick) [1042],

and glass/epoxy / intumescent coating (0.030" thick) [1047]. In all cases, the panels were exposed to

97
Heat Release, kW/m2

200

200 400 600 800 1000 1200 1400 1600 1800 2000

Time (s)

Figure 6. Heat Release Rates for GI/EP With and Without Fire Barriers

a heat flux of 75 kW/m2 in a horizontal orientation. Interam E-10A protected the composite from

ignition for a period of 30 minutes.

Residual Strength of Composites

Recently, the assessment of composite structural performance during and after fire has become

a subject of intense discussion within the Navy community. Our experience indicates that composites

made of woven roving or fabric retain higher residual strength after fire exposure than prepreg tapes

which totally delaminate during the fire exposure due to resin charring resulting in loss of interlaminar

strength.

Since composite materials are made with organic matrices, these resins systems may undergo

viscoelastic transitions and/or chemical decomposition during thermal exposure. Below certain critical temperatures, composites will retain most of their load bearing characteristics, but above this "critical" temperature (usually the glass transition temperature), composites begin to lose their mechanical

properties rapidly and, in some cases, catastrophically. During a fire, if the resin matrix approaches

the glass transition temperature, it can no longer transfer load to the fiber. A critical temperature for

98
irreversible damage is about 500 °F for glass/vinyl ester. However, fully recoverable damage is possible only at temperatures below 200°F.

CDNSWC has initiated a comprehensive effort focused on the issue of structural strength. This

is intended to result in analytical models that can be used by naval architects to design full scale

fire-tolerant composite structures. This methodology includes determination of basic composite

characteristics at elevated temperatures, determination of isothermal material characteristics for use

in the computer model, determination of creep characteristics of materials (creep is an unacceptable

structural instability), determination of heat transfer characteristics of composite materials exposed to

fire, construction of mathematical models of basic shapes under typical loads using ABAQUS finite element analysis, and verification of these models in small and large scale fire tests using the data

generated in the full scale ASTM E-119 tests and in smaller scale tests.

Large Scale Fire Testing

The thrust of U.S. Navy's large scale fire testing program has been to understand the behavior

of composite structural systems to fire threats, and to determine the effects of various passive

protection techniques. Two approaches were taken: ASTM E-119 furnace testing for structural strength investigations and open flame testing to determine ignition, flammability, and thermal

vulnerability. These tests have been performed on hardened and unhardened composite panels.

Figure 7 shows two glass/vinyl ester composite wall sections in the ASTM E-119 facility at Southwest Research Institute. They were preloaded to 28,000 pounds to simulate the expected loading

aboard ship. The bulkhead on the right was not thermally protected and started to buckle 7 minutes

after the test began. The bulkhead on the left was built using a fire tolerant beam, and was thermally

insulated. It completed a one hour test in the same furnace.

Figure 7. Two Composite Wall Sections in the ASTM E-119 Facility

Figure 8 is a module 8 ft. x 8 ft. x 16 ft. long made of composite panels. Three modules were

tested; in two, the panels were glued and bolted to a steel framework to form the walls and ceilings

of a shipboard deckhouse mock-up. In the remaining module, the composite panels were produced

with integral composite beams. An interior wall divided each composite module into two

99
Figure 8. Composite Module During a Post-Flashover Fire Test

compartments. One compartment was used for smaller test fires to the explore material flammability

and flashover potential. The other compartment was used for a 2500 kW post flashover test fire. The

fire conditions represented by these tests are intended to represent hazards perceived for combatant

ships, and to show us how the results from small scale tests would correlate with realistic fires. Conclusions reached from these tests are that remaining uncertainties are resolvable and that future

ships will certainly benefit from structural composites.

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LOW-COST HIGH QUALITY FABRICATION

A significant issue impeding the use of composites for naval applications is the generally higher

acquisition cost of the composite system compared to the incumbent metallic (usually steel) component

or structure. For most Navy ship applications, the total material cost may range from 10-25% of the

total system cost, and the processing cost may be a very large portion of this total. In recent years, considerable progress has been made on this key issue of affordability through research and

development addressing low-cost high-quality fabrication methods combined with innovative design

concepts.

A great variety of processing methods are now available for the fabrication of composite

materials. These methods include hand layup, pultrusion, resin transfer molding, vacuum bag molding,

autoclave molding, injection molding, filament winding, and continuous laminating. Although

conventional hand layup glass reinforced plastic (GRP) materials could be used for fabricating large

naval composite structures, improved performance is achieved by using aerospace production methods

that produce higher fiber and lower void content composite structures. One approach to achieve higher

fiber contents in composite structures is to use low-temperature prepreg or wet layup materials

combined with vacuum bag and autoclave curing. An even more promising and cost effective method,

is a vacuum assisted resin transfer molding (VARTM) process employed by the Navy for a number of

high performance composite ship structural applications8,9

. This VARTM method has the advantage

of being an open mold process which minimizes tooling costs. Fiber contents of 70% (by weight) and

void contents of less than 1% have been attained using a particular VARTM process known as SCRIMP, developed by Seemann Composites, Inc. An additional advantage of this process is the

incorporated provision for capturing and filtering styrene emissions which minimize the environmental

impact.

The improved VARTM method has been exploited by CDNSWC for a variety of development

programs for the low-cost fabrication of high quality composite secondary structures for Navy

combatants and other ships. To date, the U.S. Navy has successfully demonstrated and evaluated this process for composite deckhouse, mast, foundation and hull applications produced in monocoque, single

skin stiffened, or sandwich configurations.

MATERIAL PROPERTIES AND STRUCTURAL DESIGN METHODS

Accurate and reliable mechanical property data are paramount to successful composite marine

structures design. Mechanical properties for laminated composites primarily are dependent on

constituent mechanical properties, fiber volume fraction and fabrication process quality. Variations in any of these factors can influence the mechanical properties of the material. Consequently,

experimentally determined mechanical properties are optimum for composite structural design since

measured properties account for these variations. Measured property data, however, exhibit some

degree of scatter. Scatter in stiffness data generally is low and average stiffness values are acceptable

for design purposes. Scatter in strength data, however, generally is high and strength data commonly

is represented using statistical assurances such as A-basis or B-basis.

Ideally, each marine composite structures program would include coupon testing to obtain

complete mechanical property data. Comprehensive material testing, however, usually is impractical

for short-term programs. In the absence of coupon data, many of the surveyed designs relied on

published experimental properties or on theoretically computed properties. Experimental mechanical

property data are published in a variety of sources including scientific journals, technical handbooks,

and vendor publications. Factors such as the material system, fiber content, void content, and

fabrication method for the published material system must match the proposed material system factors

in order to effectively use published data for design purposes.

101
Laminated composite material properties can be determined theoretically from constituent or lamina properties. Theoretical lamina properties can be calculated from constituent properties using

a variety of micromechanical theories. Effective laminate mechanical properties subsequently are calculated from lamina properties using, for example, Classical Lamination Theory or Effective Modulus

Theory. Measured properties, however, always are desired over predicated properties due to the

cumulative effect of assumptions used in these predictions which can lead to inaccuracy.

A typical design process for surface ship structures is initiated by using provided design criteria and a strength-of-materials approach to calculate the induced primary stresses in the deck and, hull bottom. The calculated stresses are used to modify the assumed set of cross-sectional scantlings and

the trial-and-error iterative process continued until an optimum set of scantlings is obtained. The same

process is applied to other transverse sections. For low L/B ship, transverse strength and torsional

strength of the hull must also be checked. This is true especially for a composite hull due to the low

rigidity of the composite material.

For calculating stresses in complex structural components, a strength-of-materials approach is generally inadequate and, therefore, a finite element analysis (FEA) must be used. It is possible to model the entire hull structure, but this is seldom done because the lack of knowledge of accurate loads

reduces the value of the results. The expense is sometimes justified, however, for new and unusual

configurations and materials, and for determining boundary conditions for FEA of local structural components.

COMPOSITE DEMONSTRATIONS AND APPLICATIONS IN THE NAVY

For over twenty years, the U.S. Navy has used extgremely large monolithic composite structures,

such as the GRP Sonar Domes (manufactured by HITCO) shown in Figure 9. In order to transition

additional composite technology into the fleet, the Navy has worked with industry to design and produce

a number of prototype structures and machinery components for material characterization, design

evaluation, sea-trials or other full scale tests. Some of the recent composite demonstrations are described below and their salient features highlighted.

STRUCTURAL APPLICATIONS

Advanced Material Transporter (AMT)

The fabrication of a 44-foot long, 0.35-scale manned model of the AMT, a new landing craft concept, is the U.S. Navy's first attempt to exploit the VARTM process for primary hull construction.

This is shown in Figure 10. The AMT represents a technologically advanced utility landing craft which

provides enhanced speed, mobility, and operational flexibility needed for future Navy and Marine Corps

logistic support missions. The design and fabrication of an advanced all-composite structure for the

AMT provided an opportunity for the Navy to pursue affordable technology for naval ships that also

could benefit the commercial shipbuilding industry 10. A hybrid composite structural concept was developed for the AMT with GRP single skin

stiffened structure in the hull, and balsa core sandwich structure in the decks, bulkheads, superstructure

decks and wingwalls. These structural components were fabricated separately using VARTM as were some of the connection angles for the more critical assembly joints which run in the longitudinal

directions. All the GRP laminates and sandwich skins of the AMT model used the 24 oz. woven roving

E-glass fabric and a vinyl ester resin. Medium weight balsa wood was used for the sandwich cargo deck

while lighter balsa wood was used for the cores of the sandwich bulkheads and superstructures. All

stiffeners for hull, deck and bulkheads have light weight non-structural PVC cores and were fabricated

in-place using the VARTM process. The use of the same type of fabric and [0/90] laminate of 1:1 woven roving throughout the AMT model is a manufacturing cost saving. For the hull shell, this layup

102
Figure 9. GRP Sonar Dome

Figure 10. AMT Final Assembly

provided adequate stiffness and good damage tolerance under impact due to slamming and beaching

while the hull longitudinal stiffeners can sustain the hull bending condition. Bias [ + /- 45] plies for the

hull sides and transverse bulkheads were not needed for the AMT model, since the design buckling and

shear stresses in these components were very low.

The U-shape hull of the AMT model was laid up in full thickness (0.33 in., 14-15 plies) on a female mold and resin injected in less than 3.5 hours using the VARTM process. Progressive resin

injection points at increasing distances from the hull center line were utilized to allow the resin to flow

103
outward and up the hull sides without air entrapment or fiber wrinkling. Although a single VARTM

injection was suitable for fabricating the hull of the AMT model, multiple VARTM injections may be

required to fabricate the much thicker hull of the full scale AMT. (Ply waviness has occurred in the

past when using this process for making thick laminates such as that required for a full scale AMT,

especially in regions of high curvature.) The GRP hull was then reinforced with longitudinal top-hat

stiffeners and transverse frames which were fabricated in-place using VARTM. The shallow stiffeners on the hull sides were put in first, the two transverse frames of medium depth were installed next, and

the five hull girders of greater depth were installed last. Based on hat stiffener pull-off tests, the use of the VARTM process for fabricating stiffeners and frames on the AMT hull is expected to provide

full primary bond strength.

The AMT cargo deck, bulkheads and superstructures are sandwich construction which were laid up on a simple flat mold and resin injected using the VARTM process in one step. The sandwich deck was completed in 1.5 hours. Narrow vertical slits in the balsa wood allowed the resin to impregnate

from the upper to lowerskins of the sandwich components. The sandwich deck and bulkheads were

reinforced stiffeners with tapered ends which were fabricated in place using VARTM as described

previously for the hull stiffeners and frames. The hull, deck, bulkhead and superstructure elements of

the AMT model were assembled using pre-fabricated connection angles or wet layup connections.

The fully outfitted AMT model, equipped with two Hamilton 291 waterjets powered by two

Crusader 454 gas engines, recently has been completed by Seemann Composites and delivered to the

Navy. Presently, the AMT model is assigned to the CDNSWC's Special Trials Unit at the Patuxent

River Naval Air Station, Maryland, for at-sea tests, evaluation and operational demonstration.

Lightweight Foundations

The use of composite materials for Navy ship machinery foundation structures offers many

potential advantages over current steel structures including weight reductions of up to 50 % , improved

shock and corrosion resistance, and reduced noise and magnetic signatures.

To verify the feasibility of using composite materials for important foundation structures, several

demonstration projects were conducted. One project included a one-half scale fresh water pump

foundation fabricated and subsequently tested under shock loading. The composite foundation was

designed to match existing geometrical constraints and resulted in a weight reduction of 40% over the

existing steel foundation structure". The structural adequacy of the composite foundation design was

verified based on the test results coupled with a finite element analysis. The VARTM process, described earlier, was selected for the foundation fabrication; cost estimates being approximately 50%

less than for other methods. An epoxy resin was selected for the foundation based on required strength

considerations. The fiber reinforcement was E-glass. The strength of the composite pump foundation was evaluated by high-impact shock tests (per MIL-S-901D) using a Navy medium weight shock test machine. The foundation was tested in four different orientations: vertically, longitudinally,

athwartships, and at an inclined angle of 30 degrees. A facsimile steel mass was used to simulate the

weight and center of gravity of supported equipment. The foundation was tested both with and without

resilient mounts which would be used between the foundation and the equipment bedplate on a full scale application. The composite foundation was able to sustain accelerations of up to 150 g's with no

apparent degradation.

A second foundation demonstration structure represented an equipment pallet of the type used

to support surface ship topside electronic equipment. The pallet concept allows multiple prepackaged

equipment units to be assembled and checked out prior to being lifted aboard ship as a single unit as construction proceeds. The foundation was of filament-wound construction using epoxy resin and

high-strength S-2 glass fibers. The fabricated foundation easily met the weight reduction goals of 20%

versus aluminum. The final foundation weight actually represents a 44% weight savings compared to aluminum and 60% compared to steel. In the shock qualification test phase, all the general shock

104
related failure criteria were met, and no apparent damage was observed or measured upon completion

of the multiple shock test series. During shock testing, the foundation was loaded with 3200 lbs.,

representing the loading of an electrical transformer. These foundation demonstration projects have

shown that composite foundation structures can be designed to exceed Navy combat requirements while

offering very significant weight reductions.

For offshore applications, if we assume that machinery and equipment requirements are similar

to those of larger combatant ships and the weight savings percentages can be applied to the foundation

weight aggregate totals, then the total foundation weight savings for offshore applications could be very

significant, particularly for the floating, tethered rigs that depend on buoyancy and hydrostatic stability for their operational mode. As an example of possible weight savings for naval applications, a study

of the CG-47 class mid-size cruiser revealed that approximately 390 tons was associated with foundation

weight. Assuming a conservative 25-30% weight reduction through the use of composites, a total weight

savings of over 100 tons could be realized!

Composite Mast

In order to demonstrate the feasibility of a composite mast for naval combatants, a one-half

scale, 36-ft tall, prototype mast (Figure 11) was designed, and fabricated using VARTM. It successfully

withstood the air blast test under the DISTANT IMAGE event at White Sands, in June 1991. A hybrid

material system of S-2 glass and carbon in a vinyl ester resin system was selected for the main trunk

of the mast; S-2 glass to maximize ballistic performance and carbon in +/- 45 layup to provide sufficient

torsional stiffness.

BLAST RESISTANT TOPSIDE STRUCTURES

The U.S. Navy has made considerable progress over the last six years in the development and

demonstration of blast-resistant composite design concepts and prototypes for deckhouses,

superstructures and other topside enclosures for naval combatants. These composite concepts offer

significant advantages over conventional steel structures including a 35 to 45% reduction in weight,

reduced corrosion and fatigue cracking, and improved fire containment 12

. Two composite design concepts, a single skin stiffened and a sandwich core concept have been

developed for topside applications. The stiffened concept was developed first and involved the assembly

of prefabricated hat-stiffened GRP panels using prefabricated GRP connection angles and

bolted/bonded joint details. Panel stiffeners were tapered to maximize peel resistance, to minimize

weight, and to simplify the joints and panel connections. The sandwich concept followed and utilized

prefabricated sandwich panels which are attached through bolting and bonding to a supporting steel framework. A steel framework is attractive for the construction of composite topside structures since

it is readily erected in a shipyard environment, allows for the attachment of prefabricated high-quality

GRP panels, and provides resistance to collapse at elevated temperatures under potential fire insult. The stiffened and sandwich panels were prefabricated using E-glass and vinyl ester resin materials in the VARTM process that yielded significantly higher mechanical properties than achieved using

conventional hand layup procedures.

In order to demonstrate the producibility of these concepts and their structural integrity under

air blast loading and at elevated temperatures, several full-scale test modules, 16 ft. long x 8 ft. high x 8 ft. wide, as seen in Figure 12, were built and tested. The GRP single skin stiffened module was

successfully air blast tested at the White Sands Missile Range under the MISERS GOLD and

DISTANT IMAGE events in 1989 and 1991, respectively. The limited, acceptable damage to the

module under severe loading, demonstrates the superior toughness of the structure. Fabrication

advantages of sandwich construction over single skin stiffened for deckhouse structure include further

weight reduction, a flat surface on panel interiors for ease of outfitting and possible lower production

105
Figure 11. 1/2 - Scale Composite Ship Mast

costs. A tapered sandwich panel concept fabricated using the VARTM process with a balsa core and

vinyl ester resin was selected for the construction of a sandwich deckhouse module which was also

successfully air blast tested at White Sands.

Under a collaborative effort with the Canadian Navy, blast tube tests were conducted on a

variety of one-half scale (4' x4') sandwich panel designs, including a fire-hardened concept having an

additional skin at the mid-layer of the panel. The fire-hardened concept withstood an equivalent static pressure of 155 psi without rupture. Blast tube tests were also conducted on one-half scale stiffened

panels having a variety of edge connected details, leading to the selection of a steel connection angle

and a refined bolted/bonded detail. The structural integrity of the fire-hardened structure at elevated

temperatures (1800 to 2000 degrees F) was dramatically demonstrated when the unprotected stiffened

106
SINGLE SKIN SANDWICH MODULE

STIFFENED MODULE * E*Gfass/Vinyl Ester

* E-Glass/Vinyl Ester ** Balsa Core

* 35% Weight Savings 49% Weight Savings

Figure 12. Composite Superstructure

module, without internal insulation and the top statically loaded (90 lbs/ft

2 ), withstood a 30 minute

internal sprayed fuel fire without collapse or without exceeding allowable deflections (span length / 50).

COMPOSITE MACHINERY APPLICATIONS

The Navy's composite machinery program has focused on technologies such as composite

centrifugal pumps, valves, piping, ventilation ducting, heat exchangers and composite shafting. These

composites employ primarily glass reinforced thermosetting resins such as vinyl esters, epoxies, and

phenolics. Graphite reinforced thermosets have been avoided in non-wetted parts because of the concerns of conductive graphite particles becoming entrained in the atmosphere and shorting out

electrical equipment in post fire scenarios. Some of these components, like piping, are fabricated by

filament winding. Others, like pipe fittings and valves, are made by compression molding. In order to reduce costs, efforts are underway to reduce the number and variety of spare parts and inventory by

developing "standard families" of selected machinery components produced with composites.

Primary technical issues of concern for shipboard machinery applications include structural performance under shock (simulation of near underwater explosion) and performance in fire (usually

in a hydrocarbon pool fire of 1500-1800°F). The Navy's experience with structural integrity of

machinery components under shock is that most composite components can be made to survive the

mechanical stresses and potential shock loads in a shipboard environment if properly supported, and

if the composite is not expected to carry excessive loads.

107
Composite Piping

Experience with the fire performance of composite materials has shown phenol ics to be the best

fire performers among the thermosets. In an extensive study conducted at CDNSWC, several phenolics

have shown excellent flammability, smoke, and toxic combustion product performance. For this reason, Navy is focusing on phenolics for development of corrosion resistant supply ventilation ducting and

piping.

Advanced composites made from thermoplastics such as PPS, PEKK and PEEK are also being

explored as candidates for fluid systems machinery components, especially piping and ventilation

ducting. These thermoplastics are tougher than most thermosets and are less susceptible to installation

damage. A composite piping or ducting system made from an thermoplastic could be bent, would not require adhesive bonded joints, and would require fewer fittings relative to conventional thermoset pipe.

The outstanding flammability, smoke, and combustion gas characteristics of advanced thermoplastics

composites are far better than most thermosets, including some phenolics. Questions remain, however,

about the full scale fire performance of equipment fabricated from these resins, and about strength

retention in water for certain types of glass reinforcement. Prototype S-2 glass-reinforced pipe (1.5"

diameter) was fabricated and successfully bent to 90°. Straight sections of the pipe were successfully

hydrostatically tested to 1000 psig after a simulated bend thermal cycle.

Composite piping system fire survivability has also been evaluated using glass reinforced epoxy

and vinyl ester piping systems with various fitting joint methods and under dry, stagnant water, and

flowing water conditions. The results of these tests are compared with metallic alternatives. For

example, 90-10 Cu-Ni sil-brazed joints survive 2-3 minutes with dry pipe and less than 20 minutes with

stagnant water in the pipe. Epoxy thermosetting pipe assemblies using tapered epoxy adhesive bonded

joints survived less than 3 minutes in full scale fire when pressurized to 200 psig stagnant water. The

joints failed catastrophically. However, application of a promising fire barrier around the pipe joints

improved survivability time to 23 minutes, and a completely insulated assembly survived for 30 minutes

with no leaks after the fire. Some prototype piping and installation is shown in Figure 13. The Navy is currently attempting to establish fire performance requirements for surface ship

composite piping systems and other composite machinery components. One approach being proposed

is to tailor performance requirements after International Maritime Organization (IMO) guidelines,

many of which are being incorporated into ASTM Fl 173, "Epoxy Resin Fiberglass Pipe and Fittings to be used for Marine Applications".

Composite Centrifugal Pumps

The most successful Navy composites machinery program to date, involves the development of

a standard family of composite centrifugal pumps (Figure 14). The pump family employs a limited

number of pump housing sizes, impellers, and drives to cover a wide range of pressure and flow rate requirements. The pump housing can be fabricated from glass-reinforced epoxy, vinyl ester, or polyester2

. Part of the development effort involved high velocity erosion investigations with various

fiber reinforced polymer matrix composite pump materials. These studies showed excellent corrosionerosion performance of composites relative to gun metal bronze (widely used in marine centrifugal

pumps) over a velocity range of 0 to 130 ft/sec. However, the composites did not fare as well under

cavitation conditions, where they showed generally inferior performance to the bronze. In most marine

pump applications, however, cavitation should not be a problem.

Composite Valves

Another area of Navy interest is in the development of standard composite valves. Extensive

mechanical evaluations have been done on a commercial glass-reinforced vinyl ester ball valve. The

108
CHT TANKS ABOARD JOHN F. KENNEDY

AFTER 2 YRS SERVICE

4-INCH GRP "DISCFUSER"

AERATION AERATOR

LINE PVC

WATER

WASHDOWN

NOZZLE

MAC

SENSOR

FLOAT
ANSI flange

connections

Pull from rear disassembly

Supported

cutwater

tongue

Through bolting arrangement for

4 positions of casing

Front and back

composite wear rings

Seal protector

Mechanical seals

Close clearance bushing — Composite shaft sleeve,

O-ring sealed, key drive

Hydraulic Institute \JM'

shaft extensions

Welded 2 -piece, closed

composite impeller with

molded in drive key

Pump mounting and mount support drain

Figure 14. Composite Centrifugal Pump

valve is generally 1/5 to 1/3 the weight of a typical metal counterpart, and 1/4 to 1/2 the cost,

depending on size. It is available in the 1 through 6-inch size range. When protected with a prototype

fire shield, shown in Figure 15, it survived for 30 minutes in a hydrocarbon pool fire. The valve body

remained basically intact. The valve was closed and pressurized on one side to 200 psig. It should be

noted, however, that the pressurized flanged joint, which contained a neoprene gasket, leaked during

the fire and helped cool the valve. This illustrates the important effect of fluid conditions and joining

methods when testing a particular system. Nearly 10 years of shoreside experience at the Charleston

Naval Station has shown these valves to require virtually no maintenance.

LESSONS LEARNED IN APPLYING COMPOSITES

Attempt to avoid direct substitute replacement scenarios of incumbent metallic construction

materials with either conventional or advanced composite alternatives. Direct substitution, in the sense of filling the existing dimensional design envelope optimized for a metallic alloy, with a vastly different

composite alternative (in terms of density, stiffness, strength, fatigue characteristics, corrosion

resistance, galvanic nobility, expansion coefficients, thermal and electrical conductivity, etc.) usually

prevents performance optimization of many parameters in spite of the freedom associated with the

tailorability of composites.

Make an effort to thoroughly understand the characteristics and true limitations of the incumbent

or baseline material and design that you are attempting to improve with composites technology. The

history of marine materials development has followed an evolutionary trend with materials having

performance limitations being continually superseded by superior replacements. Composite materials

110
Figure 15. Composite Test Valve With Fire Shield

can be viewed as an "enabling technology" for marine engineers striving toward broad objectives such

as improved system performance, increased payload, energy efficiency, safety, and extended service lives

in the aggressive ocean environment. Setting realistic goals associated with measurable performance

enhancements, conducting material trade-off studies using modern analytical tools, and not making

presumptions about the ability of an incumbent metallic material or a new alternative composite

candidate to meet a particular performance requirement without adequate data, are the keys to good

decisions and opportunities for significant improvements. For example, do not assume that an

incumbent component can meet fire performance requirements just because it is metal; and conversely,

do not assume composite material candidates can't meet fire requirements just because they include

polymer matrix components.

Do not reinvent the wheel. Recognize that polymer-matrix composites have gradually evolved from

the fiberglass-reinforced plastic laminates that were first introduced in the United States in the late 1940's. As a result, there is a considerable body of literature and experience on which the marine

design engineer can draw. Case histories involving 10 to 30 plus years of continuous service inseawater

or in the marine environment can be found for a wide variety of machinery and structural applications

such as: piping systems, pumps, tanks, propeller shaft coverings, sonar domes, radomes, floats, sailboats,

motor yachts, naval personnel and utility boats, minesweepers, etc.

111
There are still many areas where improved design and analysis tools are needed. These include:

laminated plate design methods for fixed or elastically restrained edges; user friendly design tools for predicting through-the-thickness normal and shear peeling stresses at details, curved sections, stiffeners,

joints, and penetrations; automated design tools for thick bolted and bonded joints; improved FEA

procedures for thick sandwich panels; quick and accurate method for estimating the natural frequencies

of a composite sandwich panels with orthotopic skins; and design tools for predicting the stresses and

deflections of sandwich panels under concentrated and patch loads. In addition, a reliable and

consistent composite material property database is essential to provide the accuracy and confidence in the design and analysis process.

Navy experience and investigations suggest significant problems exist with fiber/matrix adhesion

of continuous glass reinforced thermoplastics and carbon reinforced vinyl esters when immersed in

seawater. These combinations should be avoided for marine immersion applications until suitable

improvements are made in fiber sizings.

Low Cost Resin Systems. Evaluations of polyester and vinyl ester laminates have indicated that polyester resins, in general, have low tensile, compressive and flexural strengths and poor impact

damage resistance due to their low failure strain, usually less than 2%. However, when an isophthalic

polyester with a failure strain of almost 4% was evaluated, it was found to have static mechanical

strength and impact damage resistance equivalent to vinyl esters at half the cost.

Resin modulus plays a major role in composite compression and flexural strength. Although this trend has been observed in carbon/epoxy laminates by the aerospace industry, it may not be fully

appreciated by the marine industry.

Affordability/Property/Fire Trade-Offs. Of all the composite materials evaluated, glass/vinyl ester composites were the least desirable from the fire point of view, but most desirable from affordability

point of view. Thermoplastic composites have good fire performance characteristics, but have seawater

or affordability limitations. Phenolic based composite materials provided good fire resistance and

affordability, however, their current mechanical performance is generally unacceptable for primary

structures.

Fire performance characteristics of unprotected composite systems cannot meet the stringent fire

requirements specified for interior spaces of U.S. Navy ships or submarines. Military vessels must

perform their mission even when damaged, and must survive the fire for sufficient periods of time to

effect rescue missions. To enhance the fire endurance and survivability of composite structures,

incorporation of fire barrier treatments is necessary.

The Navy experience suggests that composites made of woven roving or fabric retain higher residual

strength after fire exposure than prepreg tapes which totally delaminate due to resin charring. Along

the way, Navy has learned to design more fire safe structures by paying attention to engineering details

during fabrication.

Because of inherent low stiffness of the material, deflection and buckling, rather than strength,

frequently govern the structural design. For this reason, many composite ship structures, especially

decks and bulkheads, are usually of a sandwich panel construction. Advantages of sandwich

construction over single stiffened skins include greater weight reduction, a flat surface on panel interiors

for ease of outfitting and possible lower production costs.

112
Significant design opportunities exist for composite structural integration. Concepts are being

developed and studied which would allow the deck structures to incorporate structural features that would serve as mounting points for equipment and may, in fact, eliminate the foundation as a separate

structural unit. An application such as an integrated deck-foundation system can take full advantage

of the inherent design flexibility of composites.

Most composite machinery components can be made to survive the mechanical stresses and

potential shock loads in a shipboard environment if properly supported.

Have patience! It took the American Automotive Industry about 50 years to recognize and

extensively begin to apply composite body panels which Henry Ford had demonstrated in 1940 (Figure

16). Can the Marine Industry be far behind?

CQh'll-QSLVl£& l£NGLNl£l£Li±NG

Henry Ford, on November 2, I 940,

wields an cue against a trunk lid

made from a highly resilient

soybean-derived

plastic.

Vudau

warn

Body panels made of a composite

material that resists impacts and

never rusts.

Figure 16. BE PATIENT

113
REFERENCES

1. Gagorik, J.E., Corrado, J.A.,Kornbau, R.W.; "An Overview of Composite Developments for Naval

Surface Combatants", 36th International SAMPE Symposium and Exhibition, Volume 36, April 1991.

2. Wilhelmi, G.F; "Composite Materials for Ship Machinery Applications", The Society of Naval

Architects and Marine Engineers", STAR Symposium/3rd IMSDC, June 1988.

3. Juska, T.; "Effect of Water Immersion on Fiber/Matrix Adhesion", CARDEROCK-SME-92/38,

January 1993.

4. DeMarco, Ronald A.; "Composite Application at Sea: Fire Related Issues", 36th International

SAMPE Symposium, April 15-18, 1991.

5. Sorathia, U; Dapp,T; Beck, C;" Fire Performance of Composites", Materials Engineering, September

1992, A Penton Publication.

6. U. Sorathia, C. Beck, T. Dapp; "Residual Strength of Composites during and after Fire Exposure";

Journal of Fire Sciences, Volume 11, No. 3, May/June 1993 (ISSN0734-9041)

7. U. Sorathia, Charles Rollhauser, W. Allen Hughes; "Improved Fire Safety of Composites for Naval

Applications"; Fire and Materials, Vol. 16, 11999-125 (1992); July-Sept 1992, John Wiley & Sons, Ltd.

8. Critchfield, M.O., Nguyen, L.B.,and Judy, T., "Low Cost Fabrication of Composite Ship Structures Using Vacuum Assisted Resin Transfer Molding", Proceedings of the Composite in Marine Applications

Symposium, The Society of Boat and Yacht Designers, 7 November 1992, Seattle, Washington.

9. "Low Cost, High Quality Composite Ship Structures Technology Demonstrated", Research Release,

Carderock Division, Naval Surface Warfare Center, May 1993.

10. Nguyen, L.B.,Kuo, J. C, Critchfield, M.O., and J.D. Offutt, "Design and Fabrication of a High

Quality GRP Advanced Material Transporter" ASNE Small Boats Symposium, 26-27 May 1993, Naval

Amphibious Base, Norfolk, Va.

11. Crithfield, M.O.,and Judy, T., "Low-Cost Design and Fabrication of Composite Ship Structures",

Proceedings of the Carles Smith Memorial Conference, 13-14 July 1992, Dunfermline, Scotland, Special

Edition of Journal of Marine Structures, Elsevier Publications.

12. Critchfield, M.O., Morgan, S.L., Potter, P.C., "GRP Deckhouse Development for Naval Ships",

Advances in Marine Structures, pgs. 372-391, Elsevier Applied Science, 1991.

114
Summary of

ADVANCED COMPOSITES: SHAPING TOMORROW

KEYNOTE ADDRESS #5 CHALLENGES AND THE FUTURE

J. Michael Bowman

Vice President and General Manager

DuPont Advanced Material Systems

Delaware Technology Park

P. O. Box 6108

Newark, DE 19714-6108

DuPont has invested more than two billion dollars of capital and R&D in Advanced

Materials and Advanced Composites. These technologies represent a major renewal

for the corporation. But the worldwide industry is currently poised on the edge of

financial collapse.

Why, then are advanced material systems still exciting to us? What will it take for

companies and nations to succeed in this field?

Advanced Composites will be among the core technologies that unlock tomorrow's

boundaries. Today we are in the midst of a materials revolution. Advanced

Composites are at the leading edge of the material systems which are taking us into the

future — in aircraft, space, automotive, industrial, biomedical, sports and electronic

applications.

Market Drivers taking us into the future are:

Protection . . .

• F-22 Aircraft whose structure is over 50% composites - allows for

greater speed, stealth and flexibility

• Fireman's Turnout Coat and Multi-Threat Suit - Protective Apparel - guarding against bullets, flame, chemicals and disease

• Smart Materials - Submarine - monitoring and reporting on its own

Energy . . .

• Composite Applications for The Tension Leg Platform - reduce weight,

address corrosion and fatigue problems and reduce maintenance costs

• Permasep Permeator - separation unit - convert salt water to fresh water

• Extended Reach/Horizontal Drilling - Mud Motor Torque Shaft - less

susceptible to wear, fatigue and corrosion - will last longer

115
Environment . . .

• Commercial Aircraft Tail Fin - 20% lighter - this weight reduction saves

jet fuel and reduces C02 output.

• Composite Fan Blades in GE Engine - lifetime two to three times that of

metal

• Bexloy® Composite Sheet used for fenders on Chrysler's LH series.

These bumpers were recycled - HMS Rose's Sails made from recycled

bumpers and soda bottles

• ZymaxxTM - graphite-reinforced polymer seal - reduces emissions

• Insituform - repairs leaking underground pipes without tearing up streets and blocking traffic

• Bioremediation Unit for leaking underground storage tanks. Absorption

and Regeneration Process - environmentally friendly

Productivity . . . • Helicopter - Composites enabled part consolidation, fewer parts, more

productive

• Satellites and Bike Wheel - examples of faster cycle time

• Bridges - reduced construction costs, faster erection, extended service life,

reduced maintenance

• Orthopedic/Prosthetic parts - improves the length and quality of life

Major Issues for Advanced Composites have to do with markets and the forces

impacting those markets. The major issues are the "Three C's" that stand as barriers to adoption: Consumption, Conservatism, and Cost. We must replace military

consumption with other market pull; overcome conservatism of engineers steeped in

the use of traditional materials; and address cost issues with new manufacturing design

technologies.

The age of the massive general solution is over. Industry made generic products and

found a broad array of uses for a narrow product line. Customers bought what was

made — take it or leave it.

Today, the limiting factor is not capital, it is knowledge. We call this the "Specific

Solution". In the business world, the specific solution means customers demand exactly

what they want and when they want it. The specific solution completely changes how

we work in the market.

Second Key Learning "Systems Approach". We must ask what the whole system is trying to accomplish and then seek the simplest, most efficient solution. To do this, we

must establish a network of technology and business partnerships.

Alignment of a nation's industry, academic community and government on a few key

goals will win the day in the global race for good jobs, expanding economies and

improved quality of life.

116
Studies Relating to the Use of

Fibre Reinforced Composites

in the Offshore Industry

Professor A G Gibson

Centre for Composite Materials Engineering

Herschel Building,

University of Newcastle upon Tyne, UK NE1 7RU

SYNOPSIS This paper discusses some of the results of the

Marinetech Research programme on 'Cost-Effective Use of Composites

Offshore' . In particular, the outcome of a study of the fire performance of

composites based on E-glass woven rovings and four different

thermosetting resin systems: polyester, vinyl ester, epoxy and phenolic

will be discussed. It was found that, in terms of ignitability, heat release,

smoke and toxicity, the phenolic resins were in a different performance

class to the others. It was also found that, in thick sections, composite

laminates showed a surprisingly slow rate of burn-through in furnace

tests and lower than expected heat release. This phenomenon has led

to applications in heat and fire protection. A model for laminate

degradation in fire demonstrates that this effect is associated with the

endothermic decomposition of the resin. The effect occurs with all classes of resin.

Introduction

The Marinetech Research programme on the 'Cost-Effective Use of Fibre

Reinforced Composites Offshore' has been running since 1987 and involves six

academic institutions in the UK, along with over 20 industrial and governmental

sponsors. The programme has studied many of the factors, relating to mechanical,

environmental and fire performance which influence the possible use of

composites offshore. This paper discusses some particularly important results

relating to fire behaviour.

The offshore industry, where there have been few applications until recently, is now

showing considerable interest in the use of fibre reinforced plastics (FRP) (1-5).

This comes as a result of experience with these materials in other areas, including

marine applications (6-9), and has been at least partly driven by recent changes in design and regulatory philosophy. One of the results of the outcome of the Piper

Alpha Enquiry has been a movement away from prescriptive regulatory measures

(which included a rather rigid definition of combustibility) towards a more

performance-based approach. This has considerably reduced the barriers to the

use of FRP, but composite-based design solutions need to be shown by the

operator to be safe and effective in the light of expected hazards. Documentation

based on previous installation experience is important in this area, and the UK

Offshore Operators Association (UKOOA) has recently been very active in

117
providing procedures for assembling such documentation.

Other factors driving the expansion in offshore use of composites are their relatively

light weight and corrosion resistance, which reduce installation costs and throughlife costs respectively. The most significant immediate applications and markets lie in two areas:

(a) filament wound pipework for aqueous services, especially fire water, and

(b) lightweight walls and partitions for blast and fire protection.

An example of a glass reinforced epoxy pipework installation is shown in Figure 1

The light weight of the FRP pipes, and the ease with which adhesively bonded

joints can be made greatly simplifies and reduces the cost of installation. One

application involving fire-resisting panels is shown in Figure 2. In this case, twinskinned construction, using a special refractory core material, gives an excellent

combination of mechanical strength and fire resistance.

Applications rely on corrosion resistance and lightness, but depend critically on the

response of the material to fire, a factor which will be discussed later. Given the

size of the offshore industry worldwide, the potential market for FRP pipework alone

could eventually be in excess of 40,000 tpa. Other applications, such as cladding

and panelling can be expected to exceed this.

Limits to Market Penetration

One important factor restraining the offshore market has been lack of knowledge on

the part of composite suppliers concerning the structure of the offshore industry.

Installation of new or even retrofit components involves a complex interaction

between at least four parties:

-the operator -the operator's design house

-the offshore contractor -the certifying authority

To achieve market penetration for a particular application it is necessary to

convince all four parties of the validity of the FRP solution. Most operators are now

aware of at least some of the benefits of using composites and are taking active

steps to see that these materials are given consideration. The certifying authorities,

too, are increasingly willing to give a fair hearing, so long as appropriate

performance-based documentation is provided. Unfortunately, by no means all design houses are familiar with FRP, which results in over-specification or overestimates of installation costs, which lead to alternative materials being

chosen. Driven by the operators, the designers and contractors are beginning to show a greater awareness of FRP, but this is an important area where education

and documentation are still needed. It is no co-incidence that the companies that

have experienced the greatest success in penetrating the offshore market are those which have existing connections or experience in the area of marine and

offshore contracting and installation.

Other difficulties which have limited the recent rate of expansion are lack of design

data and working experience, problems which are now being rectified: the

available documentation and guidelines on the offshore use of FRP are improving

and staff are beginning to be trained in the new skills and procedures required for

installation.

118
Fire Behaviour

The aim was to establish a set of baseline performance characteristics for

candidate offshore composite materials. The results relate to woven roving

laminates with four different matrix resins: isopolyester, vinyl ester, epoxy and

phenolic, fabricated by contact moulding. Materials details are given in Table 1

.

Table 1 Materials evaluated in the Marinetech Research Fire Test

Programme

Reinforcement OCF Fiberglass woven rovings

(1 ply gives ~0.5mm thickness in final laminate)

Resins*

Isophthalic polyester DSM Stypol 73/2785

Vinyl ester DSM Atlac 580/05

Epoxy Ciba Geigy Araldite LY1927/HY1927 (amine cure)

Phenolic BP Cellobond J2018/L + Phencat 10 acid catalyst

* Contact moulding grades, laminated, cured and post-cured to manufacturer's

directions.

There is no single property which defines the suitability of a material for use in applications where fire is a hazard: the required attributes vary according to circumstances. Three aspects of fire response are important for offshore use of

composites:

(i) ignitability/heat release,

(ii) smoke/toxicity, and

(iii) fire resistance.

Heat Release and Ignitability

Figure 3 shows a comparison of typical cone calorimeter heat release results on

polyester, epoxy and phenolic laminates. Vinyl ester has been omitted as it shows

very similar behaviour to polyester resin. With polyester and epoxy there is a small

induction period followed by a rapid rate of heat release, corresponding to burning

of the resin at the laminate surface. Following depletion of the resin from the

surface layers of the laminate the heat release rate then falls to a lower value,

before a second, much broader peak corresponding to the combustion of gaseous

decomposition products from within the laminate. This is typical of many

thermosetting resin laminates. The phenolic resin laminate shows very different

behaviour, with longer time to ignition and much lower peak and overall heat

release rates.

Figure 4 shows the peak and average heat release rates as a function of

irradiance. Once again the behaviour of the phenolic laminates is substantially

different from that of the others. It should be noted that the irradiance levels in real

hydrocarbon fires, which have been the subject of some debate, are higher than

those achievable in the cone calorimeter, possibly of the order of 200kW7m2.

However it can be seen that the heat release begins to approach a steady value

with increasing irradiance.

Figure 5 shows the effect of laminate thickness, up to -21 mm, for the four resin

119
systems with woven rovings. The heat release rate has been divided by the

thickness to give the release rate per unit volume of laminate. It can be seen that as

the thickness increases this quantity falls to a value much lower than that observed

for thin laminates. To exploit this potentially useful effect it seems desirable to have

laminates about 8 mm or more in thickness.

Figure 6 shows the relationships between time to ignition and irradiance in the

cone calorimeter test. Again, the superiority of the phenolic system can be seen. It should be noted, however, that in the region of irradiances covered, there is no

threshold level below which ignition or flash-over will fail to occur- it is probable

that even the phenolic system would ignite if subjected to low irradiance in this

range for a sufficient period. (It is worth noting, by contrast, that the phenolic

system shows no significant flame spread in the frequently used BS476 part 7

spread of flame test).

Figure 7 shows average smoke generation rates, again obtained from the cone

calorimeter. Again the phenolic system is superior. A range of other smoke and

toxicity tests provided further evidence of the superiority of the phenolic system in this respect.

Fire Resistance

The integrity of thick laminates in the furnace tests is impressive, as can be seen

from the Table 2, with penetration times of the order of hours for the cellulosic test curve. For the hydrocarbon curve the burn-through times are reduced, but the

phenolic composite still lasts for over an hour.

Table 2 Resistance of 9mm thick woven roving laminates in the

indicative furnace fire test

Resin Fire Curve Time to 160°c Penetration time

Type (min) (min)

Polyester Cellulosic 28 182

Hydrocarbon 15 38

Vinyl ester Cellulosic 20 175

Epoxy Cellulosic 23 194

Phenolic Cellulosic 33 110

Hydrocarbon 18 72

Burn-through of the laminate occurs progressively, the resin being depleted from

the surface layers, leaving successive plies of the glass reinforcement, which

eventually fall away.

The fire resistance times (for the average temperature of the panel cold face to

reach 160°c or for a hot spot to reach a temperature of 170°c) are, as might be

expected, shorter than the penetration times. It is interesting to note that the slow

burn-through effect is not very resin-dependent. Although phenolics are shown by

the cone calorimeter test to be better in terms of heat release this is not strongly

reflected in the indicative test, although the phenolic does give the best result for

the NPD tests. In fact all four types of resin are currently being used in thick

laminates for heat protection applications offshore and elsewhere.

120
The factors contributing to the slow burn-through of thick laminates in fire, are:

(i) Transport properties of the laminate. The fact that the thermal

conductivity and diffusivity of FRP are lower than those of steel is clearly an

important factor. However, our computer simulations suggest that that this is not

the main effect operating.

(ii) Transport properties of the residual glass.

The reinforcement, depleted of resin, remaining on the surface of the laminate has

a lower thermal conductivity than that of the laminate itself. We have observed that

procedures which help retain the depleted reinforcement on the panel surface,

such as the addition of Ceepree (a proprietary ceramic frit, used in fire protection),

silica or ceramic fibre plies, can improve fire resistance.

(iii) Endotherm due to decomposition and vaporisation. The

processes of resin decomposition and vaporisation are highly endothermic and

therefore temporarily delay the conduction of heat through the laminate. The

volatilisation of any water present in the laminate will have a similar effect.

(iv) Convection of volatiles. As the gaseous products diffuse through

the laminate towards the hot surface they can be expected to produce a cooling

effect. In addition, when they reach the laminate surface they may form a protective

thermal boundary layer. Although the volatiles are flammable, their contribution in a hydrocarbon fire is probably insignificant, compared to the thermal release taking

already place in the fire.

Modelling the Fire Behaviour

A computer model for the fire-ablation process in a hydrocarbon fire was

constructed, taking into the above effects. The model was used to investigate the

significance of effects (i)-(iv) above and it was found that the most important effect

operating was the endotherm due to resin decomposition- the heat absorbed by

the resin decomposition process is almost entirely responsible for the interesting

and potentially very useful behaviour of thick panels.

The computer model was found to be very effective in predicting the thermal

profiles through panels, one example of the output, for a polyester panel, being

shown in Figure 8. Once the model had been verified using experimental test data

it was possible to use it to design structures for given fire performance. Figure 9, for

instance, shows the predicted thickness of single skin panel required to achieve

fire protection in a hydrocarbon fire, for a range of different times and acceptable

rear face temperatures.

Fire Protection Applications

The slow burn-through effect can be used to great advantage in passive composite

fire protection. One application example, relating to riser protection, is shown in Figure 10: here the material acts to give corrosion as well as fire protection.

Development of H60 and H120 Panels

In many areas of offshore use panels are required to achieve the stringent H60 or H120 rating, corresponding to resistance values of 60 and 120 minutes in the NPD

test. Twin-skinned construction is attractive and weight-efficient for composite

panels. Often, partitions and cladding are required to resist both blast and fire

121
loading. With composite sandwich construction the fire performance of thick

laminates can be enhanced by the use of fire-resistant core materials. Special

consideration is required when choosing these core materials, as most

conventional cores have poor fire performance. The materials with the best

thermal performance, ceramics, tend to be either brittle or to be in a non-structural

form. Two classes of material are potentially useful: compressed ceramic or cementitious board, and phenolic-based syntactics. Unfilled phenolic foams are

too friable for sandwich panels, but syntactic foams containing expanded mineral

fillers and other 'endothermic' additives do have suitable properties. There is considerable scope for further development of core materials to achieve the

optimum combination of refractory properties, shear strength and density and

several manufacturers are responding to this challenge. A number of companies

now supply blast and fire-resistant panels, of increasing sophistication, to the

offshore industry. An example has already been shown in Figure 2. Conclusions

There are many potentially promising new applications of FRP in the offshore

industry, the more significant areas being pipework (for aqueous services and fire water) and panelling for blast and fire protection.

Phenolic resins have the most favourable performance in terms of ignitability, heat

release and smoke generation, so these materials may be favoured for areas

involving personnel. All resins, however, show a very useful laminate thickness

effect, which results in a slow rate of burn-through that can be used in fire

protection applications. This effect is mainly due to endothermic decomposition of

the resin.

Acknowledgements

The work was part of the MTD/Marinetech Research multi-sponsor programme on

Cost-effective use of Fibre Reinforced Composites Offshore, which is supported by

the UK Marine Technology Directorate Ltd and a consortium of companies. Special

thanks are due to the industrial sponsors of the programme for their support and for

permission given to publish the results presented here: Admiralty Research

Establishment, AGIP(UK), Amerada Hess, Ameron bv, Amoco Research, Balmoral

Group, Bow Valley Petroleum, BP Exploration, BP Research, Brasoil, British Gas,

Ciba-Geigy, Conoco, Defence Research Agency, Dow Rheinmunster, Elf

(Aquitaine), Elf (UK), Enichem (SPA), Exxon, Fibreforce Composites, Hunting

Engineering Ltd, Kerr McGee Oil (UK) Ltd, MaTSU, Marine Technology Directorate

Ltd, Mobil Research and Development, Mobil North Sea Ltd, Norsk Hydro, UK

Ministry of Defence (Navy), UK Offshore Supplies Office, Phillips Petroleum, Shell

Expro, Statoil, Total Oil Marine, UK Department of Energy, VSEL and Vosper

Thomycroft. The research programme involves the Universities of Glasgow,

Liverpool, Salford, UMIST, and Nottingham, as well as Newcastle upon Tyne.

Particular acknowledgement is also due to our collaborating partners, Professor J

M Davies and his research group at Salford University. The following have

contributed to the results presented here: Dr. CM. Worrall (now with Kobe Steel

(Europe)), Mr John Hume (Warrington Fire and Materials), Mr J.A.D. Wilcox (now

with PERA International), Dr Y-S Wu and Professor P Bettess.

122
References

1 "Design of Marine Structures in Composite Materials", Smith, C.S., Elsevier

Applied Science, Barking, Essex, UK (1990).

2 "Composite Materials in Marine Structures", Vol. 2, Chapter 1 1 , ed. R A Shenoi

and J F Wellicome, Cambridge University Press, 1992.

3 Gibson, A G and Spagni, D A, 'Recent developments in the use of composites

offshore', Conf. on Polymers in a Marine Environment', Inst, of Marine Engrs,

London 23-24 Oct.1991.

4 Williams J.G., "Developments in Composite Structures for the Offshore Oil

Industry", paper OTC 6579, 23rd Ann. Offshore Technology Conf., Houston, May

6-9, 1991

5 Ciaraldi, S., Alkire, J.D. and Huntoon, G., 'Fibreglass firewater systems for

offshore platforms', paper OTC 6926, as above.

6 Guiton, J. "An all-GRP piping, support and walkway system for tanker weather

deck applications", 'Polymers in a Marine Environment' Conference, Oct 1987,

Institute of Marine Engineers.

7 Marks, P J. "The fire endurance of glass-reinforced epoxy pipes", 'Polymers in a Marine Environment' Conference, Oct 1987, Institute of Marine Engineers.

8 Grim, G.C. and Twilt, L, "Fire endurance of glass fibre reinforced plastic pipes on board ships", paper 10, 'Polymers in a Marine Environment', Institute of

Marine Engineers, 23-24 Oct., 1991.

9 Chalmers, D W, Osborn, R J and Bunney, A, 'Hull construction of MCMVs in the

United Kingdom', Proc. Int. Symp. on Mine Warfare Vessels and Systems',

RINA, London, 1984

123
Fig. 1. An example of an offshore installation of glass reinforced epoxy

pipework (courtesy of Elf Aquitaine)
16

Time (sees)

Fig. 3. Comparison of heat release rate vs. time for three resin systems,

polyester, epoxy and phenolic at an irradiance of 80 kW/m^. Woven roving

laminates. Thickness: 6 plies

Fig.4. Peak and average release rates vs. irradiance for four resin systemspolyester, vinyl ester, epoxy and phenolic

Woven roving laminates. Thickness: 6 plies (approximately 3 mm).

125
Thickness (mm)

Fig.5. Total heat release per unit volume of woven glass composite laminates

at an irradiance of 60 kW/m2

, showing the effect of laminate thickness.

Irradiance (kW/m2

)

Fig. 6. Log-log plot of ignition time vs irradiance in the cone calorimeter test.

126
15

2

eS 10 2

w

c

u

O

oxe

Phtnollc

Vinyl •«1«r

Epoiy

20 30 40 SO 60 70 80

Irradiance (kW/m )

Fig. 7. Average smoke generation rate vs. irradiance for four resin systems.

(6 ply woven roving laminates, ~3mm thick).

TIME

Cold Face

Fig. 8. Predicted thermal profile within an 11mm thick polyester/woven

roving panel in a hydrocarbon fire test.

127
1

3

Thickness (mm)

Fig. 9. Relationship, predicted by the computer model, between the laminate

thickness and the time for the cold face temperature to reach various levels.

r ML -

Fig. 10. Cladding of a steel riser with FRP (Courtesy of Vosper Thornycroft

(UK) Ltd).

128
5. Working Group Papers

129
130
Materials Development for Cost Effective Fabrication

Dr. Doug Wilson,

BP Chemicals (Hitco) Inc.,

Fibers and Materials, Santa Ana, Ca. 92705

Introduction

For composites to be used widely in offshore applications both

economic and performance barriers must be eliminated. For the

former, emphasis will need to be placed on the cost reduction of

the composite part; a substantial element of which is associated

with labor intensive fabrication. Performance issues related to

composite durability, particularly in aggressive environments,

must also be addressed. This paper will consider some of the

material development aspects particularly associated with cost

effective manufacturing. The ability to "tailor" materials over a

very wide range, to satisfy fabrication and performance

constraints, will be discussed with reference to examples from

the aerospace and defense industries.

Material Selection and Development

Material Availability

Composite materials intended for offshore applications are not

limited to what is commonly referred to as FRP, ie, simple epoxy

resins reinforced with low performance glass fiber.

The aerospace industry has initiated the development of a wide

range of composite materials to cope with performance,

fabrication and economic constraints.

Within the class of "epoxy resins" there are a number of basic

building blocks that differ in chemistry, processability and in

final cured properties. In addition these epoxy building blocks

can be extensively formulated and fine tuned to provide the

necessary processing and properties needed for specific

applications

.

In addition, higher performance resin systems are available for

use in extreme environments. Bismaleimide (BMI) and polyimide

resins are available to provide high temperature performance (up

to about 3 00°C) . Phenolic and silicone resin matrix based

composites are also used for thermal and fire resistance.

Phenolic based composites in particular are used in applications

that require short term protection at temperatures in excess of

3000°C.

The choice of fibers is also wide. There are several types of

glass fiber available that can provide improvements in mechanical

131
properties and corrosion resistance compared to the standard E

glass. Various PAN based carbon fibers also exist. Properties

range from low to high stiffness and prices from $10/lb to over

$100/lb. Specialty fibers are also available for certain

applications. The aramid fiber "Kevlar" is capable of providing

composite laminates with good ballistic performance. The fiber is

also used extensively in pressure vessels, eg, rocket motor

cases. For thermal resistance, composites based on phenolic

resins and refractory ceramic fibers are available. These include

silica, silicon carbide, quartz and aluminosilicate type fibers.

The selection of a material system does not end with the choice

of fiber and resin. The interface plays a crucial role.

Performance improvements in the areas of thermo-oxidative

stability, toughness and hot/wet properties can be gained by

manipulation of the fiber/resin interface. This can be

accomplished by fiber surface treatment and/or by applying a

finish or size to the fiber.

i?ale of the Prepregger

The composite prepregger is responsible for developing the

material system. This involves the selection of resin type, fiber

and interface. This will be followed by extensive formulation

geared to optimize the system for a particular application. The

prepregger will impregnate the reinforcing fibers by a variety of

routes depending on the material system. The resulting prepreg is

sold to component fabricators.

The old industry perception of the prepregger is akin to that of

a magician. Resins would be formulated by a hit and miss method

employing "the eye of newt/wing of bat" approach.

In reality most prepreggers today employ an extremely systematic

approach to product development. The high standards required by

aerospace have forced the prepreggers to adopt very modern

methods especially in quality control. In the case of BP

Chemical's Fibers and Materials Division, a stepwise approach to

product development is used. This approach leans heavily on the

use of TQM principles and as such employs teamwork, problem

solving tools (flow charting, Pareto analysis, brainstorming)

,

experimental design and statistical analysis. The aim being is to

develop products that are robust ie, insensitive to minor changes

in raw materials and processing conditions. A key element of this

product development approach is, of course, intimate customer

collaboration

The prepregger is capable of tailoring both prepreg and composite

properties. This could be extremely important in developing

composite materials for offshore application. Resin systems may

have to be developed that provide easy processing coupled with

good composite performance in aggressive and unique environments.

Table (1) below summarizes the tailoring that is possible in the

hands of the prepregger.

132
Table (1) Tailoring of Prepreg and Composite Properties

Area Tailored Properties

Prepreg Lay-Up * Tack

* Drape

* Outtime

* Spring-back

Fabrication * Method

* Cure temperature

* Cure time

* Cure pressure

* Exotherm

Composite Properties * Toughness

* Hot/wet properties

* Temperature resistance

* Microcracking resistance

* Chemical resistance

Matching Materials to Fabrication Needs

Autoclave Fabrication of Large Structures

In the autoclave fabrication of large structures the material

system, ie, prepreg, must be capable of providing the required

performance in the composite as well as providing easy lay-up and

fabrication. In the case of large structures this is not that

easy.

BP Chemical's Engineered Systems Division (Gardena, Ca)

manufactures the world's largest composite structure. This

structure is a submarine bow dome. Many thousands of pounds of

prepreg are needed to fabricate the dome. Prepreg lay-up takes

approximately 6 months to complete. The structure is about 40

feet in diameter with a thickness of about 6 inches.

The huge size of the dome places some severe processing

constraints on the prepregger. The material system used must

exhibit an unusual combination of properties. The lengthy lay-up

procedure requires the prepreg to exhibit exceptionally long outtime; tack and drape must be maintained. In addition, and due to

the fact that the prepreg must be laid up on almost vertical

surfaces, ply slippage must not occur. Prepreg spring-back

ie, the undesired characteristic of the prepreg to become uncompacted must also be minimized.

Curing of such a large structure is also difficult. From a

materials development point of view the candidate resin system

must have an extremely low tendency to exothermic decomposition.

Epoxy resins do have a tendency to rapid decomposition if the

heating rate is high and bulk resin is present.

133
The prepreg rheological, physical and cure characteristics can be

manipulated by formulation of the resin system. In the case of

the bow dome such formulation would involve the choice of the

exact epoxy resin building block (s) and additives which would

seek to control viscosity, tack, drape and cure kinetics. In

addition the resin system must provide the subsequent composite

with the desired properties, and in the case of the bow dome,

would involve meeting the desired mechanical properties and nigh

levels of toughness.

The E719LT resin system developed by BP Fibers and Materials

meets all prepreg and composite requirements and has been

successfully used in the production of several bow domes. The

E719LT resin system could be a candidate for the production of

large composite offshore structures.

Filament Winding Using Prepreg Roving

Composite pipes and pressure vessels are routinely made using wet

filament winding. For offshore applications there may be a need

to develop such parts for higher performance use, eg, in

chemically aggressive environments. In certain cases the material

system needed for such environments may not be amenable to wet

filament winding.

Prepreg roving is generally thought to be a more expensive route

than wet winding. However, the advantages of the roving approach

may warrant its use. Advantages include:

- accurate control of prepreg characteristics

- the ability to handle complex matrix chemistries

- improved environmental control

Some major defense programs have made use of the advantages of

prepreg roving. BP Fibers and Materials was a major supplier of

roving to the Peacekeeper strategic missile program. The motor

case of the first stage is made from Kevlar/epoxy composite. The

case is approximately 8 feet in diameter and about 2 0 feet long.

The burst characteristics of the case must be accurately

controlled. This is determined by a number of factors including

lay-up sequence and material characteristics. Prepreg roving was

chosen over wet filament winding because very accurate control of

resin content, resin advancement, the fiber/resin interface and

the conditioning of the Kevlar fiber was needed. Such control

could only be maintained in the hands of a prepregger and by

using the prepreg roving route.

Resin Transfer Molding

Resin transfer molding (RTM) has been shown by a number of

companies to be a cost effective method of composite fabrication

for certain components. Actual economics depend on a number of

factors including the complexity of the component and the numbers

to be made.

134
RTM involves the positioning of the fiber or fabric preform in a

closed mold. Resin is then injected at elevated temperature

usually under moderate pressure or with the assistance of vacuum.

The curing operation takes place in the mold; there is no need

for an autoclave. The component is molded to net shape with a

very high degree of dimensional tolerance. There is no need for a

trimming operation.

Suitable RTM resins must possess an unusual or incompatible

balance of properties ie:

- low viscosity for easy injection

- long potlife

- single component system

- low cure temperature

whilst providing composite properties which exhibit:

- high Tg

- good hot/wet properties

- high level of toughness

There are several resin systems available that can satisfy the

above requirements, eg E905L from BP Fibers and Materials.

RTM production parts are made by BP Aerospace Composites,

Stockton. These parts are jet engine thrust reverser blocker

doors. The doors are fitted to engines that power or will power

Boeing's 737, 747, 757, 767 and 777 aircraft. The doors are

lighter than the aluminum equivalent and are cheaper to produce.

Continuous Resin Transfer Molding

In a relatively new development, BP Aerospace Composites, Auburn

has pioneered a potentially very low cost manufacturing method.

The technique is termed "Continuous Resin Transfer Molding"

(CRTM) and is a hybrid of pultrusion and conventional RTM; resin

is injected into a moving fiber/fabric preform.

Trade studies have shown that CRTM is potentially the lowest cost

route to the production of continuous constant cross section

composite stock.

Again here the development of a CRTM resin must consider an

unusual balance of properties. The resin rheological and physical

properties are similar to those required by RTM. However, very

fast cure is required, in the order of 5 minutes or so. To

accomplish this whilst achieving good composite properties is no

easy matter. CRTM resin systems are under development at BP

Fibers and Materials. One system E907 shows promise and will be

further optimized as part of an ARPA funded program on low cost

composite processing.

135
Future Thoughts

Improved economics is the hurdle for the widespread use of

composites in offshore applications. The cost of the fabricated

part must come down and the lifetime must be equivalent or better

to that of the metal part.

Fabrication is by far the dominant contributor to the high cost

of composites. Kline and Co. estimate this to be about 70% of the

total, see Table (2)

Table (2) Contributing Elements to the Cost Of Composite Parts

Element % Cost

Resins 5

Fibers 10

Prepregs 13

Fabrication 72

Consequently, many companies are investigating ways to cut

fabrication costs. Aerospace companies are looking at ways to

automate tape and tow placement. Cure cycle optimization is

possible through the use of cure monitoring techniques (eg,

dielectric analysis) . Low energy cures are also being considered.

Boeing has often talked about cure on the fly ie, very fast

curing by irradiative methods. The French aerospace company,

Aerospatiale, has successfully developed an Electron Beam method

of rapid curing and has built a commercial facility for the

manufacture of missile parts.

In all cost reduction initiatives material development plays a

key role and it will be up to the prepregger to develop new and

novel material systems that are truly capable of providing cost

effective fabrication.

Conclusions

In developing materials for cost effective fabrication the

following points should be borne in mind:

* The aerospace industry has initiated the development of a

wide range of material systems.

* Such materials can be fine tuned for specific properties

and fabrication methods

136
* The potential for low cost fabrication exists through the

use of novel manufacturing methods coupled with refinements

in material systems

* Material development and component fabrication must go

hand-in hand.

* Some aerospace technologies could be successfully

exploited to help with establishing advanced composites as

viable engineering materials for the offshore oil industry

137
138
Polymer Composites Program in the

Polymer Division at NIST

by

Richard S. Parnas, Gregory B. McKenna, and Donald L. Hunston

Polymer Division, National Institute of Standards and Technology, Gaithersburg, MD 20899

Introduction

Polymer composites are light-weight, high-strength materials whose properties can be extensively

tailored. By using these advantages, products can be dramatically improved for competitive world

markets. There are important opportunities in the areas of off-shore oil, infrastructure,

automotive, electronics, construction, commercial aerospace, medical, and many other

applications. An obvious near term opportunity is the automotive industry, and that is the initial focus of the NIST program. However, the research is of a fundamental nature and is expected to be applicable to many applications including offshore oil. Unfortunately, the potential of

composites remains largely unrealized. There are two critical barriers hindering the wide spread

usage of polymer composites: (1) the need to improve the speed, reliability, and cost effectiveness

of fabrication, and (2) the need to develop a better understanding and predictive capability for long

term performance (durability).

The programs in the Polymer Division seek to address both of these challenges. There are major

efforts in Processing Science and Durability. In the processing area, the Division has interests in

four fabrication methods: advanced autoclave cure, filament placement, press molding, and liquid

molding (LM). The major focus is on LM, which includes resin transfer molding (RTM) and

structural reaction injection molding (SRIM). This emphasis is based on the advice of industry

obtained through a variety of mechanisms, including NIST sponsored Industry Workshops. The

consensus was that LM offers the best possibility to achieve fast, reliable, and cost effective

composite production. The work on durability builds on strong programs at NIST on the

mechanics of composite resins, including work on viscoelastic properties, physical aging, and

toughening. Based on the advice of industry, the work is expanding with a new effort that is studying environmental attack on composites by moisture and temperature.

Processing Science

In LM (fig. 1), the fiber reinforcement is assembled into a preform similar in shape to the final

part, and this preform is then placed into a heated mold. The mold is closed, and a polymer resin

and curing agent are mixed and injected to fill the mold. The heat initiates chemical reactions in

the resin (curing), leading to the final part. In this process, the preform preparation can be

automated, and the resin injection can be accomplished quite efficiently. As a result, LM

139
combines some of the speed advantages of simple injection molding with the ability to make the

high performance parts associated with continuous fiber reinforcement. Flexibility in the type,

amount, and orientation of the reinforcement in every section of the mold enables the generation

of very complex parts. Moreover, since the uncured resin viscosity is low, the parts can be quite

large and three dimensional.

Because of these potential advantages, LM is the leading candidate for the fabrication of structural

composite parts in the automotive industry, and may have equal potential in offshore applications.

Effective use of liquid molding requires further developments in both preform fabrication methods

and the technology required for process optimization and on-line process control. Preform

suppliers and others have large efforts in preform fabrication technology. To complement these

efforts, the National Institute of Standards and Technology (NIST) has initiated a major program

to address the scientific issues associated with process optimization and control. This program

has four tasks: Materials Characterization, Process Simulation Models, Process Monitoring and

Control, and Sample Preparation and Application to Parts.

Materials Characterization

The first task focuses on characterization of the material properties associated with processing, i.e. preform permeability, thermal conductivity of the resin with and without the reinforcement, and

cure behavior of the resin. Preform permeability measures the resistance offered by the preform

to the flow of the resin. Since the reinforcement can have very different resistances to flow in

different directions, the permeability, K, is a tensor. Thus, several measurements both in the

plane and through the thickness of the preform material must be conducted to evaluate K. The

resistance to flow is also very sensitive to the fiber volume fraction so this dependence must be

determined. Several techniques are available at NIST to measure the permeability, and a variety

of special molds and data analysis methods have been developed to minimize experimental errors and facilitate measurements at a variety of fiber volume fractions. For many cases where the part

geometry is a shell-like structure, it is adequate to determine only the in-plane components of the

permeability, and this significantly simplifies the characterization. Further details and examples of

permeability measurements are given in ref. [1].

An important result of the permeability measurements is the demonstration that K, for woven

composite reinforcements, is sensitive to the fabric architecture. The radial filling patterns

displayed in Figure 2 were obtained with woven glass fabrics typically used in RTM, and all three

fabrics were identical except for their weave patterns. The permeability tensors of the three fabrics were not only different in geometry, as illustrated, but in magnitiude as well. The sensitivity of K

to preform architecture, and the wide variety of preform designs, leads to the requirement of

either standardizing permeability measurements or developing predictive methods of computing K.

The task of materials characterization therefore has the goal of developing the technology to predict the permeability from a knowledge of preform microstructure and fiber surface treatment.

This would be an important advance because a preform could then be designed to optimize both

performance and processibility. Although this technology is well beyond current capabilities,

progress is being made [2]. In the interim, a standard reference material for permeability is being

developed to fill the need for a method of accurately determining the permeability.

140
The measurement of thermal and cure properties for the materials involved relies heavily on

process monitoring facilities at NIST. The objective in developing these facilities was to take

advantage of NIST's position as an outstanding measurement laboratory by assembling a wide

range of process measurement techniques including a variety of spectroscopic, optical, dielectric,

ultrasonic, and viscometric methods. A total of ten different techniques have been adapted to process monitoring in this program [3]. This capability permits the examination of the chemical

and physical changes that occur during processing at size scales ranging from individual chemical

bonds up to bulk properties such as viscosity and viscoelasticity. By applying these techniques

individually and in combinations, a detailed picture of the changes can be achieved.

Process Simulation

The second task in the Processing Science Program is the development of process simulation

models. These models can be conveniently divided into two categories: macroscopic and

microscopic. Macroscopic models employ the volume averaging approach to achieve

computational efficiency. This approach resolves the mold into volume elements that are large

enough so that variations in local features such as the arrangement of individual fibers in space, or

the interactions between fluid and fibers average out, and thus only the averaged properties appear

in the model. Such treatments are generally quite good for analyzing macroscopic events such as mold filling.

The macroscopic models are less useful, however, for predicting other important occurrences such

as void formation since these events often depend on local features. To deal with this,

microscopic models, which include some or all of the local features, are needed [2,4]. Although

it is possible to simulate the entire part in microscopic detail, the computational time becomes

prohibitive. As a result, events dependent on local features are simulated by first using

macroscopic models of the part to predict boundary conditions on the local area, and then that area

is simulated using a microscopic model.

A complete process simulation would include many factors such as resin flow, heat transfer,

chemical reactions, etc., as well as the interactions between these factors. Chemical reactions, for

example, generate heat which must be considered in the heat transfer relationships. In certain

cases, it is possible to separate some of these factors and thereby simplify the modeling. Often,

the mold filling may be completed before the chemical reactions produce significant effects.

When the use of such simplifications is possible, the analysis can be accelerated. For many cases,

the simulation of liquid molding is similar to the reservoir simulations conducted to design oil recovery operations.

Process Monitoring / Control

The third task in the NIST program involves on-line process monitoring. The purpose is to develop this technology and then use it to address two areas. First, experiments are being

conducted to test and refine the process simulation models. Second, the technology is being

explored for on-line process control. For testing the simulation models, the first step is an

examination of flow behavior during mold filling. Complicating factors such as corners, edges,

embedded objects, 3-dimensional effects, etc. are isolated and their effects on flow patterns

studied. The results are then compared with the predictions of the computer simulations to refine,

141
and verify the underlying flow models. The principal tool in such studies is flow visualization.

One drawback of this approach, however, is that visualization, which is performed using molds

having one or more clear sides, can provide information only about what is happening at the

surface. Consequently, sensors such as fiber optic probes are being developed to measure flow

front positions inside the preform.

Cure monitoring is also an important element of the process monitoring effort. A small number of

the ten monitoring methods mentioned earlier have been chosen for additional development. For

example, a current research effort is using optical fiber evanescent wave fluorescence experiments

in an attempt to develop a single sensor for both flow and cure monitoring. Fluorescence has been

shown to provide accurate cure monitoring data [3], and this capability is now being applied to

liquid molding.

Sample Preparation and Application to Parts

The final task involves the fabrication of samples for testing in another NIST program which

considers the performance and durability of polymer composites. In addition, this task is applying

the developments in the LM program to the study of realistic parts through cooperative efforts

with industry. One such example is a program between NIST and the Automotive Composites

Consortium (ACC). The ACC is a joint effort between Ford, Chrysler, and General Motors and

was formed to conduct precompetitive research that promotes the use of composites in structural

applications. The ACC is demonstrating the results of their research by fabricating a series of full size parts. The first part chosen was the front end structure of a Ford Escort (fig. 3), and the

fabrication method of choice was SRIM. NIST is cooperating with the ACC by conducting

materials characterization and process simulations to help develop the technology required to optimize the fabrication of such a part. The permeabilities for the different reinforcement

materials used in the part were measured and used as input data for the simulation model.

Figure 4 shows the data from a simulation. The flow front positions at various times are indicated

by bold lines. As can be seen in the figure, such results can indicate how evenly a mold fills for a given preform and injection point. In this case, the last areas to fill are at the ends of the part

which means a minimum of three vent locations would be needed to prevent air from being

trapped in these regions. The model also predicts the pressure distribution from which the

minimum mold clamping pressures and wall thicknesses can be calculated. Such results are

particularly useful for examining the trade-off between injection pressure and filling time. The

simulation also predicts many other features of the filling pattern that must be considered in

optimizing the tool design and process. For example, it shows regions that are closed off by the

flow before they are filled and weld lines where two flows converge. By using this information,

process simulation programs can play a critical role in developing cost-effective processing for

polymer composite materials.

A final point to note is that the input mesh for the flow analysis was obtained from the mesh used

for the stress analysis that helped design the part. This suggests that a unified program could

eventually be developed that would permit simultaneous consideration of both design and

fabrication. The ability of such a program to balance and optimize both areas is a truly exciting

possibility and represents an ideal goal for the future of such programs.

142
Durability

The newest work on durability focusses on characterizing the response of composites to environmental humidity [5]. This work builds on current activities in the Polymer Division that are developing methods to determine fiber-matrix interface properties [6]. A second major task

compliments the interface studies by developing and utilizing techniques to characterize the

microstructure of the interface region. Of particular interest is recent work that uses this capability

to determine the distribution of moisture near the interface after exposure to water [7]. Finally, a program to study the compression response of composites leverages other expertise in the Polymer

Division in the areas of physical aging and nonlinear viscoelasticity of solid polymers [8]. Finite

element codes are being developed that incorporate viscoplastic resin behaviors [9]. In the future

these codes will include the ability to treat non-isothermal histories and nonlinear viscoelastic

material behaviors.

Measurement of Interface Strength and Durability

The fiber-matrix interface is perhaps the least understood feature of a composite, and yet it plays a

critical role in behavior such as durability. To study this aspect of a composite, NIST has

implemented two widely used methods to determine interface strength: the single fiber

fragmentation measurement and the micro-drop pull-off test. There is now an active effort to refine and improve these tests [6]. Studies from this laboratory [5] have shown that the

fragmentation sample, which is a single fiber composite, can serve as a useful model system for

determining the effects of moisture on the interface. However, it was found that the glass fiber is also degraded by moisture. This finding is important both because it may be an important

degradation mechanism in the composite but also because the fiber strength is needed in the

analysis of the interface strength. To address this problem, a new analysis method was recently

developed which extended work by Wagner [10] to permit the simultaneous determination of fiber

strength and interface strength.

In the current program on durability, samples for the single fiber fragmentation test are being

prepared by different processing methods and with different fiber surface treatments. In addition, a range of special sizings is being applied and the resulting surface coating characterized by

various chemical and spectroscopic methods. The samples are then exposed to water for various

periods of time and tested. Initial results show clear indications of degradation in both the fiber

and the interface. Analysis of the supernatant water indicates the presence of ions extracted from

the fiber (see fig. 6). Through analyses of both the chemistry and mechanics that occur during the

exposure, the degradation mechanisms will be identified and characterized. To complement these

studies with single fiber composites, a comprehensive series of experiments is planned with actual

composite materials. This work is being coordinated with the Automotive Composites Consortium

and suppliers to the automobile industry.

Characterization of the Interface Region

To compliment the measurements described above, NIST has developed a novel method to characterize the interfacial region between polymers and solid substrates using neutron reflectivity

(NR). Although the technique requires the use of flat surfaces, it can not only determine the

143
segment density of the polymer near the interface, but can also study the morphology of coupling

agents and analyze the moisture concentration in the region. For example, the initial work

employed a silicon-polyimide (PI) interface and found the existence of an unexpectedly high

concentration of moisture in the 25 A region of polymer adjacent to the solid surface [7]. A high

water concentration has long been postulated to explain various moisture related problems

encountered in composites, protective coatings, and electronic packaging but had never been

demonstrated and quantified prior to this measurement. Figure 5 shows the water content as a

function of distance away from the interface after the sample had been exposed to water vapor for a week at 23°C. The water content within this thin layer reached 16% by volume, as compared to the bulk saturation level of 2.4% in PI. Neutron reflectivity provides a unique tool for studying

durability of the interface region.

Aging of Polymeric Resins and Performance of Composites

As a part of the overall program on composites in the NIST Polymer Division, there has been

considerable effort to characterize the underlying physics of aging of the neat resins. This is because the prediction of the performance of composite materials depends upon the ability to estimate accurately the state of residual stress both in the resin and at the fiber- matrix interface.

Without adequate models of the nonlinear viscoelastic response of the neat resin in non-isothermal

processing/use histories, estimating the residual stress is very problematical. Of particular

importance have been studies that show currently available models to be inadequate for describing

the changes in viscoelastic and yield responses of thermosetting resins [8,11]. To this end, work

is ongoing to evaluate a series of solid polymer constitutive laws that are based upon the physics

of material clocks. In coordination with this work, finite element codes are being programmed to incorporate material nonlinearities such as plasticity [9], and more recently we have begun to consider non-isothermal, viscoelastic codes as well.

A good example of the importance of aging effects in composites arises from an examination of

Figure 7, in which the yield response of a model epoxy system is shown at different aging times

after a quench from above the glass transition temperature to below it. As can be seen, with just

1000 h of aging, the yield strength increases by over 60%. When the fracture or impact resistance

of the resin phase in the composite is important, such resin aging can be detrimental to the

performance of the composite because of a concurrent increase in brittleness. In summary,

physical aging is expected to play a role in the evolution of composite properties such as stability to water or other solvents, fracture toughness, and the coefficient of thermal expansion. Finally,

work is beginning in this laboratory to examine the influence of moisture on the aging response of

neat resins.

Summary

The NIST program in polymer matrix composites has two thrust areas, Processing Science and

Durability. Both of these areas are engaged in research designed to solve problems critical to mass production and usage of composites in a variety of applications, including offshore oil. The

processing effort is focused on Liquid Molding because that fabrication method has been identified

144
as holding the most promise for mass producing structural parts of complex geometries. The

durability effort is focused on environmental effects at the fiber matrix interface because that area

has been shown to be of critical importance to the long term performance of composite materials.

References

[I] R. S. Parnas and A. J. Salem, "A Comparison of the Unidirectional and Radial In-Plane

Flow of Fluids through Woven Composite Reinforcements," Polymer Composites , in press

(1993).

[2] F. R. Phelan Jr., "Advanced Composite Materials: New Developments and Applications,

Proceedings of the 7th Annual ASM/ESD Advanced Composites Conference," 175, ASM

International, (May 1991).

[3] D. Hunston, W. McDonough, B. Fanconi, F. Mopsik, F. Wang, F. Phelan, and M.

Chiang, "Assessment of the State-of-the-Art for Process Monitoring Sensors for Polymer

Composites," U.S. Department of Commerce, NISTIR-4514, June 1, 1991.

[4] R. S. Parnas, and F. R. Phelan Jr., "The Effect of Heterogeneous Porous Media on Mold

Filling in Resin Transfer Molding," SAMPE Quarterly. 22(2) , 53-60, (1991).

[5] C. L. Schutte, W. McDonough, M. Shioya, M. McAuliffe, and M. Greenwood, "The Use

of a Single-Fiber Fragmentation Test to Study Environmental Durability of

Interfaces/Interphases between DGEBA/mPDA Epoxy and a Glass Fiber: Effect of

Moisture," Composites , (submitted).

[6] W.G. McDonough, P.J. Herrera-Franco, W.L. Wu, L.T. Drzal, and D.L. Hunston,

"Fiber-Matrix Bond Tests in Composite Materials," Proc.23rd Int. SAMPE Tech. Conf.,

23, 247 (1991).

[7] W.L. Wu, W.J. Orts, C.J. Majkrzak, and D.L. Hunston, "Water Absorption at Polyimide

Silicon Interface," Polym.Eng.Sci. (submitted).

[8] G.B. McKenna, M.M. Santore, A. Lee, and R.S. Duran, "Aging in Glasses Subjected to Large Stresses and Deformations," J. Non-Crystalline Solids . Hi, 497 (1991).

[9] M. Y. Chiang and H. Chai, "Plastic Deformation Analysis of Cracked Adhesive Bonds

Loaded in Shear," Int. J. Solids and Structures (submitted).

[10] H.D. Wagner and A. Eitan, Appl.Phys.Lett. 56, 1965 (1990).

[II] C. G'Sell and G.B. McKenna, "Influence of Physical Aging on the Plastic Behavior of

Model DGEBA/Poly(propylene oxide) Epoxy Glasses," Polymer. 22, 2103 (1992).

145
Curing

Agent Resin

Finished Part

Figure 1 : In liquid molding, a fiber preform is placed into the mold, the mold is closed, and

a resin system and curing agent are mixed and injected to fill the mold.

Chemical reactions are then initiated by heat, and the final part is formed.

CNF Crowfoot CNF 8-Harness JPS 8-Harness

Fi Kure 2: Radial flow patterns of fluid permeating woven glass fabrics.

146
Figure 3 : Diagram of the front end structure fabricated by liquid molding in the Automotive

Composites Consortium program.

Flgure 4- Mold filling simulation for the ACC demonstration part. The bold lines represent

the flow front positions at various time during injection.

147
Water at Interface

0.20

^ 0 05

10 20 30

Distance (A)

Figure 5 : The concentration of moisture is shown as a function of distance into a polyimide

film on a silicon substrate.

0.12

? 0.08

oo

c

2. 0.04

c

oo

0.00

i

B

O o »

r—i o CM H W a w

ad p. M +

•—i —* + >.M

n a 0

CM Pi a W W

100

Figure 6: Comparison of the content of calcium in water

for distilled water, epoxy and single fiber

specimens exposed to distilled water for

5,520 h and 75°C. E-glass fiber in

DGEBA/mPDA epoxy.

o

a.5

COCO

LlI crhco

z.o

COCO

LU

ccCLo

u

0.1 C0MPRESSI00.2

N STRAIN

0.3

Figure 7: Typical compression stress-strain curves obtained at Tg-10°C for epoxy glass

increasing times te after a quench fr<

148

above Tg

.
POLYMER COMPOSITE MATERIALS PERFORMANCE CRITERIA

FOR OFFSHORE PETROLEUM PRODUCTION: AN OVERVIEW

John P. Dismukes and Michael J. Luton

Exxon Research and Engineering Company

Route 22 East, Annandale, NJ 08801

Introduction

Fiber-reinforced polymer composites for structural applications were first introduced into service

about 50 years ago, during World War II as radomes and small boat hulls and airframe bodiesfl].

The glass fiber reinforced polyester and epoxy polymers introduced at that time, provided a basis for

developing consumer and industrial markets that took advantage of the now accepted composite

characteristics of light weight, parts consolidation for ease of fabrication, installation, and resistance

to chemical attack at moderate temperatures. Examples of current composite product applications

include: boat hulls, sewer pipe, appliance bodies, furniture, electronic circuit boards, secondary

structural parts in the automotive industry, piping and vessels in the chemical industry, performance

parts in aircraft, golf clubs and tennis rackets. In 1992, North American manufacture of fiberreinforced polymer composites exceeded 1 million tons/year. As illustrated in Table 1, low-cost,

moderate performance glass-fiber

composites for the transportation and

marine industries accounted for about half

of the sales. High performance, high cost composites based on carbon or polymer

fibers and specialty polymer matrices, were

produced in much lower volume for the

aircraft and aerospace applications.

Over the past thirty years, low cost polymer

composites have been steadily introduced

into onshore oilfield production operations,

primarily to substitute for carbon steel in

relatively low temperature applications

experiencing severe corrosion, such as lift pump sucker rods and low pressure produced water lines.

For example, glass fiber reinforced polymer (GRP) pipe has been in use since the early 1970's in

Exxon's Conroe, Texas field [2] for oil-well flow lines, gathering lines and produced-water injection

lines. Based on an acceptable performance in service, the nominal operating limit for existing GRP

pipe is = 25 Bar at 100°C [2,3]. Examination of buried pipe after periods of up to 25 years have

indicated good retention of properties [4]. Also, pressure testing of new pipe for up to 18 months at 75°F, with 300-600 psi dry or wet C02

, showed no degradation or chemical attack [5]. In marketing

these products to onshore operators, composite manufacturers have had to address the issues of

handling, damage tolerance and joining, since composite mechanical behavior differs markedly from

that of steel, the structural material of choice in oil fields for the last 100 years. They have not,

however, had to cope with the extensive regulatory requirements on flammability, fire safety and

toxicity which must be addressed for ship and offshore platform use [6-8]. For example, the

TABLE 1 Representative 1 992 North American Markets For

Polymer Composites.

STATISTIC AEROSPACE TRANSPORTATION MARINE

TONS/YEAR : 10,000 361,000 150,000

USE: Primary Structural Components

Secondary Structural ComponentsSecondary Structural Components

EXAMPLE Epoxy/Carbon Polyester/Glass Polyester/Glass

COST $10->$100/lb $3-4/lb $3-4/lb

(Source: Modern Plastics Magazine, 1993)

149
International Convention for the Safety of

Life at Sea (SOLAS), 1974, as amended

[9], indicates that structural materials for use in marine environments shall be steel or 'equivalent material'. Nevertheless, the

U.S. Navy, in conjunction with NIST. has

pioneered the use of composite piping for

shipboard applications [10], and has

sponsored research on the materials

flammability and toxicity for shipboard use

as piping and deck structures [6-8].

Extensive research and testing in Norway,

the United Kingdom and North America

has led to acceptance of polymer

composites on offshore platforms for

secondary structural applications, such as firewater systems, produced water return

lines as well as decks and gratings [11].

Figure 1 shows current and potential applications of polymer composites on offshore platforms now

being addressed by manufacturers of conventional, low cost polymer composites. Installed offshore

platforms number about 5000 in North and South America and about 6100 total Worldwide [12].

Hence, a significant market exists in platform retrofit and in new construction, incorporating state-ofthe-art composite materials.

Hence, the research frontier involves developing advanced materials at affordable cost, and

establishing life prediction capability for conventional and deep water platforms. For example.

Tension Leg Platforms (TLP's), considered in Working Group #7 on Advanced Applications, can

capture system design advantages from the use of high performance polymer composites in TLP

risers, TLP tethers, topside primary structural components, and downhole tubulars for use up to 220°F.

Figure 1 Representative Current and Future Composite

Applications on Offshore Platforms

TABLE 2. Performance Criteria For Composite Application In Offshore Production Operations.

The purpose of this paper is to provide an overview of fundamental aspects and

criteria for mechanical performance and

damage tolerance, that is strength,

stiffness, impact toughness. In addition,

it addresses environmental performance

and durability, that is thermal, mechanical

and chemical stability, over the range of

offshore operating conditions, shown in

Table 2. The assessment also includes

evaluation of current composite costs and

future requirements for widespread

offshore use. Near and Long term

research initiatives are identified that are required in order for polymer composites to make a

significant impact on offshore operations for oil and gas production.

Parameter Secondary Loading Primary Loading Downhole

Tubing/Casing

Temperature -50'C to + 40*C -5CTC to +40*C +25°C to +220*C

Environment Air, Sea Water Air, Sea Water HC's. HjO. H,S. CO:

Stress State

Tensile. Compressive Tensile. Compressive Tensile. Biaxial. Compressive

Reliable Life

>20 yrs >30 yrs >20yrs

150
Current Performance and Economics of Polymer Composites Versus Metals

The tensile strength, modulus and price for representative steels, which have been the primary

material used historically, offshore, for structural components, pressure vessels, piping and downhole

tubulars are summarized in Table 1 . The different strength levels used for piping, which is typically

welded, and for tubulars, which employ threaded connections, are indicated. From a cost and

strength standpoint, low carbon steel is the favored material. When neither corrosion allowance nor

inhibitors are acceptable

corrosion control strategies,

carbon steel can be

replaced by higher priced

corrosion resistant alloys or

alloys of titanium. The

mechanical properties of

metals over the typical,

offshore, operating

temperature range of -50°C

to +220°C are relatively constant. Hence, for

metals, the influence of

temperature on corrosion

resistance arises primarily

from the temperature

dependence of interface

reaction kinetics and on

the stability of protective

films formed on the metal

surface.

TABLE 3. Performance And Cost Of Representative Metals Used

In Offshore Applications.

MATERIAL

Density

(gm/cc)

Piping

Strength

(MPa)

Tubing

Strength

(MPa)

Compress.

Modulus

(GPa)

Tensils Modulus

(GPa)

Price

($/lb)

Low Carbon Steel 7.83

a 415b 760 204 204 0.50

316 Stainless Steel 8.03 208 415 191 191 3.00

2205 Duplex Stainless Steel 8.03 415 760 191 191 4.00

Incoloy 825 8.17 415 760 194 194 8.00

Hastelloy C-276 8.89 415 760 193 193 15.00

Titanium (Grade 2) 4.43 345 760 108 108 25.00

'P-60 110; Prices from Reference 1 3 and vendor discussions.

Glass fiber polymer composites are of increasing interest in secondary structural applications in

offshore operations because of their corrosion resistance at moderate temperatures, low weight and

reduced maintenance costs. The intrinsic mechanical properties of representative inorganic and

organic fiber reinforcements, thermoset and thermoplastic polymer matrices are summarized in

Table 4. Also listed are the current prices for these materials. In contrast with metals, the thermal

properties of thermoset and thermoplastic polymers, used in composites, can vary significantly over

the temperature ranges given Table 2. Accordingly, it is important to consider the temperature

dependence of their mechanical properties and their resistance to corrosion. For operation under

ambient offshore temperatures (-50°C to +40°C), empirical near term experience substantiates the

reliability of commercial composite products made from glass fiber and thermoset polymers.

Neither empirical experience nor predictive methodologies are available for assessing the reliability

of composites, exposed for longer times to severe environments and higher temperatures, that is, up

to about 220°C.

The mechanical properties of commercial filament-wound composite piping, with 60% by volume of

fiber, are summarized in Table 5. The table also lists vendor prices for glass-polyester and glassepoxy pipe, and estimated prices for developmental, carbon-epoxy pipe, see footnotes to Table 6. It

151
TABLE 4. Performance and Cost of Representative Reinforcing Fibers and Polymer Matrices.

REINFORCING

FIBERS

Density

(gm/cc)

Tensile Strength

(GPa)

Axial Modulus

(GPa)

Transverse Modulus

(GPa)

T(g)

CO

T(hd)

CO

T(m)

CO

Price t

($/lb)

E-Glass 2.56 3.40 76 76 600 600 NA 0.70 SiC 3.20 3.50 400 400 NA NA >2000 NA

C (diamond)' 3.52 3.50 1200 1200 NA NA >3000 NA

Carbon/AS4 orHS 1.76 4.00 245 14 NA NA >3000 9.00 Keviar 49 1 44 3.70 129 7 NA >400 NA 10.00

MATRICES Density

(gm/cc)

Tensile Strength

(GPa)

Tensile Modulus

(GPa)

Compress

Modulus

(GPa)

T(g)

(°C)

T(hd)

CO

T(m)

CO

Price

(S/lb)

i nermoseis

Polyester(lsophtalic) 1.27 0.075 3.4 3.4 120 100 NA 0.55

Vinylester 1.25 0.075 3.4 3.4 120 100 NA 0.55 Epoxy(DGEBA/DDS) 1.16 0.080 2.7 2.7 130 120 NA 1.20 ThermoDlastics

Polypropylene 0.91 0.036 1.4 1.4 -8 60 165 0.50 Polyphenylene

Sulfide

1.35 0.066 3.8 3.8 88 120 288 3.00

Polyetheretherketone 1.32 0.100 3.9 3.9 143 152 334 30.00

* Intrinsic properties; materials not available, t Prices from Reference 14 and manufacturers.

TABLE 5. Performance and Cost of Commercial Polymer Composite Pipe.

COMPOSITE

MATERIAL3

Density

(gm/cc)

Weeping

Stress

(MPa)

(hoop)

Ultimate

Stress

(MPa)

(hoop)

Ultimate

Stress

(MPa)

(axial)

Tensile

Modulus

(GPa)

(axial)

Compress

Modulus

(GPa)

(axial)

Price

($/lb)

E-glass/Polyester1 2.04 95 >300 70 17.3 0.167 3.10

3

(218 mm OD, 0.38 mm wall)

E-glass/Epoxy1 2.00 95 >310 100 16.4 0.23 3.103

(218 mm OD. 0.36 mm wall)

C-AS4/Epoxy2

(96.5 mm OD, 0 92 mm wall)

1.52 Not Measured

1,300 710 36.7 0.42 9.01*

a Filament wound pipe, 0.6 volume fraction fiber.

1 ± 55° layup;2 90° 6 l± 30° 2 layup; Reference 15.

3 From A.O. Smith Fiberglass. * Estimated as indicated in Table 6.

152
is significant that E-glass/polyester and E-glass/epoxy pipe are finding acceptance as produced-water

return and fire water lines, in spite of six-fold higher cost/pound and four-fold lower usable stress under fluid containment conditions[2-4, 16], compared with low carbon steel piping. However,

because a higher wall thickness is required in carbon steel piping than necessary for pressure

containment, for example as a processing requirement and to provide a corrosion allowance, the

weight-per-unit length of carbon steel pipe in the 8-12 inch-diameter range can be a factor of 10

higher than for composite pipe suitable for low pressure water usage (150-300 psi at up to 100°C).

The authors are not aware of any data on the threshold stress for weeping or loss of fluid containment

for carbon-epoxy piping. This absence probably reflects aerospace industry practice, where carbon

fiber-reinforced polymer composites typically require the use of an internal liner or bladder to guard

against loss of fluid containment. Although the cost per pound of carbon-epoxy is a factor of three

higher than glass-epoxy, the density is 25% lower and the modulus is a factor of three higher. This

suggests the possibility of lower strain, and hence higher stress levels for the incidence of weeping.

Hence, carbon-epoxy piping might be cost effective on a cost/foot basis with glass-epoxy piping, if superior weep stress thresholds can in fact be achieved.

Technology and Economic Gaps Between Current Offshore Usage and Future Requirements

The technology hurdles to the use of polymer composites in the offshore involve the entire range of

sequential activities, from conception to final retirement. These activities include material design

and synthesis, manufacturing processes and fabrication, joining and installation, field inspection and

repair and finally recycling. These technical hurdles may be grouped according to three principal

categories: 1) Mechanical Performance, 2) Chemical Characteristics, and 3) Environmental

Response. Economic gaps are associated with each of these activities, involving costs at time of

material purchase, during construction and during life cycle operation.

Mechanical Performance

The mechanical properties that are considered in this paper include strength, stiffness, toughness and

damage tolerance as well as the effects of compressive loading, fatigue and creep. These

characteristics are the subject of companion papers in Working Group #2. The status of current

properties and the short comings of strength and stiffness are illustrated in Table 6, which lists these

properties for unidirectional polymer-composite laminate products with 60 volume percent loading

of continuous fibers. Included in the table are vendor prices for glass-polyester and glass-vinylester

products. With the exception of rod made from glass-fiber and polyester, vinylester or epoxy, which

is used as gratings, handrails and ladders offshore and as sucker rods onshore, all the other materials

are developmental. To provide a basis for assessing the current and future potential of these

materials, under conditions of tensile loading, projected commercial prices of developmental,

unidirectionally aligned (UDA) polymer composites are also estimated and shown in Table 6. Rated on price per pound, the most inexpensive UDA polymer composites are six times the cost of 60 ksi

low carbon steel. However, for primary structural components, designed to support load in uniaxial

tension, polymer composites compare very favorably with metals on the basis of load carrying

capacity per unit cost, because of their four-fold lower density and higher strength. A clear

comparison between metals and composites in terms of strength, and specific cost, load capacity per

dollar, for offshore applications, can be obtained from Figure 2. It can be seen from the figure that

unidirectional E-glass/Polyester or E-glass/Vinylester is approximately equivalent in strength and

load per unit cost to 60 ksi carbon steel while E-glass/Epoxy has twice the strength of the same steel

153
TABLE 6. Performance and Cost of Representative Reinforcing Fibers and Polymer Matrices.

COMPOSITE Density Tensile Tensile Compress Compress Flexure Price

MATERIAL3 (gm/cc) Strength Modulus Strength Modulus Modulus

\lwlr a)

E-glass/Polyester 2.04 600 36 360 36 3.06

1

E-glassA/inyiester 2.03 600 36 390 36 3.06

1

L_ y/aoo>/ l—^JyJA

y

?£- .\J\J 00 1 000 44 612

E-glass/PPS 2.08 1,060 47 46 411d

E-glass/PEEK 2.07 1,090 53 51 11.77

3

C-AS4/Epoxy 1.52 1,500 150 952 9.01

2

Kevlar-49/Epoxy 1.33 1,360 79 272 9.15

2

C-AS4/PPS 1.60 1,830 134 938 130 117 10.41

3

C-HS/PEEK 1.59 1,970(av) 134 1,440(av) 119 123 20.443

Pultruded laminate, 0.6 Volume Fraction Fiber. From Morrison Molded Fiber Glass.

2 Estimated = materials + $2.40/lb fabrication.

3 Estimated * materials + $5.00/lb fabrication.

* Properties from References 16-18.

along with a 40% higher load capacity per unit cost. Other pipe-grade steels and the titanium alloys

have significantly lower load/unit cost compared to carbon steel; reflecting the penalty of alloying to achieve corrosion resistance. This comparison validates the cost-effectiveness of E-glass/thermoset

composites for decks, gratings, and ladders where the "ideal" strength of UDA polymer composites

can be captured together with the excellent corrosion resistance. The figure also highlights the

future potential of carbon fiber composites for platform components which are loaded in tension,

such as topsides structures and TLP tethers. Metallic materials, such as shown in Table 3, with

approximately twice the strength of piping grade metals, are also candidates. But in such

applications their increased tendency to stress-cracking adds an additional corrosion control cost,

offsetting their higher strength.

Where stiffness is a major structural criterion, Figure 3 illustrates that low carbon steel has about a

factor of four higher stiffness per unit cost compared to current UDA polymer composites.

However, where corrosion resistance is also a factor, polymer composites may still be favored, since

the stiffness per unit cost of composites is approximately equal to stainless steels. In addition,

future reductions in the cost of carbon fibers and high performance thermoplastics, such as PPS and

PEEK through economies of scale and experience, have the potential to increase the stiffness per unit cost of UDA polymer composites. In biaxial and triaxial loading, however, the strength of

composites with multiaxial fiber architectures can be significantly lower than that of UDA

154
2,500

2,000

1,500

O

z

HI

OLH

CO

1,000 -

500

Comparison Of Aligned Fiber Composites With Selected Metals

Carbon PEEK 60% Fiber Composites

Carbon ^

PPS

E-Glass

Carbon Epoxy *

E-Glass PPS

Kevlar Epoxy

E-Glass * Epoxy

E-Glass

Polyester E-Glass

Vinylester E-Glass 7X2205 Epoxy 60 ksi Polyester Carbon Steel Pipe J i I

110 ksi Carbon Steel

25 50 LOAD / UNIT COST75 kN/$10

composites in tensile loading. This short-fall represents a technology gap which is illustrated by

comparing the properties of UDA polymer composites of E-glass with polyester or epoxy in Table 6,

with those of filament wound pipe of the same materials in Table 5. The gap is apparent from the

very low 'weeping stress' [2-4,16] of filament wound pipe, which results in the factor of 7 lower

load/unit cost, shown in Figure 2, compared to the ideal UDA laminates. However, this composite

piping is still cost effective on an

installed-life-cycle basis compared to carbon steel, due to lighter weight and

corrosion resistance, which translate into

reduced installation and maintenance

costs. Figure 2 also illustrates that

composite piping is equivalent or superior in load/unit material cost to any

of the corrosion resistant alloys,

validating their selection for moderate

service temperatures up to about 65°C.

Chemical Characteristics

The chemical properties of polymer

composites impact on a wide range of

activities, including polymer and fiber

synthesis [20], the thermal properties such

as curing temperature for thermosets and

melting point for thermoplastics which

influence composite processing by

filament winding [21] and pultrusion

[22], joinability and flammability [6-8].

Technology and cost gaps associated

with these properties are discussed in

companion papers from the eight

working groups of this Workshop.

Environmental Performance

Environmental behavior of polymer

composites are a particularly critical area

in which there is at present insufficient

fundamental understanding, particularly

when the effects of temperature and

stress are combined with the effects of

corrosive environments including

hydrocarbons, H2 0, H2 S, C02

, NaCl and

other halide salts, 02 , 03 and ultraviolet

radiation. It is known that water diffuses

into thermoset polymers and can affect

the mechanical properties of E-glass and

carbon fiber composites [23-27].

Figure 2

Strength versus load capacity per unit cost for

structural materials.

re a.

CD

COD

_JD

O

o

s

COo

z

3

O

>

250

200

150 -

100

50

Comparison Of Aligned Fiber

. Composites with Selected Metals 60% Fiber Composites

2205 a

• • • • Carbon

C-276 IN 825 316 SS Steel

* Carbon O O Epoxy

Carbon Carbon

. Ti PEEK PPS

Kevlar Epoxy

E-Glass E-Glass PEEK o

PPS E-Glass O Epoxy

E-Glass

7 E-Glass

, i . , . Vinylesteri i Polyester

i i I .... 1

i , . 0.2 0.5 1 2 5 STIFFNESS / UNIT COST

10 20 MPa/$

Figure 3

Modulus versus stiffness capacity per unit cost

for structural materials.

155
However, in-depth mechanistic and kinetic understanding is lacking to provide reliable quantitative

prediction of composition and properties for the long exposure times, 20-30 years, required for

reliable operation of polymer composites on offshore structures. Recent investigation of

environmental properties is discussed in companion papers from working group #2. Environmental

life prediction is crucial to meet operator

and regulator requirements for polymer

composite reliability under primary

loading and in downhole applications, as

will be further discussed in the following

section on research initiatives.

DESIGN, SYNTHESIS, MANUFACTURING PROCESSES, FABRICATION,

JOINING, INSTALLATION, FIELD INSPECTION, REPAIR

Research Initiatives To Enable Full

Realization Of Composites In Offshore

Service

Research Issues

Generic issues critical to composite use

in offshore operations are outlined in

Figure 4, which cites the industrial

infrastructure activities of the fiber and

polymer manufacturers, the composite

manufacturer, the fabricator and the

operator of offshore facilities for oil and

gas production. It also links them with

specific research activities related to mechanical, chemical and environmental

behavior. A number of these issues are addressed in more detail in papers by

other panelists on Working Group #2.

Figure 5 emphasizes the linkage between

the components of composite

microstructure and mechanical

properties, through the influence of the

state of stress, time and temperature.

These effects are particularly dependent on direction because of the different

strengths and modulii parallel and

perpendicular to the fibers, and because

of the critical influence of interfacial

bonding on properties. In Figure 6 the

potential environmental response of

composites under exposure to corrosive

species, temperature and UV radiation

are indicated. Because the

intermolecular forces are weaker in

CHEMICAL

(Synthesis. Processing. Use) MECHANICAL

(Design and Characterization) ENVIRONMENTAL

(Life-Prediction in Application) MOLECULAR STRUCTURE AND PROCESSABILITY PROPERTY MEASUREMENT AND MODELING

DIFFUSION, ABSORBTlON,

PERMEATION, REACTION STRUCTURE-PROPERTY

RELATIONSHIPS TOUGHNESS, DAMAGETOLERANCE, FRACTURE

MECHANICS

CHEMIICAL SYNERGY

REACTIVITY AND

DURABILITY MECHANISMS OF STRENGTHENING AND

STIFFENING

CORROSION, STRESS CRACKING AND GALVANIC EFFECTS

PLAMMABILITYAKID

TOXICITY TEMPERATURE7STRESS

EFFECTS

(CREEP AND FATIGUE)

biodegradation AND

BIOFOULING

Figure 4

Composite Research Issues For Reliability, Performance

and Cost in Offshore Applications.

CREEP

t (time)

FATIGUE

H

(time)

It

TORSION SHEAR

c; It

IMPACT => s ft n

TENSION

n

n

s

< i

(yield)

u

</

./ 'A i y

FLEXURE

COMPRESSION

8

u

(buckling)

ft

ft

Polymer Matrix Interface/lnterphase

Reinforcing Fiber/Architecture

Figure 5

Influence of stress state and time on polymeric

composite microstructure and mechanical properties

(strength, stiffness and toughness).

156
Interface / Interphase

. Reactivity

. Plasticization

Polymer Matrix

. Diffusion

. Solubility/Plasticization

. Reactivity/Degradation

. Stress Cracking

Reinforcing Fiber/Architecture

. Diffusion

. Tortuosity

. Reactivity

. Stress Cracking

polymers than they are in metals, relatively small changes in temperature can exert a dramatic effect on the reactions taking place within the polymer matrix, at the fiber surface, and in the

interface/interphase region. Mechanistic and kinetic factors influencing 30-year reliability are still relatively unexplored, and quantitative

life prediction methodologies are needed.

Research Initiatives

The oil industry, the composites industry,

universities and government have

recognized the need for fundamental

scientific understanding combined with

engineering development and practical

training, as a basis for polymer

composite use in offshore operations.

Continued diffusion of existing, low cost polymer composite technology into

offshore applications to address

incentives for cost reduction and life extension can be expected. Recent

meetings on current status and required

research initiatives for expanded polymer

composite usage on offshore structures include: the 1990 National Conference

sponsored by the Marine Board of the

National Research Council [9,12,24], the

1991 Workshop sponsored by the University of Houston and the oil industry, and the 1991

Workshop sponsored by Massachusetts Institute of Technology. The initiatives needed can be

grouped into two categories: 1) Development projects to determine the potential value of more

advanced materials, such as thermoset and thermoplastic composites incorporating glass, carbon and

polymer fibers, and to establish lower manufacturing costs through improved technology and

economies of scale in synthesis and

processing, and 2) Fundamental materials

R&D to achieve radical process and

product innovations in polymer

composites having superior reliability

and performance, at affordable cost.

Figure 6

Illustration of potential environmental effects on

polymer composites from exposure to hydrocarbons

H2 0, H2 S, C02

, NaCl and other halide salts, 02 , 03 and

UV radiation.

SMALL VOLUME

PRODUCTION

HIGH COST

($10-$100/lb) STATIC AND

DYNAMIC BEHAVIOR

MANUFACTURING SCALE-UP (PROJECTED LOW COST)

Initiatives in the first category have good

potential for success over the next 5-10

years, provided integrated programs are established and engineering expertise in

structural design using composites is developed and applied on a systems

basis, with appropriate training in how to design with composites compared to metals. A logical path for introduction

OTHER INDUSTRY EXPERIANCE

MARINE PERFORMANCE TESTING (MECHANICAL/ENVIRONMENTAL)

REGULATORY COMPLIANCE

(PROJECTED 30-YEAR RELIABILITY)

REGULATORY COMPLIANCE

(PROJECTED 30-YEAR RELIABILITY)

Figure 7

Acceptance path for new polymer composites in offshore

applications.

157
of advanced composites, based on currently available fiber reinforcements and polymer matrices, is proposed in Figure 7. This approach would draw heavily on existing industry, university and

government infrastructure. A conceptual

basis for moving from the current

generation experience curve for polymer

composites to a future generation

experience curve is shown in Figure 8. This involves the application of

concurrent manufacturing principles to achieve improved performance with

conventional reinforcing fibers and

polymer matrices at affordable cost. On

the longer time horizon of 10-20 years,

Figure 8 points out the potential for

development and integration of new fiber

and polymer synthesis and processing to produce nanoscale[28] composites in a continuous operation. Essentially, this

would constitute a polymer composite

refinery. Such future polymer

composites might incorporate the strength of carbon/diamond and SiC whiskers with strong covalent

bonding to a thermoplastic matrix. The resulting, truly revolutionary, high performance materials,

could be cost effectively either injection, compression or flow molded into final shape. The

scientific and engineering challenges, here, are significant, but so also is the potential payoff.

Summary

The benefits of low cost polymer composites for corrosion resistance for secondary structural

applications has been established through steadily increasing onshore usage. Empirical experience

and confidence has been gained through their use in piping, vessels and components such as sucker

rods. Now that initial regulatory concerns in the offshore, such as flammability, have been

successfully addressed, polymer composites are being designed into offshore platforms for oil and

gas production. Here they provide improved corrosion resistance and lower life cycle cost. In

addition to piping for sea water, waste water, produced water, cooling water and firewater systems,

composites are now being used in cable trays and ladders, gratings and handrails, machinery

foundations, survival crafts and tanks and separators. New applications include living quarters, fire and blast walls, helidecks, derrick components and cranes. Market potential exists for retrofitting

the installed base of about 6000 offshore platforms worldwide, as well as for installation in new

platforms.

To address the potential of polymer composites, with 20-30 year reliability, for primary loaded

structures in topside structures, platform supports such as tension legs for TLP's as well as risers and

downhole tubulars, focused research initiatives are required. In the intermediate time frame, 5-10

years, the potential for developing improved polymer composites, through better and lower cost

synthesis and processing of conventional reinforcing fibers and polymers, needs to be addressed.

Fundamental understanding of long term mechanical, chemical and environmental reliability must

Nanoscale

Figure 8. Concept of the evolution from current to future

generation of composites technology.

158
also be developed to provide methodologies and confidence for life prediction. In the long time

frame, 10-20 years, breakthrough scientific discoveries and technological innovations will be

required to develop isotropic polymer composites having ease of processing, combined with

properties comparable to steels, coupled with 30-year reliability.

Acknowledgments

The authors are grateful for the useful technical discussions with A. Lustiger and L. Monette of

Corporate Research, J. Chang, W. Sorem and M. Watkins of Exxon Production Research and A.S.

Chiu of Imperial Oil Limited. They would also like to thank K. Oswald of Smith Fiberglass

Products Inc. and E. Streett of Morrison Molded Fiber-Glass Company for price and performance

information.

References

1. J. Delmonte, History ofComposites, pp. 1-15 in Reference Book For Composites Technology,

S. M. Lee, Editor, Technomic Publishing Company, Lancaster Pennsylvania, USA, 1989.

2. A. S. Chiu and R. J. Franco, FRF Linepipefor Oil and Gas Production, NACE CORROSION

89, No. 232, April 17-21, 1989; Ibid., Materials Performance, No. 8, pp. 64-69, August 1989.

3. C. Robbe, A New Look at the Use ofGlass-Fiber Reinforced Plastic Piping, Materials

Performance, No. 6, pp. 29-35, June 1990.

4. K. J. Oswald, The Effect of25 Years of Oil Field Flow Line Service on Epoxy Fiberglass Pipe,

NACE CORROSION '88, Paper No. 167, pp. 1-7.

5. K. J. Oswald, Carbon Dioxide Resistance ofFiberglass Oil Field Pipe Made From Aromatic

Amine Cured Epoxy, Vinyl Ester and Isophthalic Polyester Resins, NACE CORROSION '88,

Paper No. 171, pp. 1-3.

6. U. Sorathia, T. Dapp and C Beck, Fire Performance ofComposites, Materials Engineering 109,

No. 9, 10-12 (1992).

7. D. Stover, Flammability Concerns Spur New Developments in Composites, Advanced

Composites, March-April 1991, pp. 34-46.

8. T. J. Ohlemiller, Assessing the Flammability ofComposite Materials, Report No. NISTIR89/4032, National Institute of Standards and Technology, Gaithersburg, MD, January 1989.

9. National Conference on the Use of Composite Materials in Load-Bearing Marine Structures,

Volume I: Summary Report, pp. 34-37, National Academy Press, Washington DC, 1991.

10. G. F. Wilhelmi and H. W. Schab, Glass Reinforced Plastic (GRP) Piping For Shipboard

Applications, Naval Engineers Journal, pp. 139-159, April 1977.

11. H. Thon, H. Haanes, R. Stokke and S. H. Hoydal, Use ofGlass Fibre Reinforced Plastic (GRP)

Pipes in the Fire Water System Offshore, 1991 OMAE Conference Proceedings, Vol. III-B, 593-

600, ASME, 1991.

12. J. G. Williams, Opportunities for Composites in the Offshore Oil Industry', National Conference on the Use of Composite Materials in Load-Bearing Marine Structures, Volume II: Conference

Proceedings, pp. 41-65, National Academy Press, Washington DC, 1991.

159
13 B. D. Craig, J. Straatmann, and G. J. Petersen, Careful Planning Improves CRA Selection For

Corrosive Environments, Petroleum Engineer International, July 1992, pp. 26-30.

14 M. S. Reisch, Advanced Thermoplastics Producers Regroup, C& E News, August 30, 1993, pp.

24-37.

15. S. R. Swanson,'Strength Design Criteria for Carbon/Epoxy Pressure Vessels', Composites 19. 400(1988).

1 6. K. Taniguchi, M. Ohira, and M. Ishii, The Effect ofMatrix Resins on the Mechanical Properties

ofFiberglass Reinforced Pipes for Oil and Gas Production, pp. I-E/l-5 in Proceedings of the

46th Annual Conference, Composites Institute, SPE, February 18-21 (1991).

17. A. Y. Lou, T. P. Murtha, J. E. O'Connor and D. G. Brady, Continuous-Fiber Thermoplastic

Composites, Chapter 6, pp. 167-204, in Thermoplastic Composite Materials, L. A. Carlsson,

Editor, Elsevier, 1991.

18. Douglas B. Johnson and Robert G. Pearson, Brunswick Composites, private communication.

19. H. X. Nguyen and H. Ishida, Poly(Aryl-Ether-Ketone) and Its Advanced Composites: A Review,

Polymer Composites &, 57-73 (1987).

20. Jean-Michael Charrier, Polymeric Materials and Processing, Hanser Publishers, New York,

1990.

21. S. T. Peters, Filament Winding, Chapter 8, pp. 143-178 in Reference Book For Composites

Technology 2, Edited by S. M. Lee, Technomic Publishing Co., Inc., Lancaster, PA, USA, 1989.

22. W. B. Goldsworthy, Pultrusion, Ibid., Chapter 9, pp. 179-197.

23. T. Atkins and C. Batich, Environmental Stability ofPolymers, MRS Bulletin 1£, No. 9, 40-44

(1993).

24. A. Letton and W. L. Bradley, Studies in Long Term Durability ofComposites in Seawater,

National Conference on the Use of Composite Materials in Load-Bearing Marine Structures',

Volume II: Conference Proceedings, pp. 163-177, National Academy Press, Washington DC,

1991.

25. L. H. Strait, M. L. Karasek and M. F. Amateau, Effects ofSeawater Immersion on the Impact

Resistance ofGlass Fiber Reinforced Epoxy Composites, J. Composite Materials 26, 21 1 8-2133

(1992).

26. Q. Zheng and R. J. Morgan, Synergistic Thermal-Moisture Damage Mechanisms ofEpoxies and

Their Carbon Fiber Composites, J. Composite Mat. 21, 1465-1478 (1993).

27. C-C. M. Ma and S-W. Yur, Environmental Effects on the Water Absorption and Mechanical

Properties ofCarbon Fiber Reinforced PPS and PEEK Composites. Part II, Polymer Eng. and

Sci. 31, 34-39(1991).

28. R. Dagani, Nanostructured Materials Promise to Advance Range of Technologies, C&E News

Nov. 23, 1992, pp. 18-24.

160
CHARACTERIZATION OF COMPOSITE MATERIALS

Gary E. Hansen

Hercules Materials Company

Advanced Composite Materials allow the user to take advantage of the extremely high strength and

stiffness of these materials. These materials are extremely orthotropic as manufactured. This offers

the advantage of having the ability to tailor the structure by putting just enough material in the

desired orientations to sustain the expected loading. It also presents the challenge of trying to characterize a material that is very directional in its properties. A unidirectional advanced composite

material can be extremely sensitive to flaws. The good news is - even though we measure

unidirectional properties we use the material in multiple angle orientations to achieve desired

performance. In addition, we have learned much about how to test and characterize advanced

composite materials.

Let's talk about a few "lessons learned".

0 Degree Tensile Testing

We have found that when you combine an orthotropic high strength and stiffness fiber with a low

strength and stiffness resin that the properties are fiber dominated but that the ultimate failure is one

initiated by flaws within the resin rather than ultimate fiber strength. This fact is demonstrated in

Figure 1, where it is shown how the ultimate tensile strength of a given fiber in a composite is different with each resin type.

TENSILE STRENGTH WITH VARIOUS RESINS, Ksl

AS4 FIBER IM7 FIBER

BRITTLE RESIN ' 300 350

SEMI TOUGH RESIN 315 380

TOUGH RESIN 330 400

Figure 1

In addition, when testing unidirectional advanced composites with brittle epoxy resins it is possible

to introduce surface flaws in the test laminate. This is shown in Figures 2, 3, and 4. In these cases, a distinct difference in tensile strength was found when testing with a resin rich surface. We have

subsequently found that most of these problems can be avoided by testing the laminates using a 0/90

laminate and calculating the 0 degree strength by multiplying by 2 (since the 90 degree plies have

all fractured long before the 0 degree plies).

161
RESIN RICH SURFACE CONDITION OF

PEEL PLIED SPECIMENS

OLD PEEL PLY

BURLINGTON 51780 PEEL PLY

Figure 2

B=FECT OF PffiL PLY ON TENSILE STRENGTH

ferirngtcn paal ply Ml mgrwr | lir lington Old htl Ply

Figure 3

EFFECT OF EDGE TREATMENT ON TENSILE STRENGTH

UNTREATED EDGES H3ULTS

Traatad adpaa war* 30* Kb I nignsr irmn untraatad

EPOXY EDGES TVB3MOPLAST I C EDGES

Figure 4

162
By far the most influential thing to do is to use tender loving care (TLC) in the fabrication of test specimens. Always, always use a water cooled diamond blade when cutting test specimens of

advanced composites (Figure 5). We recommend the use of peel plies as a means of surface

preparation to eliminate over- sanding and creating surface flaws in the laminate (Figure 6).

EFFECT OF MACHINING

TENSILE SPECIMENS

TENSILE STRENGTH C.V. %

Figure 5

EFFECT OF GRIT BLASTING

TENSILE SPECIMENS

in 2

450

400

S 350

LUz

250

SAMPLE 1 SAMPLE 2

388

332

PEEL PLY ONLY SAND BLASTED

Figure 6

163
Composite Modulus May Not Be What It Appears To Be

A typical stress-strain curve for a unidirectional carbon fiber laminate is not linear (Figure 7).

Unlike metals, the stiffness increases slightly as the strain increases. This means that the

measurement of Tensile Modulus is dependent on where on the stress/strain curve the slope is taken.

a /4am tclic lie s*i im/c U uOQ TeN5 I Lc CUHve

TYPICAL AS4 DATA

7,000

L 6,000 0

0 5,000

"1,000

u 3,000

n2 2,000

1,000

0 j i i i i i

! I 5,000 10,000 15,000

STRAIN O'cro inchaa/incro

20, 000

Figure 7

Figures 8 and 9 show how the Modulus of a Carbon Fiber can be interpreted, depending on whether

someone would use a tangent or a chord modulus. There is a total range of 42 to 50 Msi on 0°

tensile modulus and 0.2 to 0.8 Msi on shear modulus, depending on interpretation.

0 dag TENSILE CURVES - MODULUS VERSUS STRAIN

TYPICAL IM7 DATA

0 5.000 10,000 15,000 20,000 STRAIN Cmlcro rnchM/lncro

Figure 8

This problem was demonstrated when a study was made in ASTM. Sample load/elongation traces were sent to 8 different laboratories for measurement of the slope of the lines. There were three

different curves: Linear, a +/- 20 degrees layup; stiffening, a 0 degree layup; and softening, a +/-

45 degree layup. The variability of this measurement is shown in Figure 10.

164
VARIABILITY OF MAR

MODULUS WITH STRAIN wm mm

HBMCT Ml GRMIN

jo..

1 0

- p

'

0

till 1

1

I i 1,000 2,001 1,000 4,uo 1,001 a,aoo 7,001 1,000 STRAIN C»'CTOBtr«ln5 - LONGITUDINAL Figure 9

VARIABILITY OF MEASURING

SLOPES OF TENSILE CURVES

LINEAR

C+/-2Z0

1.41

STIFFENING

CP)

4/- 3.4SK

SOFTENING 0/-453

/- 20*

Figure 10

Obviously, the error shown in this type of subjective analysis on non-linear data is not acceptable.

We must rely on more precise means for measuring modulus. We recommend using chord modulii

(i.e.- 6000 microstrain minus 1000 microstrain) based on two finite points for the following reasons:

The noise in a stress-strain trace takes place in the first 500 microstrain and primarily caused

by grip seating and alignment.

Measuring loads at specified standard strains is much more precise than attempting to draw

a tangent line to a non-linear curve.

Carbon fiber composite parts are typically designed for use in the range up to 6000

microstrain.

165
Not All Test Data Can Be Compared

There are a myriad of shear tests available: Short Beam Shear, Off-Axis Shear, Iosipescu, Rail Shear,

and In-Plane Shear to name a few. These all provide a value for shear strength. None of these

values would be the same. A rose is a rose is a rose does not apply in this case. Compression

testing is just as bad. There are many test methods available: Modified ASTM D 695, IITRI,

Celanese, with each method having several variations on the theme. The net result has been the

inability to compare data between Laboratories. There have been several innovative methods cited

in the literature but they have not yet been exposed to the test of time. Much work needs to be done

to develop robust compression test methods. There is not much effort being expended due to a general economic decline in the industry.

We Need To Agree On What Tests Should Be Run For Characterization

We need to agree on a standard test matrix which is acceptable to all end-users for product

characterization. This would, of necessity, require an agreement on test methods as well. This has

been addressed through MIL HDBK 17, a coordination committee which has been functioning for

several years. This organization has as one of its objectives to recommend standard ways of doing

things in the development of design properties for polymeric composites. Several Tables for

recommended test matrices are presented in the MIL HDBK 17 for material characterization,

screening, qualification, and development of design properties (Figures 11, 12, and 13). I recommend that you obtain MIL HDBK 17 and use this as a guide in the characterization and use of Advanced Composite Materials. This can be obtained from the Standardization Documents Order

Desk, Building 4D, 700 Robbins Avenue, Philadelphia, PA 1911-5094.

MIL HDBK 17 ALLOWABLES TEST MATRIX

MECHAN I CAL SUGGESTED TEST CONDITION AND NUMBER PROPERTY TEST a NUMBER OF TESTS OF TESTS

PROCEDURE PER BATCH 1

MIN. TEMP RT MX. TEMP

CONDITION DRY DRY WET 0 Cdeo) TENSION C*ARFO D 3039 6 6 6 90

SO C<*CD TENSION £ F I LIO D 3038 B B B 00 0 C<tofl0 COMPRESSION QVARPJ D 3410 6 6 6 SO 90 CctosO COMPRESSION CFILIO D 3410 6 6 6 90

IN-PLANE SHEAR C*453 D 3518 6 6 6 90 0 C<J*flD SHORT BEAM SHEAR * D 2344 8 30 480

13 TESTS PERFORMED ON EACH OF 5 BATCHES

23 FOR QUALITY CONTROL PURPOSES ONLY Figure 11

166
MIL HDBK 17 SCREEN I NG TEST MATRIX

NUMBER OF SPECIMENS

TEST CTD RTA ETW EVALUAT 1 ON EMPHAS 1

S

LAMINA' Q06QJ TENS ION 3 3 3 P 1 BER

0 Cdag^ COMPRESSION 3 3 FIBER/ MATRIX

+/- 45 CdOOD TENSION 3 FIBER MATRIX

0 CdegQ/BO Cd»flj SHEAR- LAMINA}

C+/- 45 CdeoD - LAMINATED

LAMINATE: OPEN HOLE COMPRESSION 3 STRESS RISER

OPEN HOLE TENSION 3 STRESS RISER

BOLT BEARING

1 3 BEARING

COMPRESSION AFTER IMPACT 3 IMPACT DAMAGE

1 PASTNER HOLE EFFECTS

2 PER NASA REFERENCE PUBLICATION 1092

Figure 12

MIL HDBK 17 PROCESS CHANGE QUALIFICATION

TEST MATRIX

MB. CP BATCHES GATES EMVIICM TB t TOTAL

LAM I Wk WCPWTT

compati iiLmr 1 compatibility 1 CCMPATIBILI rr

1 OWATIfl I LI'

1' 8 3 4* *» 3b 6 1 2 3 4k 46 St e 1 2 3 4* 4b 3d 3b 6 1 2 3 4a 4b 3b 1 UOMBITWINAL TBMBILI 1 I 2 a 9 1 4 4 4 4 4 9 8 I E E I E E E E a IS 18 M 24 30 30 33 TMMC TBSILE 2 a 3 3 3 3 4 4 4 3 s 2 2 8 2 e 2 1t 24 24 30 30 38

ldmsitudinal —irmaBirr 1 3 3 3 1 •3 1 4 4 4 4 4 3 1 2 2 2 2 a 2 2 a IB 11 24 34 30 30 38

1 9 a a 3 J 3 4 4 4 4 4 3 e 2 2 2 2 2 2 1 16 E4 E4 30 30 99

1 m^^»^ atscaAJt 1 1 a J 3 4 4 4 4 4 3 a E 1 S E E E E E 9 1B 16 24 24 30 30 36

34 AS SO 135 1E0 1501SD 1BC

1J COMPATIBILITY II V « IN TAU I 1 I 1 C IF OHIIIMN. MATBPJIAL CONST I TUWT1 ANE AVAILABLE CP IBS* LOT, PES IN MIX3 DO CM BATCH WW LI Ml. IP THtY ARE NOT AVAILABLE, PRODUCE TO BATCHBS P*BM A HBV PIBBf LOC/PSBIM MOT, 0M1 ON EACH LINE

a) tvb Bj»vinoiiiri should m rro amd the worbt case

43 quality tmmma -nan must be pirfopmed paa imoivioual spec i pi cation. Figure 13

167
There are organizations striving to assist in the development of data bases of Advanced Composite

Materials. A new approach to data reporting is being proposed in ASTM Committee D30 to formalize the link between test methods and computerization guides and to meet the needs of testing

laboratories and materials fabricators and users. This approach combines the formats for

computerization developed in coordination with Committee E49. Three facets of this approach are fundamental to its success:

Formats for computerization

The use of the formats as the basis for data reporting sections for all lamina/laminate

mechanical property

The expanded range of requirement levels

Three formats for computerization of composite materials data have been developed to date:

El 309, Guide for the Identification of Composite Materials in Computerized Material

Property Databases

El434, Development of Standard Data Records for Computerization of Mechanical Test Data

for High Modulus Fiber-Reinforced Composite Materials

El471, Guide for the Identification of Fibers, Fillers and Core Materials in Computerized

Material Property Databases

The good news is - people are working the problems for characterization of Advanced Composites

Materials. There has been and Ad Hoc Committee for Composites Standardization that has prepared

a plan for the harmonization and standardization in the use of Composites. Figures 14 and 15 show

the organization of the group and how they would work in concert to develop Standards for: MATERIAL SPECIFICATIONS

TEST METHODS

PROCESS SPECIFICATIONS

DESIGN ALLOWABLES

We are still seeking government funding to make this happen. The composites manufacturing and

using industries have come together and agreed to work toward a common goal - Standardization.

SACMA, ASTM, AIA, MIL HANDBOOK 17, are all working for the common cause of doing things

better and more consistendy. Participation in these groups would enhance anyone's perspective into

the effective use of very complex - and very useful - materials.

I may have painted a gloomy picture. It was only to alert you to the challenges in getting the full use of very versatile and hard working materials. There are many resources available to make it easier and to put you well up on the learning curve. Use these and enjoy the benefits of a terrific

family of Engineering Materials.

168
INDUSTRY MANUFACTURERS SUPPLIERS AGREEMENT

FUNDING CONSORTIUM

UM - AIA

GOVERNMENT TECHNICAL

FUNDING FUNDI NG

INTN *L COORD.

STEER I MS GOMITTEE

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MIL-HDBK-17

FAA, AIR ROOCS, NAVY, AfiMV NIIT

TECHNICAL DIRECTOR

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MIL-HDK-17

TASK FONC1 MATERIAL SPECSTASK FORCE PROCESS SPECSTASK FORCE TEST METH306TAEK FORCE TASK FORCE

CRITERIA k DESIGN

ALLOWABLES

SAE/AfcC cuvac

TECHNICAL SOCIETIES

Figure 14

PROPOSAL FOR STANDARDIZATION

CONSORTIUM WILL COORDINATE

EXISTING ACTIVITIES

MANUFACTURING - AIA

SUPPLIERS - SACMA

MIL-HDBK-17

DOO/FAA

NIST

EVALUATE 8. DEVELOP

STANDARDIZATION

PROCEDURES

MATERIAL SPECS

PROCESS SPECS

TEST METHODS

INTERNATIONAL STDS

CRITERIA

DESIGN ALLOWABLES

PUBLISH & CONTROL

SAE/AMS

ASTM

MIL-HDB<-17

Figure 15

169

SOME PERSPECTIVES ON THE USE OF COMPOSITES

FOR OFFSHORE OPERATIONS

Prof. S. S. Sternstein, Director

Center for Composite Materials and Structures

Rensselaer Polytechnic Institute

Troy, N. Y. 12180

Introduction

The use of composites for load bearing structural applications entails the

simultaneous consideration of a number of issues, including but not limited

to, economics (materials costs, fabrication costs, maintenance costs and

repair and replacement costs), suitability to task (e.g., are the derived

benefits worth the effort), performance factors (e.g., are weight, strength

and/or stiffness critical factors) and special considerations such as lifetime,

safety and reliability, ease of construction transport to the site and in the

case of interest here, environmental resistance. Previous uses of composites

have largely been dictated by the need for high strength to density and/or

stiffness to density ratios. This is especially true for aerospace applications.

In the case of offshore operations, it would appear (based on the author's

admittedly scarce knowledge) that environmental resistance benefits

(relative to steel, for example) and the potential lifetime benefits deriving

therefrom, as well as possible economies deriving from reduced weight and

increased specific stiffness may be important life cycle considerations for

the use of composites for both structural and piping applications.

Environmental Considerations

It is well known that most thermosetting matrix composites (especially the

epoxies) are prone to absorb water to some extent. The result of such

absorption generally lowers the glass transition temperature and results in

reduced matrix modulus at any given temperature. In addition, it is also

well known that when moisture slowly diffuses into a composite but is

forced to leave quickly, such as occurs when a hot spike occurs during a

supersonic maneuver) the moisture causes damage in the form of

delaminations, holes and fiber-matrix separation. While the severity of a hot

spike is not likely in offshore operations (at least not to the extent such as

occurs in an airplane) there is cause for concern due to the extensive

exposure to water which will occur. Thermal cycles which are likely to

occur such as in piping may result in some undesired diffusion effects. In

addition, hydrostatic pressure effects are also present and must be

171
considered since they will affect the degree of water absorption due to well

known thermodynamic principles.

The effects of other solvents present in crude oil may also be of importance

and may lead to effects similar to those for water or worse, for example,

solvent induced stress cracking such as occurs in many engineering

thermoplastics. It is this author's belief that solvent and water effects may

in fact be the most important considerations for the selection of matrix

materials for composite piping and possibly also for structural components.

The choice of a suitable interface sizing for fibers (especially for glass) is also

largely dictated by solvent and water effects. It is essential and prudent that

the point of view be adopted that matrix cracks will always allow exposure of

the fiber-matrix interface to the environment.

The author will address several phenomena associated with the effects of

solvents and water on composite structural materials. Previous work has

shown that interaction of a solvent (water or otherwise) with the matrix of a

composite leads to inhomogeneous swelling, a complex phenomenon which

can be modeled using mechanics and thermodynamics. Briefly, the

presence of two or more phases having different chemical affinity for the

solvent results in concentration and stress gradients within the composite.

Under certain conditions, hydrostatic tension centers (cavitation sites) can

also be produced, leading to failure of the matrix. Depending on a variety of

factors, the solvent concentration can be higher or lower at the interface

than away from the interface. In general, the affinity of the composite for

either solvent or water uptake can be readily shown to be stress and stress

state dependent. Changes in stress level or stress state can cause the

internal solvent or water field to move around. Thus it is possible for a

"thermodynamic magnet" to exist which drives water to the interface.

Hence, the choice of a suitable fiber sizing is emphasized.

Several examples of solvent and water effects in composites will be

presented during the workshop. A theoretical framework developed by the

author [1,2,3] can be used to understand and predict many environmental

effects, using a limited amount of experimental data on the constituents

(fibers, matrix and interface) and the microstructure of the composite.

Relatively simple experiments combined with the theoretical analysis can

provide major insights into the suitability of a given system for long term

environmental exposure and the likelihood of success, as well as providing a

rational basis for materials selection.

Structural Considerations

One of the more complex tasks encountered by offshore construction of

composite materials is likely to be that of joining. Inasmuch as composites

are inhomogeneous, highly anisotropic materials, the transfer of loads from

one member to another entails stress diffusion. As a general rule diffusion

lengths in composite materials are far larger than in isotropic materials.

172
Consequently, the wrong type of joint may overly load the outer plys of a

composite laminate and result in failure of the outer plys and perhaps the

whole structure at loads far lower than net section uniform stress

calculations would predict. This type of problem, in which the overload

occurring in outer plys causes premature failure, is especially important in

structural components carrying compression loads. It is especially

important that designers of composite structures be aware of the stress

diffusion characteristics of composites and that they allow for such effects.

A successful engineering and design methodology for composites in offshore

applications (both structural and piping) must address the effects of joining

methods on stress diffusion in the surrounding structure and its effect on

lifetime and environmental resistance.

References

1) S. S. Sternstein, Inhomogeneous Swelling in Filled Elastomers, J.

Macromol. Sci, Pt B, Physics, B6(l), pp 243-262 (1972).

2) T. Kotani and S. S. Sternstein, Birefringence Analysis of Inhomogeneous

Swelling in Filled Elastomers, in Polymer Networks: Structural and

Mechanical Properties, Edited by Chompf and Newman, Plenum Press, N. Y.,

pp 273-291 (1973).

3) F. Lumban Tobing, M. S. Shephard and S. S. Sternstein, Finite Element

Analysis of Moisture Effects in Graphite-Epoxy Composites, Computers and

Structures, Vol. 16, No. 1-4, pp 457-469 (1983).

173
174
MATERIAL PERFORMANCE: MICROMECHANICAL

MODELING OF COMPOSITE FRACTURE

John A. Nairn

Material Science and Engineering, University of Utah

Salt Lake City, Utah 84112, USA

Introduction

Whenever composites are used in structural applications, it is important to be able to predict when they will fail. The field of fracture mechanics can be defined as the engineering discipline that seeks to predict the conditions

under which a load-bearing body will experience growth of damage [1]. Thus, what we seek is a fracture mechanics

of composites. In homogeneous, isotropic materials, such as metals, it is possible to analyze the stresses at the

tip of a generic crack and use those results to predict crack growth. The tools for predicting crack growth are

stress intensity factor or energy release rate. In principle, a similar approach can be used for composites, but, in practice, the heterogeneity and anisotropy of composites makes the process difficult. Instead of being describable

by generic cracks, damage in composites can take many forms. There can be cracks in the matrix, cracks in the fiber, cracks at the fiber/matrix interface, and cracks with any variety of locally heterogeneous environment.

These cracks can grow by multiple paths depending on loading conditions and on the crack-tip environment. Thus we see matrix cracking, fiber cracking, interfacial failure, longitudinal splitting, and delamination. A thorough

understanding of composite failure requires analyzing all crack types and all crack paths.

Another term for the fracture mechanics of composites is micromechanical modeling of failure or micromechanics of damage. The development of micromechanics of damage models always involves two equally important

steps [2]:

1. Analyzing the stresses in the presence of damage

2. Proposing and verifying failure criteria for the prediction of damage growth

These two steps were the same ones that were followed in developing fracture mechanics of metals. In Griffith's original fracture paper [3], he began with an elasticity solution for the stresses around a sharp crack and calculated

the energy release rate for crack growth. For step two he postulated that crack growth occurs when the energy

release rate reaches a critical value. This postulate has been verified by many experiments. In composites, the

stress analysis step is usually more complex than it was in metals. Indeed, there are many important composite

crack geometries for which no exact elasticity solution can be found. Instead, we must resort to approximate

methods or to numerical methods such as finite element analysis.

However accurate the stress analysis or refined the finite element analysis, the entire exercise will be for naught, if attention is not paid to step two. Neither stress analysis nor finite element analysis tell us anything

about failure; these must be coupled with some failure criterion before predictions of failure can be made. In the fracture mechanics of metals, failure is always predicted by using one of two failure criteria—critical energy

release rate or critical stress intensity factor. Because these two failure criteria are uniquely related to each,

there is, in fact, a single unifying failure criterion that ties all metal fracture problems together. In contrast, the

literature on composite fracture has no unifying failure criterion. We find, for example, assumptions of failure at some maximum level or stress, some maximum level of strain, some quadratic combination of stresses or strains, some average stress over a representative unit volume of material, some shear stress at the interface, or under

whatever conditions seem convenient. I suggest that this seemingly random approach to composite fracture is unlikely to be successful. In this paper, I will discuss some specific examples of developing micromechanics of damage models for composites. For each example, I will cover steps one and two of the analysis process. I will pay particular

attention to step two and give experimental evidence to verify or reject any failure criterion. The discussion

175
at the end of the paper will describe the unifying fracture concepts that emerge from the small set of failure problems covered in this paper.

Microcracking

The first form of failure in most laminates is matrix cracking or microcracking in the off-axis plies [4-21].

Microcracking is commonly studied in [(S)/90n] s or [90n /(S)] s laminates, where (S) denotes any orthotropic

sublaminate and microcracking occurs in the 90° plies. There are many reasons for studying microcracking.

Microcracks not only change the thermal and mechanical properties of laminates [14, 22, 23], but also present

pathways through which corrosive agents may penetrate into the interior of the laminate [9]. When prevention

of leakage is important, the mere presence of microcracks may represent a technological failure of the structure. Perhaps most importantly, microcracks act as nuclei for further damage such as delamination [13, 17, 24],

longitudinal splitting [8, 9], and curved microcracks [19, 25]. Because microcracks are precursors to the cascade

of events that leads to laminate failure, we would have little hope of understanding laminate failure or of predicting

long-term durability if we did not first develop a thorough understanding of the phenomenon of microcracking.

The first microcracking problem is predict the onset of microcracking, or the strain to microcrack initiation. Because the first microcracks do not cause catastrophic failure, it is possible to continue loading after microcracking. Typically this loading will cause additional microcracks. The second microcracking problem is to predict

the increase in microcrack density with increasing load. Eventually the existing microcracks will nucleate further damage which will propagate into laminate failure. In this section, I will discuss micromechanical modeling of

microcrack initiation and of microcrack density as a function of load. Microcrack Initiation

Before any microcracks form in a laminate, laminated plate theory gives an accurate analysis of the laminate

stresses. We thus begin by using laminated plate theory for step one of the micromechanics model. A simple

model to predict microcrack initiation, known as first-ply failure theory, is to assume that the 90° plies will crack when the stresses in the 90° plies reach the strength of the unidirectional lamina material. We imagine a composite under uniaxial load of oq in the x direction, where the x direction is parallel to the zero degree fibers. The x- and ^/-direction tensile stresses in the 90° plies of the undamaged laminate can be written as

"2? - <U + k^xT <$ = k%v°° + kZT (D

where km and fc( /, are mechanical and thermal stiffnesses of the 90° plies, T is the temperature difference between

the specimen temperature and the stress-free temperature (T = Ts — To), and superscript (1) denotes the 90°

plies. The mechanical and thermal stiffnesses can easily be evaluated from laminated plate theory [2]. We denote the transverse and axial strengths of the unidirectional lamina material as a? and aa- A simple

maximum stress failure criterion predicts first ply failure when a^j = a? or

Because the shear stresses are zero in the 90° plies, the slightly-more-complex Tsai-Hill failure criterion predicts

first-ply failure when [26]

r (')2 _JiU)x (?A

2 a J1)*-J*

y0 ~ axQ u

yQ Of

"$>> + - = < (3)

This equation can easily be solved for <7o- Figure (1) shows some experimental microcrack initiation results and

compares them to the predictions of first-ply failure theory. Only one first-ply failure theory curve is shown

because predictions using the maximum stress or Tsai-Hill criteria are identical. First-ply failure theory works

well for laminates with thick 90° plies. This result is expected because the results must asymptotically approach

the results for a transverse tensile test on a unidirectional laminate. For laminates with thin 90° plies, however,

first-ply failure theory is completely wrong. Imagine relying on first-ply failure theory to design a cross-ply

laminate that resists microcracking. The recommendation would by to maximize the thickness of the 90° plies;

the correct answer is to minimize the thickness of the 90° plies.

The problems with strength-based theories led Parvizi et al. [7] to propose that microcrack initiation occurs when the energy released due to the formation of the first microcrack exceeds the critical energy release rate

176
o

CO

l_o

2

o

CO

CO CO

Energy Release Rate Theory

First Ply Failure Theory

1 1

0 1 2 3 4 5

Total Thickness of 90° Plies (mm)

Figure 1: The strain to initiate microcracking in E glass/Shell Epikote epoxy [0/90/0] laminates as a function

of the total thickness of the 90° plies [6]. The 0° plies each have a constant thickness of 0.5 mm. The two curves

give theoretical predictions for the strain to initiate microcracking using first-ply failure theory (the maximum

stress and the Tsai-Hill predictions are identical) or energy theory.

for microcracking—G^. Laminated plate theory only gives the stresses and energy in the undamaged laminate.

To calculate the energy after the formation of a microcrack, we need to analyze the stresses in the presence

of microcracking damage. Numerous authors have presented one-dimensional solutions to the problem [4, 5,

8, 15, 27-32]. It can be shown that all these analyses reduce to the same shear-lag equation and thus are equivalent [2]. Hashin used variational mechanics to derive the first two-dimensional, analytical stress analysis

for a microcracked [0m/90n] a laminate [33, 34]. Nairn et al. extended Hashin's analysis to include residual thermal

stresses and to handle both [(S)/90n] s laminates and [90n /(S)}3 laminates [2, 21, 24, 35-37].

Using the modified Hashin's stress analysis to calculate the energy release rate for formation of the first microcrack and assuming that the crack forms when that energy release rate exceeds Cmc, lead to the following

prediction for the strain to initiate microcracking [2]

£init —

^

* 1 ^C1 (C4 -C2 + 2 v/fJ^)

(4)

where is the x direction modulus of the undamaged laminate and C\ to C4 are constants that depend on

the mechanical properties and geometry of the laminate [2, 36]. A comparison between the predictions of this energy theory and experimental data is given in Fig. 1. The energy theory agrees much better with experimental

data than first ply failure theory. In particular, it agrees with the constraint effect that causes the stain to

initiate microcrack to rise sharply for laminates with thin 90° plies. The agreement of the energy theory for laminates with thick 90° plies is not as good. This region of poor agreement may represent a region where

the approximate variational stress analysis is not good enough to give an accurate calculation of the energy

release rate. Unfortunately, it is difficult to resolve all issues by focusing on initiation experiments. Initiation experiments yield only one data point per laminate. The results are thus prone to experimental scatter and

sensitive to laminate flaws or to local laminate heterogeneities in toughness. The preferred experiment is to continue loading and measure the microcrack density as a function of applied load. These experiments yield

many data points per laminate and the results are less sensitive to laminate variability [2, 21, 36].

177
600

500

400 h

300

— 1 1 1 "

Stresses: Variational Mechanics

Criterion: Energy Release Rate

O

1 200

100

[0n /90m ] s [90n /0 m ] s

25

1/2. 35

Reduced Crack Density (°C m/J )

Figure 2: A master curve analysis for 18 Hercules AS4/3501-6 carbon/epoxy laminates [36]. To avoid inherent

scatter of microcrack initiation data, results for crack densities less than 0.3 mm-1 were eliminated.

Microcrack Accumulation

To predict microcrack density as a function of applied load, many authors have advocated an energy release rate

failure criterion [2, 18, 21, 30, 31, 35-37]. In brief, the next microcrack is assumed to form when the total energy

release rate associated with the formation of that microcrack, Gm, equals or exceeds the microcracking fracture toughness of the material, G^. Nairn et al. [36] used the modified Hashin's analysis and solved for the applied

stress as a function of crack density, D:

where Y(D) is a calibration function that depends on crack density, laminate mechanical properties and laminate

geometry (see Refs. [2, 36] for an analytical expression of Y(D)). Equation (5) leads us to define a reduced stress and a reduced crack density as

reduced stress: or = — oq

(6) reduced crack densi+y: DR = ~^wJc^uy(d)

A plot of or vs. Dr defines a master plot for microcracking experiments. If the variational analysis and energy

release rate failure criterion are appropriate, a plot of or vs. Dr will be linear with slope v^mc and intercept —T. Because Gmc and T are layup independent material properties, the results from all laminates of a single

material with the same processing conditions should fall on the same linear master plot. Thus constructing a master plot of microcracking data for a series of different laminates is an excellent way to evaluate microcracking

theories. Figure 2 gives a master plot for 18 different layups of carbon/epoxy laminates [36]. Among the 18 different layups are laminates with interior 90° plies ([(5)/90„]J laminates) and laminates with surface 90° plies ([90n /(5)]J

178
600

100

1 1

Stresses: One Dimensional

Criterion: Energy Release Rate

[0„/90J,

[90n /0 m ] s

10 20 30 40 50 60

Reduced Crack Density fC m/J

1/2

)

Figure 3: A master curve analysis of all AS4/3501-6 laminates [36] using a one-dimensional stress analysis

and an energy release rate failure criterion.

laminates). Among the supporting sublaminates (5) are unidirectional sublaminates (0n ) and angle-ply sublaminates (±9 where 9 = 15° or 30°). The analysis of microcracking in surface 90° plies requires a new variational

mechanics stress analysis [37], but the final results can be reduced to the same master equation in Eq. (5). The

only change is that the Y(D) calibration function is replaced by new calibration function specific for cracking of surface plies [36].

I claim Fig. 2 verifies both the validity of an energy release rate failure criterion and the accuracy of the

variational mechanics stress analysis. Thus it verifies both steps in the micromechanics model for microcracking.

There are three facts that support this claim. First, all laminates fall on a single master curve plot within

a relatively narrow scatter band. Second, the results for [(5)/90„] 3 laminates (open symbols) agree with the

results for [90n /(5)] s laminates (solid symbols). Third, the slope and the intercept of the master curve result

in Gmc = 279 J/m2 and T = —93°C. Both of these results are reasonable measured values for these physical

quantities [2]. The master plot treatment is useful for examining the relative importance of the stress analysis and failure criterion steps in a typical micromechanics model for fracture. First we consider replacing the variational analysis

with the often used one- dimensional analysis of stresses in cross-ply laminates [4, 5, 8, 15, 27-32]. By using the

energy release rate criterion, it is possible to reduce the one-dimensional stress analysis predictions to the same

master equation in Eq. (5), except that Y{D) changes from the variational mechanics results to a simple one- dimensional result [36]. Figure (3) gives the master plot for the same 18 laminates in Fig. 2. When compared to the variational analysis, all one-dimensional analyses have serious problems. Most importantly, the results from

individual laminates do not overlap each other. A characteristic of one-dimensional analyses is that the results from [(5)790,,], and [9Qn/(S)]a laminates segregate into two groups. One dimensional analyses do not distinguish

between [(S)/90n] 4 and [90n/(S)]a laminates and thus could never be expected to explain the experimentally

observed differences between them [2]. The slope and the intercept of the master curve give Gmc = 44 J/m2 and

T = -|-124°C. Neither of these fitting constants is reasonable. The residual stress term (T), in particular, must

certainly be negative for laminates that are cooled to room temperature after processing.

If one plots laminate stiffness as a function of microcrack density calculated by a one-dimensional analysis and

by the variational analysis, the differences are marked, but hardly dramatic [2]. It is thus somewhat surprising

179
0 5 10 15 20

Reduced Crack Density ('C/MPa )

Figure 4: A master curve analysis of all AS4/3501-6 laminates [36] using a variational mechanics stress analysis

and a maximum stress failure criterion.

to find truly dramatic differences between the fracture predictions based on the two analyses. A qualitative

interpretation of the differences can follow from realizing that stiffness is a global property while fracture is an instability event. It is relatively easy to calculate global properties. When calculating instability processes, however, minor differences in input stresses can lead to dramatic differences in predictions. In other words,

the increased accuracy in the stresses attributed to the variational analysis was crucial to the predictions of microcracking.

Accepting the variational mechanics analysis as accurate, we can examine the effect of the failure criterion used in the second step of the micromechanics model. Numerous authors have suggested using strength-based

models to predict microcracking [4, 7, 15, 16, 20, 29]. If we implement the strength criterion using the variational

mechanics stress analysis we find a master relation of [2]

where 0(0) is a calibration function that depends on crack density, laminate mechanical properties and laminate

geometry (see Refs. [2, 33-36] for an analytical expression of 0(0)). For strength theories, the reduced stress is the same as for energy theories, but the reduced crack density is redefined as

reduced crack density: Dr = —pj--7—-—y (g)

Thus the slope of a strength-theory master plot is the transverse tensile strength of the lamina material.

Figure (4) gives the master plot for the same 18 laminates in Fig. 2. When compared to the energy release rate model, the strength modal has serious problems. Most importantly, the results from individual laminates

do not overlap. In particular, the results from [(S)/90n] 3 and [90n/(S)} 3 laminates segregate into two groups. Experimental observation shows that the load required to cause high crack densities in [(5)/90n] a laminates is lower than in [90n /(S)]3 laminates [2]. The energy release rate failure criterion correctly predicts this effect and

all results reduce to the same master plot. The maximum stress failure criterion does not predict the surface vs.

180
interior effect. The slope and the intercept of the master curve give ar = 23 MPa and T = +140°C. Neither of these fitting constants is reasonable.

Interface Failure

The interface between the fiber and the matrix in composite materials influences many bulk properties. In continuous-fiber composites, the interface affects shear strength, shear modulus, off-axis properties such as de- lamination and longitudinal splitting, compression strength, impact strength, fatigue durability, and environmental stability. The interface is even more important in short-fiber composites. By influencing the process of

stress transfer between the matrix and the short fibers, the interface additionally affects on-axis strength and

on-axis modulus. Whenever one contemplates developing or using new composite materials, that development

program should include work on the interfacial properties of that composite.

Some popular tests for characterizing the fiber/matrix interface include the fragmentation test [38-43], the

fiber pull-out test [44, 45], the microbond test [46, 47], and the microindentation test [48]. All these specimens

involve complex stress states, but the test results are almost always analyzed using simplistic equilibrium, shearlag, or elastic-plastic analyses. In the next section, we consider an improved micromechanics model of one of these tests.

Microbond Test

In the microbond test, a small amount of resin is deposited on the fiber surface in the form of a droplet. The

droplet is debonded from the fiber by pulling the fiber while restraining the droplet with a microvise [46, 47]. Qualitatively speaking, the higher the debond force, the tougher the interface. Microbond experiments are usually

analyzed using an average shear stress failure criterion. By integrating the equations of stress equilibrium it is possible to derive an exact relation (i.e., the stress analysis step is done exactly) between the average interfacial shear stress, (rr2 ), and the fiber force, F:

where ry is the fiber radius and / is the length of the microdrop. The simplistic analysis of microbond tests assumes

that the interface fails when the average shear stress equals the interfacial shear strength, ric. The inadequacy of the average shear stress failure criterion can be demonstrated by comparing predictions to experiment. Equation

(9) predicts that the force to debond the microdrop is linear in the microdrop length, /. Figure 5 shows some

experimental data for epoxy droplets on E-glass fibers [49]. The debond force is not linear in /, but rather levels

off for long droplets. These results are experimental proof that failure of the fiber/matrix interface in these

specimens is not controlled by the average shear stress along the interface. The average shear stress failure criterion is poor because it is unrealistic. This result is not surprising because

refined stress analysis shows that the interfacial shear stress is nonuniform [50]. There is a stress concentration

at the point where the fiber enters the droplet. The largest component of the stress concentration is a tensile stress in the radial direction. The average shear stress approach ignores this tensile radial stress and implies a

shear failure mechanism. SEM observations, however, suggest an interfacial crack propagation mechanism with

the crack initiating where the fiber enters the matrix [51]. One method to account for the complex stress state

is to abandon the average shear stress analysis and adopt an energy release rate approach [50]. By extended Hashin's variational mechanics stress analysis for laminates to the axisymmetric geometry of

droplets, it is possible to derive an accurate stress analysis of the microdrop specimen [50]. Using this stress

analysis, the energy release rate for initiation of a fiber/matrix debond in a microbond specimen is

G,(0) = /Vm " /WT + f33 T

2

( X

'e (0) ~ X'eip)) + fo°l(Xe(P) + Xo(p)) (10)

where am is the average stress on the droplet; and /?i to fa, Xe(p), and Xo(p) are constants and functions that

depend on specimen dimensions and on fiber and matrix mechanical properties [50]. An energy-based micromechanics model for the microbond specimen is to assume that the droplet debonds from the fiber when the energy

release rate for initiation of crack growth exceeds the fracture toughness of the interface, GiC . The experimental

results in Fig. 5 indicate that the energy release rate model provides a much more realistic interpretation of the

results. Furthermore, the measured interfacial toughness of Gic = 218 J/m2 is more likely to be a quantitatively

useful material property than is an effective interfacial shear strength.

181
0 100 200 300 400 500

Droplet Length (pm)

Figure 5: The debond force for a series of epoxy droplets on E-glass fibers [49]. The two curves give theoretical predictions using either an average shear stress or a critical energy release rate failure criterion. The inherently scattered microbond data has been smoothed by taking running averages of data with similar droplet lengths.

The error bars indicate the standard deviation of the averaged data.

Discussion and Conclusions

Micromechanics models of composite fracture are an important part of the science of composite materials. All micromechanics models involve at least two important steps—analysis of stresses in the presence of damage

and prediction of failure using some failure criterion. The above examples show that if either of these steps is deficient, a seemingly rational model can be contrary to experimental observation.

Consider the stress analysis step first. The complexity of composite fracture problems means that we will always be resorting to approximate solutions or to finite element analyses. When working with approximate

solutions, it is important to verify that those solutions are sufficiently accurate. When dealing with fracture problems, the accuracy requirements are more stringent than when dealing with simpler problems such as pre- dicting plate stiffness or displacements. For example, one-dimensional, shear-lag models do a reasonable job of predicting plate stiffness as a function of microcracking damage [2]. Those same stress analyses, however, are inadequate for fracture problems. The only acceptable method of verifying a stress analysis for micromechanics

of damage models is to show that it makes valid predictions about fracture properties. Hashin's variational

mechanics methods [33, 34] have been verified as a useful stress analysis for predicting microcracking [2, 36]. Finite element analysis is a powerful tool for analyzing the stresses in complex structures. In principle, finite element analysis can be used to study many fracture problems, but, in practice, it can be cumbersome. The

main problem is that predicting damage growth inevitably means analyzing the stresses for various amounts

and various forms of damage. Each new damage state requires a new finite element calculation. For example,

predicting the microbond data in Fig. 5 would require a separate finite element calculation for each droplet size. The time and expense required to generate such results prohibits the use of finite element analysis as the primary

stress analysis tool. I claim instead that there is great incentive for developing micromechanics models based on analytical stress analyses, especially when composites are being contemplated for new applications such as marine structures. Finite element analysis is best used as a experimental technique that can verify the accuracy

of the stress analysis or suggest ways it can be improved [2]

It is disappointing to read a paper on composites fracture and find an elegant stress analysis method rendered

182
useless by inattention to the step of choosing an appropriate failure criterion. This problem is too common in the

composite literature, but easy to recognize. After spending several pages on the stress analysis or on numerical

methods, a typical flawed analysis will deal with the failure criterion in a single unsupported and probably

unrealistic sentence such as: "the next crack was assumed to form when the average stress within an element

reaches the strength of the material." The examples in this paper show that the failure criterion warrants greater

attention. If it is not chosen carefully, the micromechanics model will not work regardless of the accuracy of the

stress analysis. A pattern that emerges from the microcracking and microbond experiments is that we should

tend to favor fracture mechanics methods, such as energy release rate, and try to avoid strength-based methods.

This conclusion is no surprise to anyone accustomed to fracture analysis in metals. No progress would ever be

made in the analysis of metal fracture by resorting to simplistic failure criterion such as maximum stress criteria. Likewise, no progress will be made in the fracture mechanics of composites until the models are based on sound

failure criteria.

I close with some suggested techniques for reading the literature on micromechanics of damage models. A

series of questions should always be asked: How was the stress analysis done? Is it accurate enough? In particular,

is it accurate enough to be used in fracture predictions and not just in stiffness predictions? If the stress analysis

required finite element analysis, is it flexible enough to handle different amounts of damage? Would you be

able to use the analysis to support your own work? (Analytical models tend to be more portable than finite element-based models). Was sufficient attention paid to selection of the failure criterion? Is the failure criterion rooted in fracture mechanics principles? If not, was the selection of a nonstandard failure criterion justified?

Most importantly: was the entire micromechanics of damage model verified by comparison to a large body

of experimental evidence? (Models that are supported by only a single set of experiments should be treated

with skepticism). Finally, an exercise for the reader is to ask these questions about the failure predictions in commercially- avail able laminated plate theory software. Your answers and results such as those in Fig. 1 show

that their calculations should not be trusted.

References

1. M. F. Kanninen and C. H. Popelar, Advanced Fracture Mechanics (Oxford University Press, NY, 1985).

2. J. A. Nairn and S. Hu, in Damage Mechanics of Composite Materials, edited by R. Talreja (Elsevier Science

Publishers, Barking, UK, 1993) in press (scheduled for January 1994 release).

3. A. A. Griffith, Phil. Trans. Roy. Soc, A221, 163 (1920).

4. K. W. Garrett and J. E. Bailey, J. Mat. Set, 12, 157 (1977).

5. K. L. Reifsnider, Proc. lJ^th Annual Meeting of SES, Lehigh, PA, November, 373 (1977).

6. A. Parvizi, K. W. Garrett, and J. E. Bailey, J. Mat. Sri., 13, 195 (1978).

7. A. Parvizi and J. E. Bailey, J. Mat. Sri., 13, 2131 (1978).

8. J. E. Bailey, P. T. Curtis and A. Parvizi, Proc. R. Soc. Lond. A, 366, 599 (1979).

9. M. G. Bader, J. E. Bailey, P. T. Curtis, and A. Parvizi, Proc. 3rd Int'l Conf. on Mechanical Behavior of

Materials, 3, 227 (1979).

10. F. W. Crossman, W. J. Warren, A. S. D. Wang, and G. E. Law, Jr., J. Comp. Mat Supplement, 14, 89

(1980).

11. W. W. Stinchcomb, K. L. Reifsnider, P. Yeung, and J. Masters, ASTM STP, 723, 64 (1981).

12. D. L. Flaggs and M. H. Rural, J. Comp. Mat., 16, 103 (1982).

13. F. W. Crossman and A. S. D. Wang, ASTM STP, 775, 118 (1982).

14. A. L. Highsmith and K. L. Reifsnider, ASTM STP, 775, 103 (1982).

15. P. W. Manders, T. W. Chou, F. R. Jones, and J. W. Rock, J. Mat. Sci., 19, 2876 (1983).

16. P.W.M. Peters, J. Comp. Mat, 18, 545 (1984).

17. R. Jamison, K. Schulte, K. L Reifsnider, and W. W. Stinchcomb, ASTM STP, 836, 21 (1984).

18. M. Caslini, C. Zanotti, and T. K. O'Brien, J. Comp. Tech & Research, Winter, 121 (1987). (Also appeared

as NASA TM89007, 1986).

19. S. E. Groves, C. E. Harris, A. L. Highsmith, and R. G. Norvell, Experimental Mechanics, March, 73 (1987).

20. K. C. Jen and C. T. Sun, Proc. of the Amer. Soc. Comp, 5

th Tech. Conf, 350 (1990).

21. S. Liu and J. A. Nairn, J. Reinf. Plast. & Comp., 11, 158 (1992).

22. D. S. Adams and C. T. Herakovich, J. Thermal Stresses, 7, 91 (1984).

23. D. E. Bowles, J. Comp. Mat, 17, 173 (1984).

183
24. J. A. Nairn and S. Hu, Int. J. Fract., 57, 1 (1992).

25. S. Hu, J. S. Bark, and J. A. Nairn, Comp. Sci. & Tech., 47, 321 (1993).

26. R. M. Jones, Mechanics of Composite Material (Scripta Book Company, Washington, DC, 1975).

27. S. L. Ogin, P. A. Smith, and P. W. R. Beaumont, Comp. Sci. & Tech., 22, 23 (1985).

28. D. L. Flaggs, J. Comp. Mat., 19, 29 (1985).

29. H. Fukunaga, T. W. Chou, P. W. M. Peters, and K. Schulte, J. Comp. Mat, 18, 339 (1984).

30. Y. M. Han, H. T. Hahn, and R. B. Croman, Comp. Sci. & Tech., 31, 165 (1987).

31. N. Laws and G. J. Dvorak, J. Comp. Mat., 22, 900 (1988).

32. R. J. Nuismer and S. C. Tan, J. Comp. Mat, 22, 306 (1988).

33. Z. Hashin, Mech. of Mat, 4, 121 (1985).

34. Z. Hashin, Eng. Pract Mech., 25, 771 (1986).

35. J. A. Nairn, J. Comp. Mat, 23, 1106 (1989). (See errata: J. Comp. Mat. 24 (1990) 233).

36. J. A. Nairn, S. Hu, and J. S. Bark, J. Mat. Sci., 28, 5099 (1993).

37. J. A. Nairn and S. Hu, Eng. Fract. Mech., 41, 203 (1992).

38. A. A. Fraser, F. H. Ancker, and A. T. DiBenedetto, Proc. 30^ Conf. SPI Reinforced Plastics Div., Section

22-A, 1 (1975).

39. L. T. Drzal, M. J. Rich, J. D. Camping, and W. J. Park, Proc. 35th Conf. SPI Reinforced Plastics Div.,

Section 20-C, 1 (1980).

40. W. D. Bascom and R. M. Jensen, J. Adhes., 19, 219 (1986).

41. W. D. Bascom, K-J. Yon, R. M. Jensen, and L. Cordner, J. Adhesion, 34, 79 (1991).

42. H. D. Wagner and A. Eitan, Appl. Phys. Lett, 56, 1965 (1990).

43. B. Yavin, H. E. Gallis, J. Scherf, A. Eitan, and H. D. Wagner, Polym. Comp., 12, 436 (1991).

44. L. S. Penn and E. R. Bowler, Surf. Interf. Anal, 3, 161 (1981).

45. M. R. Piggott, P. S. Chua, and D. Andison, Polym. Comp., 6, 242 (1985).

46. B. Miller, P. Muri, and L. Rebenfeld, Comp. Sci. & Tech., 28, 17 (1987).

47. U. Gaur and B. Miller, Comp. Sci &. Tech., 34, 35 (1989). 48. J. F. Mandell, E. J. H. Chen, and F. J. McGarry, Int. J. Adhes., 1, 40 (1980).

49. R. J. Scheer, Application of a Variational Mechanics Stress Analysis and Energy Based Failure Criteria to the Microdrop Debond Test for Evaluation of the Adhesion Quality of Several Fiber-Matrix Systems, PhD

Thesis, University of Utah, September 1993.

50. R. J. Scheer and J. A. Nairn, Composites Engineering, 2, 641 (1992).

51. L. S. Penn and S. M. Lee, J. Comp. Tech. & Res., 11, 23 (1989).

184
IMPACT DAMAGE TOLERANCE OF FRP COMPOSITES

IN OFFSHORE APPLICATIONS

Francis S. Uralil

Shell Development Company

P. 0. Box 1380

Houston, TX 77251-1380

INTRODUCTION

Glass fiber reinforced plastic (FRP) composites offer several advantages over

traditional offshore construction materials (i.e., steel and aluminum) due to their low

thermal conductivity, excellent mechanical properties, superior corrosion resistance,

good chemical resistance and high strength to weight ratio. Composites on platforms

can impact the cost through (1) weight reduction that leads to substantial cost savings

for floating structures, (2) lower protective requirements (coatings and corrosion

inhibitors), (3) lower installation cost, and (4) improved safety and reliability. Though

the materials cost may be higher for composites than steel, the savings in total life- cycle costs (including fabrication, maintenance, decommissioning, etc.) may be

substantial.

On an offshore platform impact events arise from dropped and falling objects and

shrapnel from explosions. One of the impediments to wider use of FRP offshore has

been the concern about its resistance and reliability under impact loading. The

subcritical damage resulting from an impact may go unnoticed and subsequently

reduce the lifetime of the part with failure occurring below the initial design stress

level. The extent of damage on composite materials will depend on the shape of the

impactor and the velocity of impact. Composites in general absorb impact energy by

plastic deformation, delamination and fiber pull out. Compared to metals and

thermoplastics, fiberglass reinforced thermosets do not undergo large amounts of

plastic deformation. Delamination is a function of interlaminar tensile and shear

strengths which depend primarily on matrix properties. The fiber-matrix bond is also

critical for increasing energy absorption, thus improving impact strength. The

contribution from each type of energy absorption varies widely. As a result, there may

not be a clearly defined point at which a catastrophic failure of a component will occur. The failure may have to be defined in terms of tolerable levels of fiber breakage or

185
delamination1

.

Several test methods are available for characterizing the impact behavior of FRP

materials. The most commonly used test methods are:

Charpy

Izod

Falling weight

Ballistic impact

The pendulum impact tests with small rectangular test specimens (Charpy, Izod) are

of limited value in measuring the toughness and predicting the real impact

performance of FRP products2

. The falling weight tests may be better as they can

measure fracture initiation energy, impose biaxial stresses on the specimen, and the

results have been shown to relate to other properties related to toughness

(microcracking, strain to failure of matrix), and with actual field experience. The

instrumented impact tests will provide more information about the various stages of

the impact event and the damage mechanisms.

Impact studies on FRP test coupons show that the specimens can sustain the impact

without affecting the strength if the level of impact energy is insufficient to produce in the material, stress levels higher than the ultimate strength3

. There is also evidence

that the damage was mostly controlled by the level of impact energy and not

significantly affected by the velocity of impact, in these experiments.

FRP gratings, panels, and pipes are beginning to be used extensively in offshore

applications. Though the impact resistance is a concern in all these applications, a

well established methodology for characterizing impact behavior in these applications

has not been established. Some of the published studies on impact behavior of FRP

gratings, panels and pipes are discussed below.

FRP GRATING

Impact tests comparing steel with molded and pultruded FRP grating has shown that

although composite gratings perform differently from steel grating, they may have

equally acceptable impact performance4

. In these tests a 135 kg (298 lbs) valve was

dropped from 2.5 m (8.2 ft) onto an FRP grating; no damage was recorded; in other

tests a 35 kg (77.2 lbs) impactor of 75 mm (2.95 in) diameter was dropped from 3.75

m (12.3 ft) on the grating. Post impact observation indicated that all gratings needed

to be replaced, but the remaining strength was sufficient to not require immediate

replacement (i.e., the grating was strong enough to walk on, but it may not have

survived another impact). The pultruded gratings outperformed the molded ones.

186
Impact study of open composite structures (floor grillage) by Marinetech North West

(Project CP-01)5 has shown that the energy absorption to failure under dynamic

conditions is a little larger than that measured under static conditions, and increases

with the velocity of impact. Also there was evidence of a threshold value of impactor

energy, below which no damage was observed. Above this threshold, permanent

damage and a corresponding reduction in strength and stiffness was observed.

FRP grating is considered less impact resistant than steel grating. Impact damage

may not be readily visible even though the grating may be substantially weakened due

to delamination. Some feel that FRP grating should only be used where there is no

risk of dropped objects to be lost by penetration of the grating. Recognizing that the

load requirements vary between locations on the platform, some users indicate that

they limit FRP gratings to the less severe areas.

FRP PANELS

The fire and impact performance of various composite panels have been the subject

of a number of research programs in Europe6,7,8,9,10. The superior performance of FRP

panels has been successfully demonstrated in these studies. Marinetech North West

(Project CP-08) 10 had performed a large number of impact tests on sandwich panels.

The variables examined included the effect of skin and core construction, multiple

impact, impactor geometry, and impact energy. Models for impact strength retention

as a function of impact energy levels were proposed. Static indentation tests were also

performed. Comparison of load-deflection curves has shown that the sandwich panels

failed at similar loads and deflections in both static and impact tests, thus suggesting

the use of static tests for predicting performance. The failure process of the panels

were found to be dependent on the geometry of the indentor with the cones and

pyramid geometries causing more localized damage. Some of these panels were able

to withstand impact energies up to 300 kJ (2.2x1

0

5 ft-lb) and blast pressures up to

1.33 bar (20 psi).

FRP PIPING

The impact resistance of FRP piping may depend on the accepted failure criterion. If the onset of cracking of the inner layer is defined to be the failure point, that may be

reached at rather low levels of impact energy, typically, 5-10 J (3.7-7.4 ft-lbs). If the

loss of ability to maintain function until replacement is the criterion, the level of impact

energy required may be substantially higher.

A modified ASTM drop weight test procedure (ASTM D2444) was used by Ameron11 to

study impact behavior of FRP pipes. The failure height was defined as the height at

which cracking of the inner liner was observed. A linear increase in failure height with

increasing wall thickness was observed (diameter kept constant), but only slight

increase in failure height was observed with increasing pipe diameter (wall thickness

187
kept constant).

Impact tests of six different types of 4-inch diameter FRP pipes of 16 to 20 bar

pressure rating were used to demonstrate that the pipes were functional after

exposure to impacts of about 70 J (52 ft-lbs), an energy level considered typical for

impact events on an offshore platform3

. The instrumented impact studies by Haanes,

et al

3 showed two distinct stages in the force -deformation curve: (1) a steep rise to a

local peak, possibly indicating the onset of resin microcracking, and (2) a region of

gradually increasing force indicating various energy absorbing failure mechanisms

(delamination, fiber pull out, etc). The initial stage of failure may be resin dominated

and the latter stages may be controlled by the reinforcing fibers.

How different levels of impact energy can influence the ability of the pipes to maintain

function (transport water under pressure) was studied by Stokke, et al

12

. In these

studies, leakage rates after impact for filament wound 4 inch epoxy pipes subjected to a range of impact energies were measured (Table 1 12

). The leakage of 4.1 ml/min

resulting from an impact of 500 J (372 ft-lbs) corresponds to a loss of a drop of water

every 3 seconds and is essentially not detrimental to the functioning of the sea water

pipe system until repair can be made. They have also shown that the impact damage

was independent of (a) the impact location (at a support or in between supports) and

(b) whether the pipe was empty or filled with water. At the same impact energy, a

larger contact area between the loading nose and the pipe surface will reduce the

impact damage3

.

An empirical relationship between the extent of visible damage and the energy level

of impact was suggested by Reid, et al

13

. Significant amount of localized damage,

mainly in the form of delamination, could occur due to relatively low levels of impact

energy (Table 2)

13

. However, the area of delamination was found to be consistently

less for the internally pressurized pipes filled with oil than for empty pipes. It was

apparent that some of the impact energy was absorbed and distributed by the bulk

compression of the fluid in the pipe. The resistance of the pipes to penetration of the

projectile was less for oil filled pipes. The pipes behaved as if stiffer when oil filled than when empty, and were perforated at far lower energy levels. Impact tests on

internally lined pipes showed less damage and no sign of leakage unless the liner was

broken in the impact process.

NEEDS/OPPORTUNITIES

Though impact performance is a concern for offshore applications of FRP composites,

there is a need to better define the impact tolerance required for the various

applications. The tests available for evaluating impact behavior in these applications

should to be standardized and various stages of damage development needs to be

understood. These tests must be based on good science, application specific, and

acceptable levels of performance should to be established.

188
Table 1. Leakage Rate (ml/min) After Impact for a FW 4 Inch Epoxy Pipe

Impacted by Energies From 20-500 J In Empty Condition 12 (Diameter of Impactor: 75 mm; Support Spacing: 4 m)

Energy

Pressur

e

20 J 50 J 70 J 80 J 100

J 120

J 150J 200J 300J 500J

10 bar 0 0 0.1 0.2 0.3 0.3 0.8 1.5 1.5 2.1

20 bar 0 0.6 0.8 0.8 1.0 0.8 1.6 2.2 4.0 4.1

Table 2. Observed Damage Sequence for FRP Pipes Under Impact Loading 13

EVENT ENERGY (J) WHEN FIRST OBSERVED

Wall Thickness = 4.3mm Wall Thickness = 8mm

Resin Whitening

Cracking of Inner Liner

Formation of Parallel

Cracks in Resin Rich Top

Coat in Direction of Fibers

Inward Collapse of Inner

Liner

10

10

39

86

10

20

38

132

Perforation 638 916'

* Projectile embedded in pipe wall, no visible hole present.

189
REFERENCES

1. Hu, C. S.; Diab, B.; Walker, S.: "The Use of Alternative Materials in Blast and

Fire Resistant Structures", Inst. Mar. Eng. Offshore Open, Post Piper Alpha

Conf., London, UK, February 1991, Paper No. 8.

2. G. E. Owen, Jr. "A Comparison of Impact Tests for Assessment of Fiberglass

Reinforced Plastic Toughness ", Polymer Engineering and Science, Volume

21, No. 8, Mid-June 1981, pp 467-473

3. Haanes, H.; Stokke, R.; Thon, H.. "Performance of Glass Fiber Reinforced

Plastic (GRP) Pipes Under Impact Loading", 10th ASME and Offshore Mech.

and Arctic Eng. Int. Conf., Stavanger, Norway, June 1991, pp. 569-576.

4. International Grating, Inc., Houston, Texas, USA.

5. The Cost Effective use of Fiber Reinforced Composites Offshore - Phase I. Marinetech North West, Manchester, U.K., Project CP-01

6. P. R. Godfrey and A. G. Davis, The Use of GRP Materials in Platform Topsides

Construction and the Regulatory Implications, Proceedings of the Ninth

International Conference on Offshore Mechanics and Arctic Engineering,

Houston, February 18-23, 1990, p. 15.

7. Mableson, R.: "Composite Fire and Blast Protection, 10th ASME and Offshore

Mech. and Arctic Eng. Int. Conf., Stavanger, Norway, June 1991, pp. 601-605.

8. The Use of Alternative Materials in the Design and Construction of Blast and

Fire Resistant Structures, Work Package No.65 (Wimpey Offshore), June 1991,

JIP Blast and Fire Engineering Project for Topside Structures (Royal/Dutch

Shell sponsored).

190
9. A. G. Davis and P. M. Nixon, Fire Testing of Structural and Partitioning Glass

Reinforced Plastic Panels, 1991 OMAE - Volume lll-B, Materia.s Engineering,

ASME - 1991, p.585.

10. The Cost Effective use of Fiber Reinforced Composites Offshore - Phase I. Mannetech North West, Manchester, U.K., Project CP-08

11. Ameron, Corrosion Resistant Piping Division, Technical Data Report No. EB15

12. R. Stokke: The Norwegian Approach, Maritime and Offshore Use of Fibre

Reinforced Composites, June 2-3, 1992, IBC Technical Service Ltd.

13. S. R. Reid and G. G. Corbett: Performance of GRP pipe Under Impact Loading,

Mantime and Offshore Use of Fibre Reinforced Composites, June 2-3, 1992,

IBC Technical Service Ltd.

191
192
THE EFFECT OF SEAWATER ON POLYMERIC COMPOSITE MATERIALS

Walter L. Bradley, Pin-Lin "Ben" Chiou, and Tim S. Grant

Offshore Technology Research Center and Mechanical Engineering Department

Texas A&M University, College Station, Texas, 77843-3123

INTRODUCTION

Polymeric composite materials are being examined as an alternative to traditional steels for the

construction of production risers in deep sea oil recovery. The use of light weight polymeric composite

risers would significantly reduce the buoyancy requirements and thus the size and cost of the surface

structure. The long-term durability of composites in the seawater must be characterized before their

full potential can be realized since current utilization of composites is mainly in applications where

design stresses are relatively low and moisture effect may not be apparent. It is important to develop a

better understanding of the magnitude and mechanisms of seawater degradation.

A composite structure is subjected to moisture absorption and fatigue wave loading in seawater.

Several investigations have examined the fatigue behavior of polymeric composites in the seawater

environment with general conclusions being some or little degradation in performance, comparing to

that in air 1 ^. However, few have studied the effect of seawater exposure on damage development and

failure mechanism, which may ultimately determine whether there is any seawater degradation.

In this report, the effect of seawater exposure on failure mechanism and damage development of

fiber reinforced polymeric composites was studied with laminate specimens using transverse tensile

test and edge delamination test. Since the matrix resin and interface are most affected by the moisture

absorption, the transverse tensile test, which is most sensitive to the change in matrix and interface

dominated properties, can be used conveniently to study the degrading effect of seawater. It is also

important to study the moisture effect on the delamination since it is the most dominant form of

damage in the fatigue life of composites5 . The effect of moisture on the delamination may be

beneficial, due to the relief of residual thermal curing stresses and matrix plasticization, or detrimental,

due to induced chemical and/or physical degradation of the fiber/matrix interface6. In a later study, filament wound tubular specimens were also used in studying the stress corrosion

cracking of glass fibers. Although glass fibers are generally susceptible to stress corrosion cracking in

both acidic and alkaline environments, there has been few reports on the performance of glass fiber in

seawater. It is important to examine the feasibility of using glass fiber from the economic standpoint.

DEGRADATION OF TRANSVERSE STRENGTH

Materials

Three carbon/epoxy systems and four carbon or glass/vinylester systems have been tested. System

A is T2C145/F263 (Hexcel), a typical carbon fiber reinforced tetraglycidyl diaminodiphenyl methane/

diaminodiphenyl sulfone (TGDDM/DDS). System B is IM7/977-2. The 977-2 resin (ICI/Fiberite) is a hybrid of TGDDM and polyethersulfone. System C is IM7/SP500-2. The SP50O-2 (3M) is a flourene epoxy. Both B and C have DDS as the crosslinker. Two vinylester resins, Derakane 41 1 and

510 (Dow), were also examined. Systems D and E are 41 1 and 510 reinforced with carbon fibers. The

510 resin is a flame retardant vinylester. Systems F and G are 41 1 and 510 with glass fibers.

Experimental Procedures

Specimens were exposed to distilled water, seawater, and seawater at 3,000 psi hydrostatic

pressure. Simulated seawater, which was mixed from distilled water and a synthetic sea salt, was used

193
instead of natural seawater. At 3,000 psi, an ocean depth in excess of 5,000 ft is simulated. Moisture

absorption characteristics was determined by weight gains at exposure times of 7, 21, and 90 days.

Weight gain after one week typically reached about 90% of the weight gain achieved in three months

with 4 ply thick specimens, indicating a nearly saturated condition; transverse tensile specimens were

also conditioned for periods of 7, 21, and 90 days to determine whether the degradation continued over

time.

The transverse tensile specimen had a dimensions of 1.5 inches long by 0.25 inch wide with a reduced cross sectional area in the midsection of the specimen. The purpose of the reduced area was to control the location of fracture and to reduce the likehood of failure due to incipient flaws.

Independently, interfacial shear strength were also determined for carbon/epoxy systems.

Measurements were performed by Dow Chemical with the Interfacial Testing System.

To study the failure mechanism, post-mortem examinations and in-situ three point bend tests were performed in an SEM. Coated specimens was tested on a loading stage in the SEM in an effort to observe the fracture process in real time. Three point bend test was used because it gave more stable

crack growth than the transverse tensile test

Results and Discussion

CarbonlEpoxy Systems

For the carbon/epoxy systems the moisture gained by specimens conditioned in seawater is lower

than those conditioned in distilled water, and a pressure of 3,000 psi didn't seem to have a significant

effect on the amount of absorbed moisture. Weight gains at 90 days for carbon/epoxy systems are shown in Figure 1(a) as percentage change of the resin weight. 7 and 21 day data yielded slightly

lower levels, but they are not included.

3.0

2.5

2.0

r 1.5H

| 1.0

0.5

0.0

distill m seawater

E seawater + P

m

Art. w

(a)

T2C145

F263

IM7

977-2

IM7

SP500-2

12

«10

O) 8

H w

CO

a3>

co

c:03

(b)

dry

distill m seawater

s seawater + P

T2C145

F263

M7

SP500-2

Figure 1. Weight gain and strength degradation for carbon/epoxy systems.

(a)Weight gains after 90 day conditioning

(b)Transverse strength degradation after 90 day conditioning

The lower moisture gained by the specimens immersed in seawater may be accounted for by

considering the resin as a semipermeable membrane. If the salt is not absorbed by the resin, osmotic

pressure will result and reduce the driving force for the moisture to diffuse into the resin. On the other

hand, hydrostatic pressure can have two competing effects. The pressure can reduce the free volume in the resin, reducing the locations where water molecules can accumulate, but the pressure also provides

194
a greater driving force for moisture absorption. From the result presented, it seemed that 3,000 psi was

insufficient to have a significant effect, with only a slight increase in the moisture absorption in

seawater at 3,000 psi compared to that at atmospheric pressure. Minimal pressure effects also have

been observed in other thermosetting resin composite systems7' 8 . The result of transverse tensile tests is shown in Figure 1(b), comparing the results from dry and

conditioned specimens. Again, only the data at 90 days are shown since there is little difference in the

data at 7 and 21 days. For all three carbon/epoxy systems studied, there didn't seem to be any time

dependence effect. System A exhibited moderate degradation in the transverse tensile strength after

immersion, but system B and C are not much affected. Results obtained from the interfacial shear test are not presented here, but they are consistent with the transverse tensile test in their indication of

reduction in interfacial strength due to moisture absorption effects.. System A has the highest transverse tensile strengths when dry, but it suffered about 17%

degradation after immersion. Systems B and C have lower strength when dry, but they don't seem to suffer any degradation after immersion. The moderate strength loss of the system A is a result of the

moisture-induced interfacial degradation. SEM examinations of both fractured specimens and realtime three-point-bend specimens revealed a difference in the failure mechanism between system A

and systems B and C. Latter systems exhibited interfacial failures for both dry and conditioned

samples. For system A, there is a transition from matrix cracking to failure at the interface. When dry,

the fracture occurred principally in the resin and no preference to follow the interface was observed.

Once conditioned, the fracture showed a strong preference to follow the interface. The absorbed

moisture degraded the interface in system A, causing a change of the failure mechanism from matrix

cracking to interfacial failure, resulting in a degradation in the transverse tensile strength. Systems B

and C have relatively weak interface when dry, and absorbed moisture does not have an effect.

Vinylester Matrix Systems

The weight gain in seawater and pressurized seawater for vinylester systems is shown in Figure 2. The moisture gained by 510 vinylester systems is less than that by 411 systems, but the carbon

reinforced systems gained more than the glass reinforced systems. In general, the weight gains are higher for samples in the distilled water. It was expected that the 510 resin, having a brominated

backbone, tends to absorb less moisture. It was unexpected that the moisture gains for carbon

reinforced systems are higher than those of glass reinforced systems, especially for the case of

pressurized seawater. It is possible that the carbon fiber reinforced vinylesters have a relatively weak

interface, which may provide additional locations for moisture to diffuse and accumulate. A difference

between carbon and glass reinforced systems is that the former has a higher fiber content (Vf = 0.6 vs.

0.5), thus having more interfaces.

Contrary to carbon/epoxy systems discussed previously, there seems to be a time dependence in

the degradation of vinylester systems except system G, which is glass fiber rinforced 510 vinylester.

Results of the transverse tensile test are presented as percentage Figure 3. The two carbon fiber

reinforced systems have the lowest dry strength, indicating the weakest interface. These systems also

exhibited a strong time dependent nature of the degradation process.

The low strength exhibited by the carbon reinforced systems supports previous speculation of a poor interface. The time dependent degradation observed is probably associated with the time

dependent degradation of the interface. With post-mortem and real-time SEM examinations, it was

observed that the initiation of failure for all of vinylester systems was at the interfaces fro both dry and

conditioned samples. For samples conditioned in moisture for longer times, more numerous and

diffused interfacial failure sites were observed. This led to premature fracture of samples conditioned

for 21 and 90 days.

195
2.0

1.5

c

CO°>1.0

x:D)

<D$

0.5

21

7 day

H 21 day

0 90 day

I

i

55:

m

z IV:

0.0 I

(a)

Figure 2. Weight gains for vinylester systems in (a) seawater, and (b) pressurized seawater

carbon

41

carbon

510

glass

41

glass

510

carbon

(b) 411

carbon

510

glass

411

glass

510

carbon carbon glass glass carbon carbon glass glass

(a) 411 510 411 510 (b) 411 510 411 510

Figure 3. Strength loss of vinylester systems in (a) seawater and (b) pressurized seawater.

Summary

The degradation of polymeric composites made with thermosetting resin matrices have been

studied with the transverse tensile test and SEM using samples conditioned in distilled and seawater.

A hydrostatic pressure of 3,000 psi only has a minimal effect on the amount of absorbed moisture and

degradation. Interface in composites plays a critical role as the moisture-induced degradation is often

associated with a reduction in the interfacial strength. Depending on whether the moisture has an effect on the failure mechanism, a system with superior strength when dry may suffer relatively large

degradation after moisture exposure. Systems that have relatively weak interfaces and fail in the

interface when dry may suffer only a minor degradation. Several systems have been identified wchich

showed minimal moisture degradation.

196
FATIGUE DAMAGE DEVELOPMENT IN EDT SPECIMEN

Materials

The composite system used in this study was the TACTIX 556 resin (Dow Chemical) reinforced

with IM-7 (Hercules) carbon fibers. The 556 resin is a low moisture absorption epoxy novolac resin.

Quasi-isotropic laminates with a stacking sequence of [45/0/-45/90]s were supplied. The average ply

thickness is 0.0063 inch, and the fiber volume fraction is about 46%, as determined by the acid

digestion method. Laminate plate was cut into samples of 9 inches long by 0.5 inch wide for testing.

The as-cut sample is referred to as dry sample in this study. Sample edges were polished to facilitate

examination under an optical microscope. Unidirectional laminates of 6 and 10 plies and [±45]2S

laminate were made separately and later used to measure lamina elastic properties and hygrothermal

coefficients.

Experimental Procedures

Tabbed samples of 0.5 inch wide [06], 1 inch wide [90ioL and 1 inch wide [±45]2S, were used in

determining lamina elastic properties of El, Ej, vlt» and Glt- Standard tensile testing procedures were used with T-type strain gages to measure strains.

Coefficients of thermal expansion were also measured with T-type strain gages on [Oio] two inch

square samples. The transverse coefficient of moisture expansion was measured with a simple fixture

that can hold [906] samples vertically in a seawater bath. Dial gages of 0.0001 inch resolution were

used to monitor the expansion continuously. The weight gain was measured separately with samples

cut from the same laminate. Since the moisture expansion in the fiber direction is too small for the dial

gage to measure accurately, the coefficient in this direction was assumed to be zero. The same substitute seawater was used for moisture conditioning and wet fatigue testing. Some of

the sample cut from [45/0/-45/90]s laminates were pre-conditioned to different moisture gains. Edge

delamination test (EDT) in fatigue were performed under tension-tension load-controlled mode with a maximum stress of 40 ksi (= 40% laminate UTS). R = 0.25 with a frequency of 0.1 Hz, which was

selected so that the synergistic effect, if any, of delamination growth and seawater exposure can be

characterized in reasonable time periods.

An environmental chamber was built for wet fatigue testing so that the specimens can be tested

while immersed in seawater. The testing consists of wet fatigue tests in the chamber with dry samples

and conditioned samples of 0.25%, 0.40%, and 0.44% (saturated) moisture gains. Dry fatigue tests were also performed with dry samples (0.0 % moisture).

The polished edges of samples were examined using an optical microscope, which was also used

to measure the lengths of cracks on sample edges. Since the crack area across the width of the sample

cannot be determined from sample edges, it was measured with an ultrasonic C-scan unit. The crack

area was determined by tracing the scanned copies on a digitizing tablet.

Results and Discussion

The lamina elastic properties are listed in Table 1 , and the coefficients of thermal and moisture

expansion are listed in Table 2. Sample configurations used in testings are also listed. The longitudinal

modulus was obtained from a [06] laminate that had a slightly higher fiber volume fraction than the

[45/0/-45/90]s laminate. A longitudinal modulus of 18.5 Msi, which gives a calculated laminate

modulus close to experimentally measured ones, will be used in later calculations.

The moisture absorption of the [45/0/-45/90]s laminate is approximately Fickian with a saturation

level of about 0.44% of the laminate and a diffusion coefficient of 3.5X10-7 in2/hr. [06] unidirectional

laminate with slightly higher fiber volume fraction yielded slightly lower saturation level, and the

parameters obtained from the multiaxial laminate will be used later. The dry laminate modulus (£q) was experimentally determined as 7.16 Msi, which is close to the

197
calculated modulus of 7.19 Msi with El = 18.5 Msi. Moisture gain of 0.44% at saturation decreases

the laminate modulus about 4% to 6.89 Msi, also obtained experimentally.

The influence of seawater exposure on mode I fracture toughness had been examined by other

investigators using double cantilever beam specimen 1

, but the experimental results were complicated

by the presence of fiber bridging, which enhanced the delamination resistance and can be avoided by

using a multiaxial EDT specimen.

Table 1. IM7/556 lamina elastic properties

El (Msi) Ej (Msi) Glt (Msi) vlt

19.8 1.25 0.737 0.345

lOel [90i 0J [±45]2S |06 ]

Table 2. IM7/556 lamina coefficients of hygrothermal expansion

ocl (nin/in/°F) aj (|iin/in/°F) Pl Oiin/in/%) PT (piin/in/%)

0.568 22.99 0 2940

[Oiq] [90io] [906]

Inspection of the fatigued EDT sample revealed that the characteristics of the edge cracking is different between dry and conditioned samples. The edge cracking forms at the -45°/90° interface, in 90° plies and at the mid-plane 90o/90° interface. For dry samples, the dominant mode of cracking is the delamination at the -45°/90° ply interface. These cracks are long and straight, occasionally jump to the opposite -45°/90° ply interface through 90° transverse cracks.

The dominant edge cracking mode of the conditioned samples has switched from the -45°/90°

interply delamination to the cracking in 90° plies. The crack path is usually irregular, and it is either at the 90°/90° interface or within 90° plies. The total crack length for these two edge cracking mode as a function of the initial moisture for all samples is shown in Figure 4. The effect of moisture is seen to decrease the delamination at the -45°/90° ply interface, but to increase the crackings in 90° plies.

The extent of crack growth across the width of the specimen as obtained from the throughthickness C-scan is shown in Figure 5 as a function of fatigue cycles. The crack area (A) is normalized

against the entire area (Aq). Since the C-scan image is a through-thickness representation of all crackings, it is a representation of the -45°/90° delamination or 90° intraply cracking. It can be seen

that the extent of crack growth for conditioned samples is not worse than that of dry samples. Since

the initially dry sample tested wet exhibited a crack growth similar to that of the dry sample in the dry

test, the moisture effect during fatigue cycling of this system appears to be insignificant.

From the energy standpoint, the suppression of the -45790° delamination is expected. The strain

energy release rate (SERR) can be calculated using laminate analysis and finite element analysis9" 11

. The effect of cool-down stresses resulting from the cure cycle is to raise the SERR, while the

moisture-induced swelling tends to reduce the SERR by relieving the residual thermal stresses. Provided no significant interfacial degradation is present, the reduced interlaminar residual stresses can

give a decrease in the SERR required for delamination onset9' 1 ^. Analysis based on laminate theory that include hygrothermal effects as presented in references 12 was applied to the composite system studied here. The lamina elastic properties and coefficients of

hygrothermal expansion listed previously (with El = 18.5 Msi) were used in the calculation. The

SERR is presented in Figure 6 for the delamination at the -45790° interface and the midplane

delamination at the 90790° interface. The temperature difference was assumed to be -270°F, and the

198
strain was calculated from the laminate modulus with a applied stress of 40 ksi. The -45°/90°

delamination has the highest available SERR, followed by that for the 90/90 delamination and that for

the 0%45° delamination, which is not included in the figure. Non-uniformly distributed moisture was

considered.

initial moisture content, % cycle

Figure 4. Edge cracking characteristics. Figure 5. Crack area as a function of cycle.

There is a substantial increase of the SERR when both mechanical and thermal residual curing

stresses are considered (shown as M+T in the figure) as compared to considering only mechanical

stress (shown as M). If the effect of moisture is also considered (M+T+H), the SERR decreases as moisture content increases. Since the system studied here has a small moisture gain, the effect of

moisture is relatively small.

Since load-controlled fatigue tests were used here, the strain increases as the fatigue cycle increases

due to the modulus reduction. The SERR calculated shown above is thus the SERR initially available.

If the SERR increase due to the modulus drop is considered however, the SERR for the 90790°

midplane delamination is still smaller than that for the -45790° delamination.

For the case of fatigue test with dry sample, the delamination is expected to occur at the -45790°

interface because the available SERR is slightly higher than that of the 90790° midplane delamination.

For the conditioned samples, the delamination at the -45790° interface is retarded because the SERR

available is less from the stress relieving effect of the moisture-induced swelling. But the SERR for

the 90790° delamination also decreases when the swelling effects are considered, thus the edge

cracking in the 90° ply can only occur when there is a moisture-induced degradation of the 90° ply.

The edge cracking mode switch observed is very similar to that observed by Lee 12 who studied the

effect of different fiber type on the SERR for edge delamination onset. As the delamination switched

from the straight interply failure to the zig-zag intraply failure, the SERR decreases. He concluded that

the fibers with lower interfacial strength required less SERR and produced irregular intraply failure.

Since there is only one composite system used in this study, the observed edge cracking mode switch

should be a result of a lowering of the interfacial strength caused by the seawater absorption.

The absorption of seawater caused the degradation of the interfacial strength for the system studied

here and the SERR required should be less when there is moisture present. However, the overall

growth of cracking is slightly less for tests with pre-conditioned samples, as shown in Figure 5. There

can be two explanations for this contradiction. The first is that the intraply cracking has larger crack

area due to its irregularity and zig-zag pattern. A second possible reason is that there are indications of

199
fiber bridging for the 90° intraply cracking. As observed on the specimen edges, the 90° intraply

cracking often produces loose fiber ends and bundles.

Summary

For the carbon/epoxy composite laminate studied, the seawater exposure has no adverse effect on

the growth of fatigue edge cracking. Moisture tends to decrease the available strain energy release rate. Seawater exposure does seem to cause degradation in the interfacial strength but this degradation leads

to edge cracking mode switch. The overall resistance to edge crack growth of the pre-conditioned

sample is enhanced by the seawater exposure due to a combination of moisture-induced stress relief

and edge cracking mode switch.

0.2 0.3

moisture content, %

Figure 6. SERR as a function of moisture content.

0.5

STRESS CORROSION CRACKING OF GLASS FIBERS

Materials

The composite systems used in this study were E-glass and S-glass fiber reinforced epoxy resin,

which is based on EPON 828 resin. Filament wound tubes of [90/±35/90] with an integral rubber

liner were supplied (Brunswick Composite). The tube has additional layers of hoop wound on both

ends, and a low modulus epoxy resin was later cast on both ends to prepare the tube for testing.

Microscopic inspection of the tube cross section revealed a high void content (-6%), which is a result

of the wet-winding manufacturing process used. Tubes were not conditioned before testing.

Experimental Procedures

Since the primary goal is to study the stress corrosion cracking of glass fibers, it was decided to conduct open-ended tube test. In the testing, pressure was introduced into the tube, which was allowed

to slide on the pressure seal, creating only the hoop loading. The pressure was held constant, and this

is similar to the creep test in which the tube can be submerged in seawater while under pressure.

Results and Discussion

Only preliminary data was obtained at this point, and the result is shown in Figure 7. For the

pressure ranges studied, no difference was observed for tubes tested dry or wet.

200
150

CO 100

CO

to

CD CO

CLo

oX 50

00

o

A

O

V•

A

S2 wet

S2 dry

E wet

E dry

S2 static E static

n I I ' \0 „ „2 < n4 « A6ml i iii in 10u 10^ 10^

Time to burst, hr Figure 7. Time to burst at different pressure levels.

REFERENCES

1. Sloan, F. E. and Seymour, R. J., The Effect ofSeawater Exposure on Mode I Interlaminar

Fracture and Crack Growth in Graphite!Epoxy, Journal of Composite Materials, Vol. 26, pp.

2665-2673, 1992.

2. Hofer, K. E. and Skaper, G., Fatigue Endurance of Glass Reinforced Plastic Laminate Material

in a Marine Environment, Proceeding of the 40th Annual SPI/RPI Conference, Session 12-B,

January, 1985, p. 1. 3. Sandifer, J., Effects of Corrosive Envirnments on Graphite/Epoxy Composites, in Progress in

Science and Engineering of Composites, T. Hayashi, K. Kawata, and S. Umewaka, Eds.,

ICCM-IV, Tokyo, 1982, pp. 979-986.

4. Macander, A., Silvergleit, M., and Edelstein, H. P., Marine Durability of a GraphitelEpoxy

Composite Subjected to Static and Fatigue Loading, ICM3, Cambridge, England, 1979, pp.333-

343.

5. Fatigue of Composite Materials, K. L. Reifsnider, Ed., Composite Materials Series Vol. 4,

Elsevier, 1991.

6. Marom, G., Environmental Effect on Fracture and Mechanical Properties ofPolymer

Composite in Application of Fracture Mechanics to Composite Materials, K. Friedrich, Ed.,

Composite Materials Series Vol. 6, Elsevier, 1989, ChaplO.

7. Pollard, A., et al., Influence ofHydrostatic Pressure on the Moisture Absorption of Glass

Fiber-reinforced Polyester, Journal of Materials Science, Vol. 24, pp. 1665-1669, 1989.

8. Avena, A. and Bunsell, A. R., Effect of Hydrostatic Pressure on the Water Absorption of

Glass Fibre-reinforced Epoxy Resin, Composites, Vol. 19, pp. 355-357, 1988.

9. Hopper, S. J., Toubia, R. F., and Subramanian, R., Effects of Moisture Absorption on Edge

Delamination, Part I and II, in Composite Materials: Fatigue and Fracture, Second Volume,

ASTM STP 1 1 10, T. K. O'Brien. Ed., American Society for Testing and Materials,

Philadelphia, 1991, pp. 89-125.

10. O'Brien, T. K., Raju, I. S., and Garber, D. P., Residual Thermal and Moisture Influence on

the Strain Energy Release Rate Analysis of Edge Delamination, NASA TM-86437, Langley

Research Center, Hampton, Virginia, 1985.

201
1 1 . Schanz, U. and Kress, G., Influence of Temperature and Moisture on Total Strain Energy

Release Rate Associated with Edge Delamination of Composite Test Coupons, Composite

Science and Technology, Vol. 35, pp. 219-233, 1989.

12. Lee, S. M., Failure Mechanisms of Edge Delamination of Composites, Journal of Composite

Materials, Vol. 24, pp. 1200-1212, 1990.

202
INFLUENCE OF SEAWATER ON TRANSVERSE

TENSILE PROPERTIES OF PMC

Leif A. Carlsson and Frederic Pomies

Department of Mechanical Engineering

Florida Atlantic University

Boca Raton, Florida 33431

INTRODUCTION

Polymer matrix composite (PMC) materials are candidates for

use in off-shore and marine structures because they offer

substantial weight reduction, good fatigue resistance, and low

susceptibility for corrosion compared to metals. It is, however,

recognized that the marine environment, Fig. 1, presents some

unique challenges due to the presence of numerous ionic species and

micro-organisms and long exposure times.

PHYSICAL

moisture history

• drying

freeze- thaw

cycles

- BIOLOGICAL

- Bottom stains bio-damage

CHEMICAL

- Sea water

- ultraviolet

MECHANICAL

- Hydrostatic pressure

- slamming

- vibration, loading

speed

impact

Figure 1 Typical marine environments.

When a polymer matrix composite (PMC) is subjected to water,

potentially any of the three major components of a composite, viz,

fiber, matrix and interface, Fig. 2, may be affected once water

penetrates the interior [1]. It is generally accepted that glass

and carbon fibers do not absorb water and remain unaffected by

water [2]. Polymers, however, absorb water to an extent governed

by the network structure (thermosets) , or the degree of

crystallinity and polarity of the molecules (thermoplastics) [3].

The interface may be a weak link for the integrity of a composite

material and has recently been the subject of substantial attention

[4-9].

203
Fiber / Matrix

Interface

Figure 2 The three components of a composite material,

fiber, matrix and interface.

It is the objective of this paper to review some recent work

on marine environmental effects on PMC performed at Florida

Atlantic University [10-12]. Distilled water and seawater were

considered. To monitor matrix and interfacial degradations due to

water uptake, unidirectional composites were subjected to

transverse tension after immersion. Experimental results were

compared with micromechanical predictions.

EXPERIMENTAL

Materials and Testing

Carbon/bismaleimide (BMI)-epoxy, E-glass/epoxy,

E-glass/polyphenylsulf ide (PPS) and carbon/epoxy , Table 1, and

neat PPS were examined. Panels with [0] 8 , [90] 16 and [±45] 2s

stacking sequences were laid up and processed according to the

appropriate specifications, see Table 1. Carbon and glass fiber

volume fractions were determined according to ASTM standards D3171

and D2 584, and the void content was determined from a quantitative

image analysis [13].

204
Table 1 Composites examined in the experimental program. V

fiber volume fraction.

FIBER MATRIX PROC. TEMP.

°C

Vf

G40-800

Carbon

5245 C

BMI-Epoxy

\ LIlci KlUbcL J

177 0.55

NCT-301-2G150

/108 Carbon

Epoxy

(thermoset)

130 0.55

E-Glass 5216 Epoxy

(thermoset)

140 0.53

E-Glass LG40-70 PPS

(thermoplastic)

330 0.53

As can be noticed, Table 1, the fiber volume fractions of the

various composite systems are similar. The void content did not

exceed one percent for any of the composites and may be neglected.

Environmental Conditioning

Several specimen geometries were prepared for immersion in

distilled water and natural seawater at room temperature

(RT,20±1°C) and 35±1°C. The salt concentration of the

seawater was approximately 3.5 %. To maximize the water uptake,

the specimens were immersed with the cut edges exposed. The total

soaking periods were 4600 and 4800 hours for the 25.4 x 229

mm coupons, and 5000 and 5200 hours for the 50 x 100 mm neat PPS

and composite panels at 35°C and RT, respectively. To monitor the

uptake of water, quantified by the moisture content, M, the

specimens were periodically removed from the tanks, dried with

absorbing paper and weighed on an Analytic Balance accurate within

±0.0001 g.

Transverse Tensile Testing

Transverse tensile testing of the composites was performed

after 4800 hours of immersion at 35°C in distilled water and

seawater. The specimens were immersed without endtabs and strain

gages to avoid deteriorations of the bonding and gage performance

due to water absorption. End-tabs and strain gages were attached

prior to testing using M-Bond 200 adhesive.

205
RESULTS AND DISCUSSION

Water Absorption

Table 2 lists the moisture contents reached at the end of the

immersion periods. Only the PPS neat resin and glass/PPS immersed

at 35°C were fully saturated. Carbon/BMI-epoxy, and glass/PPS at

RT were close to saturation, while glass/epoxy and carbon/ epoxy

were relatively far from saturation.

Table 2 Moisture contents of composites and neat PPS. Soaking

time for the 25.4 x 229 mm coupons was 4,600 hours, and

5,000 and 5,2 00 hours for the 50 x 100 mm panels at

35°C and RT, respectively.

==

Planar Moisture Content, %

Material dimensions Distilled Water Seawater

mm RT 35°C RT 35°C

glass/epoxy* 50 x 100 0.63 0.96 0.57 0.94

25 .4 x 229 1.08 0.97

carbon/ epoxy* 50 X 100 0.84 1. 13 0.80 1.07

25 .4 X 229 1.21 1.14

carbon/ BMI

epoxy** 50 X 100 0.60 0.66 0.57 0.65

25 .4 x 229 0.63 0.61

glass/PPS 50 x 100 0. 17** 0. 18 + 0.13** 0.15+

25 .4 X 229 0. 18+ 0.16+

PPS 50 x 100 0.05 0.02 0.02 0.02

*) not saturated

**) close to saturation

+) saturated

The presence of salt water reduces the water absorption. The

large size of the sodium chloride molecules contained in seawater

(as well as other ionic species) appears to be limiting the

diffusion of water into the matrix. The thermoset matrix composites

absorbed more water than the glass/PPS composite. The small water

uptake by the glass/PPS composite is attributed to the

semicrystalline nature of the thermoplastic PPS polymer where the

crystallites essentially are impermeable to moisture. Neat PPS

absorbed less moisture than the glass/PPS composite which is

explained by moisture transport along the fiber/matrix interface

("wicking)" via the exposed edges. Increased temperature was found

to increase the rate of diffusion, but the saturation moisture

content was not affected. For carbon/BMI epoxy, glass/epoxy and

carbon/epoxy , analysis of the diffusion data indicates that water

is absorbed at similar rates perpendicular and parallel to the

fiber direction [10,12].

206
Transverse Tensile Properties

Transverse modulus, E2 and strength, X2 T were measured for the

dry specimens and after 4,800 hours immersion in distilled water

and seawater. E2 was not significally changed after water

absorption except for glass/PPS that lost about 60 % of its dry

modulus [10,12], despite its low water absorption, Table 2. The

substantial reduction of E2 is attributed to extensive

fiber/matrix debonding induced by water.

Figure 3 shows transverse tensile strengths for the dry

and wet composites. All composites experienced large reductions in

X2 T due to water absorption. The least degraded system, carbon/BMIepoxy, lost approximately 30 % of its dry strength. For glass/epoxy

and carbon/epoxy the strength reductions ranged from 55 to 65 %,

while glass/PPS lost 85 % of its dry strength implying a severe

degradation of the fiber/matrix interface. Within the scatter in

transverse strength, seawater and distilled water are equally

severe . Kn ,

,

Figure 3 Dry and wet transverse tensile strengths.

SEM observations of transverse fracture surfaces of the dry

composites displayed resin adhering to the fibers [10,12] which

indicates adequate fiber/matrix adhesion. The fracture surfaces of

the wet specimens displayed numerous bare fibers and a wide

variation in depth which indicates severe degradation of the

adhesion between the fiber and the matrix due to penetration of

water. The substantial transverse strength losses observed thus

appear to be due to interfacial degradation by water absorption.

ANALYSIS OF TRANSVERSE MODULUS AND STRENGTH

Micromechanical analysis of the transversely loaded composites

investigated in the experimental program was performed using

finite element analysis and the Cooper-Kelly Model [11,14],

Fini* » element models were constructed of representative

volume elements (RVE) of the composites assuming a simple square

5C

Carbon/

bmi-epoxy CZ) Dry Wet (distilled water) Wet (seawater)

207
packing geometry. Fiber volume fractions of 0.50 and 0.60 were

considered in order to encompass the experimental range of fiber

volume fractions. The RVE was submitted to loading and boundary

conditions representative for transverse tensile loading.

The initiation of a fiber /matrix debond was predicted by using

a quadratic interfacial failure criterion,

(f£)2 + (^V=l (1)

where Tj. and r ro are the radial and shear interfacial stresses,

respectively, and R and S are the corresponding interfacial

strengths in tension and shear. A debond is thus expected to

initiate when the left hand side of eq. (1) reaches unity.

A failure hypothesis may be defined by assuming that

transverse failure of the composite occurs at the externally

applied stress o2 = X^T when the failure criterion, eq. (1) , is

satisfied. Such a failure hypothesis may be most appropriate for

brittle matrix composites with a strong fiber/matrix interface

where debonding is expected to lead to ultimate failure [11,15].

In composites with a weak interface and/or ductile matrix, the

transverse strength is expected to be more closely linked to

failure initiation in the matrix. Failure of the matrix was thus

also investigated using the von Mises failure theory [11] and the

Cooper and Kelly Model (CKM) [14],

*2 = om {l " AVf

] (2) n

where am is the tensile strength of the matrix, and Vf is the fiber

volume fraction. This equation is valid for completely debonded

fibers. If the tensile strength of the fiber/matrix interface is

incorporated, the CKM is modified to

*2 =

" 4_± ] + o±

. (3)

TT

where a J is the average tensile stress necessary to separate the

fiber from the matrix. Notice that an upper bound estimate, X2 T

=cJm is obtained when a ^' = am

. In the micromechanical analysis of fiber/matrix debonding, the

interfacial strengths (R and S) are required. Experimental methods

for determination of such data are not readily available, and ideal

bonding was assumed by taking the interfacial tensile and shear

strengths as the matrix tensile and shear strengths. Moisture

swelling coefficients for the BMI-epoxy and the exopy matrix

composites were assumed to be the same as for 3 501-6 epoxy, 0 = 3.2

x 10~3 /%M [9]. The moisture swelling coefficient for PPS

has not been published, and micromechanical analysis of wet

glass/PPS was therefore not performed.

208
Failure prediction was performed for each composite by

calculating the fiber/matrix interfacial stresses due to cool-down

to RT from the processing temperature, Table 1, combined with

the actual moisture pick-up after immersion, Table 2. Because of

the similar degradations experienced in distilled and seawater, we

considered only distilled water.

Correlation with Experimental Results

The transverse modulus of the composites could be predicted

from finite elements with good accuracy both in the dry and wet

states [11] which indicates that the elastic properties of the

constituent fibers and matrices and the modeling are appropriate.

The predicted transverse stress levels corresponding to debond

initiation and matrix failure generally decreased with increased

amounts of absorbed moisture which is in agreement with

experimental trends, but because of the ideal fiber/matrix bond

assumption and a matrix strength that is assumed to be unaffected

by water absorption, the predictions tended to exceed the

experimentally observed strengths. The CKM assuming a weak

fiber/matrix interface was generally over-conservative. Comparison

between the CKM and experimental strengths indicate a fiber/matrix

interfacial tensile strength about half the matrix tensile strength

for the dry thermoset composites, while the wet thermoset and dry

and wet thermoplastic composites suffered from very low apparent

interfacial strengths (0-20% of the dry matrix strength)

.

SUMMARY

Degradation of transverse mechanical properties of polymer

matrix composites subjected to water environments have been

discussed. Transverse tensile loading was selected because the

transverse properties are sensitive to degradations of the

fiber/matrix interface and matrix.

It was found that the amount of water absorption is not a reliable indicator of the degradation of the composite. In fact,

the glass/PPS composite showed the least water absorption, but

lost most of its transverse properties. All composites absorbed

somewhat more distilled water than seawater, but distilled water

and seawater degraded the properties similarly. Predictions of

the transverse modulus were in overall agreement with experimental

data, but strength predictions based on fiber/matrix debonding and

matrix failure were less reliable. This is in part attributed to

the lack of appropriate strength data for the matrix and interface.

More reliable predictions would require a complete experimental

characterization of matrix and interfacial properties (dry and

wet) . The accuracy of the strength predictions may also suffer from

the assumption of a regular (square) microstructure. Failure may

actually initiate locally in a region of closely packed fibers.

Currently, research in this area is extended to investigate

the influence of water exposure on interlaminar shear strength and

delaminat.on toughness [16,17].

209
ACKNOWLEDGEMENTS

Thanks are due to Dale Wilson of BASF (Charlotte) , Dave Nesbit

of Composite Craft (Orlando) and Ben Bonazza of Phillips Petroleum

(Bartlesville) for donations and processing of materials. The

authors are also grateful to Touy Thiravong of the University of

Delaware for his help with specimen preparation and testing, and

Peter Davies of IFREMER (France) for additional support.

REFERENCES

1. L. T. Drzal, "Adhesion of Graphite Fibers to Epoxy Matrices":

I. "The Role of Fiber Surface Treatment", J. Adhesion, Vol.37,

1982, pp. 1-30.

2. G. S. Springer (editor), "Environmental Effects on Composite

Materials", Technomic, 1981.

3. N. J. Johnston, T. W. Towell and P. M. Hergenrother , "Physical

and Mechanical Properties of High-Performance Thermoplastic

Polymers and Their Composites", in Thermoplastic Composites

Materials (L. A Carlsson, editor) , Elsevier Science, 1991,

pp. 27-71.

4. K. H. G. Ashbee and R. C. Wyatt, "Water Damage in Glass

Fiber/Resin Composites". Proc. Royal Soc. , London, Vol. A 312,

1969, pp 553-564.

5. A. Blaga and R. S. Yamasahi, "Mechanisms of Breakdown in the

Interface Region of Glass Reinforced Polyster by Artificial

Weathering", J. Mater. Sci., Vol. 8, 1973, pp 654-662.

6. D. H. Kaelbe, P. J. Dynes, L. W. Crane and L. Maus,

"Interfacial Mechanisms of Moisture Degradation in Graphite

Epoxy Composites", J. Adhesion, Vol. 7, 1974, pp. 25-54.

7. L. T. Drzal, M. J. Rich and M. F. Koenig, "Adhesion of

Graphite Fibers to Epoxy Matrices" III. The Effect of

Hygrothermal Exposure", J. Adhesion, Vol. 18, 1985, pp. 49-72.

8. T. Juska, "Effect of Water Immersion on Fiber/Matrix

Adhesion", Ship Materials Engineering Department, Research and

Development Report, Naval Surface Warfare Center, Carderock

Division, CARDEROCK DIV-SME-92/38 , January 1993.

9. D. F. Adams, "A Micromechanics Analysis of the Influence Of

the Interface on the Performance of Polymer Matrix

Composites", J. Reinf. Plast. Comp. , Vol. 6, 1987, pp. 66-88.

10. F. Pomies, "Degradation of Composite Materials in a Marine

Environment", MS Thesis, Department of Mechanical Engineering,

Florida Atlantic University, Boca Raton, Florida, August 1992.

210
11. F. Pomies and L. A. Carlsson, "Analysis of Modulus and

Strength of Dry and Wet Thermoset and Thermoplastic Composites

Loaded in Transverse Tension", accepted for publication in J.

Compos Mater., 1993.

12. F. Pomies, L. A. Carlsson and J. W. Gillespie, Jr. "Marine

Environmental Effects on Polymer Matrix Composites", accepted

for publication in Composite Materials. Fatigue and Fracture

(Fifth Conference), ASTM STP XXXX, 1993.

13. D. Hull, "An Introduction to Composite Materials", Cambridge

University Press, 1981.

14. G. A. Cooper and A. Kelly, " Role of the Interface in the

Fracture of Fiber - Composite Materials", Interfaces in

Composites, ASTM STP 452, 1969, pp. 90-106.

15. F. Pomies and L. A. Carlsson, "Analysis of Initiation and

Propagation of a Fiber /Matrix Debond", Proc. Am. Soc. for

Compos. 6th Tech. Conf., Albany, New York, October 7-9 1992,

Technomic, pp. 558-568.

16. P. Davies, F. Rannou, W. J. Cantwell, F. Pomies and L. A.

Carlsson, "Durability of Composite Materials in a Marine

Environment - a Fracture Mechanics Approach", Proc. ICCM-9

(A.Miravete ed. , 9th International Conference on Composite

Materials, July 12-16, 1993, Madrid, Spain, 1993, Vol. VI,

pp. 308-315.

17. F. Pomies. " The Influence of Aging on Fracture Mechanisms in

Composites", Final Report, Cooperative Research Program

between Florida Atlantic University and IFREMER, Department of

Mechanical Engineering, Boca Raton, Florida, July, 1993.

211
212

L
ASSESSING THE GLASS EPOXY INTERFACE

AFTER ENVIRONMENTAL EXPOSURE

H.D. Wagner* , A. Lustiger and S. Ling

Exxon Research and Engineering, Route 22E, Annandale, NJ 08801

INTRODUCTION

One of the major uncertainties in the use of glass-epoxy composites in the offshore

is the resistance of the material to the most ubiquitous of offshore environments: water.

The effect of water on epoxy based composites has been quite well characterized in

aerospace applications. As a result of the recognition that water indeed has a deleterious

effect on the service life of these composites, mechanical testing in so-called hot wet

environments is de rigeur in the qualification of these materials in the aerospace industry.

This recognition has to a large extent also driven the development of semicrystalline

thermoplastic composites due to their excellent environmental resistance

However, this aerospace experience is of limited use when designing offshore

structures. While the aerospace environment involves moisture exposure of intermittent

relatively short duration at elevated temperature, the major offshore applications will

involve ambient temperature exposure for periods up to 30 years. The offshore community

therefore needs to generate its own set of data to address the issue.

Characterizing this environmental effect is complicated by the fact that in glass

reinforced composites water degrades the fiber, plasticizes the matrix and weakens the

interface. Therefore, all three effects need to be characterized.

This paper is a brief summary of work which has taken place at Exxon Research

and Engineering Corporate Research Labs in the development of a means of studying and

isolating the effect of water on the epoxy-glass interface.

EXPERIMENTAL

The epoxy used in these experiments consisted of DER 331 mixed in stoichiometric

proportions with Jeffamine D230 hardener. The glass fibers used were from Owens

Corning, and contained an epoxy compatible sizing.

Two micromechanical test methods designed specifically for interface strength

measurement were evaluated. The first test, the microbond technique1

, involves the

formation and curing of resin droplets on glass fibers. The fiber/ droplet is suspended at one end from a force gage, and the filament is gripped by a microvise. The microvise

exerts a downward force on the droplet during contact, at which point either shearing of

* Permanent Address: Weizmann Institute of Science, Department of Materials and Interfaces, Rehovot Israel

213
the droplet occurs or the fiber breaks (Figure 1). In the former case, the droplet size, as well as the force at which the droplet is sheared is recorded .

The second test which was evaluated was the fragmentation test. 2 In this test, a single

fiber is embedded lengthwise down the center of a tensile dogbone specimen of the epoxy,

in this case containing a one inch gage length. The specimen is pulled on an Instron

machine until fracture, and the number of fiber fractures as well as the length of each

fragment was measured (Figure 2).

In an important modification of the experiment, fiber breaks were monitored in situ using

acoustic emission apparatus. Using this method, the exact stress at which individual fiber

breaks occurred could be measured. The importance of continuous monitoring is described by Wagner et al2 as a means of determining the strength of the fiber at the

critical length. This data is important for conversion of the data into interfacial shear

strength values.

In a critical addition to the test, debonded lengths were measured using optical

microscopy after failure in the test. The significance of this measurement will become

apparent in the subsequent discussion.

Testing was mostly done after water exposure for various times at 95C. This severe temperature condition was chosen in order to maximize the environmental effect on the

interface.

RESULTS AND DISCUSSION

Microbond data for unexposed droplets, and droplets exposed to water for 24 hours at 95C are shown in Figures 3 and 4. It is readily apparent that although the test is appropriate to gauge interface integrity in unexposed systems, in exposed samples the

glass fiber invariably broke before shear in the droplet. Similar results were obtained when

samples were exposed to water at 65C. As a result, it was determined that the microbond

test cannot be used to gauge interfacial shear strength as a function of exposure to

moisture in these systems under these conditions.

Results of the fragmentation test when run and interpreted conventionally leads to the

same conclusion. Figure 5 shows no apparent change in fragment length as a function of

immersion time.

The reason for the anomalous microbond and fragmentation results can be attributed to the fact that the environmental exposure affects the strength of the glass as well as the

interface. The weakening of the glass results in fiber failure in the microbond test. In the

fragmentation test, the weakening of the fiber results in a balancing of the effect of a

214
weaker interface with the lower fiber strength. According to the Kelly-Tyson equation,

interfacial shear strength is defined by:-*

where crfis the fiber strength, d is the fiber diameter, and l c

is the measured fragment

length.

Fragment length is a both an inverse function of interfacial shear strength and a direct

function of fiber strength. Since both these changes are happening simultaneously during

water exposure, this relation becomes an equation with two variables. Measurement of

fragment length is therefore an insufficient gauge of interfacial shear strength under these

conditions.

If the fragmentation specimens are examined under the optical microscope after testing

(Figure 6) one would see that there is in fact a very significant trend as a function of

immersion time. In the unexposed state, fracture of glass is accompanied by matrix

cracking in the shape of a bow tie at the point of fracture. However, after exposures as

short as 30 minutes, one begins to see fiber-matrix debonding on either side of the fiber

break in addition to the matrix cracking. After about 10 hours, one sees only the

debonding, without the matrix cracking, while after 300 hours, one can see regions of

debonding even where there are no fiber breaks.

It would therefore appear that in the case of environmental exposure, a shift of emphasis

in data interpretation is warranted. Instead of measuring fragment length, a much more

appropriate way to interpret the data in the test would be to measure the length of the

debonded regions.

Referring to Figure 7, we consider a relatively brittle single fiber, embedded in a more

ductile, infinitely sized polymer matrix. A tensile stress is applied to the composite parallel to the fiber until the fiber breaks sequentially arise, from the weakest fiber site to

progressively less critical flaw sites. Only the portion of the process that takes place in the

linear elastic region of the tensile test is considered. It is assumed that a fiber break is accompanied by the simultaneous formation of a debonding region on both sides of the

fiber break, as has in fact been observed experimentally. This region is very small in the

presence of a good interfacial bond, but can be very large for weakly bonded systems. The

length of the debond is Ld on both sides of the fiber fracture, and the fiber stress, Of,

which is zero at the fiber break site and is considered negligible in the debond region,

builds up along a region of total length (counting on both sides), until the average fiber stress level cr{ * is recovered. Such stress build up is assumed to be near, for simplicity, as

in the Kelly Tyson approach., implying a constant shear in the build up zone. As a result of

the fiber fracture, the strain energy in the fiber length Ld + S prior to the break is transformed into an energy contribution necessary for the formation of interfacial

debonding.

215
Therefore, the strain energy in the debond region before debonding plus the strain energy

in the stress recovery zone is equal to the energy to break the fiber plus the energy to

debond the fiber in accordance with the following relation:

( m2

) = Yi (2 m2

) + y$ {rmLd )

where Ef and r are the Young's modulus and fiber radius respectively. Referring to Figure

7, the stress profile along each of the stress build up zones is <Tf (x) = [x/(<5/2)]c7f *.

Inserting this in the integral above, and rearranging, the following equation results:

^f = A + (B/Ld )

where:

A = (rcrf *2 )/4Ef

B = r{(fcf *2 )/(l2E f )-/f }

Equation 2 gives the interfacial energy in terms of the fiber parameters crf Ef , /f

, and r, of the stress transfer length S, and of the stress level C7f * at which the fiber breaks and

associated interfacial debonding occur. The value of cy * should, ideally, be determined

by continuous monitoring of the fragmentation experiment. 5 j^ie fiber parameters, Ef,

and r are known either from the literature or via measurements. The stress transfer

length S varies with the applied stress (or strain) level, and may be estimated from the

photoelastic pattern surrounding a fiber break, or it may be accurately measured by more

sophisticated techniques such as microscope Raman spectroscopy. ^ Note that, unlike the

classical fragmentation test procedure, the aim of which is the calculation of an interfacial

shear strength based on saturation data, the present analysis is based on measurements

taken from that part of the fragmentation test that takes place far below the saturation

limit. This has the advantage that it allows the testing of composite materials systems in

which the strains to failure of both fiber and matrix are relatively close to each other, and

therefore never reach saturation in a fragmentation test. Using the proposed new

approach, their interfacial adhesion may be quantified at the condition that a measurable

amount of debonding is present. Note that: (i) the constant A is the limiting value of

interface energy when very large debonded length are present; (ii) strongly bonded

composites give rise to short debonded lengths and thus very high interfacial energies,

which in turn cause the composite to fail by matrix fracture at the fiber break site, rather

than by interfacial failure there.

It is important to realize that the theoretical scheme presented here is only approximate,

and (at this point of our research program) only points to a possible direction for a

216
reinterpretation of the fragmentation test in terms of energies rather than of stress. Some

of the approximations involved are the following:

• The energy balance analysis in Eq. 1 compares energies before and after the fracture of

the fiber and of the interface over a certain length. A more strictly correct analysis,

which would instead involve the incremental growth of a debonded crack along the

interface, is currently under investigation.

• Eq. 1 does not account for the energy that is dissipated into the possible formation of

matrix damage around the fiber break just prior to interfacial debonding (for example,

the formation of matrix cone-like breaks, or of matrix yielding), as well as for the

energy due to the fiber breakage that is dissipated into acoustic waves. Also, as previously mentioned, all pre-existing fiber stresses (such as residual thermal of

fabrication stresses) are not included for simplicity.

• The debonded region is assumed to be frictionless although in most composites stable

debonding most probably occurs with increasing load precisely because of the

presence of such frictional forces.

The results in Figure 8 thus shows the fragmentation data, reinterpreted in light of the

interfacial energy criterion, involving the measurement of debonded lengths.

CONCLUSION

The microbond test is apparently inappropriate for gauging moisture effects on the epoxyglass interface (at least under severe conditions). In contrast, the fragmentation test is indeed an effective means of assessing the effect of water on the fiber matrix interface, but

only if microscopic assessment of debond length is included in the analysis. An advantage

to this approach is the fact that it enables determination of interfacial adhesion for

composite systems which never reach saturation in the fragmentation test.

The development of this test method is but one step in joint activities between Exxon

Production Research, Exxon Research and Engineering and Imperial Oil Limited to assess the reliability of composite parts in the presence of moisture and hydrocarbon

environments.

217
REFERENCES

1 U. Gaur, G. Desio and B. Miller, Plast. Eng. p. 43 (October 1989)

2 L. T. Drzal, M. J. Rich, J. D. Camping, W. J. Park, Proc. 35th Conf. SPI Reinf. Plast.

Div. 20-C (1980), 1. 3 B. Yavin, H. E. Gallis, J. Scherf, A. Eitan and H. D. Wagner, Polym. Comp. 12, 436

(1991).

4 A. Kelly and W. R. Tyson, J. Mech. Phys. Sol. 13, 329 (1965)

5 H. D. Wagner, A. Eitan, Appl. Phys. Lett. 56, 1965 (1990)

6 A. N. Netravali, L. T. Topoleski, W. H. Sachse, S. L. Phoenix, Comp. Sci. Tech. 35,

13 (1989)

218
FIGURE CAPTIONS:

1 Schematic of micrcbond test

2. Schematic of fragmentation test

3. Microbond test results before moisture exposure

4. Microbond test results after moisture exposure

5. Fragment length versus water immersion time at 95C

6. Optical microscope appearance of specimens after environmental exposure and

fragmentation testing

7. Fiber break and interface debonding in the fragmentation test. Applied stress is parallel

to the fiber, also showing tensile stress in the fiber around the break site.

8. Interfacial energy versus immersion time in water at 95C

219
220
60

GLASS/EPOXY

DRY

• Interface Failure

40

20

• /

• /

/

\ r

o 1

1 J I 0 20000 40000 60000

EMBEDDED AREA (/xm*)

3

60

GLASS/EPOXY

24HR @ 95C

v Fiber Failure

40

20

v

w

V

V

tf7

V V

v

V

V

20000 40000 60000

EMBEDDED AREA (/zm )

Interface

Fniline

0

221
z 2000 o

ccu

§ 1600

GLASS/EPOXY

DISTILLED WATER/95C

1200

800

X

H

13

Z

m

H

Z1JU.I e

o

gl 400

UJJ

go

i2

0.1 I 10 100

IMMERSION TIME, t (HR)

1000

222
Dry state

Matrix faiiure

No interface faiiure

Short immersion times @ 95C

Fiber faiiure

Matrix faiiure

interface ciebonciing

Medium immersion times @ 95C

Fiber failure

interface debonciing

Long immersion times @ 95C

interface debonding

223
224
0)

ud

w

uu

tdU

125

100

75

50 -

25-

100 150 200 250

Immersion Time (hours)

350

8

225
226
Analysis-Based Design Tools for Offshore Applications

Stephen W. Tsai

Stanford Composites Design Center

Department of Aeronautics and Astronautics

Stanford University

Stanford, CA 94305-4035

ABSTRACT

Design of filament-wound pipes for many applications for offshore engineering

have been driven more by manufacturing and empiricism than by micromacromechanics analysis tools. As demand of strength and durability

increases for more critical services in piping and vessels, predictability of

deformation and failure modes becomes indispensible. Computer simulation of

the physical processes of manufacturing, loading and environmental conditions

is the first step in developing a rational basis of design. A few approaches to

these issues will be outlined in this paper. In particular the case of the

grid/frame structure would be a natural extension of cylindrical structures for

future offshore applications.

BACKGROUND

The use of composite materials in aerospace vehicles has been acceptionally

successful for the last twenty years. As applications move from secondary

structures to primary ones, comprehensive database, design and manufacturing

methodologies are available. Growth in aerospace structures has accelerated

to include horizontal and vertical tails of Boeing 777, and dramatic applications

in high bypass engines for B-777 and beyond.

Other industries are trying to follow the model of the aerospace industry in their

introduction of composite materials to their products. Windmill rotor blades,

rollers and drive shafts are examples of reliable applications of composite

materials. Others are emerging. Offshore applications require no

fundamentally different performance. Safety, cost effectiveness, resistance to

fire, 30-year life, certification, maintenance and others are common to nearly all industrial applications. The phycial size of the offshore however is a challenge.

Again, if we can understand the fundamental physical behavior we can design

and manufacture whatever is needed.

SPECIFIC TASKS

We would like to propose specific tasks in support of offshore applications.

Most of these are derived from aerospace applications and can be easily

adopted to the environments and requirements of offshore situations. These

tasks are generic in nature and can be equally applied to cylindrical and

structures in general.

227
Piping Design

Piping and cylindrical vessels are easy to analyze either as a thin or thick wall

construction. Externally applied forces and moments are also easy to analyze.

Process parameters that includes the curing stresses, matrix nonlinearity and

interfacial strength can all be modeled, by for example an integrated micromacromechanics analysis, and optimized accordingly. The presumption that

there is a complete chaos in predicting the weeping strength of a pipe as

material/process parameters change appears to be unwarranted. Even the

linear analysis will point to the optimum wrap angles that would be best to

increase the weeping and burst pressures. Guessing without the guidelines

from analysis would be hopeless.

Prediction of long term behavior has been developed for many years.

Viscoleastic models for solid propelants are available and should be used to

design and interpret test data for creep, stress relaxation and reliability.

Test coupons often present an issue. For pipes subjected to internal pressure,

we would recommend a ring specimen loaded hydrostatically with internal or

external pressures. This may provide the most reliable test method. We have

used rubber O-rings as the medium to exert the pressure. This is easy to do

and can generate hundreds of data points.

Joints

Bonded and bolted joints are unavoidable and must be modelled, tested and

designed. Again, modern analytic modelling is available. The key in our approach is to include the progressive failures of the adhesive layer, interface

and individual plies. We are not aware of many existing models that have the

progressive failure capability. Once the static performance of the joints are understood, we can then extend it to long term behavior through time

dependent modelling like that used in the propelant technology. Again our

attempt is to minimize empiricism. Predictability depends on the understanding

of the failure modes. Plotting and analyzing test data are at most a point design

approach. We need modelling and confirming tests before we can have a

theory. Joints, fittings, pipes and vessels can be treated by the same approach,

with different geometries and boundary conditions. Thus an investment in the

fundamental behavior will pay dividends for different applications.

Material/processing engineers often take a different viewpoint from the

mechanics oriented engineers. To gain confidence in composite materials, we

must learn to work with one another.

• Effects of Defects, Damage and Repair

With a progressive failures capability, user-friendly finite element analysis tools are available to model the following:

Manufacturing defects: nonuniformity, voids, wrinkles, debonds, gaps,

laps and surface blemishes.

228
Operational damages: impact, puntures, delaminations, indentations,

scratches, corrosion and fire.

Repair: strength and stiffness recoveries from bonded plugs and

patches, and bolted doublers.

With this effects of defects tool, which is formated for use by non specialists, a

consistant, rationally derived accept/reject criterion of composite structures can

be established. Again, modelling is the key to this tool. With modern

computers, we have made great progress using this approach. The aerospace

companies have supported this enthusiastically.

GRID/FRAME STRUCTURES

Beyond pipes and vessles, the next frontier of composite structures may be

grid/frame structures. We hope to achieve competitive performance and cost

targets for these structures for high volume civilian applications. We plan to

adhere to the following approaches:

To use GFRP and CFRP in unidirectional format (not laminates) to

form flat, curved and cylindrical configurations as the primary load-carrying

structures

To use organic matrix unidirectional tapes with on-line or in-situ

consolidation (without bagging and autoclaving)

The traditional use of multidirectional laminates for composite materials have

several intrinsic weaknesses:

Lower in-plane properties than longitudinal properties

Low interlaminar strength

Labor intensive layup process

Costly bagging and autoclaving operations

Costly and inefficient joining

The most challenging task is to translate the exceptional longitudinal properties

of composite materials to useful structural forms. The potential of composite

materials can increase substantially if we can assemble structures with a

minimum reduction in the longitudinal properties.

Pultruded sections are normally unidirectional and thus have the maximum

stiffness and strength. Sections however are not complete structures. Joints are often needed to combine pultruded sections by mimicking steel structures.

Only a small portion of the total longitudinal properties are translated into the

final structures.

229
Sandwich panels are most efficient in flexural rigidity and are relatively easy to

produce. The face sheets are made of laminates which again utilize only a

portion of the unidirectional properties. The panels are often made by hand,

susceptible to moisture incursion, and difficult to inspect and repair.

Stiffened panels are also made of laminated composites, difficult to assemble,

not amenable to automation, and not easy to repair.

Three examples of the grid structures are shown in the figure below:

V/vr

ISO GRID •aI

8 = 90

Width

Spacing

IRTHO GRID ANGLE GRID

The advantages of grid structures are many:

All ribs are unidirectional and are intrinsically stiff, strong and

tough. It is nearly indestructible. The traditional specific stiffness and strength

comparisons, shown below, are valid for grid structures:

5

03 m

u

a

o,

to

3 --

2

--

1 --

GFRP

O metals

H 1 100 200

Specific Stiffness, 106 in

CFRP

300

Thus even GFRP can be used to compete with steel and aluminum! They have

the same specific stiffness, and many times the specific strength.

Grid structures are damage tolerant. Like in a "Chinese torture"

strain to failure is many times that of laminates. The ribs are unidirectional and

thick, and test data show that the ribs and joints do not delaminate.

230
Continuous filament winding or tape placement process has been

demonstrated for grid structures. The speed of on-line consolidation for

thermoplastic composites is rapidly increasing. There is no theoretical limit how

high the rate of consolidation can reach. For thermosetting composites, in-situ

curing without bagging and autoclaving is also possible. The cost of processing

will be lower than the cost of material, which is normally difficult to achieve with

the conventional thermosetting process.

Grid structure is open and modular. Inspection will be easier than

sandwich panels. Repair can also be modular; e.g., replacing unit cells.

TECHNICAL BARRIERS

To date grid structures have seen only limited applications. Examples include

civil engineering (space) structures, W.W.II English bomber Wellington's

fuselage, and, more recently, the horizontal stabilizers of Airbus A330 and 340,

and an USAF space structure. With the exception of the AF structure, the

remaining designs are difficult to fabricate and do not utilize the superior

longitudinal properties of modern unidirectional composites. Using on-line or

in-situ consolidation, it is feasible to continuously produce a grid structure. This

approach that allows automation is fundamentally new. The key to success lies

in the mold design and the interlaced joint shown in the figure below.

The intersecting or interlaced ribs provide the opportunity to fully utilize all the

unidirectional properties. The success of the joint (having a smooth transition)

has been demonstrated in thermosetting plastic composites. This needs to be

demonstrated in thermoplastic composites using the on-line consolidation

fabrication. The damage tolerance of the interlaced joint has been

demonstrated. Reduntant load paths appear to be present in this structure.

Unidirectional rib Intersecting ribs

Another barrier is the design and fabrication at joints (connections), openings

and concentrated load introduction points. These issues are different but not

more difficult than those with any structure.

231
The proposed grid design is to eliminate mechanical joints at the rib

intersections. Not only can efficiency of the grid structures increase, automated

manufacturing is now feasible. The same seamless design will be applied to

frame structures, examples are shown below:

Trailer/container Platform

For offshore applications, we see grid/frame structures for floors, housing, and

other load bearing situations. Test data have demonstrated the phenomenal

resilience of the grid structure under static loading. Redundant load path is the

primary factor for this outstanding character. It is anticipated that dynamic

resilience and long term performance will be equally superior to the

conventional stiffened panels and shells. This structural concept, for example,

is being considered for the containment ring of a new generation of gas turbine

engines that is over 10 feet in diameter. With automated manufacturing

capability, cost of structures is expected to be the lowest of all composites

manufacturing. We are therefore very optimistic about the future of grid/frame

structures.

CONCLUSIONS

We would like to combine the experience of aerospace and offshore

engineering to face many challenging problems. We believe that analytic tools are critical to bring safe and cost effective structures to use. There are no

fundamental limitations of composite materials for such applications. In fact,

composite materials may be the only option that is available to meet the

requirements of future offshore applications.

It is important to invest in the relevant technolgy in modelling, testing,

manufacturing, assembly and maintenance of composites components and

systems. An agressive program that would bring industry, government and

academia can lead to important applications in a very short time. The risks are low and the payoff can be beyond our fondest dream.

232
COMPOSITE APPLICATIONS IN OFFSHORE OPERATIONS

King H. Lo

Shell Development Company

Westhollow Research Center

3333 Highway 6 South

Houston, TX 77082

Introduction

The properties of polymeric composites, including low density, excellent corrosion

resistance, high static and fatigue strength, low maintenance and low life-cycle cost, clearly

demonstrate that composites are desirable materials of construction for offshore uses. The

polymeric composites of interest here are mainly fiber-reinforced thermosetting resins; the fibers

being glass (mainly E-glass) and carbon; and the resins being vinylester, polyester, epoxy and

phenolic. The material cost per pound of polymeric composites is higher than steel. When

composites are not used for or viewed upon as providing needed enabling technology, the initial cost of composite components could be of major concern in offshore applications. The cost of

glass fiber reinforced components can range from $2-5/lb. When carbon fiber is needed to

improve structural performance, the cost of composite components will be significantly higher.

For viable offshore applications, components must be made economically by low cost

manufacturing processes such as filament winding, pultrusion, resin transfer molding, or contact

molding and from the lowest cost resins and fibers.

A brief discussion on the status of topside and below water surface applications is given

below. Some issues relating to the design and performance rating of FRP line pipes are presented

with the objective of stimulating thoughts and discussion on the design of composite components

for offshore operations.

Topside Applications

Glass fiber composites are used for piping, grating, process equipment and a variety of

other applications on topside offshore structures (Table 1). In addition to the benefits that can

be derived from using composites as mentioned earlier, other motivations for topside uses include

reduce initial cost, eliminate corrosion problems, improve safety and reliability, and ease of

installation. Topside applications of composites are generally perceived to be technically feasible.

Component and system design are within existing capabilities and field experience is gaining in existing installations. Topside uses can also benefit from a long record of proven performance

in otherwise comparable installations onshore. Nevertheless, it is recognized that the differences

in performance requirements between land-based and offshore installations can be significant and

may influence design, material selection, installation and cost.

The impact of composites on the initial cost of offshore installations cannot be realistically

estimated without giving considerations to such issues as specific design and performance

requirement, and cost of corrosion protection, transportation and installation, for examples. For

floating platforms, where weight savings could potentially yield large cost savings, an estimate

of the relative economic advantage of composite components can be obtained by calculating the

cost of composite per ton of replaced steel. Simply,

C($/ton steel replaced) = 2000*(1-X)*A - 2000*X*M - 2000*B

233
lablej.. Potential Polymer Composite Applications On Platforms

Platform Topside

Vessels

Tanks

Process Equipment

Pressure Piping

Fire Water Piping

Sea Water Intake Piping

Utility Piping

Drain Piping

Equipment Enclosures

Decks

Equipment Skids

Grating

Handrails

Ladders

walkways/Stairways

Cable Trays

Crew Quarters

Blast Walls

Electronic Cabinets

Helidecks

Flare Blooms

Bumpers

Escape Devices

TLP Below Water Surface

Production Risers

Riser Stress Joints

Tendons

Mooring Cables

Floatation Modules

Buoys

Drilling

Drillpipe

Drilling Riser

Core Tubes

Choke and Kill Lines

Riser Fairing

234
where

C = cost of composite component (before installation) which replaces one ton of steel

X = weight saving with composite in %/100

M = incremental payload cost, $/lb

A = cost per pound of composite, $/lb

B = cost per pound of replaced steel, $/lb

Putting C and B equal to zero in the above equation, the percentage of weight savings at which

sufficient incremental payload cost is realized to pay for the cost of the composite component

is given by:

X(C = B = 0) = A/(A + M )*100 %

Table 2 shows the percentage of weight savings that could contribute to the total cost of the

composite component for various combinations of incremental payload cost and composite

component cost.

Table 2 . (% Weight Savings at which Weight Saved Pays for Component)

A($/lb)

2.5 5.0 10 15 20

M($/lb) X(%)

2.5 50 67 80 86 89

5.0 33 50 67 75 80

10 20 33 50 60 67

15 15 14 40 50 57

If the cost of the replaced steel component is included, cost break-even can be achieved at lower

weight savings than those shown in Table 2.

Despite the benefits that can be achieved with composites, several issues need to be

addressed in order to further increase the use of composite components on platform topside.

Regulatory requirements and their implications concerning fire safety and reliability of composite

installations need to be clarified and understood. The likelihood and consequences of accidental

impact on the long term performance of composite components such as gratings and piping, for

examples, are of concern and need to be accounted for in the design of composite components.

A rational approach will need to be developed for using/extrapolating test results from laboratory

scale test to assess the effect of impact loadings on full scale structures. Replacement quidelines

will also need to be established. For new applications, extra initial efforts spent on training,

system design, specifications, joining requirement and qualification, equipment testing and

inspections, for examples, will ensure satisfactory installations. Further, development of uniform

industry specifications for design, manufacturing, testing and quality control will help to expand

the applications of composites on platform topside.

235
Below Water Surface Applications

On floating platforms, such as tension leg platforms, possible applications below the water

surface include such components as tendons, risers, and mooring systems, for examples, (Table

1 ). In these applications, the impact of composites on platform cost and performance is obtained

mainly through weight reduction and/or lessening cathodic protection. A system approach is usually required to realize the full benefits of using composites. Carbon fiber, glass fiber, and

kevlar fiber all appear to have a place in these applications. In contrast to topside components,

actual field experience for below water surface applications is limited.

Composite tendons and risers are, in general, structurally more demanding than topside

components. Dimensions, loading requirements and design features will set these components

apart from other prior offshore applications. A substantial effort in various areas including

design, engineering, connection, terminations, procurement, risk assessment, qualification,

fabrication, NDT, transportation and assembly will be needed to demonstrate the acceptability

of composites as engineering materials for these critical components. Tendons and risers will probably not be used without some forms of full-scale testing, qualification and verification.

Unfortunately, the time required for component development is usually not available within most

deep water projects. For entry in these applications, these composite components will probably

need to be ready at the start of a project.

In view of the high development cost for below water surface applications, industry

cooperation on composite component development appears very desirable and should be

encouraged. Evidence of broad interest could stimulate composite suppliers to commit

themselves to product development and encourage regulatory agencies to establish the

appropriate guidelines, standards and specifications.

Some Related Issues

As mentioned earlier, to increase the use of polymeric composites in existing potential

applications and to expand their use into more demanding operations, uniform standards and

specifications in component design, performance requirements, ratings, dimensions, fabrication,

quality control, risk assessment, transportation, installation and repair will need to be established

(for both onshore and offshore applications). Uncertainties in product long term performance must

be reduced and ability of product to resist damage in field conditions must be increased through

proper design and material selection. Prudence must be exercised through proper training and

understanding of composite characteristics to avoid unnecessary premature field failures. On the

other hand, excessive conservatism will needlessly increase cost and price composite

components outside the competitive range of conventional steel constructions.

FRP line pipes are used extensively in both onshore and offshore applications and will be

employed here to illustrate some of the elements discussed above. Despite a long record of

proven applications, the allowable service temperature and pressure for these components are still commonly determined by empirically derating manufacturer's pressure and temperature ratings.

It is obvious that such a practice will inevitably incur potential penalty on the initial cost of the

components and in some cases lead to rejection of the product in favor of the cost of steel

construction. However, this is usually done to avoid uncertainties and variations in product long

term performance and to ensure continued service without failure. Results of a recent study (Ref.

1) clearly show that a wide disparity in product long term performance could exist between

measured values and calculated values based on manufacturers' published data. The urgent need

236
to reduce uncertainties in product long term performance through uniform and rational rating

(testing) methods is evident. A performance-based purchase specification for FRP pipes and

fittings based on API Specification 15HR and 15LR is recently proposed (Ref. 2). This

specification is aimed at ensuring that products will survive long term service at rated operating

conditions with a minimum known strength margin.

In addition to reducing performance uncertainties through the use of uniform rating

methods and specifications, products need to be improved to meet increasingly demanding

operating conditions. This will require an understanding of the relationship between product

design and the failure mechanisms that control the performance of the product. For FRP line pipes, the onset of weeping or leakage is an indication of the loss of serviceability of the product.

The convoluted path(s) of matrix cracking and ply delamination in the pipe wall controls weeping

and should be addressed in product design and performance evaluation (Ref. 3).

For illustration, Tables 3 and 4 show the calculated room temperature stress distributions

in principal material directions for different layers of two identically rated FRP line pipes subjected

to a rated pressure of 800 psi. Tables 5 and 6 show the corresponding calculated stress

distributions at 150 °F. These calculations are based on the assumption of linear elastic

behavior. Resin properties and fiber volume fractions are also assumed to be the same for both

line pipes. It is recognized, however, that with the assumed fiber angles and ply thicknesses used

in the calculations, these line pipes may not truly represent the commercially available products.

However, the results shown in Tables 3-6 can be used, at least qualitatively, to bring out several

important issues. Some of these issues are discussed below.

It is quite obvious from the stress distributions that weeping in both pipes (A and B) will be governed by the matrix dominated properties of the composites. Even though the pressure

ratings of the two FRP line pipes are identical, their through thickness stress distributions in the

matrix phase of the composites are quite different. To understand the merits of the two different

designs and identify opportunities for product improvement, an appropriate failure criterion for

matrix cracking together with some progressive failure propagation mechanisms must, therefore,

be used to properly evaluate the performance of these two FRP line pipes. This may require

some research and development effort to study the onset of weeping in FRP line pipes.

Table 3

Stress Distributions* (psi) in Pipe-A at Room Temperature

Ply # Longitudinal

Normal

Transverse

Normal

In-Plane

Shear

12

4

5

6

7

13090.7

7871.0

13507.6

7861.5

13965.4

7851.9

14468.7

2228.8

31 10.8

2174.7

3129.7

2117.0

3152.1

2055.3

-6.5

152.3

1.9

173.7

10.9

197.1

20.7

237
Table 4

Stress Distributions * (psi) in Pipe-B at Room Temperature

Ply ft Longitudinal Transverse In-Plane

Normal Normal Shear

1 9874.6 2289.0 -1 75.7

2 10071.6 2254.9 188.7

3 10190.3 2234.8 -21 1.1

4 10407.5 2199.3 226.4

5 10550.5 2177.4 -251 .1 6 10791.0 2140.3 269.1

Table 5

Stress Distributions (psi) in Pipe-A at 1 50 °F

Ply # Longitudinal Transverse In-Plane

Normal Normal Shear

1 14376.0 1057.9 -217.7

2 9474.3 1863.7 70.0

3 14584.7 992.5 -207.6

4 9453.6 1837.7 52.7

5 1423.7 924.0 1Q7 ft

- 1 y / .u 6 9432.7 1814.2 34.0

7 15096.4 852.4 -185.9

Table 6

Stress Distributions (psi) in Pipe-B at 1 50 °F

Ply # Longitudinal Transverse In-Plane

Normal Normal Shear

1 10883.3 1554.7 244.4

2 1 1093.2 1484.5 -252.5

3 10975.5 1469.6 228.5

4 1 1 195.1 1398.8 -234.5

5 1 1098.0 1381.6 209.3

6 1 1329.7 1310.1 -213.1

238
Table 7

Stress Distributions* (psi) in Pipe-C at 150 °F

Ply # Longitudinal

Normal

Transverse

Normal

In-Plane

Shear

12

3

4

56

1 1477.5

1 1723.2

11610.6

1 1865.6

1 1774.0

12040.6

885.4

819.6

814.6

748.9

742.2

676.6

520.1

522.2

544.5

548.8

572.8

579.7

planar stress distributions at mid-plane of each ply

For both FRP line pipes (A and B), the magnitudes of the matrix dominated stress

components at 150 °F are lower than those at room temperature. If the matrix dominated

properties of the pipe composites are not significantly affected at 150 °F, it is likely that the

short term hydrostatic strength of these FRP line pipes at 1 50 °F could be at least equal to if not

greater than the short term hydrostatic strength at room temperature. Test results given in Ref.

[1-2] on some FRP line pipes seem to support the above observation. Hence, if the

recommended long term pressure ratings of these FRP line pipes are based on short term

hydrostatic strength, this might lead to the erroneous conclusion that temperature has no effect on the pressure rating of the pipes. However, test results do indicate that the long term

performance of FRP line pipes is strongly dependent on the test temperature. Therefore, the

combined effect of time and temperature must be included in determining the long term

performance of FRP line pipes.

To design for long term performance, the long term rupture characteristics of the matrix

dominated composite properties in the intended service environment must be properly accounted

for. These long term rupture characteristics are, in general, not easily determined and usually

not readily available in the design phase of the products. Hence, a rational approach to determine

the long term performance of FRP line pipes through testing will need to be established to

minimize the need to excessively derate the performance of FRP line pipes. These test results

together with calculated stress distributions such as those given in Table 3-6 could then be used

as an engineering guide to improve product design, qualify component variants of similar design

and fabrication, and for the selection of resin matrix for different applications. For example,

Table 7 shows that a slight change in the fiber angle of the FRP line pipe in Table 6 (pipe B) can

lead to a significant change in the ratio of the transverse normal stress component to the in-plane

shear stress component. If test results also indicate that an improvement or reduction in the long

term performance of the FRP line pipe is also obtained, then by adjusting this stress component

ratio, improvement in long term performance can be obtained for a family of products of similar

design and fabrication.

It is important to point out that the above brief discussion on design and performance of

FRP line pipes are constructed solely for the purpose of stimulating thoughts and discussion on

improving composite component design and performance for offshore/onshore applications. It

is by no means comprehensive and other factors that could impact the final design are not

included in the discussion. It is imperative, however, to fully utilize the design know-how gained

239
and accumulated in other composite applications to successfully improve and expand product

design so as to encourage further use of composites for offshore applications.

References

1. G. G. Huntoon, and J. D. Alkire, "Design and Performance Properties of Oilfield Fiberglass

Tubulars", 64th Annual Technical Conference and Exhibition of the Society of Petroleum

Engineers, October 1989, SPE 19728.

2. E. T. Provost, "Extending the GRP option, A Performance-Based Purchase Specification for

GRP pipes and Fittings", 12th International Conference on Offshore Mechanics and Arctic

Engineering, OMAE 1993, Glasgow, Scotland.

3. S. R. Frost, "The Fatigue Performance of Glass Fibre/Epoxy Matrix Filament Wound Pipes"

ICCM-9, Madrid, July, 1993.

240
Flammability and Fire Safety of Composite Materials for Offshore Operation

Takashi Kashiwagi and Thomas G. Cleary

Building and Fire Research Laboratory

National Institute of Standards and Technology

Gaithersburg, MD 20899

Introduction

There are many possible potential fire scenarios on an offshore platform. Two different

types of fires are possible: an open fire caused, for example, by a spilled fluid; and fire in a compartment, possibly started by cooking in a crew compartment. Since the use of composite

materials as replacements for steel on offshore platforms is gradually increasing, fire safety issues

might become more critical due to the combustible nature of composites. Since composite

materials are generally more difficult to burn themselves than the polymer resins they contain,

the initiation of fire on these materials by a small flame, such as a match flame, is extremely

difficult and therefore, they would not likely be the first material ignited. However, if a nearby

fire becomes large enough to emit sufficient amounts of heat and thermal radiant flux,

neighboring composite materials could be ignited and sustain combustion, contributing to the

spread of the fire. Even if a composite material did not burn under such conditions, it could

experience sufficient heat input to cause thermal degradation of a part of the polymer resin

leading to delamination and weakened structural strength. Here it will be assumed that the fire

is not initiated on the composite material. However, if there is a fire nearby, the issue of whether

or not a composite material does ignite and burn or experience loss of structural strength is the

desired information.

A schematic illustration of the fire safety of any system utilizing composite materials

(including offshore oil platforms) is given in Fig. 1. At first, potential fire scenarios can be

considered which may expose available composite materials on a platform to heating. The

characteristics of the fire such as heat release rate and thermal radiant flux can be calculated

using currently available fire models. Then, using the applied heat load from the assumed fire scenarios, the fire performance of specific composite materials can be evaluated using fire growth

models having as inputs fire properties measured by modern bench scale test methods. A similar

approach can be applied to assessing the strength of the composite material exposed to the fire. The results would indicate whether the composite materials ignite and have flames spread over

them, and to what degree their structural strength is weakened. Using these predicted results, a design company could determine the trade-offs between material and suppression system costs and allowable damage level. For example, momentary ignition but no flame spread and no

structural damage might be a permissible option. This paper briefly describes the current level

of knowledge and predictive capability for various fire scenarios, such as open fires and a fire in a compartment. Modern bench scale flammability test methods are briefly described and a calculation of fire spread over a vertical composite wall in a compartment made of a composite

material is described using the measured flammability properties of the composite material as inputs to a fire growth model.

241
Combustible

Materials

Fire Models

Potential

Fire Scenario

Composite

Materials

Suppression

Systems

Flammability

Properties

Fire Growth Model

Structural Model

Structural Strength

Characteristics

Acceptable Damage Level &

Cost

Fire Characteristics

Structural Damage

Figure 1 A schematic illustration of a fire safety approach

Open Fire

The global aspects of the combustion process of an open pool type fire are reasonably

well understood. A small fraction of the total heat release from the flame (about 1-2%) is fed

back to the pool surface by radiation and convection. Radiative transfer is the main energy

feedback process for large diameter (roughly above 10 cm diameter) hydrocarbon pools except

for alcohols with small molecular weights. Typically, approximately 30% of the heat release

from the combustion of hydrocarbon fuels is emitted from a flame as thermal radiation.

However, this value tends to decrease with an increase in a pool diameter when the diameter

becomes large, for example, about 3 m for heptane and 2 m for kerosene [1]. This decrease is probably caused by trapping of radiation due to soot blockage. An increase in the size of the

flame increases the heat release rate which in turn increases radiant flux emitted in all directions

from the flame. Therefore, when a flame becomes large, such as in the case of an oil well

blowout, a radiant flux from the flame may be sufficient to ignite remotely located combustible

materials and contribute to their continued burning. An infrared emission spectrum from the

combustion of a crude oil shows a broad emission band from particulates in the flame

superimposed with C02 and H20 emission bands. Fuels containing aromatics tend to generate

more particulates thus the emission spectrum would be dominated by the broad band emission

from soot and consequently, the radiated fraction of the heat release tends to be higher than 30%.

On the other hand, small alcohols such as methanol do not generate a large quantity of

particulates and the emission spectum is dominated by molecular emission bands of CO 2 and

H20 and thus conversely, their radiated fractions of heat release are roughly 15-20%. It appears

that there are no significant differences in radiated fraction of heat release between buoyancy

driven flames (for example a pool flame on a spilled fluid) and jet flames (driven by the initial momentum of a fuel flow, such as a blowout flame) [2, 3].

242
The energy feedback from a pool flame to the pool surface continues to heat the pool,

gasifying the liquid fuel which then feeds combustible gases to the gas phase. This coupling

between the gas phase and the condensed phase determines the burning rate of the pool flame

and also the heat release rate. Thus, the liquid pool fire is a complex, coupled combustion

process.

The above combustion process has been described by two different types of models; a global algebraic model and a solution to the set of partial differential equations describing the

underlying conservation laws. The global approach is based on a single spatially uniform flame

temperature with a specified or calculated emissivity of the flame or more precisely the soot

volume fraction in the flame [4]. The flame temperature is specified or calculated from a global

energy balance among heat release and heat loss by emitted radiation and cooling by the

entrained ambient temperature air into the flame (dilution). A schematic description of this

idealized pool flame is shown in Fig. 2. The radiative feedback rate is calculated using the mean

beam length approximation

*a 1

Flame Height, H [C02],[H20],fv ,T

m Q'Vad +

Q" conv

Cylindrical Flame

Radiative Emission

Air Entrainment

Condensed fuel

Pool diameter, D

Inputs:

Combustion Properties

Fuel Properties

H„

Calculate:

Flame Height, Hf{Q*)

Air Entrainment, Ma(Hf)

Flame Temperature, Tf{Ma, Xa, Xr

) Mean Beam Lenght, Lm(Hf, D)

Gas and Particulate Emissivity, E(fv , r, Tf)

Radiative Heat Transfer, Gray Gas Approximation

Q"rad(Tf. Lm. E- fv) Convective Heat Transfer - Stagnant Film Approach

Stoichiometry, r Condensed Phase Emissivity

Figure 2 A global pool burning model

[5] which is based on flame

height and pool diameter.

The combustion efficiency

and the radiated fraction of

heat release are also needed

inputs in the calculation.

Typical results of the burning

rate of heptane and crude oil are shown in Figs. 3 and 4 as

a function of pool diameter.

In these figures, point symbols represent experimental

data measured by different

researchers and the lines are calculated results. The calculated results for heptane pool

flames appear to be in rea- sonable agreement with the

experimental data but the

calculated results for crude

oil underestimate the mass

burning rates significantly.

This discrepancy might be

caused by uncertainty in the

thermal properties of the

crude oil, given their unique

composition. The heat re- lease rate and radiation flux

243
from these flames to an outside target (for example a composite material) can be calculated from

the model.

0.1

0.01

frac=0.1

e=0.92

Babrauskas

Gore et al Koseki & Hayasaka

Shinotake et al Koseki & Yumoto

Mulholland et al Present Study

Klassen et al. Klassen et al burndown

model

0.5 1.5

D (m)

Figure 3 Heptane burning rate

0.1 r

£

x 0.01 3

U5

to 2

0.001

frac=0.11

e=0.92

-model (X =0.32)

m" Koseki (kg/m2-s) m" Evans et al (kg/m2-s)

2.5 7.5 1 0

D (m)

The second approach

is based on solving partial

differential equations based on continuity, momentum,

energy and species concentrations (so called field equation

modeling). Such models

contain quite complex equations and require a numerical

analysis. Still, the complexity and limited understanding

of the underlying processes

require approximations. One

often used approximation for

solving these equations is the

k-E turbulence model to describe the turbulent flow field

by using a description of the

turbulent kinetic energy and

its dissipation rate [6]. One

advantage of this approximation is that several codes are commercially available. However, they often need some

modification such as the

inclusion of soot in a radiative transfer calculation to calculate a specific problem.

The codes also require a considerable learning period

before they can be used ef- fectively. One drawback to the k-E models is that this

approximation smooths the

dynamic behavior of pool

flames (large fluctuations)

and only statistically averaged

quantities (mean components)

are calculated. A different

Figure 4 Crude oil burning rate

244
.... <;>>->. :;,.<">V.-

/..v:i^r-.^>'-'-.>r.'>;v;-;-r

INITIAL SPHERICAL DISTRIBUTION

'C:-'y.S'i • •

jpninii"""-

NECKING DUE TO HILL'S VORTEX FIELD

Fig.5 Pool flame by Large Eddy Simulation [7]

approach to solving the differential equations is by use of the Large Eddy Simulation

method with a Lagrangian

thermal elements submodel

[7]. This approach breaks the

process up into two different

scale effects. Phenomena that

typically occur on length

scales below the resolution

limit of the computational

heat release driven EXPANSION grid in simulations of large

scale fire induced flows, such

as diffusion-controlled combustion and radiative emis4 !*T'^/t- sion, are modeled in the subvffr : grid-scale thermal elements.

As an example of this calculation, 2000 thermal elements

are convected in a simple

flow field constructed from a

V

•:

: prescribed vorticity distribu-

//•f/^V.! tion and a pool flame is described by the flow interactions of the thermal elements

which are combusting and

radiating. Typical results are shown in Fig. 5. Although

the flow field needs further

improvement to describe fully

the pool flame flow field, the

results can capture the

TWO SEPARATE "CLOUDS"

dynamic behavior of the pool flame which cannot be calculated from the two approaches

previously described (global approach and the use of the k-e turbulence model). The approach

of the Large Eddy Simulation seems promising and may be used more often in the future. Its principal drawback is the considerable computational resources required to perform such

calculations.

The effects of ambient winds on open pool fires can be significant. There are often winds

on an offshore platform. The effects of cross-winds on pool fires have been only sparsely

studied. A rule of thumb that is commonly used is that a 2m/s wind will bend a pool flame by

45°, and the flame tends to hug the ground downwind of the fuel surface to a distance of ~ 0.5D,

245
where D is the pool diameter [8]. This can significantly increase the fire exposure of items

downwind, either by causing direct flame impingement, or by increasing the levels of radiant heat

flux [9]. Two recent studies obtained flame length correlations with the cross-wind velocity and

pool diameter for pool fires of diesel oil [10] and for high velocity gas jet flames [11]. There

are few theoretical studies; the most recent study used the k-£ turbulence model to calculate

wind-blown pool fire in a large tunnel [12]. More experimental and theoretical studies are needed to understand and characterize the effects of cross-winds on pool flames.

Fire in a Compartment

A schematic illustration of a fire and the fire induced flow field in an enclosure is shown

in Fig. 6. The opening on the right side in the figure could be an open window or a doorway,

etc. Heat release from the fire acts as a pump to drive combustion products upward to fill the

upper part of the compartment. When the stratified layer of combustion products (smoke)

becomes lower than the top of the opening, some of the products flow out (flow rate is expressed

by mg

) and fresh air flows into the compartment, satisfying mass continuity in the compartment.

The steady-state temperature increase for the upper layer may be approximated by

A T - C (-^-)1/3

where Q is the rate of heat release within the compartment, A0is the opening area, H0

is the

opening height and C

is a constant. When a

fire starts inside a compartment, the heat

release rate from the

fire gradually increas- es with the spreading

of flame. This in- creases the upper

layer temperature as shown in the above

equation. A conse- quence of an increase

in the upper layer

temperature is an

increase in thermal

Figure 6 An illustration of fire in a compartment

radiant flux from the upper layer to exposed combustible materials. The thermal radiant flux

enhances the combustion and flame spread rate of exposed combustibles which increase their heat

release rate. This coupling between the upper layer and the combustible materials results in an enhancement of the fire, driving it to the so-called "flashover" condition. The most common

TEMPERATURE PROFILE, Tr

246
120 -

definitions of flashover are: (a) the transition from a localized fire to the general conflagration

within the compartment when all combustible surfaces are burning; and (b) the sudden

propagation of flame through the unburnt gases and vapors collected under the ceiling with

flames exiting through

the opening. Three

distinct regions of

compartment fire

burning, fuel controlled burning, ventilation controlled burning, and flashover

region are classified

in a plot of burning

rate with respect to the opening factor of

A0H0 shown in Fig.

7 [13].

Over the last decade numerous

computer models have

Fig.7 Compartment burning rate as a function of

ventilation parameter [8]

1600

1400

1200

1000

800

K

K

K

K

K

X(m)

Fig.8 Temperatures and velocities

of flame in a compartment [15]

been developed to calculate aspects of fire and its effects in compartments. Two different approaches

have been utilized similar to the above open fire cases: Zone modeling is based on the application of mass and energy conservation principles to a homogeneous hot upper layer and a cool lower gas layer

in a compartment. Field equation modeling is based on solutions of the three dimensional transient

Navier-Stokes equations with the conservation of

energy and chemical species equations. The basic

equations used in zone models have been derived by

Quintiere [14]. There are numerous zone models

which differ in detail and in application, but all use

basically the same principle. Most of these models

use a specified burning rate in the compartment

rather than calculate burning rates even though, in

general they are coupled with the compartment.

Recent field models using the k-e turbulence model

247
have calculated fire behavior in a compartment including thermal radiation and gas

phase chemical reactions [15,16]. The calculated temperature distribution in a compartment from Ref. 15 is shown in Fig. 8. Although these models are usually

limited to a single compartment due to the complexity of the required computations, burning behavior and its interaction with the compartment can be described.

Another field equation model is based on the Large Eddy Simulation method

similar to the model discussed in the open fire section [7]. The calculated

dynamic behavior of the movement of hot layers in a complexly shaped of a compartment is shown in Fig. 9. In this calculation, the location of the fire is in a small horizontal compartment next to the large room

at the left side and its heat

release rate is specified.

Although the source of the

fire is specified in this calculation, it permits the detailed

dynamic nature of the flow to be determined,which cannot

be obtained from models using

the k-£ turbulence model.

Fig.9 Calculated dynamic movement of hot layers [7]

In principle, the field equation modeling approach is more general. It is only bound by the universality of its turbulence and combustion models, presuming sufficient spatial and temporal

resolution is achieved. Nevertheless all computer modeling results need to be examined against

experimental data.

Fire Exposure to Composite Materials

Since a typical composite material cannot be ignited by a small flame such as a match, the

most likely fire scenarios involving composite materials is the exposure of these materials to a nearby flame, as described above. The approach espoused here is to examine whether a material

ignites and burns based on predictions of the performance of that material for various possible

fire scenarios. This is accomplished through the use of fire growth models with the measured

flammability properties as inputs to the models followed by validation of the results with a

limited number of full scale tests. This approach can be applied to composite materials. Such

an exercise is demonstrated here. Key flammability properties are piloted ignition delay time,

heat release rate, burnout time, and flame spread characteristics (all as a function of external

incident flux). The first three properties are measurable with a Cone Calorimeter [17] and the

first and the fourth properties are measurable with a Lateral Ignition and Flame Spread apparatus

[18], LIFT. The sample size for Cone Calorimeter tests is about 10 cm x 10 cm and for the

LIFT test is about 16 cm and 80 cm. The maximum external radiant flux exposure in the Cone

Calorimeter is about 100 kW/m and generally tests are performed at various radiant fluxes. A

typical heat release rate curve for a glass reinforced polyester sample, GRP, is shown in Fig. 10.

A flammability diagram for the GRP sample is shown in Fig. 11 as the combined results obtained

from ignition and lateral flame spread tests. Here, the abscissa is the external irradiance, the left ordinate applies to lateral flame spread rate while the right ordinate applies to time to ignition.

248
600

^ 500 " Ei 400

a

to

e

CC 300

- 20 0

"

100 -

400 600 1200

Time (s)

1 600 2000

Figure 10. Rate of heat release vs. time for GRP material.

Flame Spread

E

E,o

CO CC

-o

CB

Q.

Ignition

O LIFT Ignition Data

Cone Ignition Data

Model Fit

1200

1 000

800

600

1 0 2 0 30 40 50 60 70

- 400 c

200

60

External Irradiance (kW/m2

) Figure11. Flammablllty diagram for GRP material. The left ordinate applies

to the flame spread rate, while the right ordinate applies to time to ignition.

This plot summarizes

the ignition and lateral flame spread characteristics of the material. In general, a shift

of both curves to the

right would indicate

better performance in

terms of ignition and

flame spread behavior.

One model that

yields good predictions of transient heat

release rate in a compartment and the time

to flashover was re- cently developed [19].

This model is generalized to handle differ- ent sample orientations (wall, floor, and

ceiling configuration),

but has only been

validated for wall and ^ wall plus ceiling

configuration. Six

| basic flammability

J> properties, ignition

o characteristics, aver- age heat release rate, thermal properties,

burn time, lateral flame spread parameter, and minimum

temperature to sustain

flame spread, are determined from the

above results using

the Cone Calorimeter

and LIFT. The calcu

lation of the fire behavior initiated from a well-calibrated sand burner in a compartment made

of the GRP material was made to compare the predicted results with the experimental data.

249
Calculated Pyrotysis Front

• • • Calculated Bum-out Front

k Experimental Pyrolysis Front

_i_

100 200 300 400 500 600 Time (s)

Figure 12. Pyrolysis front position vs. time for the GRP module 200 kW

wall fire. Experimental and predicted values are shown. Predicted burnout front position is also shown.

500

400

300

200

100

Calculated Temperature

A Experimental Temperature

1 00 200 300 400 500 eoo

Time (s)

Figure 13. Average upper layer temperature vs. time for the GRP

200 kW wall fire. Experimental and predicted values are shown.

A brief description of

the large scale fire tests on

the GRP composite material

is given here. The composite

module was 2.4m high by

2.4m wide by 4.8m long. A

dividing wall was installed

which formed two isolated

2.4m by 2.4m by 2.4m cubic

compartments. A door 0.41m

wide by 1.5m high located

0.41m off the base was cut

into the wall adjacent to the

interior dividing wall. The

composite module was

formed from 2.4m by 4.8m

sheets which were bolted and

glued to an internal, steel I- beam frame. The I-beam

frame was welded to a steel

floor. The room walls and

ceiling were comprised of the

composite material. One test was performed with a 200

kW ignition source (0.48m x 0.48m propane sand burner)

which was placed against an

interior wall. The ignitor was

on for 300 s. The flame

spread up the wall, across the

ceiling, and partially down

the opposing wall. The model predicts the flame spread

up the wall and across the

ceiling, but the predicted

progress of the pyrolysis front

lags the measured progress of

the pyrolysis front, as shown

in Fig. 12. Gas temperatures

in the room were obtained

from thermocouples spaced

evenly from 0.15m to 2.29 m

from the floor. The gas

temperatures achieved in the

250
upper portion of the compartment provide an indication of the fire severity. The average upper

layer temperature as a function of time was obtained from the averaged temperature of two

thermocouples at heights of 1.68 and 1.98 m from the floor. The upper layer temperature was

calculated from Eq. 1 using the two-zone model as described above with the calculated total heat

release from the sand burner and the composite material. The comparison of upper layer

temperature history is shown in Fig.13. From time 0 to about 70 s, heat was released only from

the sand burner. At about 70 s, the composite material ignited and flame started spread upward

as shown in Fig. 12 and consequently upper layer temperature increased with an increase in total heat release. At 300 s, the sand burner was turned off and also nearly at the same time the

bottom part of the wall burned out as shown in Fig.12. These two events significantly reduced

the total heat release and accordingly the upper layer temperature dropped rapidly. The predicted

upper layer temperature agrees reasonably well with the experimental results as shown in Fig.13,

Further experiments were conducted with different ignition source strengths and locations and

generally the predicted results agreed reasonably well with the experimental data even though the

model contains a number of approximations.

Summary

The last two decades of active fire research studies have made significant progress in

understanding fire phenomena, identifying and measuring important flammability properties,

allowing for the prediction of fire growth. It is strongly recommended that off-shore platform

users and designers apply the current body of knowledge as much as possible and avoid

unnecessary repetitive fire research studies. Of course, certain unique features of offshore

platforms, their environment and of composite materials require further study, but the basic

principles of fire dynamics can apply to the offshore platform. Also, it is important to use the

concept of an overall fire safety strategy such as the use of early detection, suppression system,

for a offshore platform instead of relying strictly on composite material performance.

Reference

1.Yang, J.C., Hamins, A., and Kashiwagi, T. "Estimate of the Effect of Scale on Radiative Heat

Loss Fraction and Combustion Efficiency", to appear in Combustion Science and Technology.

2. Hamins, A., Klassen, M., Gore, J., and Kashiwagi, T. "Estimate of Flame Radiance via a Single

Location Measurement in Liquid Pool Fires", Combustion and Flame, 86:223-228 (1991).

3.Sivathanu, Y.R. and Gore, J.R. "Total Radiative Heat Loss in Jet Flames from Single Point

Radiative Flux Measurement", Combustion and Flame, 94:265-270 (1993).

4. de Ris, J. "Fire Radiation - Review", Seventeenth Symposium (International) on Combustion,

The Combustion Institute, Pittsburgh, 1003-1015 (1978).

5. Hottel, H.C. and Sarofin, A.F. "Radiative Heat Transfer", McGraw-Hill Co., NY, (1967).

6.Annarumma, M.O., Most, J.M., and Joulain, P. "On the Numerical Modeling of BuoyancyDominated Turbulent Vertical Diffusion Flame", Combustion and Flame, 85:403-415 (1991).

7. Baum, H.R., Ezekoye, O.A., McGrattan, K.B. and Rehm, R.G. "Mathematical Modeling and

Computer Simulation of Fire Phenomena", Ninth Symposium on Turbulent Shear Flows,

Volume 3, Paper No.30-2, (1993).

8. Drysdale, D. "An Introduction to Fire Dynamics", John Wiley and Sons, (1985).

251
9. Pipken, O.A. and Sliepcevich, CM., Industrial and Engineering Chemistry: Fundamentals,

3:147-154 (1964).

10.Defaveri, D.M., Vidili, A., Pastorino, R., and Ferraiolo, G. "Wind Effects on Diffusion Flames

of Fires of High Source Momentum", J. Hazardous Materials, 22:85-100 (1989).

11. Kalghatgi, G.T., "The Visible Shape and Size of a Turbulent Hydrocarbon Jet Diffusion Flame

in a Cross-wind", Combustion and Flame, 52:91-106 (1983).

12.Apte, V.B., Green, A.R., and Kent, J.H. "Pool Fire Plume Flow in a Large-Scale Wind

Tunnel", Fire Safety Science - Proceedings of the Third International Symposium, 425-424

(1991).

13.Quintiere, J.Q. "Growth of Fire in Building Compartments", ASTM STP 614:131-167 (1976).

14. Quintiere, J.Q. "Fundamentals of Enclosure Fire Zone Models", J. Fire Protection Engineering,

1:99-119 (1989).

15. Holen, J., Brostrom, M. and Magnussen, B.F. "Finite Difference Calculation of Pool Fires",

Twenty-Third Symposium (International) on Combustion, The Combustion Institute, p. 1677-

1683 (1990).

16. Kumar, S., Gupta, A.K. and Cox, G. "Effects of Thermal Radiation on the Fluid Dynamics

of Compartment Fires", Fire Safety Science - Proceedings of the Third International

Symposium, p.345-354 (1991).

17.Standard Test Method for Heat and Visible Smoke Release Rates for Materials and Products

Using Oxygen (ASTM E1354), American Soc. for Testing and Materials, Philadelphia.

18. Standard Method for Determining Material Ignition and Flame Spread Properties (ASTM E

1321), American Soc. for Testing and Materials, Philadelphia.

19.Cleary, T.G. and Quintiere, J.G. "A Framework for Utilizing Fire Property Tests", Fire Safety

Science - Proceedings of the Third International Symposium, Elsevier, p. 647-656 (1991).

252
FIRE, SMOKE, AND TOXICITY RESEARCH WITH COMPOSITE PIPE

A HISTORY OF PAST AND PROPOSED FUTURE WORK

BY SPECIALTY PLASTICS, INC., LOUISIANA STATE UNIVERSITY, AND THE U.S. NAVY

Kevin Schmit, Project Engineer

Specialty Plastics, Inc. 15915 Perkins Road

Baton Rouge, LA 70810

Introduction

Composite pipe has many unique characteristics that distinguish itself from conventional metallic materials

and even other plastics. Characteristics such as lightweight, high strength to weight ratio, corrosion resistance,

and flexibility all define the products in the composite pipe industry. These unique traits, however, can prove

to be a hindrance in the design of composite pipe systems if not properly understood. One characteristic of

composite pipe that must be investigated in certain applications is the product's fire characteristics and its smoke and toxicity emissions. This is critical in the design of active fire protection systems. Composite pipe,

when properly designed, can have advantages in fire water systems for marine applications over carbon steel,

copper nickel, stainless steel, and other exotic alloys.

Louisiana State University' and Specialty Plastics, Inc. ofBaton Rouge, LA have had extensive experience with

the United States Navy in developing advanced composite piping systems characterized by exceptional fire, smoke, and toxicity properties for shipboard applications, and, in general, marine applications. Research work

completed to date has included laboratory, bench scale experiments for screening purposes on various resin

systems, toxic emissions testing on phenolic, epoxy, and elastomer-modified vinyl ester resins, and bench-scale

fire testing on pipe samples. Proposed future work in the area includes standardized testing on advanced

composite piping systems both with and without passive fire protection and pilot scale testing of complete

advanced composite piping systems, including pipe, fittings, and joints. The goal in these tests are to determine the survivability and performance integrity of the advanced composite pipe system when exposed

to possible fire hazard conditions.

Fire, Smoke, and Toxicity Research with Advanced Composites

Fire testing has had an extensive history with fiberglass reinforced plastic products. To rehably substitute

composite pipe in fire safety applications where ferrous alloys have long dominated, extensive testing and

experimentation must be performed. This ensures a properly designed product adequate for its environment.

One such example ofthe research performed in this area by Louisiana State University and Specialty Plastics, Inc is a research project entitled "Composite Piping Systems - Phase II." This project was completed under

253
. :.,..;/' . MK) Phase II grant for the United States Navy. The principal

investigators on the project were Specialty Plastics, Inc. and Louisiana State University of Baton Rouge, LA.

However, companies from Acoustic Emissions, Inc. in Conroe, TX to Woodside Offshore, Ltd. in Perth,

•vY.--.'ii;\ 'j'i-.t '-ripz bid in the research .activities. The goal in this project, in the area of fire resistance and

smoke toxicity, was to provide experimental data on fire and smoke for advanced composite pipe. From this,

the resin matrix and reinforcement that performed best in the fire, smoke, and toxicity categories were

identified and recommended for further study.

Several screening tests were performed under this research project. This included smoke emissions tests, mass

loss tests, and toxicity tests. A schematic of the laboratory-scale smoke test chamber used in the screening

SMOKE-FREE FLOW

HOSE TO VACUUM FAN

AIR FLOW METER

TIMER

GAS FLOW CONTROL

m

llllil

— FILTER PAPER

SMOKE AND

COMBUSTION

PRODUCTS FLOW

SMOKE CHAMBER

'DOOR

VACUUM CONTROL

SAMPLE

FLAME

BURNER

rnwmm

MOUNT

X

DOOR

FLOOR PLATE

SECTION A-A

Figure 1. A bench scale smoke test chamber was used to measure the smoke and toxicity characteristics of

various resins.

254
#1 Mil-Spec #2 Mil-Spec Epoxy #1 Epoxy #2

Epoxy #3

Epoxy #4

Epoxy #5

Epoxy #6

Epoxy #7

Epoxy #8 M

Epoxy #9

Epoxy #10 S Fire Retardant Vinyl Ester #1

to Fire Retardant Vinyl Ester #2 £ Fire Retardant Vinyl Ester #3 £ Fire Retardant Vinyl Ester #4

Flexible Vinyl Ester #1

Flexible Vinyl Ester #2

Flexible Vinyl Ester #3

Furan

Isophihalic Polyester #1

Isophihalic Polyester #2

Phenolic - 10% Glass Filled Phenolic - 40% Glass Filled Phenolic - 84% Glass Filed Urathane Vinyl Ester

Vinyl Ester with Reactive Elastomer

.0001 .001 .01 .1 1 MASS (GR)

Error bars give the upper bound for the 95% confidence interval of the mean of each class of resin -< Pipe resin selected for additional study

figure 2. A comparison of the smoke and char mass produced from various resin exposed to flame.

tests is shown in Figure 1. Again, this setup was designed for comparison purposes. Thus, the

experimentation needed only to be scientifically reproducible; it did not have to follow existing standards.

The pipe samples (a total of 27 were tested) were burnt using a propane source in an ArapohoeTM smoke

chamber for 30 seconds. Weight measurements of the filter paper, sample, and decharred sample were taken

after completion of the test. Typical results for this screening test are provided in Figure 2. From the tests

it is evident that the phenolic resins are superior to all others in terms of the smoke mass and char mass

produced. The elastomer modified epoxy vinyl ester resin also showed excellent results in both categories.

Although this resin does not perform nearly as well in the fire category as the phenolics, it has exceptional

mechanical and impact properties which the phenolics lack.

Toxicity tests were also performed for screening purposes. The best performers in the smoke test category were further tested in this area for CO, C02

, and HCN.

Bench scale testing went even further with a laboratory-scale fire test rig. This laboratory level experiment

exposed a full-scale pipe sample to fire conditions for a fixed period of time at a fixed temperature curve. Refer to Figure 3. This particular dual wall pipe sample, composed of a vinyl ester resin matrix inner pipe, a polyphosphazene fire retardant foam, and a phenolic resin matrix outer pipe withstood a fire test at 1 1 00°C

for one full hour in the dry condition. Typical results from this bench scale test are shown in Figure 4.

255
Crossection A-A

Burner and

Flame

Fire Resistant Foam

Outer Pipe

Flame

Meeker

Burner

TC# = Thermocouple number

9 = Thermocouple location

*** Drawing is not to scale

r igure 3. A laboratory-scale fire test rig was used to test various passive fire protection systems for pipe.

Future Work on Fire, Smoke, and Toxicity with Advanced Composites

As stated in its original goals, the research work performed for the United States Navy under the SBIR grant

provided only screening results of a few basic materials with the intention of identifying the best materials

for further research. Thus, it did not go far enough to prove the acceptability of composite pipe in specific

fire applications.

A proposal for a much more expanded series of experimentation on fire characteristics has been presented to the United States Navy by Specialty Plastics, Inc. and Louisiana State University in the form of a separate

256
SBIR grant. The goals, in the fire category, are to evaluate the fire performance properties of advanced

composite pipe systems by performing tests in accordance with ASTM E662 and El 62 in addition to pilot- scale fire tests on entire piping systems, including pipe, fittings, and joints.

The proposed pilot-scale furnace is shown in Figure 5. This project, which is a joint venture of industry, the

university, and the United States Navy, has been designed to test entire pipe systems and follows the

guidelines set by the ASTM F25. 13.03 Fire Subgroup and the newly proposed ASTM Fl 173 standard.

In the proposal, this facility is to be operated by the Mechanical Engineering Department of Louisiana State University in concert with Specialty Plastics, Inc. at the Fireman's Training Facility near the LSU campus in

Baton Rouge, LA. The facility's greatest advantages are its flexibility in design and its mobility. The pilottest rig will have a removable burner system to simulate various fire conditions, will allow pipe, fittings, and

joints to be tested, and will be transportable to and from test sites, if necessary. Activity at the test rig will

included tests for the U.S. Navy for screening purposes and material selection for ship-board applications,

standardized tests for industry participants for screening purposes for offshore and, in genera, marine

applications, and research activity for the university.

Benefits of the Proposed Future Work

As stated above, the benefits of the proposed research work in the fire and safety area will benefit all of the

participants in the activity. The United States Navy will be able to test piping systems to screen possible

candidates for further large-scale tests. The facility will also allow the Navy to compare materials for possible

257
STACK

PRESSURE

RELIEF

PIPE

SUPPORT

REFRACTORY

/ LINING

1 m

1.3 m SIEVERT

BURNERS

J3- PRESSURE

SUPPLY

Pressure (NI

TMG

fR

N °R

GAGE ;

OVERALL SCHEMATIC

-1.5 m± 0.1 m0.8 m ±0.05 m

A At- I

I \ I PIPRESSURE

12.5 cm ±0.1 cm GAGE

Burner

Cross

Section

PRIMARY DIMENSIONS

Figure 5. The proposed fire test rig at the LSU Composite Fire Test facility.

use in fire applications for on-board ships.

The industrial partners in the research activity will be able to test their own piping systems for their specific

applications to screen composite material systems. The industry participants will also be able to use the

facility to test systems according to standards, such as the proposed ASTM Fl 173 standard. Various piping

systems, such as dual wall systems, insulated pipe, and fire-retardant resin based systems can be tested. These

passive fire-retardant systems can be compared with unprotected systems for selection of the optimal design

for future large-scale testing, if so required.

The university will benefit from the program by participating in research activity. This activity will be for

both the U.S. Navy and the industry participants. Corporations can provide grants to the university for specific use at the fire test rig and requires the support of the university in the research and development of advanced

composite material systems for fire applications. Likewise, the United States Navy, through the SBIR

program, can consult the university for assistance in its research with advanced composites.

Summary

While the research completed in 1991 under the Phase II program achieved many goals in evaluating the fire

258
characteristics of advanced composite piping systems for marine applications, there is a great need for

additional research and development to be performed to further investigate the advantages of advanced

composite piping systems for fire applications in the marine industry. The proposal for further research and

development under the Phase III program continues the progress made in Phase II. Furthermore, the proposed

pilot-scale fire test facility provides a hub of research activity that benefits all of the participants, the U.S.

Navy, industry, and the university.

References

1. American Petroleum Institute, API Recommended Practice 14G, Third Edition, 1993.

2. Ashland Chemical, "Hetron® and AropolTM Resin Selection Guide for Corrosion Resistant FRP

Applications," Bulletin 2026-1, Copyright 1993.

3. DOW Plastics, "Derakane Epoxy Vinyl Ester Resins Chemical Resistance and Engineering Guide," Form

296-00320-1 092X SMG, October 1992.'

4. Pang, Su-Seng, Ph.D. and Lea, Richard H., "Composite Pipe Systems - Phase II," Final Report, 1991.

5. Putnam, D.R. and Wilhelmi, G.F., "Analysis of Shipboard Application Limits of Glass-Reinforced Epoxy

Resin Piping Material Based on Emergency Fire Conditions," Commander, Navy Sea Systems Command,

Washington, D.C. 20362

259
260
TWENTY YEAR HISTORY OF SUCCESSFUL APPLICATIONS

OF COMPOSITE PIPE IN SEA WATER SERVICE

R. H. "Dick" Lea and Kevin Schmit

Specialty Plastics. Inc. 15915 Perkins Road

Baton Rouge, Louisiana 70810

Introduction

Since the 1950's composite pipe has been considered a viable alternative to carbon steel, stainless steel and

copper nickel pipe in sea water applications. The most obvious benefits of utilizing composite pipe for

offshore applications is its excellent corrosion and erosion resistance as well as its attractive cost. Case

histories exceeding twenty years have been reported in the Gulf of Mexico. A typical example is a water

flood system installed by Exxon in Block 16 in 1970. In U. S. Navy tests conducted in the early 1980's, the

erosion, chemical, abrasion and fouling characteristics of composite pipe were shown to be superior to coppernickel pipe. The American Petroleum Institute (API), The American Society for Testing and Materials

(ASTM), The International Maritime Organization (IMO), and The Norwegian Petroleum Directorate (NPD),

in addition to groups such as the United Kingdom Offshore Operators Association (UKOOA), are all working

on standards and guidelines to provide adequate engineering documentation for the expanded use of composite

pipe systems. Innovative strategies for promoting University-Industry-Government Co-Beneficial Collaboration

are recommended.

Background

The Composite Pipe Industry grew out of a U. S. Government Research Grant issued during World War II to find a viable alternate to protected steel, stainless steel and other exotic materials which were in short

supply. The early applications included well casing and oil field gathering fines. Some of these installations

of over thirty years are still in use. Today, composite pipe can be designed to handle hot wet chlorine gas

at temperatures up to 250 °F (121 °C) in chemical process lines, down hole tubing to 4000 psi (275 Bar) for

marine applications, and chilled water in the world's largest office buildings for cooling systems.

In order to appreciate the design flexibility ofthese materials one must have a basic knowledge of composites.

In Dr. A. Brent Strong's book entitled, Fundamentals of Composites Manufacturing, he provides this definition

of a composite, "The combination of a reinforcement material (such as glass fiber) in a matrix or binder

material (such as resin)." This definition implies that the materials act in concert — that is, one helping the

other — hence the term, composite. The matrix (resin) in a fiberglass composite provides protection against

adverse environmental effects while the reinforcement (glass) provides the strength.

A standard in widespread use today that describes and classifies one type of composite pipe is ASTM D2996,

the Standard Specification for Filament-Wound "Fiberglass" Pipe. This specification covers machine-made

(by the filament winding process) reinforced thermosetting resin pipe (RTRP) only, however, it does not

address the fittings or joining methods. In spite of this, it is a good standard to assist the user in

understanding composite pipe. It describes the filament winding process to manufacture tubular goods by

261
FILAMENT WINDING MANUFACTURING PROCESS

Rotating Mandrel

Resin Bath

Continuous Filament Spools

1. Fibers are pulled at a controlled speed to maximize

saturation with the resin.

2. Fibers are pulled under controlled tension tor proper

weight ratio and to eliminate imperfections.

3. Fibers are placed at the proper winding angle for optimized strength.

4. Fibers are wound at plus/minus degrees until one

complete closure is made. This is repeated until the proper thickness has been achieved.

Figure 1. The filament winding method is an automated process where numerical controls are sometimes

employed.

winding continuous fibrous glass strand roving or roving tape onto the outside of a mandrel in a predetermined

pattern under controlled tension. Refer to Figure 1.

The construction of these products is as follows. The liner is described as the inner portion of the wall

exposed to the fluid at least 0.005 in. (0.13mm) in thickness which does not contribute to the strength in the

determination of the hydrostatic design basis. It is the reinforced wall thickness, which is the total wall

thickness minus the liner and/or exterior coating thickness, which is used in the mechanical calculations. Refer

to Figure 2 for the basic construction of filament wound pipe . The user of composite pipe should be familiar

with this specification and understand its contents and limitations, prior to designing or specifying a composite

pipe system.

Erosion, Chemical, and Fouling Characteristics

In one erosion investigation reported by the Navy, three 2-inch diameter flange piping assemblies,

incorporating pipe, elbows, and tees were located upstream and downstream of throttling globe valves in the

wide open position. One assembly included both 90/10 and 70/30 copper-nickel spools to serve as a baseline

for comparison. Assemblies Number 1 and 2 were operated at 11 and 17 ft/sec respectively for twelve

months. Assembly Number 3 was operated at 25 ft/sec for three months.

Seawater temperature, dissolved oxygen content, ph, salinity, and average velocity were monitored during the

exposure periods. After one year of operation, final inspection showed no signs of erosion or any other

damage to the inside of the composite pipe test spools. The 90/10 and 70/30 copper-nickel test spools,

however, showed definite signs of progressive erosion damage. Assembly Number 3 which operated with

composite pipe at 25 ft/sec also showed no signs of any damage after a 3-month exposure period.

262
FILAMENT WOUND PIPE

Erterlor Corrosion Barrier

Structural Cog*

Secondary Corrosion Barrlsr Primary Corrosion Barrier Mandrsl (Mylar coated)

Veil with g*l coot and UV protection

Filament Winding (0.06 in. per closure)

PRIMARY CORROSION BARRIER

10-20 mils (0.01-0.02 In.) thick 10% glass reinforcement (by weight) C-Vell or Synthetic veil

SECONDARY CORROSION BARRIER

0-90 mils (0.00 - 0.09 In.) thick Special liners up to 480 mils 25X gloss reinforcement (by weight) 0.75 or 1.5 oz Chopped Strand Mot

Chopped Strand Mat (0.045 In. per ply)

Veil (0.01 In. per ply)

STRUCTURAL CAGE

1/16" - 1" thick Speclol designs exceed 1" thickness 50-70% glass reinforcement (by weight) Continuous gloss roving

EXTERIOR CORROSION BARRIER

10-20 mils (0.01-0.02 In.) thick 10% gloss reinforcement (by weight) C-Vell or Synthetic veil Can Include UV, gel coat, and/or pigment

Figure 2. Typical construction of filament wound pipe. Materials of construction and tolerances vary from

manufacturer to manufacturer.

263
Chemical resistance tests completed in accordance with ASTM C582 by various composite pipe manufacturers

and resin manufacturers conclude different grades of composite pipe can handle a wide range of chemicals.

Composite pipe is in services such as gasoline, jet fuel, chlorine, sodium hypochlorite, carbon dioxide, carbon

disulfide, fatty acids, hydrochloric acid, nitric acid, sodium hydroxide, sulfur chloride, sulfuric acid, and

naturally, sea water, desalination water, waste water, potable water, deionized water, demineralized water,

produced water and steam condensate. The designer of composite pipe systems should refer to current resin

manufacturer's standards or check with the individual manufacturer for specific recommendations.

Temperature resistance is limited to 250 °F (121 °C) in most chemical services. A good source for chemical

resistance is the Fiberglass Pipe Handbook published by The Composites Institute ofthe Society ofthe Plastics

Industry.

Marine fouling tests conducted as far back as 1950 by J. L. Basil for the U. S. Navy at Wrightsville Beach,

North Carolina showed that while composite pipe collected marine organisms in quiet seawater, after a 14-

month exposure the fouling that occurred was easily cleaned and there was no evidence of attack by marine

borers or other marine life. This is to be expected because marine fouling can occur on any non-protected

surface which will not leach a metal salt or other agents toxic to marine life. Most resins used in the

construction of composite pipe are considered inert to marine life, offering no food value and producing no

toxic effects.

Platform operators in the Gulf of Mexico have reported no fouling problems in 12-inch diameter seawater

circulating lines operating continuously for approximately five years at maximum velocities of 5 ft/sec. Fouling does occur, however, in lines that are shut down for one-month periods while heat exchangers are being cleaned.

In one of the longest continuous exposures of composite pipe to natural seawater, three fifteen foot sections

of 6-inch diameter pipe were installed in the seawater system at the Francis L. LaQue Corrosion Laboratory

in Wrightsville, Beach, North Carolina. These sections were removed for inspection in September 1976, after 17 years of service. Inspection revealed that although 1-inch of hard marine fouling had accumulated on the

inside diameter (as expected), the inside surface of the pipe was in excellent condition after the fouling was

removed. The three sections of pipe were returned to seawater service after cleaning.

If fouling in composite pipe is considered a problem and it is impossible to maintain water velocities above

2 ft/sec. continuous chlorination as low as 0.25 parts per million can completely eliminate all marine growth.

More recent tests completed this past summer in Fort Lauderdale, Florida at a Naval Surface Warfare Center

test site concluded composite pipe compared favorably with both titanium pipe and copper nickel pipe in

ultraviolet water treatment and ozonation tests. These tests were the result of reports of severe corrosion,

erosion, and marine growth blockage of copper nickel (90/10 and 70/30) seawater piping systems on board

U. S. Navy surface ships. The final report should be available by the Spring of 1994.

For those of you interested in the API investigation into materials suitable for sea water applications, we

suggest you obtain a copy of the current API 14G Document entitled, "Recommended Practice for Fire

Prevention and Control on Open Type Offshore Production Platforms". This document, available now,

provides a summary of the advantages and disadvantages of carbon steel pipe, stainless steel pipe, coppernickel pipe and composite pipe in fire water systems using sea water on offshore platforms.

264
Fire Endurance and Heat Transfer Characteristics

One area of concern regarding composite pipe systems is their characteristics under a sustained fire and/or

explosion. Of primary concern is the ability of the pipe to withstand the severe environment which would

be present under such a scenario. Obviously, the critical design parameter for fire water systems is for the

pipe to be able to deliver quench water to the fire until all personnel are evacuated or the fire is brought under

control.

Since many of the resins used in composite components are flammable, it is clear that most composite pipe

systems used in offshore applications may need to be insulated and protected from direct fire impingement.

Manufacturers ofcomposite components are actively involved in the design and development ofnew protective

coatings which range from simple intumescent coatings to advanced dual-wall configurations.

A distinct advantage of composite pipe, often overlooked, is their inherent resistance to heat transfer. Compared to metallic pipe, the thermal conductivity of composite pipe is substantially lower. This advantage

can be significant and should not be overlooked or underestimated as designers make greater use of composite

pipe.

To illustrate this qualitatively, consider the following example. Suppose a bare 102 mm (4 in.) pipe is exposed to a fire. Assume that the pipe has a 6.4 mm ( 0.25 in.) wall thickness and that the pipe is in the dry

condition (the most severe condition). For this example we will let the heat load vary from 0 to 1 kW/m2

. Given a heat load and the thermal conductivity of the pipe, one can readily estimate the temperature difference across the pipe using Fourier's Law of heat conduction:

- T^r = (Q/k) [rQ \n(rjr)]

where:

Q = the heat flux (W/m2) Tmur = the outer piPe skin temperature (°K)

dinner ~ &e mner VlVe s^n temperature (°K)

router ~ me 0llter piPe radius (in this case 57 mm or 2.25 in.)

1— £ao*Y

vinyl SlMl V Cjpp«r — Caneni*

' Magnnla

3 20 40 SO 10 100 1Z0

Plpa will Thi«n»ji (nun)

. 9. E2ect of Pipe Thickness for Diffsrenc Mattr-.ais at 500 W/m: Heat Load.

Figure 3. Comparison of different pipe materials under variable heat loads.

265
rinner = the inner pipe radius (in this case 51 mm or 2 in.)

k = the thermal conductivity of the pipe (W/m-°K)

Results of this simple analysis for a number of pipe materials are shown in Fig. 3. In the figure, the

temperature differences between the outer and inner pipe skin (Touter - Tirmer) are compared over the range of

heat loads shown.

The purpose of Fig. 3 is not to provide absolute data; rather, the graph is meant only for comparative

purposes. Note, the smaller the temperature difference, the better the heat conductor. Copper, with a very

high thermal conductivity and low resistance to heat transfer, would experience essentially no temperature

difference across the pipe under a 1 kW/m2 (317 Btu/ft

2 -hr) heat load. Under the same load a carbon steel pipe would experience a 0.1 °K temperature difference.

On the other hand, a composite pipe system with an epoxy vinyl ester resin would experience a 75°K

difference while the pure epoxy resin system would exhibit a 20°K difference. For comparative purposes, two

insulators are given (concrete at 9°K and magnesia at 100°K). Magnesia is considered a very good insulating

material. According to Fig. 3, the composite pipe systems chosen would exhibit heat transfer characteristics

bracketed by two good insulators, concrete and magnesia.

Economic Characteristics

There have been numerous studies completed within the past ten years on this subject. A report issued in

April, 1987 by the Naval Surface Warfare Center in Annapolis, Maryland stated, "Composite Pipe ranks as the lightest and the least expensive corrosion resistant piping material that can be used in the marine industry."

(Conroy, 1987). The current API 14G document states, "The use of fiberglass pipe has the advantages (over

carbon steel, stainless steel and copper nickel pipe) of corrosion resistance, lighter weight, lower cost, and ease of installation." Each composite pipe manufacturer can furnish prices for estimating if cost studies are not

currently available within your own company.

Naturally, when discussing composite pipe systems, there is a wide range of prices available to the customer

depending on his needs. Composite pipe comes in various resin systems, liner thicknesses, wall thicknesses,

and joint designs. Flexibility to design composite pipe systems to meet specific or individual piping

requirements remains one of the greatest advantages of composite pipe over alloys. Each manufacturer of

composite pipe manufactures various "series" or "grades" of composite pipe to meet these specific needs. As

with Sch. 5, Sch. 10 or Sch. 40 carbon steel or 304 vs 316 stainless steel or 90/10 vs 70/30 copper nickel pipe,

prices vary based on a wide range of variables.

Future Work Proposed by the U.S. Navy in Cooperation with Louisiana State University

The U.S. Navy is interested in an additional series oftests to determine the fire endurance levels of composite

pipe in accordance with newly developed IMO Standards and the proposed ASTM Fl 173 (Epoxy Resin

Fiberglass Pipe and Fittings to be Used for Marine Applications) standard currently being revised. Rather than

merely test pipe, the proposed facility will be unique since it will have the ability to perform fire tests on the

entire composite piping system, consisting of pipe, fittings and joints. The facility will test composite piping

systems bare and with protective coatings/jackets. The results of this research effort will provide future

266
designers optimum characteristics for efficient use of materials.

The manner in which the facility is designed will allow Louisiana State University scientists to test under a

variety of fire conditions benefiting the U.S. Navy, who is a primary sponsor, the industry participants, and

the university. Both the Navy and industry partners will be able to use the facility for screening tests on entire

composite pipe systems and to perform tests according to fire standards to evaluate promising composite

materials. The university will be able to use the facility as a research hub performing research and

development in the advanced composites field.

The estimated cost for such a facility is $100,000, of which $50,000 is expected from U. S. Navy funding.

A special Foundation Account has been established at Louisiana State University. Conoco and Mobil Oil have

already contributed to the support of such a project. This is a typical example of the "Innovative Strategies

for Promoting University-Industiy-Government Co-Beneficial Collaboration" that will be needed to keep the

American industrial base strong and competitive in the future.

Summary

Composite Pipe, even though around since the 1950's and with over one billion lineal feet of composite pipe

in service in the United States alone, is finally becoming the "system of choice" in the offshore oil and gas

industry as well as the petro-chemical industry all over the world. In addition to many of the raw materials

being products of the american petro-chemical industry, with companies such as Amoco, Shell, Conoco and

Mobil being major resin producers along with many others, these materials offer:

Exceptional corrosion resistance where temperatures are under 250F (121C)

Low installed cost (no hot work permits required), minimum maintenance (no repainting cost),

low life cycle cost with over twenty (20) years case histories in sea water service

Excellent hydraulic characteristics (C Factor = 150), with resistance to erosion and fouling

Lightweight (six-inch composite pipe weighs approximately four (4) pounds per foot vs twenty (20) pounds per foot for Sch. 40 carbon steel pipe)

High strength to weight ratios

Flexibility of design to meet customer needs

In 1990, the Department of Defense Critical Technologies Plan classified composite materials as a critical technology. The U. S. Congress has provided funding to several federal agencies to foster development of

the United States' capabilities in composite manufacturing processes to benefit the Department of Defense and

maintenance of the United States defense industrial base.

References

(1) American Petroleum Institute, API Recommended Practice RP 14G, Third Edition, 1993.

267
(2) American Society for Testing and Materials, ASTM D2996-88, Standard Specification for FilamentWound "Fiberglass" Pipe, 1988.

(3) Conroy, D., "Glass Reinforced Plastic (GRP) Piping For Naval Shipboard Applications," U. S. Navy

Report, David Taylor Research Center (1987).

(4) Cundy, V. A., Griffin, S. A., Lea, R. H., and Pang, S. S., "Use of Advanced Composite Pipe

Technology to Design Seawater Systems on Open Type Offshore Production Platforms," Proc. 1993

OMAE - Volume III-A. Materials Engineering. ASME (1993).

(5) Houghton, C. J., "An Engineering Documentation Scheme for GRP in the Oil Industry," Phillips

Petroleum Company United Kingdom Ltd., England, March (1993).

(6) Lea, R. H., Montgomery, V. T., and Pang, S. S., "Innovative Strategies for Promoting UniversityIndustrial Co-Beneficial Collaboration," Proc. ASEE Gulf-Southwest Section Meeting. Austin, Texas,

April 1 - 2 (1993) .

(7) Society of the Plastics Industry, Fiberglass Pipe Handbook. SPI, Second Edition, 1992.

(8) Strong, A. B., Fundamentals of Composites Manufacturing: Materials. Methods, and Applications. Society of Manufacturing Engineers (1989).

268
ADVANCED COMPOSITES FOR THE OFFSHORE INDUSTRY:

APPLICATIONS AND CHALLENGES

Mamdouh M. Salama

Conoco Inc. P. O. Box 1267

Ponca City, OK 76402-1267

ABSTRACT

Innovations and technological advances are essential to the success of the offshore industry in meeting

the challenge of continuing its effort to exploit natural resources in deeper waters. Although the

traditional engineering material for offshore structural applications is steel, other materials such as composites are now being seriously considered for several critical applications. The primary motives for using composites are to improve efficiency and reliability, and to reduce life cycle cost. In addition to the current use of composites for vessels, tanks, low pressure piping, cable tray, grating, and fire and

blast walls, there are several other applications that are currently under development. These applications

include production and drilling risers, riser stress joints, riser tensioners, TLP tendons, drill pipes, high

pressure coiled tubing and spoolable flowlines and reinforcement for flexible pipes. However, efficient exploitation of composite materials to satisfy economic or performance requirements is most likely to be

successful if an integrated approach is developed to address the currently existing technical, financial and

emotional barriers. This paper reviews some critical applications of composites for deepwater

developments and identifies the current barriers that must be eliminated to ensure the success of these

applications. The paper also presents an approach to eliminate these barriers.

INTRODUCTION

The oil industry is continuing its effort to exploit oil and gas reservoirs in deeper waters (> 1500 ft). Exploration in water depths of 7000 feet (2134 meters) was performed, and Shell's Augur Tension Leg

Platform (TLP) was recently installed in 2860 feet (782 meters) in the Gulf of Mexico. In addition,

designs for 4000 ft are currently in progress for potential developments in the North Sea and west Africa.

Figure 1 provides historical and projected water depth for exploration and production activities. A single

deepwater project can easily be a multi-billion dollar capital investment, and the new technology needed

to extend current capabilities to the deeper waters of new license areas may lead to expenditures for the

novel subsystems measured in hundreds of millions of dollars. New technologies are required to enable

the industry to proceed with a significant number of such new projects, particularly under the pressure

of low oil prices. Therefore, serious effort was devoted toward the evaluation and the application of

innovative approaches to reduce capital and operating costs. Part of that effort involved the use of

innovative and cost competitive materials that can improve performance and reduce maintenance costs while increasing reliability, improving safety and providing enabling capabilities beyond those achieved

with currently used materials. Advanced polymeric composite materials offer the potential of achieving

these goals. The efficient exploitation of composite material is, however, only possible if materials,

structural and manufacturing technologies are utilized in an integrated approach. This will ensure greater

design flexibility and promotes system oriented solutions.

Composite materials have been receiving much attention in the offshore industry as demonstrated by the

many special meetings and workshops held in the U.S., Norway and UK. This interest is motivated by

composites light weight, corrosion resistance and excellent fatigue performance. In addition, composites

269
offer a unique advantage because they provide the flexibility for engineering the materials properties to meet the design requirements. Composites can be tailored to achieve specific mechanical properties such

as high axial strength and stiffness, or high circumferencial strength and low axial stiffness. They also can be tailored to achieve specific thermal properties such as low thermal conductivity and low coefficient

of thermal expansion. In order to ensure the successful implementation and commercialization of

advanced composites, development programs must involve the key companies from each element of the

supply chain and from engineering contractors and regulatory agencies. The development program must

draw on the vast knowledge of the defence and aerospace companies and should include serious economic

analysis at key junctures to ensure that the results are truly aligned with the strategic needs of deepwater

development.

This paper reviews current and potential applications of advanced composites in the offshore industry.

The paper also identifies and presents ways to eliminate barriers that limit the acceptance of advanced

composites for critical applications in deepwater developments.

APPLICATION OF ADVANCED COMPOSITES

So far, the main emphasis of potential applications of advanced composites for the offshore industry is focused on high pressure tubular barrier (above 1000 psi pressure) which are either discrete (20 to 80 feet length) for use as drilling and production risers, choke and kill lines, pipes, tubing and casing, or continuous (many thousands of feet long) for use as coiled tubing and flowlines. For the continuous case, the pipes are of relatively small diameters (< 5 inch) and, therefore, can be spooled. These spoolable

composite pipes have been proposed for use as coiled tubing, and subsea flow and control lines. High

pressure composite coiled tubing (Sas-Jaworsky and Williams, 1994) is currently attracting major attention

because it provides enabling capabilities to workover, logging and completion of highly deviated wells.

The proposed coiled tubing is constructed of a hybrid composite of glass or aramid and carbon fibers. In addition to conventional composite pipes, several companies such as Wellstream and Coflexip are evaluating the application of composites instead of steel for axial and hoop stress reinforcements for

deepwater flexible pipes (Figure 2) to reduce weight which will significantly reduce deck and installation

loads. The hoop stress is carried by circumferentially wound flat strips of thermoplastic fiber glass

composites and both axial and hoop loads are carried out by composite wires formed into helixes.

There are other applications, that do not fall under the high pressure tubular classification such as TLP

tendons that use a strand assembled of many continuous small diameter carbon fiber rods or laminate

construction containing carbon fiber rods. The use of composite rods by the oil industry is not new.

Fiberglass sucker rods with metallic end fittings have been in service for more than 15 years. Amoco has

developed and used spoolable sucker rods in the form of uniaxial carbon fiber composite ribbon (Lea and

Winkler, 1994). Composite sucker rods are used because of their light weight and high fatigue and

corrosion resistance. There are many other applications, which are not unique to the offshore industry,

where primarily fiberglass composites are currently being used on offshore platforms. These include

storage tanks, vessels, low pressure pipes, torque shafts, structural parts, seals, grating, fire and blast walls, cable trays, etc. The motives are lower weight, less maintenance and reduced installation costs. As an example, composite cable trays can save 150 to 250 tons of weight on an offshore platform

(Chang, 1993).

In this section, the discussion will focus on three applications that are selected because they can be

characterized as advanced composites and because they have the highest potential in providing enabling

capabilities and in achieving major cost saving to deepwater developments. The tension leg platform

(TLP) concept (Figure 3) is the most likely concept to be used for developing large deepwater reserves. The TLP is a buoyant platform connected to the sea bed by vertical mooring lines called tendons, tethers

270
or tension legs. An excess buoyancy over weight assures that the tendons remain in tension for all weather and loading conditions. The platform's mooring permits large motions of surge, sway and yaw

under the effect of wind, wave and current, while remaining stiff in heave, pitch and roll. The primary

advantage of the TLP concept over other floating production concepts is allowing the well systems to be

tied back to the TLP's deck similar to conventional platforms, with the main control valving (Christmas

Tree) at the deck level. This provides maximum safe access to the wells for monitoring and remedial

work. Currently, there are four TLPs in operation (Conoco's Hutton and Jolliet, Saga's Snorre and

Shell's Auger), a fifth being fabricated for installation in 1995 (Conoco's Heidrun) and a sixth in the

design stage for installation in 1996 (Shell's Mars). Shell's Augur TLP was installed in 2860 ft (872 m)

water depth and Mars will be installed in 2930 ft (893 m)in the Gulf of Mexico. Table 1 provides the

principal technical data for Conoco's TLPs. The three key TLP systems that are most affected by an

increase in the water depth and, therefore, will be considered in this report are the tendons, production

risers and drilling risers. TENDONS

Tendons are impacted by not only the need for more length but more importantly by the effect of

increased length on the platform heave and pitch natural period. It is the current design practice to limit

these periods to less than 4 seconds to avoid resonance which is known to increase fatigue loading and

may also increase the extreme load. Although this limitation can greatly affect the cost of the carbon

fiber composite tendon system for which higher fatigue loads may not constitute a problem because of

its superior fatigue resistance, the natural period limit is still imposed because the increased load will

affect both the foundation and the connections to the hull. In addition, the current state of the art of

hydrodynamic analysis does not allow sufficient confidence in load predictions when the natural periods

are increased. Discussions on this issue and how it affects the design of the composite tendons are presented by Salama (1984). The required section modulus (EA) of a single TLP tendon can be estimated

as follows (Salama, 1984):

£A = 4 LjW + 0.4 D) (1)

8 n T

2

Where:

E = Elastic modulus of tendon materials, psi

A = Cross section of a single tendon, in2 L = Tendon length, ft W =: Platform weight, lb D = Platform displacement, lb g = gravitational constant, 32.2 ft/sec

2 n = Number of tendons

T = Heave natural period, sec

An attractive composite tendon solution that has been evaluated is based on the use of a strand constructed

from 3 to 5 mm continuous carbon fiber rods as shown in Figure 4. The strand can be terminated,

similar to a steel bridge strand, using potted terminations. Other termination concepts such as a loop type can also be considered. The strand is very light weight with a density of 0.044 lb/in3 (1.22 g/cm3). The

results of static and fatigue properties of terminated 250 tonne 2 inch (54 mm) diameter strand

demonstrated outstanding properties (Walton and Yeung, 1987; Yeung and Parker, 1987; Salama, 1988).

Table 2 presents a comparison between fatigue performance of the carbon fiber strand and a carbon steel

271
welded tendon. In order to achieve the 4 second design criterion for a Heidrun type concrete TLP in 4400 feet in the North Sea, the required tendon stiffness per corner is about 300 MN/m. Under these

condition the maximum stresses in the tendon will be about 20% of the tendon strength if fabricated using

P-55 (55 x 106 psi modulus) carbon fibers. The utilization if P-120 (120 x 106 psi modulus) carbon fibers are used is about 35% . A P-55 carbon fiber composite tendon will have a mass of about 14,000 mT (@

30 x 106 lb). The weight of the fiber alone exceeds 8000 tonnes (@ 18 x 106 lb). The cost of this tendon

system will exceed 1/2 billion dollars. These numbers demonstrate that there is sufficient business

incentive for both fiber and composite manufacturers to support the development of the composite tendon

system. This is in addition to the other potential applications for high stiffness composite strands such

as suspension bridges, floating islands to support military operations and subsea suspension tunnels.

There is also a major thrust by several companies to develop low cost high modulus pitch based carbon

fiber (60 to 100 msi). Success of these development will result in an improvement of the strain to failure

of these fibers and in bringing their cost down to the range of $10 to $20 per pound. The use of these

fibers will allow fabrication of rods that have an elastic modulus much higher than steel. Also, the use of low cost short (few inches long) pitch carbon fibers instead of continuous fibers may result in major

reduction in the tendon cost by about 50% without impacting its size and weight. Note that if this system

is made of steel the mass of the tendon system will be more than 80,000 tonnes and more than 16 tendons

per corner will be required, which may not be practical.

As discussed above, steel tendons may not be technically and/or commercially feasible for large TLPs

in deepwater. Even in cases when a steel tendon is feasible, i.e. for small TLPs, the total cost of a composite mooring system can be lower than a steel system and more reliable. The three key components

of the cost of a TLP mooring system are the cost of tendons, cost for connections to hull/foundation (e.g. flex joints, top and bottom connectors, tension and inspection monitoring systems), and cost of

installation. The costs of the tendons and installation are the most affected by increased water depth.

Table 2 provides a comparison of materials and installation costs for both steel and composite tendon for

a small TLP in 4000 feet in the Gulf of Mexico. The cost of the carbon fiber strand is very competitive

with steel tendons. For a 350,000-lb strand, the cost is 500 to 700 $/ft compared to a steel tendon of

the same capacity of about 300 to 400 $/ft. The weight of the strand in air is 6.6 lb/ft compared to 200

lb/ft for steel. The strand diameter is about 4 inches while the steel pipe will be much larger depending on the buoyancy requirement. It needs to be noted that beyond 2500 ft water depth the use of a neutrally

buoyant steel tendon is not feasible because of collapse considerations and, therefore, the weight of the

tendon becomes an important parameter. Because of the smaller size and weight of the composite

tendons, their installation cost will be lower than steel tendons. Installation of composite tendons is feasible using both reeling and towing methods. It is estimated that the installation cost of a steel tendon

in 4000 ft of water is in the range of $1000 to $1500/ft while the installation cost for composites is in the range of $500 to $1000/ft. In addition to lower installation cost, it is also feasible to reduce the cost of a tendon system by talcing advantage of the composite properties to simplify the top and bottom

assemblies and possibly eliminating the expensive flex joints.

In addition to the carbon fiber strand concept, there are other concepts that are attractive candidates for

TLP tendons and need to be evaluated. These include high modulus aramid ropes, carbon fiber laminates

and composite pipes. Composite pipes which can be fabricated using braided aramid or glass pipes that contain axial carbon fiber rods possess several attractive properties. This concept will be more costly

because it will require more fibers, but it offers the advantage of being neutrally buoyant which is a

desired property from both weight and installation view points. Installation cost can be very high and a configuration that reduces this cost is desirable. Neutrally buoyant tendons can be towed in one piece

and installed. Stranded type tendons can be either towed using flotation to achieve the required buoyancy

or reeled. The reeling approach may not, however, be feasible if large diameter tendons are required

because of the physical limits of the reel size.

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PRODUCTION RISERS

The second important TLP system for which composites represent an optimum solution for deepwater

is production risers. Composite risers can not only reduce the required pretension but they may also

allow the rigid connection of the riser to the platform, thus eliminating the expensive tensioners.

Composite production risers are probably the most mature of composite applications because they have

been the subject of several major studies within the last few years. Several major oil companies

sponsored a major development and evaluation study of a 9 5/8 inch composite production riser to prove

the concept. The study was done during the period of 1985 to 1989 by the Institute Francais du Petrole

(IFP) and Aerospatiale. The riser pipe (Figure 5) was fabricated of a hybrid of carbon fiber and S-glass

fibers. The pipe could withstand a combined pressure of 15,000 psi and an axial tension of 450 tonne. The pipe was also designed to withstand a collapse pressure of 5400 psi. The study included several

static, fatigue, multi-axial loading and damage assessment tests. Major portions of the results have been

published by IFP and Aerospatiale (Ordu and Guichard, 1986; Sparks, et. al, 1988 and 1992). As a follow-up to this study, Brunswick, Coflexip, IFP and aerospatiale engaged in a project to reduce the cost of the risers by optimizing the manufacturing process and the design. The design optimization included

simplifying the metallic threaded joint (Figure 6), using the lower cost E-glass instead of the S-glass, and

changing fiber lay to achieve zero thermal and pressure induced axial strains. Table 4 provides a comparison between steel and composite 9 5/8 inch production riser as currently proposed by Brunswick.

Although the cost of the composite riser is higher than steel, the total riser system cost will be lower due

to reduction in payload and tensioner costs by taking advantage of the several unique properties of

composites. These properties include low density, low axial stiffness, zero coefficient of thermal

expansion and infinite bulk modulus.

In addition to the production riser pipe, composites are being considered for other riser components such

as taper joints and tensioners. The riser taper joints provide a smooth transition between the flexible riser pipe and the relatively rigid subsea wellhead and thus prevent the overstressing of the riser itself. The

currently considered taper joints are fabricated of a hybrid of a steel or titanium riser pipe with a taper outer filament wind wrap of fiberglass and carbon fiber composite. The tensioners are used to compensate for the platform movement and keep the riser in tension under all loading conditions to prevent riser buckling. The tensioner is a non linear spring with high initial stiffness to generate the

required mean riser tension followed by a low stiffness to accommodate operating stoke without

increasing the riser tension. Currently, the tensioners used are short stoke hydropneumatic motion

compensators that are both complex and expensive. Several simpler composite alternatives are being

considered including a pipe section that achieves the non-linear behavior by designing the pipe to

elastically buckle after certain specified load. So far, none of these systems has been evaluated.

DRILLING RISERS

The third major TLP system that will be considered are the drilling risers. A drilling riser is similar to the production riser except that it has larger diameter (18 to 22 inches as compared to 9 to 11 inches for production risers) and it should be able to be run and retrieved within a reasonable time, i.e. it should

have a quick make-up and break-out connections. Also, the drilling riser is designed for shorter service

life, 15 years versus 30 years for the production riser. For deepwater TLPs, titanium instead of steel is considered the preferred material for drilling risers. The cost of a titanium drilling riser may exceed

$10,000/ft while the cost of a composite riser may be less than half that value. Therefore, several

companies including Westinghouse and Brunswick have demonstrated the feasibility and the cost benefit

advantage of composite drilling riser pipes and composite taper joints.

BARRIERS TO THE APPLICATION OF ADVANCED COMPOSITES

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There are three types of barrier that must be recognized to ensure the required acceptance and the

successful applications of advanced composites for the critical offshore applications. These barriers

involve technical, financial and emotional issues. While most of the efforts are focused on addressing

the technical and financial issues, the emotional issues are, generally, ignored. Emotional issues, while

very critical, are more difficult to resolve and, therefore, should be treated very seriously. Both the

technical and financial barriers are not unique to composites, they are applicable to any new material.

Eliminating these barriers will offer significant opportunities to leverage major benefits for the oil industry with high payoff of potential billions of dollars for the composite industry.

Technology Barriers

As with other materials, there are many factors that must be considered in materials selection of

composites. These factors include strength, stiffness, fatigue resistance, creep resistance, wear resistance,

defect tolerance, weight, inspectability, repairability, fire resistance, toxicity, environmental degradation

resistance, etc. With the current emphasis of the offshore industry on reliability based design, analytical

methodologies and sufficient data bases to allow proper risk assessment are important to meet regulatory

requirements for both design and manufacturing. The lack of these data is, however, not unique to composites and, therefore, should not serve as justification for not using composites. We only need to

reflect on how much money is spent and how many papers are published annually to address technical

issues concerning steel such as corrosion, fatigue and welding to conclude that lack of knowledge has never prevented engineers from using steel. But when an engineer trained in steel design and

construction attends a composite meeting where needs for further research are being identified, he may

mistakenly conclude that design and fabrication of composites are not mature enough for his application.

Therefore, the reader should not interpret the technical needs identified in this section as a must before

considering the application of composites, but rather as a requirement to improve the capability to optimize composites from reliability and cost view points.

Fortunately, major technical strides have been achieved through the application of composites for aerospace and military applications that can pave the way for the commercial marine applications.

Computer programs for detailed stress analysis are well developed. There is, however, a need for design

methodology and user friendly composite design software for material tailoring and for assessing

multiaxial failure and structural performance under transportation, installation and operational loads.

There is also a need to identify loads and requirements for storage, transportation and installation of

composite components.

There is a wealth of material performance data for composites. The marine environment may actually

be less demanding than current applications for composites. However, composites must be able to survive

20 to 40 years unattended, therefore, data and models to predict long term degradation are required.

Although composite components are used as blast and fire walls, there is a major misconception regarding

fire and impact resistance of composites. Since composites, unlike metals, allow the fire to be localized

and contained because of their low thermal conductivity, fire resistance test methods that are developed

for metals may be inapplicable for composites because composites will allow more time for the offshore

operators to tackle the fire and/or escape. Also, smoke and toxicity have been areas of concern in the

past but with advances in the resin technology and the expanded use of phenol ics, this issue should not be of major concern.

Fabrication technology for the simple geometries that are being considered by the offshore industry is relatively mature and requires little capital investment to increase production within a short time.

However, there is a need to develop high speed continuous processing technology that addresses

manufacturing processes (filament winding, pultrusion, braiding, resin transfer molding and hybrid) for

274
cost effective manufacturing. Manufacturing of composites utilizes many material forms including dry,

hybrid fibers, wet, prepreg tape, woven fabrics, preforms. Each of these forms has its own process

control requirements such as curing, fiber placement, compaction, consolidation.

Termination of composites remains an area of concern since batch process filament winding manufacturers

are limited in length to 30 to 75 ft and, therefore, requiring many connections which are always

considered as the weak link in the system if not properly designed. This may not be an issue for a

critical applications such as tendons because the strength utilization of the composite is low (@ 20%).

Therefore, efficient termination may not be required. Effective terminations for pressure containing

systems such as risers are well developed. The effort should be focused on optimization to achieve cost minimization.

Adequate technology and procedures for inspection and quality control are available. However, the

development of standard quality control manuals for these techniques is necessary to simplify procurement

and certifications. Since marine components are intended to be in continuous service for 20 to 40 years, developments in the area of in-service integrity monitoring using implanted sensors and fiber optics will

be valuable to eliminate the need for the expensive removal of the composite components for inspection.

Since the successful application of composites in the offshore industry can potentially result in the annual use of 100's of millions of pounds, environmental issues due to replacement and disposal need to be

seriously considered. This may impose some restrictions on materials selection to allow recycling.

Financial Barriers

Because of the high capital investment and the strict certification requirements, selection and

implementation of composites is only feasible when the pay-off value is judged to be greater than the cost

at an acceptable risk. Therefore, the current use of composites in the offshore industry is limited to applications where the risk is low and the savings are modest. These applications involve low pressure

fiberglass water handling pipes and vessels. The reliability of these systems have been clearly

demonstrated by many years of successful service in the petrochemical industry.

The breakthrough for composite applications will, however, be realized when large savings can be

achieved for high risk components. The large savings can be realized in terms of financial savings as

a result of the lower actual or life cycle cost of the composite system, or in terms of revenue generation

as a result of the enabling capability of composites, or in terms of both cost and revenue. Although the

cost of composite components can be lower than the cost of equivalent components made of a special

alloy such as titanium, it will be more than the cost of steel components. Therefore, it is critical to evaluate the application of composites in the context of system performance and functional requirement

and not in terms of individual components. Composites can simplify the total system by eliminating

expensive components and thus, the cost of the system will be lower even though the cost of the

composite component may be higher. Potential applications under this category include production and

drilling risers, TLP tendons and high pressure spoolable pipes (e.g. coiled tubing and flowlines). In addressing these applications, it is critical that composites technology be challenged beyond its current

state because advances continue to be made on structural concepts, and metal components are evolving.

Some of these changes may change the economic equation for composites as it is perceived today.

It must be realized that the financial incentive (cost and revenue) is necessary but not sufficient condition

to ensure the acceptance of advanced composites in the offshore industry. Two additional factors must

be considered. The first factor is the availability of production facilities to supply the required composite

components within the time frame of a project. The offshore usage of composites will involve large scale

275
orders which may be far higher than required by aerospace or military. For example, production risers for a single TLP for 4000 ft water depth may involve more 200,000 feet of 10 inch diameter pipes that require more than 2 millon pounds of carbon/fiberglass composites. Also, a single TLP may require more than 20 million pounds of high modulus fibers for its tendon system which may approach the current world annual production capacity of these fibers. The paradox is how can a project team commit

to the concept knowing that the production capacity is currently not available, or how can a manufacturer

justify the required investment to develop the necessary production capacity without being awarded a contract? The solution to this problem will require the development of a modular production facility

which allows rapid expansion and contraction of the production capacity at minimum cost.

The second factor is prototyping and development of sufficient performance data on full scale components

to ensure reliability and give confidence in the safe application of these materials. The cost of such an

effort for a single component will be several million dollars. Here lies another paradox: oil companies

are not willing to commit the financial resources to develop the required data unless the data will be used on a specific project which is under development. When the project is under development and funds are

available, it is practically impossible to consider composites because it would be too late to develop basic

data on time to be useful to the project. Although joint industry sponsored programs have been successful

in proving the concept of composite production risers, they were not able to attract sufficient participation

to generate the necessary funds to optimize both materials selection and manufacturing and to develop

the necessary data for commercial applications. There is a need for alliances and consortia because

resources are limited and no one company has the necessary skills to succeed. One approach to addressing

the challenge may lie in a joint sponsorship of these program by government and industry. Programs

such as the Advanced Technology Program (ATP) that is administered by the National Institute of

Standards and Technology offers hope to achieve these objectives. Resources from this program is currently being tapped by the University of Houston's Composite Engineering and Application Center

for Petroleum Exploration and Production to develop the required information.

Emotional Barriers

There are several factors that contribute to resistance to using composites for critical applications in the

offshore industry. These factors can be classified in five basic categories: change of culture, lack of

standards, lack of available resources, oil industries' short attention span regarding needs, and oil industries' minimal tolerance of failure.

The application of composites constitutes a change of culture to many engineers. Application of

composites places designers who are trained mainly in steel structures outside their comfort zone. It is important to overcome the "can't weld, do not want" mindset. To add to the complications, current design rules do not provide any guidance on use of composites and, therefore, a simple design criteria such as a safety factor becomes a major issue for the designer. This makes it more often easier to ignore

the benefits of composites than confronting the design procedure issues. In order to minimize the impact

of this barrier, focus should be placed on the few critical components where composites can make major

impact on the economics of offshore facilities and design codes for these components should be

developed. Developing the design code should be one of the highest priority items.

The perceived lack of standards to allow certification of composites is a major hindrance to composite

applications. The offshore industry follows strict guidelines that are being adopted or developed by

certifying authorities. The lack of guidelines make some certifying authorities reluctant to give approvals

for composite systems by imposing strict interpretation of standards and codes due to the lack of

understanding of the material. It must be recognized that not all regulatory bodies react to the application

of new materials the same way. Some are much stricter than others. Even in the absence of regulations,

276
the Norwegian Petroleum Directorate (NPD) has been very receptive to accepting innovations when cost efficiency and safety have been demonstrated. As an example, although the Norwegian codes clearly

restrict the use of non-metallics for safety systems, NPD was willing to waive the requirement and

approve Amoco's request for the use of fiberglass piping for the fire water system on the Valhall

platform. This approval was conditional on Amoco performing risk assessment analysis and fire survivability tests, and developing performance based specifications and quality control procedures for

manufacturing. Other regulatory bodies may insist that codes of practice and performance data be

developed before applications are approved. Therefore, it is very important to initiate early interaction

with the certifying authority to provide them with better understanding of composites and to identify the

type of date required to alleviate any concern that they may have.

There is a perceived lack of available resources to support the application of composites. Almost all marine design engineers lack training in design of composites. This should not be surprising since very

few universities have mandatory course requirement for design of composites for mechanical, civil and

marine engineers, while all schools have a mandatory course on steel design. This barrier can be easily

addressed if universities make a course on design of composites mandatory for all of its undergraduate

engineering disciplines.

The oil industry is reactive with short attention span regarding needs. This statement may be unfair

because this may not be unique to the oil industry and also because the oil industry is one of a few

industries that can not forecast the price of its product, because it has no control over the forces that influence the price of its commodity. Therefore, when prices are high, interest in deepwater and

technologies that support it is high. The interest diminishes when the price of oil falls. However, it is important to understand the reality that it is very difficult to sustain sufficient interest for long term

programs to optimize and qualify the design of composite components. Therefore, it is important to focus

the study on the few critical systems that can clearly demonstrate composites cost and reliability

advantages over conventional systems. Also, it is critical that an accurate definition of the performance

requirements for these systems be established and an optimum design be developed before implementing

any costly prototype and testing program.

The offshore industry is less tolerant of failure because of the resulting high financial and environmental

risks. In order to impact the deepwater developments, composites need to be used in highly critical components such as tendons and risers where failure of these components can be very expensive. A

failure of a tendon system may jeopardize a multi-billion dollar investment and a failure of a riser system

may result in major spill with its environmental and safety hazards. Therefore, it is imperative that the

system reliability be demonstrated to clearly show that a composite tendon or riser system is more reliable

than a steel system.

CONCLUSIONS

1. The technology currently exists to effectively apply composites for several critical deepwater

components such as TLP tendons and production and drilling risers.

2. In order to take full advantage of the tailoring and special properties of composites and therefore

optimize the cost of composite systems, it is necessary to develop a clear definition of system

functions and to avoid the temptation to use composites as substitutes for steel components and

thus subject them to the same constraints.

3. The current use of composites is limited not necessarily by technical and financial barriers but

rather by emotional barriers which must be clearly identified and addressed. These emotional

277
barriers include issues such as change of culture, lack of standards, lack of available resources, lack of long term commitment, and fear of failure.

4. Although composites provide enabling capability for deepwater development, their use will only

be justified on an economic basis. Therefore, economic benefits must be clearly demonstrated.

Recent studies have shown that the use of composites for tendons and risers will make it both

technically and financially feasible to extrapolate the water depth of existing TLP structures to two

to four times the water depth.

5. Although tendons, production and drilling risers constitute critical systems, emphasis should be

directed toward the optimization of the tendon system because it offers the most potential for

major saving. In comparison, the cost of a composite tendon system for 4000 ft TLP may exceed

$600MM, while the cost of fifty production risers may be less than $80MM and the cost of a composite drilling riser may be around $30MM. Also, while the concept of composite risers is well established, the concept of tendons represents an area where innovations can be made.

Tendons will also benefit greatly from advances in high modulus pitch based carbon fibers, high

modulus aramid fibers, thermoplastic resins and innovative manufacturing methods.

6. Since offshore applications will require large quantities of composites on an infrequent basis, it

is critical to develop a modular production facility to allow the rapid expansion and contraction

of production capacity at minimum cost. The impact of the fluctuation in demand may be reduced

if the lower cost of fibers and fabrication generates large new markets.

7. There is a need to establish a comprehensive program to develop the required data to quantify

component and system reliability and to establish certification guidelines. Since financial resources

are limited and no one company has the necessary skills to succeed in developing composites

systems, there is a need to form alliances and consortia.

278
REFERENCES

J. Chang (1993), "Applications of Advanced Composites", Presentation during the First Int. Workshop

on Composite Materials for Offshore Operations . University of Houston.

J. F. Lea and H. W. Winkler (1994), "What is New in Artificial Lift," World Oil . Vol. 214, No. 4, pp. 107-113.

P. Ordu and Guichard (1986), "Design and Tests of High Performance Composite Tubes for Use in Deepwater Drilling and Production Systems," Proc. of OMAE Specialty Symposium on Offshore and

Arctic Frontiers . M. M. Salama, ed., ASME, pp. 353-359.

M. M. Salama (1984), "Lightweight Materials for Mooring Lines of Deepwater Tension Leg Platform,"

Marine Technology. Vol. 21, No. 3, pp. 234-241.

M. M. Salama (1988), "Material for Mooring systems," Materials for Marine and Structures. Treatise

of Materials Science and Technology . Academic Press, Vol. 28, p. 411.

A. Sas-Jaworsky and J. G. Williams (1994), "Advanced Composites Enhance Coiled Tubing

Capabilities," World Oil . Vol. 214, No. 4, pp. 57-66.

C. Sparks, P. Odru, H. Bono, and G. Metivaud (1988), "Mechanical Testing of High Performance

Composite Tubes for TLP Production Risers," 20th Annual OTC Conference. Paper OTC 5797.

C. Sparks, P. Odru, G. Metivaud, and C. Le Floc'h (1992), "Composite Riser Tubes: Defect Tolerance

Assessment and Nondestructive Testing," 24th Annual OTC Conference. Paper OTC 6894.

J. J. Walton and Y. C. Yeung (1987), "Flexible Tension Members from Composite Material," Proc. of

6th Int. OMAE Symposium . (M. M. Salama, et. al, eds.) ASME, V. 3, pp. 7-14.

C. T. Yeung (1987), "Composite Tension Members for Structural Applications," Proceedings of the 4th

International Conference on Composite Structures . Paisley, pp. 1.309-1.320.

279
TABLE 1 PRINCIPAL TECHNICAL DATA FOR CONOCO'S TLPS

Project

Location

First Production

Hutton

UK, North Sea

1984

Jolliet Gulf of Mexico

1989

Heidrun

Norwegian N. Sea

1995

Water Depth 150 m 536 m 350 m

Recoverable Reserves (est.) 200 MMBO 40 MMBO 750 MMBO

Design Production Rate 100 MBOPD 35 MBOPD 200 MBOPD

Number of Wells slots 32 (10 pre-drilled) 20 (all pre-drilled) 58 (9 pre-drilled)

Total weight, Incl. risers 48,500 tonnes 12,150 tonnes 258,000 tonnes

Displacement at MWL 63,300 tonnes 16,600 tonnes 288,000 tonnes

Tendon Pretension at MWL 14,oUU tonnes 4,450 tonnes OA f\f\f\ *Anm,f JU,UUU tonnes

Pretension/Displacement 0.23 0.27 0.104

Tendons:

Number

Outside Diameter

Thickness

Min. Yield Strength

16

260 mm

92.5 mm

120 ksi

12

609 mm

20.6 mm

65 ksi

16

1118 mm

38 mm

70 ksi

Columns:

Number

Diameter

uoiumn centers

6

17.7 m (4

corners)

I'r.j m \£ centers,)

78 m (length)

74 m (breadth)

4

12.2 m

A74z. 7/ mm

4

30 m

ou m

Pontoon:

Height

Width

10.8 m

8.0 m

7.0 m

circular

13 m

16 m

Draft at MWL 33.2 m 24.1 m 77 m

Height, Keel to main deck 68.9 m 52.7 m 133 m (approx.)

280
TABLE 2

COMPARISON BETWEEN FATIGUE STRENGTH OF WELDED STEEL PIPE AND CARBON FIBER

STRAND WITH POTTED TERMINATION

Component Cyclic Stress, ksi Life, cycles

250 tonne (560,000 lb), 54 mm (2 inch) diameter

carbon fiber strand with potted termination,

(extrapolation: 5 inch rope has a 3,600,000 lb strength)

Max: 125

Min: 43

Range: 82

2,000,000 +

(No Failure)

X60 steel pipe, 24 inch (609 mm) O.D. and 0.8 inch

(20 mm) thickness. (3,600,000 lb yield load)

Max: 32

Min: 3

Range: 29

300,000

(Failure)

TABLE 3

COST ESTIMATES FOR 4000 FT TLP TENDON IN GULF OF MEXICO

(TENDON STATIC STRENGTH = 4,000,000 LB)

Steel Pipe P55 Carbon Composite Strand

Weight in air, lb/ft 200 8

Weight in water, lb/ft 100 3

Material Cost, $/ft 300-400 500-700

Installation Cost, $/ft 1000-1500 500-1000

TABLE 4

COMPARISON BETWEEN WEIGHT AND COST OF 9 5/8 INCH STEEL AND COMPOSITE

PRODUCTION RISERS

Steel Pipe Composite Riser

Weight in air, lb/ft Weight in water, lb/ft

42.8

37.3

12.7

6.0 __

Material Cost, $/ft 70 to 90 150 to 200

281

I
Figure 1. Historical and Project Water Depth for Exploration and Production Activities

282
NON-BONDED FLEXIBLE PIPE

BONDED FLEXIBLE PIPE

A REINFORCEMENT WINDINGS

B FLUID CONTAINING UNER

C OUTER JACKET

D STRUCTURAL MEMBERS

Figure 2. Construction of Flexible Risers

283

Low-Cost, Pultruded Rod Large Diameter Rope

Diameter

Rods

Figure 4. Proposed Composite Strand as TLP Tendon

285
EXTERNAL LINER

\

CIRCUMFERENTIAL

LAYERS

LONGITUDINAL HEUCALLY

WOUND LAYERS

(a) CROSS-SECTION

INTERNAL LINER

LONGITUDINAL

LAYER

CIRCUMFERENTIAL

REINFORCEMENT

ELASTOMER

FILM

CIRCUMFERENTIAL

BONDING

INTERNAL

LINER

METALLIC SHELLS

(3 per INSERT)

END FITTING

STEEL INSERT

(b) TERMINATION

Figure 5. IFP-Aerospatiale Composite Riser Design

286
FILAMENT-WOUND

COMPOSITE RISER

ELASTOMERIC OR

THERMOPLASTIC UNER

INTERNAL UNER

INTERNAL ENO-PIECE WITH PREMIUM THREAD

»»>: m: »xars g3

HIGH STRENGTH EXTERNAL END-PIECE DOWEL PINS

Figure 6. Brunswick Composite Riser Design

287
288

Ll
USING COMPOSITE MATERIALS TO PROTECT VULNERABLE EQUIPMENT

AGAINST JET FIRES

L.C. Shirvill

Shell Research Limited

Thornton Research Centre

P.O. Box 1, Chester CHI 3SH

England

Introduction

When the use of fibre-reinforced plastic (FRP) composite materials on offshore facilities are discussed, concerns about fire resistance are often cited as an impediment to wider use. It is therefore

perhaps a little ironic that one early use of these materials has been as passive fire protection (PFP) for

vulnerable equipment.

As a result of the Piper Alpha disaster in July 1988, the catastrophic consequences of jet fires on an offshore platform were tragically realised [1]. This sharply focused attention on the need to ensure that vulnerable equipment on an offshore installation is adequately protected against jet fires. Shell Expro, who operate in the North Sea on behalf of Shell and Esso, decided to provide,

where necessary, passive fire protection to vulnerable equipment and structures. The most severe fire event to be protected against was considered to be an impinging jet fire from a high-pressure gas leak. In the absence of any recognised test for jet fire resistance, a series of full-scale demonstrations has

been carried out to provide assurance that candidate PFP systems would provide protection in the event

of a jet fire [2]

.

Two primary examples of such protection using FRP composite materials are enclosures for

topsides emergency shutdown valves (ESVs) and protective systems applied to tubular elements

(jacket members or risers). This short paper describes jet fire demonstrations carried out on these two

systems and the findings that led to their installation offshore. Other candidate systems were also

tested and these, together with the supporting research, are described in reference 2.

Jet fire demonstrations

The jet fire used in these demonstrations represents only one realistic event, but its selection was underpinned by extensive research into the nature of jet fires. The flame, an ignited 3 kg/s, 60 bar release of natural gas, engulfed the specimen. Figure 1 is a photograph taken during one of the tests. The discharge orifice, a 20 mm hole, can be seen to the left of the picture, 9 m away from the specimen.

The required test duration was two hours; owing to a limited gas supply, the mass flow rate had

to be reduced to 2 kg/s after the first hour.

ESV enclosures

To comply with regulatory requirements [3], topsides ESVs have been installed on all of Shell

Expro's oil and gas risers in the North Sea. An additional requirement is that the ESV and its actuator

shall, so far as is reasonably practicable, be protected from damage arising from fire, explosion and

impact.

289
Figure not available at press time

FIG. 1 - Ajet fire demonstration in progress

Figure not available at press time

FIG. 2 - The FRP composite emergency shutdown valve enclosure

290
Fire protection was to be provided by enclosures and one candidate system. Figure 2, was

fabricated from FRP composite sandwich panels retained around the ESV by inner and outer steel frames.

The enclosure tested contained an 18-inch ball valve and was mounted horizontally between

two, epoxy intumescent coated, pipe spools. A dummy actuator was also fitted to the valve and in this

test it was protected by a metal foil insulation system. The basic specimen configuration and its orientation to the jet flame is shown in Figure 3. Thermocouples were attached to the valve, the

actuator, the inside of the enclosure and the inside of the pipe spools to monitor temperatures.

Actuator

I:

Valve

Flame direction

m

I Flame direction

FIG. 3 - Configuration of the valve enclosure used in the jet fire demonstrations

For these two-hour demonstrations, a maximum temperature limit of 300°C was set for the

valve. This was based on maintaining the integrity of the particular valves chosen. A different limit

might be required for other designs or operating conditions. In practice, the valve actuator must be capable of closing the valve within the first 15 minutes

of a fire. Having closed the valve, the actuator is no longer a critical component, although it may

provide a heat path into the valve body. For the demonstrations, a maximum temperature for the actuator of 100°C was the only limit set This was based on the operating limit of the actuators used

by Shell Expro and a different limit might be required for other designs.

Figure 4 shows the temperature record at selected points on the valve and actuator. After two

hours' exposure to a jet fire, the maximum temperature of the valve remained below the 300°C target

value, commensurate with safe functioning of the ESV.

In comparison, another enclosure tested, comprising insulation encapsulated in stainless steel,

did not provide the required thermal protection to the valve.

FRP panel enclosures have now been installed offshore by Shell Expro.

291
Tune from ignition, min

FIG. 4 - The temperature response of the valve in the FRP enclosure and the actuator in the all-metal enclosure

Tubular protection

Tubular elements in the splash zone (jacket members or risers) present a particularly

challenging environment for passive fire protection. For this demonstration, the protection system was

required to limit the temperature of a jacket tubular member to 400°C in the event of a two-hour jet fire engulfment. In addition the system had to have a proven anti-corrosion protection performance.

The test specimen selected for the jet fire demonstration was a steel tubular, 9 m long and 1.1m

outside diameter, with a wall thickness of 35 mm. A 50 mm thick FRP coating was filament-wound

onto part of the tubular. The same thickness of FRP with hand-applied woven rovings was applied

manually at a field joint and the remainder of the specimen was protected with an epoxy intumescent

coating that was to be used above the splash zone. Figure 5 shows the specimen before testing. In the two-hour test the maximum temperature recorded on the steel under the factory-applied

coating was 223°C and under the field joint 197°C.

FRP tubular protection of the type tested has been installed offshore on some oil and gas risers,

for which 70 mm thick FRP was needed to limit the temperature of the riser to 200°C during a twohour fire engulfment scenario.

292
Figure not available at press time

FIG. 5 - The FRP protected tubular test specimen

Summary

Recent work has demonstrated that FRP composite materials can be used to passively protect

vulnerable equipment against jet fires. Full-scale, two-hour jet fire tests have been conducted

successfully on two FRP systems, one to protect emergency shutdown valves and the other to protect

tubulars. FRP valve enclosures and riser protection systems have now been installed, where necessary, on offshore facilities in the North Sea.

References

[1] The Hon. Lord Cullen. The Public Inquiry into the Piper Alpha Disaster. DEn (HMSO) November

1990.

[2] L.C. Shirvill, "Performance of Passive Fire Protection in Jet Fires", Paper presented at 'Major

Hazards Onshore and Offshore', UMIST, Manchester, 20th-22nd October 1992 and published in

I.Chem.E. Symposium Series No. 130.

[3] Statutory Instrument 1029, The Offshore Installation (Emergency Pipeline Valve) Regulations,

1989.

Acknowledgement

The author wishes to acknowledge the contribution of his colleagues in Shell Research and

Shell Expro to this work, and in particular John Bennett, Dick Wade and Ross Connell.

293
294 I
A Course of Action for Introducing Composites into Offshore Operations

F. Joseph Fischer

Shell Development Company

As the petroleum industry has moved into deeper and deeper water for the recovery of oil and gas, weight-sensitive floating platforms have replaced stationary, bottom-founded

structures. The cost penalty for weight or vertical tension supported by floaters such as tension leg platforms (TLPs) is in the range of $5-10/lb. Hence, there is considerable

incentive to reduce the weight of equipment or structural members on these platforms and

downward forces exerted on these platforms by production and export risers, and mooring

lines. Thus, there are numerous opportunities for utilizing light-weight, high-strength

composites.

The high strength-to-weight ratio, low corrosivity, and other excellent performance

characteristics of composites have long been recognized by offshore petroleum operators but

high initial costs have prevented widespread utilization of composites. Recent factors such

as reduced market pressures from the defense industry have resulted in reduced costs for

composites to the extent that a re-examination of composites for offshore utilization is warranted.

The following figures present a general course of action for introducing composites into

offshore operations. It must be emphasized strongly that any such plan must clearly

demonstrate both technical feasibility and cost-effectiveness of any specific application.

Remarks pertinent to particular applications, e.g., composite production risers, are also

provided.

The basic objective of this course of action and critical steps of the approach being proposed

are given in Figure 1. It is important and encouraging to note that different potential

applications have differing levels of "maturity." Topsides' applications such as low-pressure

piping, storage vessels, grating, etc. are commercially available and utilization will depend

primarily upon educating potential users of such products of their existence, merits and cost- effectiveness. Other potential products such as continuous, spoolable tethers (or tendons)

for vertically mooring TLPs are attractive albeit unproven concepts.

Following the identification of a specific application, it is recommended that each step of the

proposed approach be addressed, more or less in the order presented. Once a given step has

been accomplished satisfactorily, the next step can be taken. If a satisfactory resolution

cannot be reached, it is probably appropriate to focus on a different application. As an

example, the offshore industry has felt very comfortable with the technical feasibility of

composite production risers due to the efforts of IFP and Aerospatiale, but progress has

halted due to doubts regarding the cost-effectiveness of this product.

Ultimately, product development will probably have to rely upon the collaborative effort of

295
multiple end-users and composite manufacturers in order to share development costs. An

alternative might be the development of a product for a specific project due to perceived cost savings or technically enabling performance.

Figure 2 addresses relatively mature composite products for topsides' applications. These

include low-pressure piping, fire-water systems, storage tanks, grating and blast walls. It has

been observed that North Sea operators have been much more progressive in seeking

applications for composites than have Gulf of Mexico operators. Their current practices

would thus be a good place to begin the identification of possible topsides' applications.

Discussions with existing composites' manufacturers, e.g., Morrison Molded Fiber Glass,

would also be worthwhile.

Composite production risers are the topic of Figures 3, 4 and 5. These are critical elements

of a floating production platform such as a TLP. As mentioned previously, it is believed that

their technical feasibility has been amply demonstrated by IFP and Aerospatiale through the

auspices of multiple joint industry programs. It is further believed that cost minimization

and riser "qualification" through a statistically meaningful test program are yet to be

accomplished. Brunswick Composites has shown considerable interest in the development

of a cost-effective, reliable product and has proposed a joint-industry program to accomplish

this development.

Figure 4 summarizes the status of composite production riser development while Figure 5

addresses breakeven costs for a composite riser. A number of assumptions were made in

developing the cost curves of Figure 5. First of all, it was assumed that only 90-percent of

the steel riser would be replaced with composites. In particular, the ends of the riser where

significant bending might occur would be avoided — this simplifies the performance

requirements for the composite riser. Furthermore, the riser "cost" used here is the cost of

a nominal 9

6/s-inch riser tubular exclusive of mechanical threaded connectors but including

the materials and labor for attaching the composite tubular to the metal end pieces. The riser

tubulars were assumed to be 75 feet in length. The curves basically reflect the tradeoff of

increased riser costs with reduced payload (riser-tension) costs. With regard to the latter, a multi-tube riser having an outer composite riser tubular has about one-half the submerged

weight as an all-steel riser. The abscissa for these cost curves is the product of the Riser

Tension Factor and the Payload Penalty. The top tension of the riser (supported by the

platform deck) is the product of the Riser Tension Factor and the submerged weight of the

riser. The Riser Tension Factor is typically around 1.2-1 .4.

Payload Penalty is the cost per pound ($/lb) of incremental deck payload; payload could be

the weight of physical equipment or, in this case, the force required to support a production

riser. Payload Penalty is a function of floater type and to some extent, of the offshore

operator/designer. For TLPs, current Payload Penalties are believed to be in the $5~10/lb

range.

For a Riser Tension Factor of 1 .2 and a Payload Penalty of $5/lb, the composite-riser break- even cost is estimated to be $250/ft as indicated by the lower solid curve. If, in fact, the riser

296
could be produced for $150/ft, a savings of $270,000 per riser could be realized under the

above assumptions. If 20 risers were required, the total system savings would amount to S5.4MM. The other dotted and dashed curves correspond to additional savings associated

with the riser tensioner and the threaded metal connectors used to couple the finite-length

(75-ft) riser tubulars. Possible individual tensioner savings of $100M and $200M have been

assumed. Also, savings of $1M per riser-connector pair (pin and box) have been assumed.

The "allowable" or break-even cost increases or, more importantly, potential system savings

result. It should be possible to simplify the tensioner since the load (tension) that it must

support will be halved. Furthermore, the composite tubular can be designed to be more

axially compliant than the steel riser it replaces and, hence, may not even need a tensioner.

The inner steel tubulars, including the production tubing, typically have higher tensile

strengths than the riser tubular and, hence, can tolerate higher strains. The tensioner can thus

be simplified in view of reduced performance requirements, e.g., stroke. Similarly, since the

mean and dynamic tensions in the composite-riser connectors will be much smaller than

those experienced in a steel riser, the connectors can be simplified and their price reduced.

For the case of 20 production risers, a composite-riser cost of $ 1 50/ft, tensioner savings of

$200M/tensioner and connector savings of $lM/pair, system savings of $10.8MM are indicated for a Tension-Factor/Payload-Penalty product of $6/lb. This is viewed as being

a realistic scenario.

Production risers terminate at the seafloor at fixed (built-in) wellheads. For all practical

purposes, the wellheads do not translate or rotate. Hence, large bending moments can

develop. Tapered riser sections called stress joints are commonly introduced above the

wellhead to facilitate the bending moment and curvature transition of the riser. Typical

performance requirements for stress joints are that the moment exerted by the riser on the

wellhead not exceed some design value and that the curvature within the stress joint not

exceed some other design value. Since composites are "engineered" materials, it seems

logical that they could be utilized for this purpose. Once again, cost effectiveness becomes

a very important issue. Competition with steel is a real challenge but some applications

require costly titanium when steel will not work. In this situation, demonstrating cost

effectiveness should be less of a challenge. Figure 6 focuses on composite production-riser

stress joints. An analogous opportunity exists for drilling-riser stress joints.

Figure 7 identifies TLP tendons (or tethers) as a logical application for composites. These

are the vertical members, typically steel tubulars, that moor the floating TLP hull. They

provide horizontal station-keeping by virtue of their top tensions and, more importantly, serve to virtually eliminate wave-induced heave of the floater. Heave suppression is important for the integrity of the production risers. TLP tendons must be designed to withstand large storm-induced tensions, and wave-induced cyclic-fatigue damage occurring over a period of around 30 years. Evacuated tubular tendons must also be designed to withstand hydrostatic collapse pressures.

It is widely recognized that carbon-fiber composites have tensile strengths (per unit area)

which are much higher than steel and have excellent fatigue characteristics. Furthermore,

297
they are light and can probably be used as solid cross-sections thus obviating collapse

problems. Recent discussions with Hydril/MMFG, and Bell Helicopter/Neptco indicate that

it may be possible to produce continuous, spoolable tendons by the pultrusion process. This

would eliminate the need for costly intermediate mechanical connectors used to assemble

tendons longer than about 1800 feet (the limit for neutrally buoyant tubulars) and otherwise

expedite time-consuming tendon installation.

Past experience indicates that composite tendons having the same axial stiffness as the steel

tendons they are designed to replace have about 1 0-times the required tensile strength. A

design compromise suggests itself. Tendon stiffness influences the heave, roll and pitch

periods of a TLP and, thus, will impact dynamic loading and fatigue damage of the tendons.

TLP designers do not have natural-period design requirements per se; system reliability is the issue. Hence, by reducing composite-tendon stiffness, material costs are reduced at the

expense of increasing vertical response periods. As long as sufficient tensile strength and

fatigue life exist, this cost reduction approach may be acceptable. At some point, motion

considerations may become a limiting factor. In any event, this potential application merits

additional investigation.

In the above discussion, composites have been synonymous with fiber-reinforced plastics.

Figure 8 focuses on a different type of composite, namely steel-clad concrete. TLP hulls are presently being constructed using all steel, or concrete internally reinforced with steel rods.

Others have suggested that cost savings could result from steel-concrete-steel sandwich

construction. This seems totally within the spirit of composites design. Others have even

suggested that fiber-reinforced plastics could even be considered for this enormous-volume

application. It is only offered here to stimulate thinking.

A partial list of currently or recently active composite developers and manufacturers is given

in Figure 9. For each such organization, composite products being developed or considered

are also indicated. Most of these composite products have considerable potential for

application in offshore operations.

Finally, as shown in Figure 1 0, it should be emphasized that in the view of the author, most,

if not all, of the above-mentioned composite products are not absolutely needed for

operations in current waterdepths of interest, i.e., 2000-4000 ft. As such, they are not truly

"technically enabling" at the present time. They do, however, offers some cost-savings'

potential and thus may be viewed as being "economically enabling."

For greater depths, it is highly likely that composites will be technically enabling due to needs for weight reduction for long risers and mooring elements and in order to contend with

accelerated fatigue damage.

It appears highly desirable to pursue cost-savings' applications in a relaxed atmosphere

where they are not absolutely needed so that they will be available in the future when they

may be technically enabling.

298
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COMPOSITE DEVELOPMENTS

• IFP/Aerospatiale • Production Riser (JIP) • Stress Joint (JIP)

• Brunswick

• Production Riser (JIP) • Export Riser Flex-Joint (Shell) • Drill Pipe (Amoco, Pool) • Sucker Rod (commercial)

• AEA Petroleum Services (Harwell) • Hybrid Stress Joint (JIP) • Drill Pipe (JIP)

• Hydril Consortium

• Coiled Tubing (JIP) • Production Riser • Hybrid High-Pressure Drilling Riser • Hybrid Stress Joint • Pultruded Ribbon/Rods (tendon)

• Bell/Neptco • Bundled Pultruded Rods (tendon)

JF303601

FIGURE 9 307
308
FLAMMABILITY AND FIRE SAFETY OF COMPOSITE MATERIALS

U. Sorathia

Carderock Division, Naval Surface Warfare Center

Annapolis Detachment

Annapolis, MD 21402

INTRODUCTION

Studies have shown that demands to reduce weight and improve specific structural characteristics

of Naval ships and Submarines can often be met through the use of organic matrix based composite

structures. During the past five to ten years, there has been "a resurgence of interest" in the development

and application of composites to both primary and secondary load-bearing structures as well as machinery components in Naval ships and submarines. This new interest in composite materials is due

to increased need for a corrosion free, light weight, and affordable low cost alternative to metallic

components. A significant technical issue which has limited composite use on board Naval ships and

submarines is the combustible nature, and hence the fire, smoke and toxicity of organic matrix based

composite materials.

The use of composites inside Naval submarines is now covered by MIL-STD-2031 (SH), Fire

and Toxicity Test Methods and Qualification Procedure for Composite Material Systems Used in Hull,

Machinery, and Structural Applications. This military standard contains test methods and requirements

for flammability characteristics such as flame spread index, specific optical density, heat release and

ignitability, oxygen-temperature index, combustion gas generation, long term outgassing, etc. Two guiding

criteria (1) were established for the use of composite systems aboard Navy vessels. The composite

system will not be the fire source, i.e., it will be sufficiently fire resistant not to be a source of

spontaneous combustion. Also secondary ignition of the composite system will be delayed until the crew

can respond to the primary fire source, i.e., the composite system will not result in rapid spreading of

the fire. An abridged version of MIL-STD-2031 is shown in Table 1. The Navy currently has no specific

standard for surface ships. The flammability requirements for surface ships are different than submarines.

Instead of survivability measured in minutes, as it is in submarine fires, the critical issue in surface ship

fires is the residual strength of structures at elevated temperatures for a period of 30-60 minutes.

CDNSWC, Annapolis Detachment (formerly known as DTRC), has been evaluating the fire performance of commercially available composite materials for past several years under the Materials

Block Program. This program also included work on thermal/fire barriers to protect the composite

structures against fire damage. In 1991, this program was expanded to address the residual load bearing

strength or the structural degradation of composite materials during fire.

Results from this work have been discussed in several papers (2,3,4,5,6). This paper summarizes

material flammability work performed under the Materials Block Program. This includes small scale

flammability characteristics of conventional and advanced glass or graphite reinforced organic matrix

based thermoset and thermoplastic composite materials suitable for surface ship and submarine

applications. The composite materials evaluated included vinyl ester, epoxies, cyanate esters,

bismaleimides,phenolics,poryimides,polyphenylenesulfide,polyethersulfone,polyarylsulfone,polyether

ether ketone (PEEK), and polyether ketone ketone (PEKK). This work further included the use of

integral, hybrid thermal barriers to protect the core of the composite structures. Thermal barrier

treatments evaluated in this study included Ceramic coating, Intumescent coating, Silicone foam,

309
Phenolic skin or chopped fiber reinforced sprayable phenolic, APM (Ablative Protective Material),

InteramR endothermic mat E-10A1

, and InteramR intumescent mat I-10A1

. This work further include

evaluation of residual flexural strength retained (%RSR) after exposure to 25 kW/m2 for a duration of

20 minutes (ASTM E-662) for selected composite materials. A methodology is also presented for the

assessment of residual strength of composite materials during fire exposure by inter-relationship of

mechanical property, temperature, thickness, and time.

FIRE-PERFORMANCE OF COMPOSITE LAMINATES;

The fire performance of composite materials are those characteristics which describe the response

of polymeric materials when exposed to fire. These include flame spread (fire propagation), smoke

evolution (visibility), combustion gas generation (toxicity), fire endurance (residual strength after fire exposure), heat release, ignitability, and ease of extinguishment (oxygen index).

The thermoset materials we have evaluated included fire retardant vinyl ester (VE),epoxies(EP),

cyanate esters (CE), bismaleimides (BMI), phenolics (PH), and polyimides (PI). Thermoplastic materials

we have evaluated included polyphenylene sulfide (PPS), polyether sulfone (PES), polyaryl sulfone

(PAS), polyether ether ketone (PEEK), polyether ketone ketone (PEKK), and thermoplastic nylon J-2. The flammability characteristics evaluated in this study included flame spread index (ASTM E-162),

specific optical density of smoke (ASTM E-662), combustion gas generation, residual flexural strength

(ASTM D-790), heat release and ignitability as measured by cone calorimeter (ASTM E-1354). Table

2 shows the comparison of selected glass or graphite reinforced composite materials.

As shown in Table 2, with the exception of vinyl ester, all glass or graphite reinforced composite

materials met the requirements of flame spread index (maximum 20). Also, with the exception of fire- retardant vinyl ester and thermoplastic J-2, all glass or graphite reinforced composite systems met the

requirements of specific optical density at 300 seconds (maximum 100) and maximum smoke density of

200 as per MIL-STD-2031.

Combustion gas generation is defined as the gases evolved from materials during the process of

combustion. The most common of gases evolved during combustion are carbon monoxide and carbon

dioxide, along with evolution of HCL, HCN and others depending upon the chemistry of matrix resin

of a given composite material. The Committee on Fire Toxicology of the National Academy of Science

has concluded that as a basis for judging or regulating materials performance in a fire, combustion

product toxicity data must be used only within the context of fire hazard assessment. The committee

believes that required smoke toxicity is currently best obtained with animal exposure methods for

purposes of predicting the fire hazard of different materials.

Heat release may be defined as the heat generated in a fire due to various chemical reactions

occurring within a given weight or volume of material, the major contributors being those reactions

where CO and CO, are generated and oxygen is consumed (7). This characteristic provides a relative

fire hazard assessment for materials in that the material with low heat release per unit weight or volume

will do less damage to the surroundings than the material with high release rate. The rate of heat

release, especially the peak, is the primary characteristic determining the size, growth, and suppression

': This is a proprietary material (3M Co.) . Evaluation or

reporting of this material does not constitute an endorsement by

U.S. Government

.

310
requirements of a fire environment. MIL-STD 2031 requirements of peak heat release at 75 and 100

kW/m2 are 100 and 150 kW/m2 respectively. Glass or graphite reinforced phenolic, polyimides, and many

of the thermoplastics composites met this requirement. This is shown in Figure 1.

Table 1: MIL-STD-2031(SH) Fire Performance Acceptance Criteria.

Fire Test/Characteristic Requirement Test Method

Oxygen-Temperature Index (%)

% oxygen at 25°C

% oxygen at 75°C

% oxygen at 300°C

Minimum

35

30

21

ASTM D-2863

(Modified)

Flame Spread Index

Maximum

20

ASTM E-162

Ignitability (sec)

100 kW/m2 irradiance

75 kW/m2 irradiance

ju Kw/m lrrauidnce

25 kW/m2 irradiance

Minimum

60

90

1300

ASTM E-1354

Heat Release (Kw/m2 )

LKJKJ KW/m UTaUlanCC, iCaK

Average for 300 sec 75 kW/m2 irradiance, Peak

Average for 300 sec 50 kW/m2 irradiance, Peak

Average for 300 sec 25 kW/m2 irradiance, Peak

Average for 300 sec

Maximum

1 so 120

100

100

65

50

50

50

ASTM E-1354

Smoke Obscuration

Ds during 300 sees Dmax

Maximum

100

200

ASTM E-662

Combustion Gas Generation

(25 kW/m2) CO = 200 ppm

C02 = 4%v

HCN= 30 ppm

HCL= 100 ppm

ASTM E-1354

N-Gas Model Smoke Toxicity

Screening Test

No deaths

Pass

Modified

NBSTTM

Quarter-Scale Fire Test No flashover in 10

minutes

NSWC Quarterscale test

Burn-Through Fire Test No burn-through in 30

minutes.

Burn-through Fire

Test (NSWC)

Ignitability has been defined as the ease of ignition. In general, ignition may also be looked upon

as the resistance of the polymeric material to participate in the fire scenario. MIL-STD-2031(SH) re- quires the ignitability of organic matrix based composites to be 60 and 90 seconds at radiant heat fluxes

311
312
350

300

CME

i

©

33 cc©

X

CL

250

200

150

100

100

—GL/VE(2)

+GUEP(3)

-*-GL7BMI(10) —GL/PH(19B)

-*"GUPMR(23M)

^GUPPS(24)

^GR/PEEK(26)

-*"GR/PEKK(29)

-®-GR/PAS(27)

^GR/PES(28)

^GR/PPS(25)

Flux, kW/m2

Fig. 1 : PHR vs Flux for selected composite materials.

Ignition Delay Time, Sec

1,000

100

100

Flux, kW/m2

Fig. 2: Ignitability of composite materials.

GUVE(2)

-+- GL/EP(3)

GUBMI(10)

GLVPH(19B)

GL7PMR(23)

GL7PPS(24)

GR/PEEK(26)

*

GR/PEKK(29)

-©- GR/PAS(27)

GR/PES(28)

313
of 100 and 75 kW/m2 respectively. All composite materials evaluated in this study failed to meet the

ignitability requirements. This is shown in Figure 2. It is in this area of ignitability where fire barrier

treatments provide the most benefit by delaying the onset of spontaneous ignition providing greater time

interval for the fire fighters to control the fire.

FIRE BARRIERS;

Fire performance characteristics of composite systems can be greatly enhanced by the

incorporation of fire barrier treatments. In a recent study by U.S.Navy, several fire barrier treatments were evaluated in conjunction with glass/vinyl ester and glass or graphite/epoxy composites. Fire barrier

treatments function either by virtue of their ability to reflect the radiant heat back towards the heat source or delay heat penetration by their insulative, ablative, or endothermic properties. This delays the

heat-up rate and reduces the overall temperature on back side. As an example, exposure of intumescent

coatings to flame produces a viscous carbonaceous or inorganic mass that expands into a foam by the

gas generated. This thermally stable insulating char protects the substrate from the thermal effects of

the flame.

Thermal barrier treatments evaluated in this study include ceramic fabric, ceramic coating,

intumescent coating, hybrid of ceramic and intumescent coatings, silicone foam, phenolic skin,

thermoplastic coatings, APM (ablative protective material, Interam endothermic mat E-10A, and Interam

intumescent mat I-10A. The composite systems evaluated in combination with thermal barrier treatments

included glass/vinyl ester, and glass or graphite/epoxy.

Data show that without any fire barrier treatment, all composite systems evaluated in this study

failed to meet the ignitability and peak heat release requirements of MIL-STD-2031 (SH) at radiant heat

fluxes of 75 and 100 kw/m2 respectively.

Data also show that intumescent coating (4), a hybrid of intumescent and ceramic coatings (5),

APM (ablative protective material), Interam endothermic mat E-5A, and Interam intumescent mat I-10A were the most effective fire barrier treatments for composite systems evaluated in this study. Using any

of these fire barrier treatments, all composite systems met the ignitability requirements of 90 and 60

seconds at 75 and 100 kw/m2 respectively. Figure 3 shows the heat release rates for glass/epoxy (1003)

panel by itself, glass/epoxy/APM (0.125"thick, 1004), glass/epoxy/I-10A (0.125"thick, 1041), glass/epoxy/I10A (0.250"thick, 1044), glass/epoxy/E-lOA, (0.20"thick, 1042), and glass/epoxy with 30 mils of water

based intumescent coating (1047). In all cases, the panels were exposed to a heat flux of 75 kW/m2 in

horizontal orientation.

RESIDUAL STRENGTH OF COMPOSITES:

Recently, the assessment of composite structural performance during and after fire has become

a subject of intense discussion within Navy community. Due to the nature of their construction,

composite materials do not lend themselves to easy analytical calculation of their behavior when exposed

to a high heat flux. Composites exhibit anisotropic heat transfer, they burn, give off smoke and release

heat, char, and delaminate.

Composite materials are made of organic matrix resins. These resins undergo viscoelastic

transitions during thermal exposure. Composites retain most of their load bearing characteristics below

a certain "critical" temperature. Above this critical temperature, composites begin to lose their

mechanical properties rapidly and, in some cases, catastrophically. During fire, beyond a critical (glass

314
Heat Release, kW/m2

200

150

100

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Time (s)

Fig. 3: Heat release rates for GI/EP with and without fire barriers.

% RSR (residual strength retained)

0GI/VE LUGr/EP

— Control (no FB) InL Ctg. Hybrid APM FIRE BARRIERS

Figure 4: Residual Strength (%RSR) at 23 kW/m2 for 20 minutes.

315
transition) temperature, these resins can no longer transfer load to the fiber. As such, the residual

strength of load bearing structures is much lower during fire than after fire. This critical temperature

(during fire) is about 200 °F for glass/vinyl ester. However, when cooled, (after fire), irreversible damage

does not set in until 500°F.

The percent residual flexural strength (modified ASTM D-790) retained (%RSR) after the fire test for selected composites with and without fire barriers treatments is shown in Fig. 4. As part of the

testing protocol, all specimens (3x3 in., 0.25 in. thick) were exposed to radiant heat source of 25 kW/m2

for a duration of 20 minutes during ASTM E-662 (smoke density) in a flaming mode. Specimens were

tested for flexural strength before and after the fire test. The percent residual strength retained (%RSR)

after the fire test for selected thermoset and thermoplastic composite materials is given in Fig. 3. Graphite/PEEK retained the maximum flexural strength (75%) of all composites evaluated at this level of fire exposure followed by graphite/phenolic (53%). Glass/epoxy delaminated during the fire exposure

due to resin charring resulting in loss of interlaminar strength. Also, panels treated with intumescent

coating (4) and ablative protective material (11) retain higher residual strength after fire exposure for

both glass/vinyl ester and graphite/epoxy composite systems.

CDNSWC has initiated a comprehensive effort focused on the issue of residual structural

strength during fire. This is intended to result in mathematical models that can be used by naval

architects to design full scale fire-tolerant composite structures. This methodology includes

determination of basic composite characteristics at elevated temperatures, determination of isothermal

material characteristics for use in the computer model, determination of creep characteristics of materials

(creep is an unacceptable structural instability), determination of heat transfer characteristics of

composite materials exposed to fire, construction of mathematical models of basic shapes under typical

loads using ABAQUS finite element analysis, and verification of these models in small and full scale

ASTM E-119 tests. CONCLUSIONS

With the exception of vinyl ester, all glass or graphite reinforced composite materials met the

requirements of flame spread index. Also, with the exception of fire-retardant vinyl ester and

thermoplastic J-2, all glass or graphite reinforced composite systems met the requirements of specific

optical density at 300 seconds and maximum smoke density as per MIL-STD-2031. Glass or graphite

reinforced phenolic, polyimides, and many of the thermoplastics composites met the peak heat release

requirement. However, all composites investigated failed the ignitability requirements of the current

MIL-STD-2031 of 90 and 60 seconds at 75 and 100 kW/m2 respectively.

Fire performance of composites can be greatly improved with fire barrier treatments. Data show

that intumescent coating, a hybrid of intumescent and ceramic coatings, ablative protective material

(APM), Interam endothermic mat E-5A, and Interam intumescent mat I-10A were the most effective

fire barrier treatments for composite systems evaluated in this study. Using any of these fire barrier

treatments, all composite systems met the ignitability requirements of 90 and 60 seconds at 75 and 100

kw/m2 respectively.

A methodology has been developed to understand the relationship between fire exposure,

temperature distribution, dependence of load bearing characteristics with elevated temperatures, and

residual strength. This area is being further explored, on small scale, with high temperature creep

experiments and, in future, with large scale testing for verification.

316
REFERENCES

1. DeMarco, Ronald A.; "Composite Application at Sea: Fire Related Issues", 36th International SAMPE

Symposium, April 15-18, 1991.

2. Sorathia, U; Dapp,T; Beck,C;" Fire Performance of Composites", Materials Engineering, September

1992, A Penton Publication.

3. Usman Sorathia, Charles Rollhauser, W.Allen Hughes;"Improved Fire Safety of Composites for Naval

Applications"; Fire and Materials, Vol. 16, 119-125(1992); Jury-sept. 1992, John Wiley & Sons, Ltd.

4. U. Sorathia and VJ. Forrest; "Fire Performance Characteristics of Advanced Composites",

Proceedings of the Conference on Advanced Composites, American Conference of Governmental

Industrial Hygienists, Dec. 1992.

5. Sorathia, U.; Dapp, T.; Kerr, J.; "Flammability characteristics of Composites for Shipboard and

Submarine Applications", 36th International SAMPE Symposium, Volume 36, April 15-18, 1991, San

Diego, CA.

6. U. Sorathia, C. Beck, T. Dapp; "Residual Strength of Composites during and after Fire Exposure";

Journal of Fire Sciences, Volume 11, No.3, May/June 1993 (ISSN0734-9041)

7. Tewarson, A.; "Generation of Heat and Chemical Compounds in Fires", Fire Protection Handbook

of the Society of the Fire Protection Engineering, Edited by J.P. Dinenno, 1988.

317
318
SAFETY PHILOSOPHY FOR THE USE OF

COMPOSITE MATERIALS OFFSHORE

Stephen W. Ciaraldi

Amoco Norway Oil Company

P.O. Box 388

4001 Stavanger, Norway

ABSTRACT

Within the last few years, Amoco Norway has greatly increased use of composite materials

offshore. Three major systems have now been or are in the process of being installed at the Valhall

field. These are the deluge firewater systems, the produced water treatment system and the open

drain systems. Thorough safety evaluations preceeding each of these installations, in part, to confirm acceptability of composite materials.

The safety philosophy used to justify composites offshore is summarized below. The need for

system function in an emergency situation defines the detail level for safety evaluation. When no

function is required, the evaluation concentrates on assuring that composite component failures

during an accident event will not increase personnel risks or contribute to accident escalation. When

function during an emergency is required, more thorough evaluations are used in the form of a formal risk analysis study. Such a study sets performance/function requirements of the composite

system and then evaluates anticipated behavior during all likely accident events. When necessary,

verification explosion and fire tests are performed, with test conditions derived directly from results

of the risk analysis.

INTRODUCTION

Amoco has been active in the Norwegian sector of the North Sea since 1965 and currently operates

the Valhall and Hod fields. These fields were discovered in 1976 and are located far southwest in

the Norwegian sector about 250 km (150 miles) from Stavanger. The Valhall field was developed

using a three platform concept consisting of separate quarters, drilling and processing/compression

platforms and came on-stream in 1982. The Hod field was developed in 1991 as a remotely

operated, normally unmanned satellite platform, with oil and gas production pipeline transported to and processed at Valhall. Oil processing capability at Valhall is about 23 M cu. m/d (150 M bbls/d).

Production is pipeline transported from Valhall through the Ekofisk center to shore.

Prior to 1991, use of composite materials at Valhall and Hod had been limited to a few seawater lift

risers. However, starting as early as late 1989, interest in composite piping materials rapidly grew.

This was due to recurrent availability problems with steel deluge firewater systems caused by

internal corrosion and the possible risks of nozzle blockage by corrosion products during use of the

systems. Composite materials were rationalized to be a cost effective replacement piping which

would be immune to the corrosion problems experienced with steels.

Several previous publications summarize the successful safety justification program performed for

composite firewater systems, optimizations of component designs and experiences from the 1991

319
offshore installation of a prototype system, the first of its kind in the North Sea (refs. 1-3). Since

that time, composite piping materials have been used extensively for installation of a new produced

water treatment system at Valhall and for replacement of steel open drain systems. The near future

of Valhall may involve a new platform addition to the field, for which further uses of composite

materials are envisioned.

The following briefly describes the processes used to justify composite materials offshore with

respect to safety. The justification process is based upon specific system of interest, necessity for

function in an emergency situation and the active use of safety evaluations.

DISCUSSION

Composite Systems Classifications

Piping components are perhaps the largest current uses for composite materials offshore. Storage

tanks have seen some limited use and applications for vessels operating at low pressures can be

envisioned. Secondary composite structures such as floor gratings, stairways, hand rails and cable

trays/ladders have been used offshore. More recent applications include accomodation/office

modules and fire/blast walls and panels.

With respect to safety, potential composite systems offshore can be classified into two major

groups based upon necessity for function in an acciddent/emergency situation. Function is not only

defined with respect to effective active response, such as for emergency equipment, but should also

consider if component integrity must be maintained to prevent significant increases in personnel

risks and/or accident escalation. Regardless of function necessity, personnel risk should not be

increased by excessive fire induced smoke generation, toxic gas release and/or flame spread from

the composite materials themselves. In practice, these latter possibilities are precluded by judicious

materials selection and by specifying upper limits for these characteristics based upon appropriate

standardized tests. A further classification for containment systems involves whether or not hydrocarbons or other

flammable species are present within the systems. Note that for such systems, integrity during an emergency event must be maintained.

These composite classifications are summarized below (ref. 4):

No Function in Emergencv

Hvdrocarbon Containing

Examples: None

Function in Emergencv

Hvdrocarbon Containing

Examples: process piping and vessels

No Function in Emergencv

Not Hvdrocarbon Containing

Examples: produced water, cooling

water, non-critical secondary structures

Function in Emergencv

Not Hvdrocarbon Containing

Examples: firewater systems, fire walls,

critical secondary structures

320
The exact definition of hydrocarbon containing systems is not universally accepted, but is often

taken to be in the range of several percent. Note that at the present time, the author is aware of no

composite applications offshore Norway into the realm of hydrocarbon containing systems.

Practically speaking, therefore, current composite uses offshore can be chiefly differentiated with

respect to safety based upon the necessity for function in an emergency situation.

Safety Evaluations

Recent changes in Norwegian regulations governing offshore activities have had the impact of

effectively promoting greater safety awareness into line organizations. Amoco Norway's response

has been to increase the scope of safety, work environment and external environment evaluations in

all phases of offshore construction projects, including subsequent operational phases. These are accomplished by active use of:

process safety studies (Hazop, API 14C)

reliability/availability studies

quantitative risk analyses

emergency preparedness analyses

separate working environment analyses

construction/installation safety studies

evaluation with respect to compliance to environmental standards, strategies and regulations.

Dependent on scope and impact of an upcoming construction project, these evaluations can be

simple and concise or quite detailed and lengthy. For composite materials, the lack of required

function in an emergency situation will generally result in a relatively simple evaluation, with intent

largely to demonstrate no adverse consequences of component failure, i.e., no safety threat to personnel and no contribution to accident escalation. For example, in the case of the Valhall

produced water treatment system mentioned above, acceptable composites usage was partly

dependent on no need for function (maintaining integrity) during an emergency. It was also

dependent on a redundant control and monitoring system to prevent the unknown carry-over of

significant amounts of oil from the primary separators into the composite piping of the water

treatment system, therefore assuring the system would not be hydrocarbon containing.

For composite systems offshore which must function in an emergency, more detailed safety

evaluations are needed, and often evolve into a formal qualitative and quantitative risk analysis.

The Norwegian Petroleum Directorate (NPD) has actively promoted the use of risk analyses studies

as a tool to improve offshore safety for many years (refs. 5-6). Together with emergency

preparedness regulation, this practice forms the cornerstone for recently issued revised regulations

(7). The approach systematically establishes performance/function criteria, then evaluates

performance under a variety of accident events, e.g., explosions and fires. Results of such studies

are also useful as engineering tools, as often simple modifications in design can enhance the safety

characteristics of systems at minimal or no additional cost. Additionally, the approach forces ra- tionalization into design criteria often followed mainly by common practice.

321
The main steps involved in risk analyses generally include:

definition of acceptance/function criteria

hazard identification

qualitative review

consequence analysis

frequency analysis

risk calculation and comparison to risk acceptance criteria

including evaluation of risk reducing measures.

The reader is referred to previous publications for details on application of risk analyses techniques

to safety justification of the composite firewater system at Valhall, for which system function during an emergency situation is required (refs. 1-2).

In summary, two main function criteria were assigned to the firewater system:

effective operation so as to reduce heat and radiation levels to facilitate personnel escape

from an explosion/fire situation

continued operation for exposure protection of offshore facilities for the approximate

duration of a worst case hydrocarbon fire.

Subsequently, composite firewater systems were systematically evaluated with respect to anticipated

behavior regarding explosions, fires, long term deterioration and mechanical damage. Overall, it was concluded that an appropriately engineered composite system should meet the firewater system

function requirements under all of the accident scenarios studied (ref. 8). Key to this evaluation was

results of the deluge systems reliability study, which concluded that automatic deluge (which would

fill composite piping with water within 30 seconds) would fail to occur in a fire event at a frequency

of once every 100,000 to 1,000,000 years. Based on these results and with application of a safetyfactor (partly to allow time for manual intervention in the unlikely event of deluge failure), a design

criterion for fire insulation of the composite firewater system piping was established.

Explosion and Fire Testing Philosophy

An additional benefit of risk analyses for offshore composite systems is that should any

verification/qualification testing of composite materials be required for a given application, realistic

test conditions can be readily specified. This is because the risk analyses defines the applicable

worst case accident events for the offshore platform facilities. These can then readily be applied to

test parameters, e.g., intensity and duration of fire tests.

As described in detail elsewhere, an extensive explosion/fire testing program was performed to verify acceptable behavior during accident scenarios of composite piping for the Valhall firewater

system (ref. 1). Three essentially different test types were used, including simulated explosion

testing, hydrocarbon pool fire (furnace) testing and gas jet fire testing. Test characteristics and their

relationships to the Valhall risk assessment are summarized below:

322
Test Tvpe Risk Analysis Findings Test Parameters

Simulated

J_- AJJ1UMU11

1. Design overpressure 0.3

Dal \H.J pM)

1 . Pipe strained in bending to a ueiieciion corresponuing to the design overpressure

versus optimized piping

support spacing.

Pool Fire** 1. From spilled oil/natural

gas liquids

2. Deluge water flows within

mi t\ ntpc llilUULCo

3. Worst case fire duration

80 minutes

1. Hydrocarbon Curve heating

characteristics used (initial

phase)

2. Deluge compensated heating

U6CU ^IClIlalllUcl Ul

3. Test duration 80 minutes

(some tests run 4-6 hours

without composite failures)

Jet Fire** 1 . From high pressure gas

release

2. Personnel escape duration

20 minutes

1. SINTEF jet fire test used

(ref. 9)

'

2. Minimum test duration 20

minutes (30 minutes actual)

* subsequently fire tested to assure acceptability ** deluge piping tested dry for initial 5 minutes, then filled with flowing water at nominal

working pressure for the remaining duration of tests

Because accident scenario findings from the risk analysis were based on the maximum intensity of

events having a frequency of 1 in 10,000 years and greater, the test parameters used are considered

sufficiently conservative for qualifying composite materials for Valhall.

Future Applications

In the short term, composites will likely become dominant offshore for low pressure water handling

systems such as drains, ballast water, cooling water, produced water, injection water and seawater

lift risers. No regulatory restriction problems are anticipated provided adequate system safety

evaluations are performed and include considerations for the use of composite materials. This is also

thought to be the case for non-critical secondary structural applications.

Significant future developments are possible for composite materials which must maintain function

during accident events such as firewater systems, fire walls and critical secondary structures. A

variety of designs and fire insulation systems are possible for obtaining adequate fire resistance, and

these will no doubt require verification testing. In this regard, Amoco Norway has continued to be

active in sponsoring optimization studies of insulation systems and application methods for

firewater piping, with goals of reducing costs without sacrifice to explosion and fire safety.

323
Possibilities beyond the cast intumescent epoxy half shell systems previously used at Valhall

include:

thin, intumescent paint coatings

full pipe-length, industrial application methods for intumescent epoxy coatings

composite piping with enhanced fire resistance (e.g., phenolic base, resins with fire retardant

fillers)

piping onto which an insulation coating is applied as an inherent part (latter stages) of the

maufacturing process.

Fortunately, the composite materials verification testing programs previously established for Valhall

based on the risk analyses approach have been well accepted internally and by the authorities, so

that testing can proceed on any new materials and designs in an expeditious fashion. This, of course,

is not universally the case and clearly the lack of agreement on tests and evaluation methods

represents an obvious hindrance to more widespread applications of composites offshore.

It is thought that some of the fire protection methods listed above could find application to hydrocarbon containing systems when such service becomes acceptable to offshore operators and

the authorities. However, general opinion in Norway on the use of composite materials for

hydrocarbon service is that acceptability may be dependent firstly on further developments in the area of non-destructive evaluation of composite materials. Recent developments in this area appear

promising. This, combined with a risk analyses approach to set function requirements and

verification testing approaches, should result in an eventual acceptance for composite materials in

this role. CONCLUSIONS

1 . Current uses of composite materials offshore can be safety classified with respect to necessity

for function during an accident/emergency situation.

2. When no function during an emergency is required, a relatively simple safety evaluation of

possible composite materials uses offshore may be sufficient. Lack of necessary function is confirmed by assuring component failures would not increase personnel risks or result in

escalation of an accident event.

3. When function during an emergency event is required, more extensive safety evaluation of

offshore composite systems is needed. This evaluation may include a formal risk analysis and

verification explosion and fire testing.

4. Wider application of composite materials offshore is hampered by lack of generally accepted

explosion/fire testing techniques and evaluation methods.

ACKNOWLEDGEMENTS

Amoco expresses thanks to Valhall/Hod field partners Amerada Hess Norge, Elf Petroleum Norge

and Enterprise Oil Norge for their continued support for the application of composite materials

324
offshore. The cooperative attitude of the Norwegian Petroleum Directorate in these efforts is also

appreciated.

REFERENCES

1. Ciaraldi, S.W., J.D. Alkire and G.G. Huntoon, "Fiberglass Firewater Systems for Offshore

Platforms," paper OTC 6926 presented at the 24th Annual Offshore Technology Conference,

Houston, May 4-7, 1992.

2. Ciaraldi , S. W., "Risk Assessment Approach to Offshore Safety: Part B - The Valhall

Firewater System: A Case Study, " paper SPE 24775 presented at the 67th Annual Technical

Conference and Exhibition of the Society of Petroleum Engineers, Washington D.C., 4-7

October, 1992.

3. Ciaraldi, S. W., "Experiences From the Offshore Installation of a Composite Materials

Firewater System," paper 93-893M presented at the 12th Intl. Offshore Mechanics and

Arctic Engineering conference, ASME/TWI, Glasgow, Scotland, U.K., 20-24 June, 1993.

4. Lundh, T., Advanced Materials A/S, Sandefjord, Norway, private communications,

December, 1992.

5. Norwegian Petroleum Directorate, "Regulations Concerning the Implementation and Use of

Risk Analysis in the Petroleum Activities with Guidelines," Stavanger, Norway, August

1990.

6. Olstad, H., "Risk Assessment Approach to Offshore Safety: Part A: Norwegian Regulatory

Philosophy," paper SPE 24774 presented at the 1992 SPE Annual Technical Conference and

Exhibition, Washington D.C., October 4-7.

7. Norwegian Petroleum Directorate, "Regulations Concerning Emergency Preparedness,"

Stavanger, Norway, April 1992.

8. Technica A/S, "Relative Merits of Conventional Steel Versus GRE in Firewater System Risk

Assessment," Project No. N558, Stavanger, Norway, August 23, 1990.

9. Haverstad, T. A., "Explosion and Fire Testing, Report Part 13," Final Report -

Specifications and Test Methods (in Norwegian), SINTEF FCB Report STF65 A88027,

Trondheim, Norway, 1988.

325
326
6. Working Groups and

Discussion Summary Reports

327
328
6.1 Summary and Recommendations of Working Group #1

on

Fabrication, Construction, Maintenance, and Repair

6.1.1 Working Group #1 Members

Chairman:

Gerry G. Greaves, Technical Center, Owens Corning Fiberglass Corporation, Granville,

Ohio

Cochairman:

Christopher J. Houghton, Phillips Petroleum Co. UK, Ltd., Woking, Surrey, United

Kingdom

Members:

Mark J. Courtney, Composite Products Group, Hercules, Inc.,

Wilmington, Delaware

Chris Lundberg, Spyro Tech, Lincoln, Nebraska

Richard S. Parnas, Polymers Division, National Institute of Standards

and Technology, Gaithersburg, Maryland

Michael A. Smoot, DuPont Company, Newark, Delaware

Doug Wilson, Fibers and Materials, BP Chemicals (Hitco), Inc.,

Santa Ana, California

6.1.2 Summary of Discussion

The working group was well attended by representatives of material suppliers, fabricators, oil companies, and government agencies. It began with presentations from each of the panelists

(copies of the presentations or papers, as available, are included). Group members then identified,

defined, and grouped applications. They thought the needs for each group of applications could

be different. For some applications, the technology exists and can be transferred from other

applications. For others, there are significant technological hurdles. For each group of applications, the products, typical dimensions, key requirements, fabrication methods, time horizon,

technology hurdles, research needs, and implementation recommendations were discussed.

Summaries for each of the following applications are given in the Tables 1 through 4.

• High pressure > 49 bar, topside, risers, subsea, flow, and downhole tubing

• Tanks — vented and vessels — high pressure < 5,000 psi

• Low-pressure pipe <40 bar

• Secondary structures — panels, grating housing, handrails

• Primary structure — subsea manifold and well-head protection "beams"

329
The attached general recommendations can be grouped into the following areas:

• Nondestructive evaluation

• Design and construction manual

• Education

• Joints, fittings, and penetrations

• Joint industry programs

Oil companies are aggressively pursuing means to reduce offshore construction and, thus,

operating costs to maintain profits at reduced oil prices. After discussing many potential composite applications for offshore operations, it was clear that existing composite technology can fill needs in many areas; successful performance has been demonstrated in some applications.

330
Table 1. Potential Offshore Composite Applications: Tanks and Vessels

Product(s)

Tanks:

Vessels:

vented

high pressure £5,000 psi

Typical Dimensions

Tanks:

Vessels:

14 m diameter * 14 m

1-3 m diameter x 10-12 m

Key Requirements

Chemical resistance (to hydrocarbons, H2S, C02) 120°C

Leak before burst capability

Impact resistance

Fire resistance

NDE

Repair techniques

Nozzle design

Thermal cycling

Long-term performance (30-70 years)

Fabrication Methods

Filament winding

Pultrusion

Time Horizon

Vented tanks: Short term

HP vessels: Medium term

Technology Hurdles

Side penetrations

Design concepts

Materials

Research Needs

331
Table 2. Potential Offshore Composite Applications: Low-Pressure Pipe

Product(s)

Low-Pressure Pipe (<40 bar)

Typical Dimensions

1-30-in diameter

Key Requirements

More cost effective fire resistance

NDE on joints

Fabrication Methods

Filament winding with fire-protective coating

Pultrusion

Time Horizon

Short term: <3 years

Technology Hurdles

Low-cost, integral fire-resistant system

NDE defect assessment

Research Needs

Define low-cost fire-resistant material

Identify critical-flaw acceptance criteria

332
Table 3. Potential Offshore Composite Applications: Secondary Structures

Product(s)

Secondary structures: panels, grating, housing, handrails

Typical Dimensions

Various dimensions (panel: 8 m x 3 m)

Key Requirements

Impact resistance

Fire resistance

Fabrication Methods

Pultrusion

Contact molding

Resin-transfer molding (RTM)

Time Horizon

Short term

Technology Hurdles

Education

Construction experience?

Improved fire resistance

Research Needs

Life-cycle cost and weight savings analysis

Document case histories

333
Table 4. Potential Offshore Composite Applications: Primary Structures

Product(s)

Primary structures Subsea manifolds and well-head protection "beams"

Typical Dimensions

Well-head protection: 30 m x 30 m

Key Requirements

Interface with other materials

Long-term performance

Life-cycle cost

Repairs

NDE

Impact resistance

Fabrication Methods

To be determined

Pultrusion

Time Horizon

Long term

Technology Hurdles

To be determined

Research Needs

Fabricationjofjargg| iifakk mroayras ____

334
6.2 Summary and Recommendations of Working Group #2

on

Material Performance, Damage Tolerance, Durability,

and Environmental Degradation

6.2.1 Working Group #2 Members

Chairman:

John P. Dismukes, Exxon Research and Engineering Company,

Annandale, New Jersey

Cochairman:

Allan S. Chiu, Imperial Oil Resources, Ltd., Calgary, Alberta, Canada

Recording Secretary:

Leif A. Carlsson, Florida Atlantic University, Boca Raton, Florida

Members:

Walter L. Bradley, Texas A and MUniversity, College Station, Texas

E. T. Camponeschi, U.S. Navy NSWC — Carderock Divison,

Annapolis, Maryland

Gary E. Hansen, Hercules Aerospace Company, Materials Technology,

Magna, Utah

Arnold Lustiger, Exxon Research and Engineering Company,

Annandale, New Jersey

Liza M. Monette, Exxon Research and Engineering Company,

Annandale, New Jersey

John A. Nairn, University of Utah, Salt Lake City, Utah

Robert G. Pearce, Brunswick Composites, Lincoln, Nebraska

Sandy Sternstein, Rennselaer Polytechnic Institute, Troy, New York

Francis S. Uralil, Westhollow Research Center, Shell Development Company,

Houston, Texas

6.2.2 Summary of Discussion

6.2.2.1 Background and Scope of Assessment

About 35 panelists and members of Working Group #2 participated in the definition of scope

and assessment of specific issues underlying material performance, damage tolerance, durability,

and environmental degradation of composite materials now being used or under consideration for use in offshore petroleum production operations.

335
Although recognizing that metal-matrix and ceramic-matrix composites could be suitable, the

group focused on fiber-reinforced, polymer-matrix composites because the oil industry has had

experience with low-cost polymer composites in secondary structural applications and because

they have potential in primary-load structural applications. The discussions centered on two areas of materials performance: mechanical performance and environmental response.

Following the presentations by panelists on October 26, all participants reviewed and

evaluated information and assessed the issues that had been raised in submitted questionnaires and

by individuals at the meeting. The range of topics reviewed as a basis for recommendations on the use of polymer composites in offshore operation included

• Performance requirements of polymer composite materials and structures

• State of the practice in their use in offshore drilling and production

• State of the art for potential use in offshore drilling and production

• Economics of their safe and effective use in offshore operations

• Technology hurdles in achieving prototype and commercial use

• Research needs and priorities for overcoming technology hurdles

The group structured its deliberations from the viewpoint of identifiable applications,

specifically:

• Piping, fittings, and valves (water or process fluids)

• Tanks and vessels (internally or externally loaded)

• Secondary structures (gratings, handrails, cable trays, panels)

• Mechanical components (drive shafts, turbines)

• Downhill tubular structures (drill pipe, tubing, coil tubing, umbilical tubing)

• Drilling/production risers (all composite and composite/metal)

• Primary structures (tendons, mooring ropes, beams, and plate)

Then it identified the following general incentives, based on reductions in operating expense

(OPEX) and capital expenditures (CAPEX), for utilization of polymer composite materials and

structures in existing and new applications:

• Corrosion resistance/life-cycle cost reduction

• Fatigue resistance/longer life

• Ease of fabricatioiVconstruction

• Low-temperature joining/installation

• Parts consolidation/tailored properties

• Enabling properties/system enhancement

6.2.2.2 Polymer Composites in Offshore Operations: State of Practice

For more than 25 years, polymer composite materials have been used in secondary structures onshore. Diffusion of commercial practice to offshore operations has progressed slowly but

steadily, as cost effectiveness and the requirements for safe and effective use (e.g., under fire exposure) have been demonstrated. Current offshore uses can be grouped into three categories:

336
• Low-pressure piping (<300 psi; <65 °C) - fresh and waste water - nonflammable liquid chemicals (hypochlorite, glycol, drilling fluids) - fire water

• Tanks and vessels (<150 psi; <65°C) - applications not critical during fire

• Secondary structures

(if not primary escape route or potential location for hydrocarbon jet or pool fire) - gratings - handrails - fire and blast walls with flame-resistant coatings

6.2.2.3 Polymer Composites in Offshore Operations: State of the Art

The state of the art of polymer composites applicable to offshore operations is based on

existing onshore commercial use by the oil industry, ongoing Joint Industry Program (HP)

development by the oil industry in collaboration with the composite industry, developments taken

from the aerospace industry, and governmental demonstrations and commercialization (e.g., U.S.

Navy). The general incentives above justify both short- and long-term interest in the following

performance capabilities and applications:

• High-pressure piping (300 psi < pressure < 4000 psi; temperature < 120° C) - water - hydrocarbons - flexible pipe - high-performance liners

• Tanks and vessels - accumulators (1-2 ft diameter, <4000 psi) - fuel tanks (no leaks in 15 in/fire exposed) - LPG tanks (weep before break)

• Secondary structures - improved fire resistance (phenolic resins/thinner protective coatings)

• Downhill tubular structures - drill pipes (small radius and extended reach) - coiled tubing (ongoing JIP)

• Primary structures - risers (prototypes tested/development ongoing) - TLP tethers and mooring ropes (ongoing JTP) - pultruded structural components/I-beams (ongoing HP)

• Mechanical components - drive shafts and valves (U.S. Navy)

337
6.2.2.4 Gaps between State of the Art and State of Practice

The group determined that there are four gaps that represent hurdles to be overcome in

realizing the state of practice, discussed above, in commercial offshore operations.

• From an operational standpoint, the first is cost. The importance of evaluating cost at the system level cannot be overemphasized, since many of the benefits of polymer

composites are achieved after a redesign of the system structure rather than a piece-bypiece substitution at the component level (e.g., for steel).

• Demonstration and proof of designs and of manufacturing technology are required

before turning the concept into a product.

• The cost effectiveness and manufacturability by the supplier of polymer composite

materials and structures for reliable long-life service in offshore operations must be

accepted by the operator.

• Regulations on fire resistance, structural performance and reliability, and environmental

durability under offshore conditions must be met.

The group concluded that these four gaps are interrelated, so that cooperative efforts by composite manufacturers, offshore fabricators, operators, and regulatory agencies are required to prove design concepts by product testing and to us this as a basis for operator and regulatory

acceptance. One example is the performance and cost advantages of composite risers has to be

demonstrated for depths of 3000 ft and more. Another example is demonstration of a costeffective design for polymer composite piping that will overcome the current 6 to 10 ksi "weeping

stress" threshold and the operating temperature limit of about 65 °C.

6.2.2.5 Technology Gaps between State of the Art and New Opportunities:

Primary Structures

The group concluded that the generic incentives described above for polymer composite

materials and structures could have the greatest impact in the area of primary structures, provided

that economics at the system level can be shown to be competitive with existing primary

structures, which are typically based on steel. In special applications, metal-matrix or ceramicmatrix composites may be appropriate. To meet these challenges, a number of technological

issues need to be addressed; they are

• The stiffness in the design may be critical.

• Residual strength is required after exposure to fire.

• Multiaxial loading, in tension and compression, must be considered.

• Environmental degradation of fiber, matrix, and interface must be understood and

prevented. Particularly important here are the combined effects of stress and the

environment (e.g., heat, radiation, water C02 , H2 S, and hydrocarbons).

• Galvanic corrosion is an issue for metal/composite joints and for potential

leaching out of the matrix from the composite.

• Static electrical discharge may be a problem.

• Fatigue under tension and tension/compression loads must be understood and

prevented.

338
6.2.2.6 Key Research and Development Initiatives

The group discussions indicated that a number of research and development initiatives can have a strong impact in overcoming the technical and infrastructural gaps and hurdles identified

and outlined above. Participation by the oil industry, the composites industry, the oil-field equipment-fabrication industry, and government regulatory agencies in a focused effort is required

to provide the most rapid and cost-effective route to commercial acceptance of polymer composites in new applications for offshore operations. Important initiatives are

• Establish requirements for fire resistance in composites. - fire-resistant resins (less burning, less-toxic fumes) - cost reduction of fire-resistant coatings

• Review/explore reinforcement lay-up, volume fraction, and discontinuous fiber

systems.

• Establish methodologies for life prediction in offshore environments based on

mechanistic understanding of failure processes.

• Define standardized material systems for testing and database development

(material systems are application specific).

• Develop cost-effective processes for manufacture of offshore components.

• Investigate joining of components.

• Establish requirements for damage tolerance that are linked to sequential evolution of fracture and final failure.

• Develop inspection methodologies that are linked to sequential evolution

of fracture and final failure.

6.2.2.7 Overall Conclusions and Recommendations

The most promising applications that can benefit from utilization of polymer composite

materials and structures in offshore operations were identified for the short and long term. The

Working Group #2 assessment established that the state of practice in secondary structural

applications is growing rapidly and confirmed the vision that there are strong incentives for

extending the offshore use of polymer composites into primary structural applications.

To reap this potential, cooperation and collaboration among the oil industry, materials

suppliers, fabricators, and independent and government regulatory agencies is critically needed.

Once facet of this effort should include a forum for continued international dialogue and interaction, which is essential for exchange of research and prototype development results, decisions on

regulatory requirements, and diffusion of commercial technology.

To provide guidance for more widespread application of existing design and application

practices and to prepare for new opportunities in primary structures, current knowledge of

polymer composites applicable to upstream operations should be captured and documented in a

data base for the education of designers, users, and regulators.

339
To bridge the technology and infrastructural gaps between the state of the art and new

opportunities, interdisciplinary and interorganizational research initiatives should be structured to provide fundamental understanding in enabling technologies and to implement development and

demonstration programs as a basis for manufacturing capability, operator acceptance, and

regulatory endorsement.

340
6.3 Summary and Recommendations of Working Group #3

on

Structural Design, Optimization, Testing, and Reliability

6.3.1 Working Group #3 Members

Chairman:

S. W. Tsai, Stanford University, Stanford, California

Cochairman:

T. Lundh, AMAT, Sandefjord, Norway

Recording Secretary:

K. H. Lo, Westhollow Research Center, Shell Development Company,

Houston, Texas

Members:

B. W. Cole, Amoco Research Center, Amoco Corporation, Naperville, Illinois R. D. Beck, Tulsa Research Center, Amoco Production Company,

Tulsa, Oklahoma

G. C. Eckold, AEA Technology, Oxfordshire, United Kingdom

D. B. Johnson, Brunswick, Lincoln, Nebraska

W. Phyillaier, U.S. Navy, Carderock, Maryland

J. G. Williams, Conoco, Inc., Ponca City, Oklahoma

6.3.2 Summary of Discussion

Observations

• Component design with advanced composites is based on material data.

• FRP pipe and fitting design is based on component test results.

• Composite material knowledge must be incorporated into design.

Key Elements

• Joint industry development and commitment to design and performance specifications

(users, manufacturers, suppliers, regulatory agencies)

• Uniform acceptance criteria and standards

341
Desirable Capabilitiesfrom Manufacturers

(in cooperation with users and suppliers)

• Analytical design capability for product improvement and critical applications (design

guidance)

• Ability to account for environmental effects on component performance

• Qualification testing to verify products and fabrication processes

• Manufacturing procedures, such as ISO 9000, to ensure reliability

• User-friendly system design capability (for application engineers)

• Reliability — risk assessment

• Optimization procedures

• Training

Available General Analytical Capability

• 2-D models capable of analyzing progressive failures and contacts

• Simulation of manufacturing defects, operational damage, and repair

• Rational acceptance, rejection, and repair criteria

• 3-D models and optimization capability currently under development

FRP Line Pipes and Fittings

• Low-pressure applications

• High-pressure applications - composite mechanics - controlling failure mechanisms - fabrication parameters - composite-to-metal connections - long-term performance (R&D, engineering)

o biaxial loading/failure criteria o design limits o relevant time-dependent rupture data

o available design tools (?) - temperature, pressure, and environmental interaction - uniform testing methods - optimization procedures

Composite Coiled Tubing

• Design tailoring to enhance helical buckling resistance

• Design strain limits

• Cross-section ovalization on spooling

342
Designfor Impact Resistance

• Impact specification/performance requirement

• Differences in shell and plate behavior

• Thin-walled vs. thick walled construction

343
344 I
6.4 Summary and Recommendations of Working Group #4

on

Nondestructive Evaluation, Condition Monitoring, and Inspection

6.4.1 Working Group #4 Members

Chairman:

Dale W. Fitting, National Institute of Standards and Technology, Boulder, CO

Co-Chairman and Recorder:

Allan Boye Hansen, AMAT, Sanderjord, Norway

Members:

Edward C. Grenawald, Geo-Centers, NRL, Ft. Washington, MD

William D. Cook, University of Houston, Houston, TX

Robert Finch, University ofHouston, Houston, TX

Russ Fairies, McDonnell Douglas, ST. Louis, MO

6.4.2 Summary of Discussion

6.4.2.1 The State of Practice in Composites NDE

The state-of-practice for nondestructive evaluation (NDE) of composite materials was judged

by the working group to be immature. There is very little in-service NDE performed. Uses of

composite materials thus far have largely been in low-criticality applications, where NDE was deemed

unnecessary. Some post-fabrication inspection is now done as a check on materials fabrication or construction installation. There seems to be little driving force for NDE at present. The general

feeling is "If regulations do not require it, why do it? It costs money."

The working group suggests the following answers to the question "Why do it?". For the

materials supplier and fabricators, assurance of product quality is economically advantageous since users of composites will buy quality materials and structures and avoid inferior products. A supplier

of inconsistent products will lose market share. For users of composite materials, assurance of safety

is of primary importance. The costs of a catastrophic failure are huge. There is the possibility of loss

of human life. Failure of a structure carrying petroleum products can lead to a devastating

environmental impact. Additionally, lost production from a structural or key system failure can run

into the millions of dollars.

Nondestructive testing of offshore composite structures has been limited to visual inspection,

pressure or leak testing, acoustic emission, several forms of ultrasonic testing, and more recently,

thermography. NDE is most often used after the first failure. An awareness of the need for NDE

exists; however, there is a severe lack of commitment to development and implementation of

nondestructive test procedures. The consequence of different flaw types in composites is also poorly

understood.

345
Because of human factors, NDE will be necessary, even is the material is perfect. Damage may

occur during transport to the offshore site and in handling the material. Improper assembly of

composite systems can occur. There can be incidental damage during use of the composite structure from impact damage or over pressures. Even though composites are used for their resistance to corrosion, environmental degradation from ultraviolet radiation and harsh weather can occur.

6.4.2.2 State of the Art in Composites NDE

Composites NDE is highly advanced for "in-lab" inspections. NDE research has been highly

funded for the last 20 years and a large number of techniques (relevant to composites) have been

developed. Most methods; however, have not been developed to the level where a technician can use them in the field. A high skill level is presently required to perform many nondestructive tests and

the interpretation of test results often requires a person of considerable skill. A wide variety of test methods are applicable to composites (Table 1). Some useful references which have surveyed or evaluated these methods are given at the end of this paper.

6.4.2.3 Global Condition Monitoring

It is imperative that global condition-monitoring methods be developed. These systems would

indicate whether there have been any significant changes in a material or a structure. If no changes

have occurred, the structure is likely to be in satisfactory condition. Should changes be observed, the

structure may be examined in a detailed fashion. Global monitoring methods help develop confidence

in new composite materials and structures. Such methods may also satisfy regulatory requirements

for assessing the "health" of a structure.

Table 1. Methods applicable to NDE of offshore composites.

• Acoustic emission • Nuclear magnetic resonance

• Electrostatic (capacitive) • Penetrant

• Hardness • Radiography

• Holography • Shearography

• Leak testing • Thermography

• Microwave Leak testing • Ultrasonics

• Modal analysis • Visual

346
Figure 1 shows a typical plot of the probability of failure of a material or structure as a

function of time. During a structure's infancy, failures occur with a higher incidence as the bad

parts are weeded out. During the service lifetime of a part, failure is unlikely. As the time of use approaches the end of its lifetime the incidence of failure increases. Removing a structure from

use as failure begin to be more common, prevents a catastrophic failure and uses the part for the

maximum time. The service lifetime is not only a function of the material type and manufacture,

but varies with the service history. Global monitoring can be used to gain confidence in the

lifetime assessment of a structure. It is a means for following a material or structure through its history from "cradle to grave." Global methods, which can be used to inspect large areas

inexpensively, should be used to monitor a structure periodically and also to record any events of

significance.

An example of a global monitoring method is the use of acoustic emission sensors in piping

to detect and localize leaks and impact damage. Optical methods, because they are inexpensive

and easy to implement, would be particularly useful for structural monitoring. An adhesive or a

structural material which changes color when subjected to abnormal strains or temperatures is a good example of a foolproof optical method. Attached or embedded sensors to monitor strain

and temperature have been proposed, but tests have not been performed on marine composites.

6.4.2.4 Recommendations

The desired characteristics of an NDE system for inspection of offshore oil structures are

listed in Table 2. System developers should refer to the table for guidance. There is a wide gap

between the state-of-the-art (high-technology laboratory systems) in marine composite NDE and

the state-of-practice (low tech methods such as visual inspection). Table 3 lists the recommendations of the working group for closing the technology gap.

varies with

Time

Figure 1 . Probability of failure of a structure as a function of time.

347
Table 2

Desirable NDE system characteristics.

• Desired material characteristic is measured

directly and quantitatively

• Method must be highly developed — The physics should be well understood — System optimization should be possible

• Global, as well as local, methods are needed

• Method is capable of rendering reliable data even under harsh conditions — Cold, heat, humidity, salt, undersea

• Cost of inspection is low

• System is portable

• Procedure is adaptable to a variety

of material systems

• Tests are reproducible — You get the same answer at various

times and with various operators

• Skills required for system use are easily

taught

• High reliability —Few false positives (don't "cry wolf

too often) —Few false negatives (missing a

significant flaw can be catastrophic)

• Easy to interpret test results

Table 3. Recommendations of Working Group #4.

• Fund a global condition monitoring project

• Gather a set of typical composite elements with

and without flaws (and substandard

material properties) for NDE system developers

• Be willing to design in inspectability

• Transfer technology from the laboratory to offshore

(Fund development of robust, portable systems)

• Give NDE a higher priority

(Don't make it an afterthought)

• Develop an assessment of flaw criticality

(What is the consequence of various types of flaws on

long-term performance?)

• Use a multiplicity of sensor types to decrease

false positives and false negatives

348
6.4.3 References

1 Summerscales, J. ed. Non-Destructive Testing of Fibre-Reinforced Plastics Composites,

volume 1, Barking, UK Elsevier; 1987.

2 Summerscales, J. ed. Non-Destructive Testing of Fibre-Reinforced Plastics Composites,

volume 2, Barking, UK Elsevier; 1990.

3 Summerscales, J. NDT of advanced composites — An overview of the possibilities,

British J. NDT, 32(11), 568-577 1990.

4 Summerscales, J. Manufacturing defects in fibre-reinforced plastics composites, Insight,

36(12), 936-942 1994.

5 Summerscales, J. Non-destructive examination of fibre-reinforced composites, Proceedings of maritime and offshore use of fibre reinforced composites, sponsored by Marinetech North West and Organized by IBC Technical Services Ltd., 1992 June.

6 Special Feature on Petroleum, Oil and Gas, Insight (Br. J. NDT), 36(6); 1994 June .

7 Special Feature on Offshore, Oil and Gas, Insight (Br. J. NDT), 36(9); 1994 September.

8 Special Feature on Civil Engineering, Insight (Br. J. NDT), 36(7); 1994 July.

9 Suprenant,B.A.; Sture, S. ;Noland, J.L.; Schuller, M.P, eds. Proc. of the nondestructive evaluation of civil structures and materials conference, University of Colorado,

October 1990 (Atkinson-Noland and Associates; 2619 Spruce Street; Boulder, CO

80302).

10 Suprenant, B.A.; Noland, J.L.; Schuller, M.P, eds. Proc. of the nondestructive evaluation of civil structures and materials conference, University of Colorado, May 1992

(Atkinson-Noland and Associates; Boulder, CO 80302).

1 1 Matzkanin, G.A., ed. Nondestructive evaluation of fiber reinforced composites, a state- of-the-art survey, volume 1, NDE of graphite fiber-reinforced plastic composites, March

1982 (Nondestructive Testing Information Analysis Center, NTIAC; 6220 Culebra Rd.;

San Antonio, TX 78284).

12 Bar-Cohen, Y. Nondestructive evaluation (NDE) of fiber glass marine structures, state- of-the-art review, Report CG-D-02-91 to the U.S. Coast Guard and U.S. Department of

Transportation (1990) (USCG; Avery Point; Groton, CT 06340)

349
13 Light, G.M. ; H. Kwun Nondestructive evaluation of adhesive bond quality", NTIAC89-1 (1989) (NTIAC; San Antonio, TX 78284)

14 Greene, E. ed. Use of fiber reinforced plastics in the marine industry, SSC-360, (1990)

Contains sections on applications, materials, performance, fabrication, as well as NDT.

(Ship Structures Committee; U.S. Coast Guard; 2100 2nd St. S.W.; Washington, DC

20593)

15 Fitting, D.W.; Fortunko, CM.; Teller, CM. Nondestructive evaluation of composites

used in marine structures", vol. 2, 219-234 in Use of Composite Materials in LoadBearing Marine Structures, volume 1 - Summary Report and volume 2 - conference

proceedings, Stavovy; A.; R.B. Pipes eds., 1991 (NTIS; 5825 Port Royal Road;

Springfield, VA 22161)

350
6.5 Summary and Recommendations of Working Group #5

on

Flammabiliry and Fire Retardation

6.5.1 Working Group #5 Members

Chairman:

J. D. Alkire, Amoco Corporation, Naperville, Illinois

Cochairman:

M. D. Bishopp, Safety Analysis Unit, Health and Safety Executive,

Liverpool, United Kingdom

Recording Secretary:

Steve Ciaraldi, Amoco Norway Oil Company, Stavanger, Norway

Members:

T. Kashiwagi, National Institute of Standards and Technology,

Gaithersburg, Maryland

Dennis A. Nollen, DuPont Company, Wilmington, Delaware

L. C. Shirvill, Shell Research, Ltd., Chester, England, United Kingdom

U. Sorathia, Naval Surface Warfare Center, Department of the Navy,

Annapolis, Maryland

6.5.2 Summary of Discussion

Technical issues regarding flammability and fire retardation that must be addressed are listed

below. Suggestions for procedures for implementing improvements are shown in the flow diagram

of Figure 1.

Fire Modeling

• Fire models linked to structural models

• Model of fire performance applicable to design - validate for offshore

Fire and Blast Tests

• Scale — agility - small — large - large — small

• Effect of fire/structure ratio

• Historical/statistical data base development

351
• Utilization of failure modes - standardized test methods vs. specific application

• Methodology - performance based (adopt and develop)

oUKOOA

oNIST

- fire safety of system vs. parts

Performance Requirements

• Specific location on platform (location/application)

• Conflicting requirements

• Regulatory buy-in (participation)

• Breakdown by element (i.e., smoke/toxic)

Economics

• Barrier

• Coatings - materials - installation

• Life-cycle costs - data base

Implementation

• Education on fire performance

• Training — human interface (what to expect)

• Communications - designers - labs - users - regulators - manufacturers

• Case history data base (good/bad)

• Demonstration project

• US/UKOOA information group

• Support infrastructure

• Professional societies (SPI, SACMA)

Other

• Overall safety - installation - maintenance

352
Set Acceptance Standards

T

Analyze arrangements

against risks

T

Compare arrangements

against acceptance standards

Pass

Establish performance standards

Prepare and implement

arrangements

Modify

Arrangements

i

Monitor/Audit

Figure 1. Suggestions for procedures.

353
354
6.6 Summary and Recommendations of Working Group #6

on

Facilities and Secondary Structural Applications

6.6.1 Working Group #6 Members

Chairman:

Ram Anatharaman, Fiberglass Pipe Division, Ameron, Inc., Burkburnett, Texas

Cochairman:

George G. Huntoon, Amoco Production Company, Houston, Texas

Members:

Mark E. Greenwood, Owens Corning Fiberglas Corporation, Granville, Ohio

R. H. (Dick) Lea, Specialty Plastics, Inc., Baton Rouge, Louisiana

Bill McDonald, Smith Fiberglass Products, Inc., Houston, Texas

R. M. (Mike) Rainey, Shell Offshore, Inc., New Orleans, Louisiana

Fernand Vidouse, Elf Autochem, Lacq, France

6.6.2 Summary of Discussion

(No report available)

355
356
6.7 Summary and Recommendations of Working Group #7

on

Advanced Applications

6.7.1 Working Group #7 Members

Chairman:

MamdouhM. Salama, Conoco, Inc., Ponca City, Oklahoma

Recording Secretary:

Bart Thomeer, Dowell Schlumberger, Rosharon, Texas

Members:

Jemei Chang, Materials Section, Exxon Production Research Company,

Houston, Texas

F. Joseph Fischer, Bellaire Research Center, Shell Development Company,

Houston, Texas

Alex Y. Lou, Corporate Engineering, Phillips Petroleum Company,

Barlesville, Oklahoma

Alexander Sas-Jaworsky II, Production Technology, Conoco, Inc., Houston, Texas

Winston Webber, Halliburton Manufacturing and Service, Ltd., Arbroath,

Scotland, United Kingdom

Warren J. Winters, Tulsa Research Center, Amoco Production Company,

Tulsa, Oklahoma

6.7.2 Summary of Discussion

Innovations and technological advances are essential to the success of the offshore industry in

meeting the challenges of exploiting natural resources in deeper waters. Oil and gas explorations

in water depths exceeding 7000 ft (2100 m) and field development at a depth of 2900 ft are currently underway. Although the traditional engineering material for offshore structural

applications is steel, other materials (e.g., composites) are now being seriously considered for

several critical applications. The primary motives for using composites are to improve efficiency

and reliability and to reduce life-cycle cost. The advantage of using these engineered materials can

be easily demonstrated for structural systems where high strength, light weight and superior

corrosion and fatigue resistance, as well as tailoring to meet other specifications (e.g., for stiffness

and thermal expansion), are required. The use of composites also enables greater design flexibility

and promotes system-oriented solutions. Efficient exploitation of composite materials dictated by

economic or performance requirements is possible if materials, structural, and manufacturing

technologies are utilized in an integrated approach.

357
In an effort to achieve this goal, the University of Houston organized the First International

Workshop on Composite Materials for Offshore Operations. One of eight working groups,

Working Group #7 focussed on advanced applications: barriers to the application of composites

and how to resolve these barriers. Presentations were made by Joseph Fischer of Shell, Bill

Anderson of Westinghouse Marine, and Doug Johnson of Brunswich on the use of composites for

producing and drilling risers and riser stress joints. Doug Johnson also reviewed Brunswick's

development of composite drill pipes. Alex Sas-Jaworsky of Conoco and Joe Roche of Hydril

reviewed current efforts to develop high-pressure composite coiled tubing for workover, drilling,

and completions. Charles Rogers presented the joint effort ofNEPTCO and Bell Helicopter to

develop highly aligned, continuous carbon-fiber rods that can be used for the construction of

tendons. Winston Webber of Halliburton reviewed the application of composites to tanks and

vessels and discussed problems associated with persuading certifying authorities to accept

composites. Jemei Chang of Exxon reviewed several oil industry applications for onshore,

downhole, and offshore. These applications included tubing and casing, piping, subsea well-head

protectors, reinforcement for flexible pipe, and cable tray.

The second part of the working group activities focussed on identifying current barriers to the

application of composites and how to overcome them. Detailed discussion on this subject is presented in the paper by Mamdouh Salama. Several needs were identified: the need to demonstrate economic benefits more than performance benefits; the need to evaluate a complete system

rather than focus on component substitution; the need to produce building blocks; the need to develop alliances and consortia to leverage the limited available resources; and the need to recognize that the oil industry is structurally different from the aerospace industry. The final message was that members of the offshore industry desire and are ready for the use of composites

because they are convinced that they offer the opportunity to improve operations and life-cycle costs.

Highlights of the discussion follow:

Composites —Applications

• Mooring/tendons

• Drilling/production risers

• Tubing

• Taper joints

• Coiled tubing

• Drill pipes

• Vessels

• Pipe

• Torque shaft

• Structural parts

• Seals

• Other

358
Applications

• Tubular pressure barrier - continuous: spoolable pipe (coiled tubing, flow lines) - discrete: production/drilling risers; taper joint

• Tendons (assembly of rods

Status of Technology

• Analysis: well developed

• Materials performance: wealth of data

• Fabrication: sufficient technology, low capital investment

• Inspection: adequate technology

Selection and Implementation ofComposites

• Feasible only when the payoff value is judged to be greater than the cost at acceptable risk.

Real Barriers

• Composites not considered enabling technology

• Performance requirements not well defined

• Insufficient cost savings for discrete systems

• Major investment required for reliability assessment

• Reactive oil industry — short attention span regarding needs

• Change of culture — outside comfort zone

• Less tolerant to failure

• Lack of available resources (qualified engineers)

• Limited financial resources for development

Technology Needs

• Definition of true function, not design parameters — remove constraints

• Design feasibility to establish total cost ±40%

• Quantification of component and system reliability

• Component demonstration

• Repair

Message

• Demonstrate benefit — economic not performance

• Design system based on function, not on component specifications

• Applications based on complete system, not substitution

• Production of building blocks needed

• Oil industry structurally different from the aerospace industry

• Alliances and consortia needed to pool resources and skills

359
Impact ofNew Materials

• Reduced development cost

• Reduced operating cost

• Increased reliability

• Improved safety/environment

Technology Issuesfor New Materials

• Performance

• Reliability

• System methodology

Composites — Technical Issues

• Performance

• Availability

• Cost

• Reliability

• Repair/inspection

360
6.8 Summary and Recommendations of Working Group #8

on

Certification Issues and Policy Concerns

6.8.1 Working Group #8 Members

Chairman:

Glenn M. Ashe, ABS Americas, Houston, Texas

Cochairman:

Maurice Stewart, U.S. Minerals Management Service, Field Operations,

New Orleans, Louisiana

Members:

Thor G. Dahle, Norwegian Petroleum Directorate, Stavanger, Norway

Rembert F. Jones, Jr., Carderock Division, Naval Surface Warfare Center,

Bethesda, Maryland

Ibrahim Konuk, National Energy Board, Calgary, Alberta, Canada

Ed Provost, Shell International Petroleum Maatschappij B. V.,

The Hague, The Netherlands

Chuck Rollhauser, Carderock Division, Naval Surface Warfare Center,

Annapolis, Maryland

Charles E. Smith, U.S. Minerals Management Service, U.S. Department

of the Interior, Herndon, Virginia

6.8.2 Summary of Discussion

(No report available)

361
362
List of Workshop Participants

363
364
Workshop Participants

Name, Title/Position

Aanonsen, Torbjom

Responsible, Composite Material

Technology

Alexander, James

Alkire, John D.

Research Supervisor

Anantharaman, A. S. Engineering and International Sales

Manager

Anderson, Traci

Engineering Supervisor

Andersen, William F.

Amey, Cyril E. Technology Development Manager

Ashe, Dr. Glenn M.

Director of Engineering

Bannerol, Dr. R B. Chairman

Barno, Douglas S. Market Specialist

Baron, John

Head Specialist, Nonmetallic

Materials

Company andAddress

Norwegian Contractors a/s Philip Pedersensuei 20

1320 Stabekk

Oslo, Norway

Exxon Production Research

P.O. Box 2189

Houston, TX 77252-2189

Amoco Corp.

150 W. Warrenville Road

MC: B-8

Naperville, IL 60563-8460

Ameron Fiberglass Pipe Systems

1004 Ameron Road

Burkburnett, TX 76354

3M

3M Center

Bldg. 60-1N-01

St. Paul, MN 55 144

Westinghouse Marine

401 E. Hendy Avenue

Mail StopEB-1

Sunnyvale, CA 94088

Marathon Oil Co.

5555 San Felipe

Houston, TX 77056

Technology and Business Development

ABS Americas

16855 Northchase Drive

Houston, TX 77060

Dept. of Mechanical Eng.

University of Houston

Houston, TX 77204-4792

Composites Institute 2635 Old Columbus Road

Granville, OH 43023

Shell Canada

Box 100

Calgary, Alberta T2P 2HS

Canada

Telephone and Fax Nos.

tel. (67) 12 96 37

fax (67) 12 99 90

tel. (713) 965-7168

fax

tel. (708) 420-5094

fax (708)961-7971

tel. (817)569-8643

fax (817)569-4102

tel. (612) 736-1842

fax (612)736-0431

tel. (408)735-2165

fax (408) 735-2048

tel. (713) 296-3249

fax (713) 296-3295

tel. (713) 874-6563

fax (713)874-8194

tel. (713) 743-4502

fax (713)743-4503

tel. (614)587-1444

fax (614)587-2187

tel. (403) 691-3207

fax (403) 262-9623

365
Name, Title/Position Company andAddress Telephone andFaxNos.

Barthold, Gregory B. Research Fellow

Bartholomew, H. G.

Beck, R. D.

Berscheidt, Kevin

Engineer III

Bhavsar, Rashmi

Manager, Materials Engineering

Bishopp, M. D.

H. M. Principal Specialist

Inspector

Bomba, John

Discipline Manager —Pipeline

Bowman, J. Michael

Vice President and General

Manager

Bradley, Dr. Walter L. Professor

Bravenec, Larry D.

Senior Research Engineer

Briggs, Gary

Technical Marketing Manager

ASME

1828 L Street NW

Washington, DC 20036

Mineral Management Service

Technology Assessment and

Research Branch

381 Elden Street, MS 4700

Hemdon,VA 22070-4817

Amoco Production Co.

Tulsa Research Center

P.O. Box 3385

Tulsa, OK 74102

Halliburton Energy Services

P.O. Box 1431

Duncan, OK 73536-0460

CAMCO Products and Services

P.O. Box 14484

Houston, TX 77221

Health & Safety Executive

Safety Analysis Unit

Tithebarn House

1-5 Tithebarn Street Liverpool, L2 2NZ

United Kingdom

Kuaerver Earl and Wright, Inc. 11111 Wilcrest Green, Suite 250

Houston, TX 77042

DuPont Fibers

P.O. Box 80,705

Wilmington, DE 19880-0705

Dept. of Mechanical Eng.

Texas A and M University

College Station, TX 77843

Shell Development

Resins Dept.

P.O. Box 1380

Houston, TX 77479

Brunswick Composites

15 119 River Perk

Houston, TX 77070

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

(202) 785-3756

(202) 429-9417

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

918) 660-3870

918) 660-3274

405) 251-3455

405) 251-3008

713) 749-5747

713) 749-5828

051)951-3111

051)951-3131

713) 260-7000

713) 260-7199

302) 999-5179

302) 999-4559

409) 845-1251

409) 845-3081

713) 544-8498

713) 544-8118

713) 379-2121

713) 379-2126

366
Name, Title/Position Company andAddress Telephone and FaxNos.

Brunsell, Paul

Senior Principal Surveyor/

Manager of Marketing

Buchanan, Michael

Account Manager

Cagle, Larry L. Vice President, Marketing

Caldwell, Trevor

Senior Facilities Engineer,

Deepwater

Camponeschi, Dr. E. T.

Carlsson, Dr. Leif

Professor

Chang, Jemei

Engineering Specialist

Chen, Chih-Chih

Manager, Polymers and

Composites

Chen, Dr. Y. C. Assistant Professor

Cheng, Paul C. Manager, Applied Systems

Chiu, Dr. Allen S.

Det Norske Veritas Classification

16340 Park Ten Place, Suite 100

Houston, TX 77084

Conoco, Inc. P.O. Box 2197

Houston, TX 77252

Smith Fiberglass Products, Inc. 2700 W. 65th Street

Little Rock, AR 72209

BP Exploration

P.O. Box 4587

Houston, TX 77210-4587

Materials Engineering

Code 601

NSWC-Carderock Division

U.S. Navy David Taylor

Research Center

Annapolis, MD 21402-5067

Dept. of Mechanical Eng.

Florida Atlantic University

Boca Raton, FL 33431

Exxon Production Research Co.

Materials Section, S-252

P.O. Box 2189

Houston, TX 77252

FMC Corp.

1205 Coleman Avenue

Santa Clara, CA 95052

Dept. of Mechanical Eng.

University of Houston

Houston, TX 77204-4792

Tenneco Gas Transportation Co.

P.O. Box 25 11 Houston, TX 77252-2511

Research & Technology Division

Research Center

Imperial Oil Resources, Ltd. 3535 Research Road N.W.

Calgary, Alberta T2L 2K8

Canada

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

(713) 579-9003

(713) 647-2867

(713) 293-6057

(713)293-6490

(501)568-4010

(501)568-4465

(713)560-5151

(713) 560-8866

(410) 267-2165

(410) 267-2530

(407)367-2651

(407) 367-2825

(713) 965-4097

(713)965-7860

(408) 289-3877

(408) 289-4429

(713) 743-4502

(713) 743-4503

(713) 757-3685

(713) 757-5009

(403) 284-7483

(403) 284-7595

367
Name, Title/Position

Chu, Dr. Wei Kan

Professor

Ciaraldi, Stephen W.

Senior Staff Petroleum Engineer

Coburn, Stan

Senior Staff Engineer

Coxon, Peter

Cole, Bill W.

Research Associate

Courtney, Mark J. Manager, Strategic Marketing

Cox, Joe

Product Development Engineer

Critchfield, Dr. M. O.

Head, Advanced Structures Group

Crow, Dan

Dahle, Thor G.

Principal Engineer

Dal Maso, Fabrice

Research Scientist

Davis, H. 0.

Vice President/Director,

Research and Development

Company andAddress

Texas Center for Superconductivity

University of Houston

Houston, TX 77204-5932

Amoco Norway Oil Co.

P.O. Box 388

Bergjelandsgata 25

N-4001 Stavanger

Norway

Quality Tubing, Inc. 4003 Evergreen Village Court

Kingwood, TX 77345

United States Coast Guard

Washington, DC

Amoco Corp.

150 W. Warrenville Road

MC: B-8

Naperville, IL 60563-8460

Composite Products Group

Hercules, Inc. Hercules Plaza

Wilmington, DE 19849-7099

Ameron Fiberglass Pipe Systems

1004 Ameron Road

Burkburnett, TX 76354

Naval Surface Warfare Center

Carderock Division

Bethesda, MD 20084-5000

Fiberflex, Inc. 5005 Riverway, Suite 100

Houston, TX 77077

Norwegian Petroleum Directorate

P.O. Box 600

N-4001 Stavanger

Norway

Institut Francais du Petrole 1-4 Avenue de Bois-Preau

Rucil-Malmaison Cedex

France

Kaiser Aerotech

880 Doolittle Drive

San Leandro, CA 94577

Telephone and FaxNos.

tel. (713) 743-8250

fax

tel. (51)50 22 38

fax (51)50 22 18

tel. (713) 360-6403

fax (713)456-7549

tel. (202) 267-2997

fax

tel. (708) 420-5597

fax (708) 961-7971

tel. (302) 594-6384

fax (302) 594-7099

tel. (817)569-1471

fax (817)569-0771

tel. (301) 227-1769

fax (301)227-1230

tel. (713)622-4482

fax (713) 622-7548

tel. (51)87 61 96

fax (51) 87 64 84

tel. (1) 47527187

fax (1) 47526429

tel. (501) 562-2456,

ext. 278

fax (510)568-6420

368
Name, Title/Position Company andAddress Telephone and FaxNos.

Davison, Douglas

Vice President

General Plastics and Rubber Co., Inc. 5727 Ledbetter

Houston, TX 77087

tel.

fax

(713) 644-1449

ext. 3

(713)644-6530

DeMoss, David H.

Systems Design/Applications

Engineer

Sepco

(320 Time Saver Avenue)

P.O. Box 10497

New Orleans, LA 70181-0497

tel. fax

(504) 733-7100

(504) 733-3310

Dismukes, John P. Senior Research Associate

Exxon Research & Engineering Co.

Advanced Materials Section

Corporate Research Laboratory

Route 22 East Annandale,NJ 08801

tel. fax

(908) 730-2997

(908) 730-3355

diSoudi, Lou

ACCP

Ameron FPD

13405 Northwest Frwy., Suite 1 17

Houston, TX 77040

tel. fax

(713) 690-7777

Dodendoff, John

Sales

Ciba Composites

2000 E. Lamar, Suite 600

Arlington, TX 76006

tel. fax

(817)588-3026

(817) 792-3398

Dorr, Andrea

Marketing Research Engineer

Zoltek Corp.

310McKelveyRoad

St. Louis, MO 63044

tel. fax

(314) 291-5110

(314) 291-8536

Edwards, Mark W.

Sales Manager

R-Cubed Composites

3392 W 8600 S

TTT i T 1 f\ 1 AAA

West Jordan, CT 84088

tel. fax(801)569-0401

(801)569-0817

Eichorn, Dr. Roger

Dean, College of Engineering

University of Houston

TJ_„_4.__ TV "7*71 A/1 AHOA Houston, IX //z(J4-4/yz

tel. tax

(713) 743-4200

(1 1 1\ HA 1 A^IA {li.5) /4J-4214

Ersdal, Rolf

Managing Director

COMPIPE tel. fax

Fairies, Russ McDonnell Douglas tel. fax

(314) 234-9318

Fischer, Dr. Eugene C. Head, Nonmetallics Department

Carderock Division NSWC

Annapolis, MD 21402

tel. fax

(410) 267-2574

(410) 267-2839

Fischer, Dr. F. Joseph

Research Advisor

Bellaire Research Center

Shell Development Co.

P.O. Box 481

Houston, TX 77001

tel. fax

(713) 245-7767

(713) 245-7233

Fitting, Dale W.

Materials Research Engineer

NIST IMC-853

Materials Reliability Division

325 Broadway

Boulder, CO 80303

369

tel. fax

(303) 497-3445

(303) 497-5030
Name, Title/Position Company andAddress Telephone and FaxNos.

Fogarty, Larry E. President

Fontenot, Jessie

Drilling Engineering Specialist

Frey, Bell

Manufacturing Engineer

Friedrich, R S. Engineering Division Manager

Frost, Simon

Scientist

Gathwright, Miles

Vice President, Project

Development

George, Boyd A.

Director, Engineering Research

& Service

George, Dev

International Editor

Gibson, Dr. A. G.

Professor, Roland Cookson Chair

of Composite Materials Eng.

Goins, 0. Ken, Jr. Customer Technical Service

Gordon, Ron

Senior Engineer

Gottenberg, Bill

General Plastics and Rubber Co., Inc. tel. (713) 644-1449

5727 Ledbetter ext. 2

Houston, TX 77087 fax (713) 644-5430

Phillips Petroleum Co. tel. (918) 661-6051

P.O. Box 1360 fax (918) 661-6143

Bartesville, OK 74004

Fiberflex, Inc. tel. (800) 288-3092

P.O. Box 6044 fax (915) 267-1814

Big Spring, TX 77291-6044

/vmeron, inc. lei. Engineering Division ext. 223, 228

4671 Firestone Blvd. fax (213) 564-0648

South Gate, CA 90280

Shell Research tel. (85) 644594

Billiton, Research B.V. fax (85) 640041

P.O. Box 40

6800 AA Arnhem

The Netherlands

Westwind Composites, Inc. tel. (713) 944-3834

8777 Tallyho Road fax (713) 944-4181

Houston, TX 77061

Amoco Corp. tel. (708) 420-4609

150 W. Warrenville Road fax (708) 961-7971

MC: B-8

Naperville, IL 60563-8460

Offshore Magazine tel. (713) 621-9720

P.O. Box 1941 fax (713) 963-6296

Houston, TX 77251

Dept. of Mechanical, Materials, and tel. (91) 222-8562

Manufacturing fax (91) 222-8563

University ofNewcastle upon Tyne

Newcastle upon Tyne NE1 7RU

United Kingdom

Ethyl Corp. tel. (504) 768-5629

8000 GSRI Avenue fax (504) 768-5607

Baton Rouge, LA 70820

Oryx Energy Co. tel. (214)715-4424

P.O. Box 2880 fax (214)715-4419

Dallas, TX 75221

Shell tel. (713) 544-7930

fax

370
Name, Title/Position

Greaves, Gerry

Senior Engineer

Greenwald, Edward C. Materials R&D Department

Manager

Greenwood, Mark

Research Associate

Gum, Wayne

Haanes, Havard

Research Scientist

Haas, Michael

Hansen, Allan Boye

Manager, International R&D

Hansen, Gary E.

Hennington, John W.

Director of Marketing

Hightower, Bill Regional Sales Manager

Hill, Dr. Paul

Senior Engineer

Hoffman, Pete

Company and Address

Owens-Corning

2790 Columbus Road

Granville, OH 43023

Geo-Centers, Inc. 10903 Indian Head Way

Ft. Washington, MD 20744

Owens-Corning

2790 Columbus Road

Granville, OH 43023

BP Exploration

P.O. Box 4587

Houston, TX 77210-4587

Sintef SI P.O. Box 124

Blindern

N-0314Oslo

Norway

AIMS International

15730 Sellers Road

Houston, TX 77060

AMATa/s

P.O. Box 243

N-3201 Sandefjord

Norway

Hercules Aerospace Co.

Materials Technology

Bacchus Works

M/SX11K4

Magna, UT 84044

Ameron Fiberglass Pipe Systems

1004 Ameron Road

Burkburnett, TX 76354

Ameron

13405 Northwest Freeway, Suite 117

Houston, TX 77040

British Gas PLC

Engineering Research Station

Newcastle upon Tyne NE99 1LH

United Kingdom

McDonnell Douglas

Telephone and Fax Nos.

tel. (614)587-7780

fax (614) 587-7433

tel. (202) 767-3039

fax (202) 767-0594

tel. (614)587-7259

fax (614) 587-7433

tel. (713) 560-3365

fax (713) 560-8866

tel. (22) 06 75 42

fax (22) 06 73 50

tel. (713)999-4192

fax (713)999-5657

tel. (33) 46 94 50

fax (33) 46 98 60

tel. (801) 251-3819

fax (801)251-3268

tel. (817)569-1471

fax (817)569-4012

tel. (713)690-7777

fax (713) 690-2842

tel. (91)216-0202

fax (91)268-3045

tel. (314)233-3863

fax

371
Name, Title/Position Company andAddress Telephone and FaxNos.

Hollenbeck, Kurt

Project Manager

Hoo Fatt, Dr. M. S. Postdoctoral Researcher/Lecturer

Houghton, C. J. Principal Metallurgical and

Corrosion Engineer

Huntoon, G. G.

Hushbeck, Donald

Team Leader

Jensson, J. H.

Johnson, Doug

Manager, Product Development

Jones, M. A. (Andy), Jr. Facilities/Chemical Engineering

Advisor

Jones, Rembert F., Jr. Research Engineer

Jones, Dr. Tom

Associate Vice President, Research

Texas Instruments 2501 W. University

M/S 8019

McKinneyJX 75070

Dept. of Ocean Engineering

MIT, Room 5-324A

77 Massachusetts Avenue

Cambridge, MA 02139

Phillips Petroleum Co. UK, Ltd.

Phillips Quadrant

35 Guildford Road

Woking, Surrey GU22 7QT

United Kingdom

Production Technology and Services

Amoco Production Co.

(580Westlake Park Blvd.)

P.O. Box 3092

Houston, TX 77253-3092

Halliburton Energy Services

P.O. Box 1431

Duncan, OK 73536-0460

Conoco Norway, Inc. (Tangen 7

4070 Randaberg)

P.O. Box 488

N-4001 Stavanger

Norway

Brunswick Composites

4300 Industrial Avenue

Lincoln, NE 68504

Shell Oil Co.

E and P Engineering

P.O. Box 2463

Houston, TX 77252-2463

Carderock Division

NSWC- U.S. Navy

Code 65

Bethesda, MD 20084

University of Houston

Houston, TX 77204-4792

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

(214) 952-3782

(214) 952-3773

(617) 253-5998

(617) 253-8125

(0483) 752-439

(0483) 752-277

(713)556-3144

(713) 584-7555

(405)251-4243

(405)251-3218

(4) 41 60 00

(4)41 05 55

(402) 464-8211

(402) 464-2247

(713) 241-5336

(713) 241-1179

(301)227-1534

(301) 227-1230

(713)743-9104

372
Name, Title/Position

Kashiwagi, Dr. T.

Kastor, Dr. R L. Lecturer

Kilbourn, Chris

Director of Engineering

Kitchens, Jim

Marketing Manager

Klestinec, Steve

Market Manager

FRP Products

Kruesi, Mr. A. Hugo

President

Kung, H. K.

Graduate Student

Lea, R. H. (Dick)

Leblanc, Leonard

Editor-in-Chief

Lee, M.-S.

Consultant, Structural Engineering

Lee, Robert

Engineering Manager

Lesser, Dr. Alan J. Polymeric Materials Engineering

R&D

Company and Address

Building & Fire Research Laboratory

Bldg. 224,RoomB-258

NIST

Gaithersburg, MD 20899

Dept. of Mechanical Eng.

University of Houston

Houston, TX 77204-4792

BARRACUDA Technologies, Inc. 315 Seahawk Drive

DeSoto, TX 75115

Seasafe, Inc. 209 Glaser Drive

Lafayette, LA 70508

Georgia Pacific Resins, Inc. 2883 Miller Road

Decatur, GA 30035

U.S. Composites Corp.

P.O. Box 536

(Charles Park, Bldg,#l)

Guilderland, NY 12084-0536

Dept. of Mechanical Eng.

University of Houston

Houston, TX 77204-4792

Specialty Plastics, Inc. (15915 Perkins Road)

P.O. Box 77011

Baton Rouge, LA 70879-701

1

Offshore Magazine

3050 Post Oak Blvd., Suite 200

Houston, TX 77056

Amoco Production Co.

580 Westlake Park Blvd.

Houston, TX 77253

Specialty Plastic Products

530 Sherwood Avenue

Dunmore, PA 18512

Shell Development Co.

Westhollow Research Center

P.O. Box 1380

Houston, TX 77251-1380

Telephone and FaxNos.

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

301

301

713

713

214

214

318

318

404

404

518

518

713

713

504

713

713

713

713

717

717

713

713

373
Name, Title/Position

Levy, Len

Lo, Dr. K. H.

Research Staff

Long, Randy

Lou, Alex Y. Chief Composite Engineer

Lu, Xiaohua

Graduate Student

Luckenbill, Michael

Field Service Manager

Luke, Nelvin F. Vice President/Manager

N. 0. Operations

Lundberg, Chris

Lundh, Tore

Managing Director

Lustinger, Dr. Arnold

Mableson, Dr. A. R. Technical Executive

Masters, Rodney

Matovich, Mark A. Manager

Company andAddress

P.O. Box 875

Columbia, MO 65203

Shell Development Co.

P.O. Box 1380

Houston, TX 77251-1380

Stress Engineering Services

13800 Westfair East Houston, TX 77251-1380

Corporate Engineering

Phillips Petroleum Co.

113,71C,PRC

Barlesville, OK 74004

Dept. of Mechanical Eng.

University of Houston

Houston, TX 77204-4792

Ameron Fiberglass Pipe Systems

1004 Ameron Road

Burkburnett, TX 76354

Sepco Industries

320 Time Saver Avenue

Harahan, LA 70123

Spyro Tech

4930 Superior Street Lincoln, NE 68524

Advanced Materials a/s P.O. Box 243

N-3201 Sandefjord

Norway

Exxon Research & Engineering Co.

Route 22 East Annandale,NJ 08801

Vosper Thornycroft (UK)

Victoria Road, Woodston

Southampton, Hants S09 5GR

United Kingdom

AIMS International

15730 Sellers Road

Houston, TX 77060

Shell Development Co.

P.O. Box 1380

Houston, TX 77251-1380

Telephone and FaxNos.

tel. (714)760-8510

fax

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

713) 493-8065

713) 493-7705

713) 955-2900

713) 955-2638

918) 661-7961

918) 661-0570

713)743-4550

713) 743-4503

817)569-8648

817)569-4120

504) 733-7100

504) 733-3310

402) 466-3390

33) 46 94 50

33)46 98 60

908) 730-2239

908) 730-3355

703) 445-144

703)435-512

713)999-4192

713) 999-5657

713) 493-7909

713)493-7790

374
Name, Title/Position Company andAddress Telephone and FaxNos.

Mau, Dr. S. T. Chairman

McColskey, J. David

McGill, Randy

Staff Associate

McHenry, Harry I. Chief, Materials Reliability

Division

McKenna, Dr. G. B.

Project Leader

Medlicott, Dr. Phil

Senior Mechanical/Materials

Engineer

Meisner, William I. Program Manager/Research

Scientist

Miszak, Jerry P. President

Miyase, Dr. A. Research Associate Professor

Monette, Liza

Research Physicist

Monib, M. M.

Products Manager

Dept. of Civil Engineering

University of Houston

Houston, TX 77204-4791

NIST IMC-853

Materials Reliability Division

325 Broadway

Boulder, CO 80303

API

700 N. Pearl, Suite 1840

Dallas, TX 75201

Materials Science and Engineering

Laboratory

NIST

Dept. of Commerce

325 Broadway

Boulder, CO 80303

NIST

Mechanical Performance Group

Polymers Division

Gaithersburg, MD 20899

BP Research Center

Chertsey Road

Sunbury TW1 67LN, Middlesex

United Kingdom

Amoco Performance Products,

Inc. 4500 McGinnis Ferry Road

Alpharetta, GA 30202

Tectram, Inc. Chasseralstr. ZO

CH-3178 Boesingen

Switzerland

Dept. of Mechanical Eng.

University of Houston

Houston, TX 77204-4792

Exxon Research and Eng.

Corporate Research Laboratory

Route 22 East Annandale,NJ 08801

DuPont Advanced Composites

Glasgow - Bldg. 200

Newark, DE 19714-6101

tel. (713)743-4250

fax

tel. (303) 497-5544

fax (303) 497-5030

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

(214) 720-5718

(303) 497-3268

(303) 497-5030

(301)975-6752

(301) 869-3239

(932) 762-497

(404) 772-8286

(404) 772-8289

(31)747-7055

(31)747-8347

(713) 743-4537

(713) 743-4503

(908) 730-2329

(908) 730-3355

(302) 451-3200

(302) 451-4932

375
Name, Title/Position Company and Address Telephone and FaxNos.

Moog, Karl

Structural Engineer

Morton, Dr. John

Professor and Director

Muskopf, Brian

Mechanical Engineering Group

Leader

Mott, Keith, C.P.E. Manager, New Product

Development

Myers, Robert

Nairn, Dr. John A.

Associate Professor

Niehous, Craig

Senior Account Representative

Nolet, Steven

Director of Engineering

Nollen, Dr. Dennis A.

Palmer, Dennis

Account Manager

Parnas, Richard

Pearce, Robert G.

Research Associate

Kuaerver Earl and Wright, Inc. 11111 Wilcrest Green, Suite 250

Houston, TX 77042

Center for Composite Materials

and Structures 201 Hancock Hall

VPISU

Blacksburg, VA 24061-0257

Texas Research Institute 9063 Bee Caves Road

Austin, TX 78733

Hydril Co.

P.O. Box 60458

Houston, TX 77205-0458

International Grating, Inc. 7625 Parkhurst

Houston, TX 77028

University of Utah

Materials Science and Engineering

340 EMRO

Salt Lake City, UT 841 12

PPG Industries, Inc. 530 Wells Fargo Drive #310

Houston, TX 77090

Fiberspar, Inc. 2380 Cranberry Hwy.

W. Wareham, MA 02576

DuPont Co.

(Chestnut Run Plaza)

P.O. Box 80,701

Wilmington, DE 19880-0701

Amoco

400 Ridge Crest Richardson, TX 75080

Polymers Division

Bldg. 224

NIST

Gaithersburg, MD 20899

Brunswick Composites

4300 Industrial Avenue

Lincoln, NE 68504

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

713) 260-7000

713) 260-7199

703) 231-6051

703)231-9452

512) 263-2101

512) 253-3530

713) 985-3399

713) 633-8614

713)633-3210

801)581-3413

801)581-4816

713) 440-3770

713)440-3720

508) 291-2770

508) 291-2772

302) 999-2901

214) 238-5623

214) 235-3450

310) 975-6838

402) 464-8211

402) 464-2247

376
Name, Title/Position Company andAddress Telephone and FaxNos.

Pedersen, Jan

Group Leader, Material and

Welding Technology

Phyillaier, Mr. Wayne

Structural Engineer

Plewnarz, Robert

Senior Sales Representative

Porcari, Aldo M.

Research Engineer

Poshard, David L. Manager, Petroleum Production

Posson, Mike

Division Engineer

Prahlad, S. N.

Graduate Student

Provost, Ed

Quigley, Peter President

Rainey, R M. (Mike)

Norwegian Contractors a/s tel. P.O. Box 116 fax

N-4030 Hinna

Norway

Carderock Division tel. Naval Surface Warfare Center fax

CD NSWC Code 65.2

Bethesda, MD 20084-5000

BP Chemicals (Hitco), Inc. tel. 700 East Dyer Road fax

Santa Ana, CA 92705-5614

Engineering Research and Development tel. AGIP fax

P.O. Box 12069

20120 Milano

Italy

Smith Fiberglass Products, Inc. tel. 650 N. Sam Houston Pkwy., fax

E. Suite 535

Houston, TX 77060

Rice Engineering Corp. tel. 1020 Hoover fax

Great Bend, KS 67530

Dept. of Mechanical Eng. tel. University of Houston fax

Houston, TX 77204-4792

Shell International Petroleum tel. Maatschappij B.V. fax

Exploration and Production Division

Materials & Corrosion Eng.

P.O. Box 162

2501 AN The Hague

The Netherlands

Fiberspar, Inc. tel. 2380 Cranberry Hwy. fax

W. Wareham, MA 02576

Shell Oil Co. tel. c/o MIFDT fax

1200 St. Charles Avenue

New Orleans, LA 70130

(47) 4 88 80 00

(47)4 88 80 01

(301) 227-1707

(301) 227-1230

(714) 755-7281

(714) 557-7397

2520-62910

2520-61809

(713) 445-1821

(713)445-1102

(316) 793-5483

(316) 793-5521

(713) 743-4554

(713) 743-4503

(508) 291-2770

(508) 291-2772

(504) 593-5504

(504) 593-5566

377
Name, Title/Position Company andAddress Telephone and FaxNos.

Robertson, Gordon G.

Senior Vice President

Rocchi, Joe

Senior Project Engineer,

Composites

Roche, Joe, P.E. Product Development Manager

Rogers, Charles W.

Structural Research Engineer

Rollhouser, Charles M.

Mechanical Engineer

Ruschau, Greg

Materials and Fluid Technology

Salama, Dr. M. M.

Senior Research Fellow

Sas-Jaworsky, Alexander, II Staff Engineer

Schmit, Kevin

Project Engineer

Schon, J. S. Graduate Student

Scott, Roy L

Product Manager

Seamark, M. J.

Ameron

245 South Los Robles Avenue

Pasadena, CA 91101-3894

BF Goodrich

6061 BF Goodrich Blvd,

Jacksonville, FL 32226

Hydril Co.

P.O. Box 60458

Houston, TX 77205-0458

Bell Helicopter Textron

8841 Arbor Crest Court

Fort Worth, TX 76179

(USN) CDNSWC

804 Oak Grove Circle

Severna Park, MD 21 146

ARCO E&P Technology

2300 West Piano Pkwy.

Piano, TX 75075-8499

Conoco, Inc. P.O. Box 1267

Ponca City, OK 74602-1267

Conoco, Inc. Production Technology

P.O. Box 2197 (Du 1002)

Houston, TX 77252

Specialty Plastics, Inc. (15915 Perkins Road)

P.O. Box 77011

Baton Rouge, LA 70879-701

Dept. of Mechanical Eng.

University of Houston

Houston, TX 77204-4792

Hexcel Corp.

5794 W. Las Positas Blvd.

Pleasonton, CA 94588

Balmoral Group, Ltd. Balmoral Park, Loirston

Aberdeen AB9 2BY, Scotland

United Kingdom

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

818) 683-4000

818) 683-4050

904) 757-3660

904) 757-7116

713) 985-3274

713) 985-3353

817) 236-1314

817) 280-4933

410) 261-2542

410) 261-1845

214) 754-3039

405) 767-2738

405)767-6381

713) 293-3319

713)293-4456

504) 752-2705

504) 752-2757

713) 743-4554

713) 743-4503

510) 847-9500

510) 734-9042

224) 891-000

224) 891-119

378
Name, Title/Position

Seemann, Bill President

Seiferman, Gary

Nonmetallics Engineering Team

Facilitator

Sember, William J. Manager, Offshore Engineering

Dept.

Severe, Dick

Marketing Manager

Shah, Arvind

Structural Engineer

Shrivill, Leslie C. Senior Research Scientist

Skaper, Greg

Skontorp, A. Graduate Student

Smith, Charles E. Research Program Manager

Smith, Leonard

General Manager, Coordination

Smith, Les

Company andAddress

Seemann Composites, Inc. P.O. Box 3449

Gulfport, MS 39503

Texas Instruments 2501 W. University

M/S 8019

McKenney, TX 75070

ABS Americas

ABS Plaza

16855 Northchase Drive

Houston, TX 77060-6008

3M

3M Center

Bldg. 60-1N-01

St. Paul, MN 55144

MMS

1201 Elmwood Park Blvd.

New Orleans, LA 70123-2394

Shell Research, Ltd. Thornton Research Center

P.O. Box 1 Chester, Cheshire CHI 3SH

United Kingdom

L. J. Broutman and Associates, Ltd. 3424 South State Street Chicago, IL 60616

Dept. of Mechanical Eng.

University of Houston

Houston, TX 77204-4792

U.S. Minerals Management Service

Technology Assessment and Research

Branch

U.S. Dept. of the Interior 381 Elden Street, MS 4700 Herndon, VA

22070-4817

McDermott International P.O. Box 60035

New Orleans, LA 70160

Quadrax Corp.

300 High Point Avenue

Portsmouth, RI 02871

Telephone and Fax Nos.

tel. fax

tel. far

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

(601) 868-7341

(601) 868-7372

(214) 952-3746

(214) 952-3773

(713) 874-6564

(713) 874-8196

(612) 736-3026

(612) 736-0431

(504) 736-2894

(504) 736-2426

(051)373-5862

(051)373-5845

(312) 842-4100

(312) 842-3583

(713) 743-4547

(713) 743-4503

(703) 787-1559

(703) 787-1010

(504) 587-4543

(504)587-5147

(401)683-6600

(401)683-6606

379
Name, Title/Position Company andAddress Telephone and FaxNos.

Sorathia, Usman

Materials Engineer

Srinivasan, S. Graduate Student

Sternstein, Dr. Sandy

Professor

Stewart, Maurice I.

Stinson, J. M.

Vice President

Stokke, Reidar

Head of Department

Streett, Edward B. Corporate Marketing Manager

Sturgeon, Donald

Development Manager

Su, Dr. K. B. Research Associate

Tavares, Jack

Manager, Oil Field Products

NSWC tel. David Taylor Research Center fax

3A Leggett Circle

Annapolis, MD 21402

Dept. of Mechanical Eng. tel. University of Houston fax

Houston, TX 77204-4792

Rensselaer Polytechnic Institute tel. Johnson Eng. Center 5002 fax

Troy, NY 12180

U.S. Minerals Management Service tel. Field Operations fax

Gulf of Mexico Region

1201 Elmwood Park Blvd.

New Orleans, LA 70123

Conoco, Inc. (600 North Dairy Ashford)

P.O. Box 2197

Houston, TX 77252

SintefSI

P.O. Box 124

Blindern

N-0314Oslo

Norway

Morrison Molded Fiber Glass Company tel. (MMFG) fax

(400 Commonwealth Avenue)

P.O. Box 580

Bristol, VA 24201

DuPont Composites tel. (Delaware Technology Park, Room 247) fax

P.O. Box 6104

Newark, DE 19714-6104

DuPont Co. tel. Central Research & Development fax

80304 Experimental Station

Wilmington, DE 19880-0304

Westinghouse Electric Corp. tel. (401 E. Hendy Avenue) fax

P.O. Box 3499

M/S EK-7

Sunnyvale, CA 94088-3499

tel. fax

tel. fax

(410) 267-3354

(410) 267-2839

(713) 743-4541

(713) 743-4503

(518) 276-2792

(518) 276-8784

(504) 736-2843

(504) 736-2610

(22) 06 77 76

(22) 06 73 50

(703) 645-8000

(703)645-8132

(302) 733-8878

(302) 733-8923

(302) 695-3137

(302) 695-2504

(408) 735-2864

(408) 735-3334

380
Name, Title/Position

Thomeer, Bart

Coiled Tubing Engineer

Troffer, Michael A.

Materials and Structures Project Manager

Tsai, Dr. S. W.

Professor

Turner, Ward

Senior Engineering Specialist

Tyagi, Rishi

Uralil, Francis S. Senior Research Physicist

Van Gent, Joop

Sales Manager

Vennett, Richard M.

Consultant

Vicario, Dr. Albert A.

Specialty Structures Programs

and Marketing

Wahnschaffe, Jens Graduate Student

Wanchisen, Ronald J. Chairman, CEO

Wang, Dr. S. S. Distinguished University Professor

Company and Address Telephone and FaxNos.

Dowell Schlumberger tel. 14910 Airline Road fax

Rosharon, TX 77583-1590

Submarine R&D Office tel. (PEO-SUB-R) fax

253 1 Jefferson Davis Hwy.

Arlington, VA 22242-5 168

Dept. of Aeronautics and Astronautics tel. Durand Bldg. , Room 337 fax

Stanford University

Stanford, CA 94305-4035

Exxon Production Research Co. tel. P.O. Box 2189 fax

Houston, TX 77040

Mineral Management Service tel. OCS Pacific Division fax

Shell Development Co. tel. 3333 Hwy. 6 South fax

Houston, TX 77251

Ameron tel. 4191 MZ Geldermalsen fax

The Netherlands

2405 Meadowbrook tel. Ponca City, OK 74604 fax

Hercules, Inc. tel. Composite Structures fax

P.O. Box 98

M/SX11M9

Magna, UT 84044

Dept. of Mechanical Eng. tel. University of Houston fax

Houston, TX 77204-4792

Specialty Plastic Products tel. 530 Sherwood Avenue fax

Dunmore, PA 18512

Dept. of Mechanical Eng. tel. University of Houston fax

Houston, TX 77204-4792

(713) 967-5480

(713) 967-5489

(703) 602-0942

(703)602-2951

(415) 725-3305

(415)725-3377

(713) 965-7314

(713)966-6304

(713)493-8540

(713)493-7790

(31) 3455 73341

(405) 762-5165

(405)767-6381

(801) 251-5373

(801) 251-2953

(713) 743-4543

(717) 961-2042

(717) 961-5176

(713) 743-4515

(713)743-4516

381
Name, Title/Position Company and Address Telephone and FaxNos.

Wastberg, Dr. Stig

Senior Principal Engineer

Watson, George H.

General Manager, Technical

Support

Webber, Winston

Polymers and Surface Coating

Engineer

Wenzel, Alex B.

Director

Weyant, Shane E. Regional Sales Manager

Wheeler, Dr. Lewis

Professor

Williams, Jerry G.

Production Engineering and

Research

Wilson, Dr. Doug

Vice President, Technology

Winters, Warren J.

Wong, Dr. M. S. Research Associate

Wood, Geoffrey M.

Manager, Light Materials

Manufacturing

DNV Industry

P.O. Box 300

N-1322 Hovik

Norway

Amoco Corp.

P.O. Box 3011

Mail Station F-7

Naperville, IL 60566

Halliburton Energy Services

Elliot Industrial Estate Arbroath

Angus DD11 2NF, Scotland

United Kingdom

Southwest Research Institute 6220 Culebra Road

San Antonio, TX 78238-5 166

Creative Pultrusions, Inc. (Pleasantville Industrial Park)

P.O. Box 6

Alum Bank, PA 15521

Dept. of Mechanical Eng.

University of Houston

Houston, TX 77204-4792

Conoco, Inc. (1000 South Pine)

P.O. Box 1267

Ponca City, OK 74603

BP Chemicals (Hitco), Inc. Fibers & Materials

1300 E. WakehamRoad

Santa Ana, CA 92705

Tulsa Research Center

Amoco Production Co.

P.O. Box 3385

Tulsa, OK 74102

Dept. of Mechanical Eng.

University of Houston

Houston, TX 77204-4792

Oak Ridge National Laboratory

P.O. Box 2009

M/S 8039

Oak Ridge, TN 37831

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

tel. fax

(67) 57 72 36

(67) 57 74 74

(708) 420-5774

(708) 420-5252

(241)432029

(241)432059

(210)522-2311

(210)522-3377

(814) 839-4186

(814) 839-4276

(713) 743-4502

(713) 743-4503

(405) 767-2377

(405)767-6381

(714) 755-7233

(714) 755-7298

(713) 743-8242

(713) 743-4503

(615)574-9693

(615)574-9407

382
Name, Title/Position

Wu, Dr. Y. T. Senior Development Manager

Yu, Dr. T. P. Research Associate

Yuan, Yusheng

Graduate Student

Yungblut, Glenn

Zhou, Prof. Ben-Lian

Company andAddress

DuPont

P.O. Box 80715

Wilmington, DE 19880-0715

Dept. of Mechanical Eng.

University of Houston

Houston, TX 77204-4792

Dept. of Mechanical Eng.

University of Houston

Houston, TX 77204-4792

Engineering Brach

National Energy Board

311 6th Avenue S.W.

Calgary, Alberta T2P 3H2

Canada

Institute of Metal Research,

Academia Sinica

72 Wenhua Road

Shenyang 110015

China

Telephone and Fax Nos.

tel. (302)999-2481

fax (302) 999-2718

tel. (713) 743-4539

fax (713) 743-4503

tel. (713) 743-8243

fax (713)743-4503

tel. (403)292-6911

fax (403) 292-5876

tel. (24)384-3531-7

fax (24)389-1320

383
384
8. Author Index

385
I

I

386
Author Index

Page

A 11-- — ^ T T\ Alkire, j.D. 1 C 1 351

Anatharaman, R.

*y c c 355

Ashe, G.M. 361

Bartholomew, H.G. 31

Beck, R.D. 341

Bishopp, M.D. 39, 351

X^ _ . . . _ x Tt jr Bowman, J.M. 115

Bradley, W.L.

1 /""V ^ ^ p 193, 335

Camponeschi, E.T. 335

Caplan, I.L. 91

Carlsson, L.A. 203, 335

Chang, J. 357

Chiou, P.L. 193

Chiu, A.S. 335

Ciaraldi, S.W. 319, 351

Cleary, T.G.

a i i 241

Cole, B.W. 7, 71, 341

g—y 1 n 7 x*\ Cook, W.D. 345

Courtney, M.J. 329

Dahle, T.G. 43, 361

Dismukes, J. P. 149, 335

Eckold, G.C.

Oil 341

Fairies, R. 345

T~7 * _1_ T*> rincn, K.

Fischer, F.J. 295, 357

Fitting, D.W. 345

Gibson, A.G. 117

Grant, T.S. 193

Greaves, G.G. 329

Greenwood, M.E. 355

Grenawald, E.C. 345

Hansen, A.B. 345

rage

Hansen, GE. 161, 335

Houghton, C.J. 47, 329

Hunston, D.L. 139

Huntoon, G.G. 355

Jenssen, J.H. 65

Johnson, D.B. 341

Jones, Jr., R.F. 361

Kashiwagi, T. 241, 351

Konuk, I. 361

Lea, R.H. 261, 355

Ling, S. 213

Lo, K.H. 7, 233, 341

Lou, AY. 357

Lundberg, C. 329

Lundh, T. 341

Lustiger, A. 213, 335

Luton, M.J. 149

McDonald, W. 355

McKenna, G.B. 139

Monette, L.M. 335

Nairn, J. A. 175, 335

\t ft x*V A Nollen, D A. 351

Parnas, R.S. 139, 329

Pearce, R.G. 335

Phyillaier, W. 341

Pomies, F. 203

Provost, E. 361

Rainey, R.M. 355

Robertson, G.G. 83

Rollhauser, C. 361

387
Page

JalCli 1 Jltl, 1VA.1VA. £*\JS 269j 357 J J 1 ^ac-TawnrQlrv TT A 357 DDI

Schmidt, K. 253, 261

Shirvill, L.C. 289, 351

Smith r 361 JU1

Smoot, M.A. 329

Sorathia, U. 309, 351

Sternstein, S.S. 171, 335

Stewart, M. 361

Thomeer, B. 357

Tsai S W 227, 341

KJ I dill, x . o

IRS 1 O J, JJJ

355

Wagner, H.D. 213

Wane S S 7

Webber, W. 357

Williams, J.G. 7, 77, 341

Wilson, D. 131,329

Winters, W.J. 357

Yungblut, G.R. 35

y

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