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NBS SPECIAL PUBLICATION 468

U.S. DEPARTMENT OF COMMERCE / National Bureau of Standards

National B;ireau or uiatidards

Library,. £-01 Admin. Bldg,

OCT 1 1981

1910^2

Prevention of Failures in

Coal Conversion Systems

MFPG

24th Meeting
NATIONAL BUREAU OF STANDARDS

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" Located at Boulder, Colorado 80302.
Il^al Bureau o' Standar(j5

^''^ 1 9 1977 ,c MFPG

\c . Prevention of Failures in Coal

^ Conversion Systems

Proceedings of the 24th Meeting of the

Mechanical Failures Prevention Group,

held at Battelle, Columbus Laboratories,

Columbus, Ohio, April 21-23, 1976

Edited by

T. Robert Shives and William A. Willard

Metallurgy Division

Institute for Materials Research

National Bureau of Standards

Washington, D.C. 20234

The 24th meeting of MFPG and these proceedings were

sponsored by the Institute for Materials Research of

the National Bureau of Standards, Washington, D.C.

20234; the Office of Naval Research, Department of the Navy,

Arlington, VA 22217; the Naval Air Development Center,

Department of the Navy, Warminster, PA 18974; the Frankford Arsenal, Department of the Army, Philadelphia,

PA 19137; the Federal Aviation Administration, Department

of Transportation, Washington, D.C. 20591; Battelle, Columbus Laboratories, Columbus, OH 43201; and the Energy Research and Development Administration,

Washington, D.C. 20545.

U.S. DEPARTMENT OF COIVIMERCE, Juanita M. Kreps, Secretary

Dr. Betsy Ancker-Johnson, Assistant Secretary for Science and Technology

V\ NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Acting Director

Issued April 1977
Library of Congress Cataloging in Publication Data

Mechanical Failures Prevention Group.

Prevention of failures in coal conversion systems.

(NBS special publication ; 468)

Supt. of Docs, no.: C13. 10:468.

1. Fracture mechanics—Congresses. 2. Coal gasification—Congresses. 3. Coal liquefaction—Congresses. I. Shives, T. R. II. Willard,

William A. III. United States. National Bureau of Standards.

Institute for Materials Research. IV. Title. V. Series: United States. National Bureau of Standards. Special publication ; 468. QC100.U57 no. 468 [TA409] 602Ms [662'.662] 77-608043

National Bureau of Standards Special Publication 468

Nat. Bur. Stand. (U.S.), Spec. Pubi. 468, 233 pages (Apr. 1977)

CODEN: XNBSAV

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1977

For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C- 2(M02 - Price $3.00

Stock No. 003-003-01760-4
FOREWORD

The 24th meeting o£ the Mechanical Failures Prevention Group was held

April 21-23, 1976, at Battelle, Columbus Laboratories in Columbus, Ohio.

The program was organized by the MFPG committee on the State-o£-Art and

Application under the chairmanship of Professor F. F. Ling of the

Rensselaer Polytechnic Institute. The State-of-Art committee, the

session chairmen and especially the speakers and panel participants are

to be commended for the excellent program.

The papers in these Proceedings are presented as submitted by the

authors on camera ready copy, except for some minor editorial changes.

In addition to the papers, the Proceedings include the discussions of

the talks and a panel discussion. The discussions were recorded at the

meeting and have been edited to improve readability.

Special appreciation is accorded Battelle, Columbus Laboratories, and

in particular to Mr. Robert E. Maringer of Battelle, for hosting the

meeting. Mr. Maringer was responsible for the excellent meeting

arrangements

.

Appreciation is extended to Mr. T. Robert Shives and Mr. William A.

Willard of the NBS Metallurgy Division for their editing, organization,

and preparation of the Proceedings, to Ms. Susie Armstrong and Mr. Tom.

Stewart of Battelle for general coordination, to Mr. Paul M. Fleming of

the ^«IBS Metallurgy Division for handling financial matters, to Mr.

W. Todd Eudy of the NBS Metallurgy Division for photographic work, and

to many members of the staffs of Battelle, Columbus Laboratories, the

NBS Metallurgy Division, and the NBS Institute for Materials Research

for their assistance in many ways. Special thanks are accorded to Mrs.

Marian L. Slusser of the NBS Metallurgy Division for her diligent

efforts in transcribing and typing the recorded discussions.

HARRY C. BURNETT

Executive Secretary, MFPG

Metallurgy Division

National Bureau of Standards

III

TABLE OF CONTENTS

Page

FOREWORD III

SESSION I: OVERVIEW LECTURES

1. Reliability Problems in Coal Gasification and 3

Liquefaction. H.E. Frankel* and J.R. Ogren

2. Economics of Failures in Energy Generation Systems. 27

Melvin E. Lapides

3. Demonstration of a Reliability Methodology Using Two 41

Coal Conversion Plant Models. John R. Hoffman,*

W. Tierce Long and R. Larry Williams

4. Critical Materials Problems in Coal Conversion. 50

R.W. Staehle

5. The AGA-ERDA-MPC Program on Materials for the 80

Gasification of Coal. Adolph 0. Schaefer

SESSION II: FAILURE ANALYSIS

1. Failure Analysis of Components from Coal-Gasification 97

Pilot Plants. S. Greenberg* and K. Natesan

2. Erosion Problems in Letdown Valves. J.J. Mueller 107

3. ERDA Information Center for Failure Prevention 121

in Fossil Energy Plants. J.H. Smith* and

W.A. Willard

4. Steel Plant Coke-Ovens: An Energy Conversion Process 131

with Warpage Problems. H.W. Lownie, Jr., and

A.O. Hoffman*

SESSION III: RELATED MATERIALS RESEARCH

1. Selection of Materials Used in Coal Gasification 137

Plants. M.A.H. Howes

V
2. Particle Erosion Measurements on Metals at 145

Elevated Temperatures. L.K. Ives,* J. P. Young

and A.W. Ruff

3. High-Temperature Corrosion. K. Natesan 159

4. Development of Nondestructive Evaluation Methods 172

for Coal -Conversion Systems. W.A. Ellingson,*

G.C. Stanton and N.P. Lapinski

5. Potential Materials Problems in Coal Gasification 183

Systems. A.M. Hall

SESSION IV: MATERIALS PROBLEMS IN COAL CONVERSION PILOT PLANTS

1. Low Ductility, High Temperature Failure of 191

Austenitic Materials. F.B. Hamel

2. The SRC Plant, Larry G. Samuels 192

3. High Btu Gasification Pilot Plant Experience. 195

A.J. Mac Nab

4. CO2 Acceptor Process. C.A. Schulz 199

5. Consol Pilot Plant Materials Problems. J.F. Leterle 202

6. The Synthane Coal to Gas Pilot Plant. Robert Lewis 205

7. Panel Discussion 207

LIST OF REGISTRANTS FOR THE 24th MFPG MEETING 222

MFPG PUBLICATIONS 229

The following registrants gave presentations at the symposium, but did

not submit a manuscript for publication:

G.M. Ugiansky* and C.E. Johnson, "Constant Strain Rate Stress Corrosion

Testing of Metals at Elevated Temperatures," Session III

D. Canonico, "Pressure Vessels," Session III

E. R. Fuller, "Effect of Hydrothermal Environments on the Strength of

Castable Refractories," Session III

* Indicates speaker when a paper had more than one author.

VI
ABSTRACT

These P^oceedings consist of a group of twenty submitted papers

and discussions from the 24th meeting of the Mechanical Failures

Prevention Group which was held at Battelle, Columbus Laboratories in

Columbus, Ohio on April 21-23, 1976. Prevention of failures in coal

conversion systems is the central theme of the Proceedings. A series

of overview lectures dealing with reliability problems in coal conversion systems, economics of failures in energy generating systems,

corrosion, and gaps in engineering data are presented. In addition,

failure analysis, materials problems, and related materials research

are discussed.

Key Words : Coal conversion; coal gasification; coal liquefaction;

corrosion; failure analysis; failure prevention; quality assurance;

reliability

UNITS AND SYMBOLS

Customary United States units and symbols appear in many of the

papers in these Proceedings. The participants in the 24th meeting of

the Mechanical Failures Prevention Group have used the established units

and symbols commonly employed in their professional fields. However,

as an aid to the reader in increasing familiarity with and usage of the

metric system of units (SI), the following references are given:

NBS Special Publication, SP330, 1974 Edition, "The International System

of Units."

ISO International Standard 1000 (1973 Edition), "SI Units and Recommendations for Use of Their Multiples."

E380-75 ASTM/IEEE Standard Metric Practice (Institute of Electrical and

Electronics Engineers, Inc. Standard 268-1976).

Disclaimer:

Certain trade names and company products are identified in order to

adequately specify the experimental procedure. In no case does such

identification imply recommendation or endorsement by the National

Bureau of Standards, nor does it imply that the products are necessarily the best available for the purpose.

VII

SESSION I

OVERVIEW

LECTURES

CHAIRMAN: E. PASSAGLIA,

NATIONAL BUREAU OF STANDARDS

RELIABILITY PROBLEMS IN COAL

GASIFICATION AND LIQUEFACTION

H. E. Frankel

ERDA - Fossil Energy Research

Washington, D. C. 20545

J. R. Ogren

TRW

7600 Col shire Drive

McLean, Va. 22101

Abstract: Coal gasification and coal liquefaction are two generic

techniques for converting coal to environmentally acceptable gaseous

and liquid fuels and chemical feedstocks. The two techniques are

distinctly different in many ways but, in many others, use numerous

similar components.

Significant reliability problems exist in coal conversion. The most

important aspect of the problem is the absence of a domestic commercial

industry in coal conversion. Reliability data from commercial operations do not exist and must be generated from the next best source:

ERDA pilot plants and demonstration projects.

This paper describes both the advantages and problems in reliability

resulting from the absence of a commercial industry. Critical interfaces are described between the reliability effort and mission-oriented

offices in ERDA responsible for pilot and demonstration projects.

The paper describes failure avoidance progress conducted, under ERDA

sponsorship, at the national laboratories, government latDoratories and

in private industry. Recent progress is described in development of a performance assurance approach to eoal conversion plant design.

Plans for the future are outlined.

Keywords: Coal gasification; coal liquefaction; failure analysis;

performance assurance system; reliability.

3
statement of Problem

One of the most significant aspects concerning coal conversion is that

no domestic industry exists. This sole fact has several ramifications

which must be appreciated fully to understand the critical role played

by the reliability effort in ERDA's plans.

The absence of a domestic industry means there are no commercial plants

either gathering reliability data now or that could be candidate sites

for gathering such data in the near future. Since data do not exist on

which to base reliability (and hence productivity improvements), steps

must be taken to design reliability into the equipment, to achieve a satisfactory level of conversion plant reliability.

If reliability and maintainability disciplines had been fully exercised

in the design and operation of present-day coal burning power plants,

their capacity factors would be substantially better than the ~60% presently demonstrated. This capacity factor is an average value for large

(>390MWe) fossil plants owned by a veritable host of public and private

utility companies. Power plant data were collected by FEA (Ref.l).

No such data base exists in coal conversion. Foreign technology exists

in indirect liquefaction, as for example the coal conversion complex

at Sasolburg, Republic of South Africa, but reliability data are not

available.

Absence of a domestic industry means that reliability data must be

obtained from other appropriate sources and used in design, development and operation of the pilot plants and demonstration projects.

Virtually all of these are sponsored wholly or in part by ERDA.

It is appropriate to review the operational purposes of ERDA pilot

plants. They are not operated to generate failure and failure analysis

data, but rather to generate chemical process data at an operational

scale needed by industry to decide upon the commercial viability of a process. For example, in a liquefaction process, the pilot plant would

determine the operating conditions and product mixes for different

coal sources. From these data, process economics data could be computed

and commercial viability determined.
Evaluation of an emerging process at a pilot plant level also generates

materials and equipment information. It is necessary to take advantage

of all the technological data generated to provide a baseline for improvements and to protect the investment of hundreds of millions of

capital dollars for each coal conversion demonstration plant.

The reliability problem is aggrevated by one additional problem stemming from absence of a commercial industry: that suppliers of components

can claim that their materials and components will operate in new

environments because no contrary evidence exists.

This attitude is true in many cases. The reliability analyst recognizes

that the task is to determine, from the standpoint of an integrated

plant, those components for which the above conclusion applies and those

for which it does not.

A second aspect of the problem of reliability takes advantage of the

fact that a commercial industry does not exist. This aspect calls for

incorporation of reliability into the original design of future coal

conversion plants and a step-by-step action series designed to ensure

that reliability procedures are implemented in construction and operation of future plants.

The Need for Reliability

An immediate question arises as to why ERDA requires a reliability

program in coal conversion plants when such closely associated industries as petroleum refining generally lack such formalized programs.

Coal conversion pilot plants have severe hardware problems that prevent

the accomplishment of sustained runs (Ref,2). Many pilot plant runs are

considered to be successful if they attain 100 hours of continuous,

steady state operation. In contrast, petroleum refineries typically

operate for 25,000 hours between shutdowns, and these shutdowns are

scheduled. Furthermore, scheduled shutdowns are not for the prime purpose of repairing structural components, but for rejuvenating or replacing the highly sensitive catalyst beds. Admittedly, the shutdown period

is used to re-seat valves, resurface pump parts and inspect many areas

for the appearance of unsuspected erosion, corrosion and wear.

The problem is how to achieve 25,000 hours-operation in coal conversion.

Coal conversion plants might reach this level of operability if the

nation could wait 100 years, the period of time required by the petroleum industry to acquire data permitting long-term plant operability.

5
During that period, plant operability was gradually enhanced in the face

of increasingly difficult and complex refining operations.

The benefit of a reliability program is its provision for accelerated

path toward optimized plant operation (Figure 1). The conventional

development line shows plant operability improving gradually over a period of many years. The accelerated development line shows that

high levels of operability are achievable in a much shorter time by

efficient utilization of the R&D phase of an emerging technology-based

industry.

The nation needs an accelerated program effort because it cannot afford

to spend years of precious time on a learning curve. That extended

effort must be compressed into one that will give real payoffs by 1985.

Comparison of Operating Conditions

in Petroleum Refining and Coal Conversion

Key operating parameters are compiled in Table 1 for selected conversion

processes from both currently available commercial technologies

practiced in foreign countries and second generation technologies

under ERDA development (Ref.3). The conditions are unique; they differ

from those encountered in petroleum technology. The environments are

abrasive because suspended solids are present in virtually every part

of any process. The solids are unreacted coal (char) and ash. Both can

be extremely abrasive (Ref.4).

The amount of suspended material is much higher than in petroleum technology. A typical crude petroleum after minimal cleaning (primarily

to remove sea water) contains perhaps 0.04% ash. In contrast, the

product from the Solvent Refined Coal Process (SRC), an advanced

liquefaction process, contains nominally 0.5% ash. This necessarily

means that higher ash contents were present at all areas upstream of

the final stage in the liquefaction plant. Gasification plants (Ref.4)

typically encounter abrasive solids with velocities of ^100 ft/sec

(~33 m/s). The concentration of suspended solid material can be 0.3

lb/100 scf of gas (Ref.5). Both aspects are more abrasive than current

petroleum operations.

The gaseous environment is both unique and corrosive, as shown in Table

1. H2S causes sulfidation attack on all ferrous and heat-resisting

alloys. This attack can be particularly catastrophic in nickel -rich

alloys because NiS can form. This compound melts at 800°C (1472°F) and

removes any protective scale that may have existed. Evidence that

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sulfidation is a significant root cause of component failures is

accumulating from failure analysis work. (This will be shown later.)

H2O is corrosive, and large amounts of H2O are present in the off-gas

streams of all gasification processes (Table 1). The high temperatures

pose severe conditions when it is recalled that the maximum allowable

metal temperature in a commercial jet engine is 1600°F and that this

level was made allowable only after extensive testing and characterization.

It must be observed that the temperatures in Table 1 are maximum

reaction or, in other cases, adiabatic flame temperatures rather than

material temperatures. This is fortunate because most iron-nickel

chromium heat-resistant alloys melt near 2250°F (1232'^C). They would

be totally unacceptable, for example, in the Koppers-Totzek gasifier if

it were not for its ceramic liner and good heat transfer.

The chemical environments outlined in Table 1 are new and represent the

range of operating conditions to be expected in the new coal conversion

industry. The conditions are more corrosive and abrasive than those

found in the petroleum industry. It can be expected that many hardware

items used in petroleum will be unacceptable in coal conversion.

Comparison of Reliability Needs with

Those in Fossil -Fired Power Plants

The FEA has made a concerted effort to determine reasons for large

fossil-fired power plants having capacity factors of -60%. The capacity

factors can be improved significantly by reducing the failure frequency

and attendant repair times, but knowledge of the real failure causatives

is required before equipment reliability and maintainability can be

improved. The results of an FEA-sponsored study are summarized in

Table 2 and show that the major number of outages and outage hours is

due to boiler problems, and not of the turbine or even the electric

generator (Ref.l). The utilities seem to generally recognize that the

problem, as stated, is in the boilers and that, if allowed to continue,

will become a major investment problem. Five power plants will be

required to provide the energy supplied by three good plants.

Some failure analyses, including root cause effects, are conducted at

ERDA pilot plants, and the results are compiled at the Bureau of

Standards (Ref.6). A recent tabulation (Table 3) included an examination and assessment of the failure analysis data generated by ERDA contractors. Several interesting aspects are in Table 3. The most

frequent cause of a failure remains "undetermined." The next most

frequent is sulfidation, and erosion (physical abrasion) is almost as

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high. The data are only now beginning to be compiled at the Bureau, and

are updated on a daily basis. The established trend suggests that many

failures are simply a result of poor quality control, poor fabrication,

and design defects, and can be corrected by implementing a performance

assurance system. Alternatively, there also appear to be an even

larger number of failures in corrosion, erosion and sulfidation,

requiring materials research coupled to strict management control.

The Bureau's effort is part of an ERDA program to disseminate information

on failure root causes. A newsletter (Figure 2) now being published

has about 1000 subscribers, over 60% of whom are in private industry.

Test Data

A recent series of short-term burst tests were conducted to determine

whether a coal gasification atmosphere (CGA) had any significant effect

on the mechanical properties of a heat-resistant steel. Cylinders of

310 stainless steel were pressurized for one hour at 1800°F (982°C) and

then further pressurized until rupture occured (Table 4). The gas was

air in one case and a CGA in the other. The latter had a distinct

effect; the burst strength decreased measurably when the metal was

exposed to CGA compared to air, although exposure was only one hour.

The data suggest that the materials behavior in a complex H2O - NHo -

- CH4 - H2 - CO2 - CO environment must be determined experimentally.

A Computer Analysis

Another complementary approach was adopted to evaluate the impact of

component reliability on operation of an integrated plant. A computer

analysis was conducted, and a schematic flow sheet was used to lay out

a series of valves, pumps, compressors, pipes, heaters, and to show

connections among the components (Ref.7). Because data were absent,

failure rates were estimated for each component in the system. Failure

rates of 1 x lO'^/hour, 1 x lO'^/hour and 1 x 10-4/hour were then

assigned to one component, a hydrogen plant, and the computerized system

model was run for each assigned valve. The results (Figure 3) show that

the probability of completing 200 hours of operation without failures is

nearly zero when the hydrogen plant failure rate is 10"^/hour. The same

curve shows it has only a 13% chance of surviving 100 hours of operation

without failure. This is because the system being modeled has its

components in series, and the low failure rate of 1 x 10"^/hour for the

hydrogen plant component with respect to the other system components has

a large impact on system failure rate. By the same token, failure rates

of 1 X 10"^/hour and 1 x 10"^/hour for the hydrogen plant significantly

decrease the failure rate of the system. However, it should be realized

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15
that failure rates must be extremely low in order to achieve a reasonable

acceptable level of system reliability.

The data and procedure used in Figure 3 represent simplified versions

of an actual commercial plant.

The results of the study indicate a severe reliability problem requiring

detailed evaluation and determination of failure rates for individual

components to improve plant operability. Also of great significance

is the fact that this type of analysis can be of inestimable assistance

in pointing the road to more relevant and significant R&D programs.

A Performance Assurance System

The objective of any failure prevention activity is reduction of the

numerous problems in maintaining plant operation. The current failure

reporting, analysis, and corrective action efforts disclose problems

in real-time operation, and as such are a significant input to the goal

of improved plant reliability and operability. However, more can be

done to achieve this goal. Efforts can and should be applied during

the design and development (and later) phases that will expose potential

problems before operation and simultaneously improve the data base and

cost aspects of the design.

Once the nature of a problem has been determined, corrective steps can

be taken; hence the importance of failure reporting and analysis on

operating equipment. However, to avoid the problem, recommendations

center on the objective of determining potential failures through early

analysis during the program, and incorporating design and/or procedure

changes to obviate or reduce the problem. This activity should be

followed by feedback from operations to correct problems previously

unexposed. The elements of concern are reliability, maintainability,

availability, standardization, quality assurance, cost, and service

life. These features affect plant or equipment performance. The

disciplines and activities controlling these performance features form

the major elements of a Performance Assurance System (PAS) that is

recommended for application to all ERDA Fossil Energy projects. The

success of such a system will depend upon industry's willingness to

accept and cooperate. The benefits, as shown in Table 5, are numerous

to all concerned.

16
IT
The ERDA Program

The reliability problems in coal conversion have been presented. The

Materials and Power Generation Group's current programs toward achievement of reliable plant operation will now be presented. There is a continuing need for support of all concerned to accomplish the program

goal. Table 6 presents the activities of the Materials and Power

Generation Group in Fossil Energy Research. The programs are performed

in national laboratories, government laboratories, and in private

industry. The following paragraphs summarize the effects.

Failure Analysis and Prevention Program

• Analyzes and catalogs pilot plant materials and component failures

• Advises pilot plants on failure prevention

t Indicates areas for materials and components research and development

Materials and Components Newsletter

f Disseminates information regarding ERDA/FE programs

1. Highlights coal conversion processes

2. Announces and updates programs

3. Distributes failure prevention knowledge

• Distribution free on request - 900-1000 subscribers: 61% private

industry: 21% government: 12% universities: 6% government-owned,

contractor-operated facil ities

Programs Sponsored by ERDA and Performed at the National Laboratories

• Oak Ridge

1. Feasibility Study on Prestressed Concrete Pressure Vessels (PCPV)

determine potential of PCPV in coal conversion systems and

establish feasibility of use.

18

2. Technology assessment of Coal Conversion Pressure Vessel and

Piping Materials: assess status of technology in materials

selection for coal conversion pressure vessels and piping.

3. Inspection Techniques for Wear- and Process-Resistant Coatings

for Use During Fabrication and Operations of Large-Scale Plant:

develop equipment and procedures for in situ non-destructive

testing of coating materials used in coal conversion processes.

4. Iron and Nickel Carbonyl Formation and Prevention: determine

conditions under which iron and nickel carbonyl s form when CO

is in contact with pipe steels, and develop methods of economically controlling their formation.

§ Argonne

1. Evaluation of Ceramic Refractories for Slagging Gasifiers:

evaluation of currently available refractories under conditions

existing in slagging gasifiers.

2. Evaluation of Ceramic Coatings: evaluation of ceramic coatings

and inlay refractories for erosion and corrosion resistance in

coal gasifiers.

3. Nondestructive Testing for Coal Conversion Plant Components:

evaluation of testing methods that can provide existing pilot

plants with life estimates of materials and components, that

can be extended for use in demonstration and commercial gasification plants.

4. Corrosion Behavior of Materials in Coal Conversion Processes:

use of thermodynamic data and concepts to develop models for

corrosion in coal gasification atmospheres.

5. Erosion Behavior of Materials in Coal Gasification Processes:

Formulation of analytical models for predicting material loss

due to erosion/corrosion of components used in coal gasifiers.

• Sand i

a

1. Formation of Protective Carbide and Sulfide Layers on Alloys in

Coal Gasification Environments: explore possibilities of forming protective carbide and sulfide layers by the addition of

strong carbide and sulfide formers to existing high temperature

al loys.

20
Programs Sponsored by ERDA and Performed at

Government Laboratories

• Bureau of Mines

1. Development of Improved Valve Materials for Coal Feeding and Char

Removal in Coal Gasification Processes: develop improved valve

materials using powder metallurgy, casting, electro-deposition,

and chemical vapor deposition technique, and subsequent evaluation

for wear, abrasion, erosion, corrosion, and shock resistance in

atmospheres simulating coal feeding and char removal.

2. Improved Ceramic Liners for Coal Gasification Process Vessels:

determine corrosive effects of the principal constituents of

coal gasification atmospheres on selected refractories; determine

feasibility of centrifugal casting liners for transfer lines;

investigate means of reducing spelling and cracking in ceramic

1 iners.

t National Bureau of Standards

1. Metal Corrosion: develop and evaluate testing techniques that

determine the susceptibility of materials to stress corrosion

cracking in environments encountered in coal conversion

technology.

2. Metal Wear: investigate the mechanisms of metal wear from

particle impingement, and develop test methods for evaluation of

this type of wear.

3. Ceramic Deformation and Fracture: evaluate strength and crack

propagation in various refractories suitable for use in coal

gasifiers.

4. Erosive Wear: evaluate erosive wear of ceramic materials to be

used in high wear areas of gasifiers and study of the mechanisms

of particle erosion in ceramics.

Programs Sponsored by ERDA and Performed

in the Private Sector

t Program to Discover Materials Suitable for Service Under Hostile

Conditions Obtaining in Equipment for the Gasification of Coal and

Other Solid Fuels (with Metal Properties Council)

1. Phase I - High Temperature Corrosion: laboratory corrosion

testing of various candidate alloys for gasifier internal

21
components in simulated coal gasification atmospheres at elevated

temperatures and pressures.

2. Phase II - Pilot Plant Exposure: evaluation of metallic and

ceramic materials exposed to various locations in operating

pilot plants.

3. Phase III - Aqueous Corrosion Testing: laboratory corrosion

testing of alloys in aggressive environments simulating quench

systems in coal gasification plants.

4. Phase IV - Erosion-Corrosion Testing: laboratory erosion/corrosion testing of metals and refractories at high temperatures

and pressures in coal gasification atmospheres.

5. Phase V - Engineering Properties: determination of physical and

mechanical properties of selected alloys in and after exposure

to coal gasification atmosphere at elevated temperatures and

pressures.

t Fireside Corrosion

1. Task I - High Temperature Gas Turbine Engine Components

Materials Testing Program (with General Electric Company): determine durability of selected gas turbine nozzle and bucket

materials in gas environments from the combustion of coal -derived

low Btu gas and coal -derived fuel oil.

2. Task II - Evaluation of Heat Exchanger and Turbine Materials

for use in a Coal -Fired Fluidized Bed Combustion Environment

(in contract negotiation process): testing materials suitable

for heat exchanger tubes, superheater tubes, and turbine vanes

and blades in coal -fired fluidized beds at both atmospheric

and elevated pressures.

3. Task III - Effect of Impurities in Coal Derived Fuels on Service

Life of Boiler Tubes for Advanced Power Cycle Application (with

Combustion Engineering): both laboratory and field testing of

commercial and advanced experimental materials and coatings

under design conditions simulating advanced fuel power cycle

combinations.

• Sulfidation Resistant Alloy for Coal Gasification Service (with

Lockheed Missile and Space Company): design of an iron base alloy

having a corrosion rate less than 20 mpy in coal gasification atmospheres with the mechanical properties, fabricabil ity, producibil ity

and weldability of 300-series stainless steels but containing less

than 10% Cr and Ni

.

22
• Preparation of a Data Book on High Temperature Oxidation and Corrosion of Metals and Alloys in Electrical Generation Systems (with

Battel le Columbus Laboratories and Professor Stringer at University

of Liverpool: co-sponsored with EPRI).

Programs Current in Procurement Cycle

0 Correlation of the High-Temperature Corrosion Behavior of Structural

Alloys in Coal Conversion Environments with the Components of the

Alloys and of the Corrosive Environments: establish a statistical

correlation between alloy corrosion rates and gas composition, temperature, and pressure and the level of major alloying elements in

alloys to be used for internal components of coal gasifiers.

• Determination of the probability of Alkali Degradation and Corrosion

of Refractories and Metals in Various Coal Gasification Processes:

determine the amount of alkali vapor in the atmosphere of various

coal gasification processes in order to assess the probability of

alkali degradation and corrosion of refractories and metals in the

gasification environment.

• Improvement of the Mechanical Reliability of Monolithic Refractory

Linings for Coal Gasification Process Vessels: develop improved

materials, lining designs, and operating procedures for monolithic

refractory linings of gasifier process vessels in order to reduce

or eliminate cracking during curing, drying, and heat-up of the

refractory lining.

• Study of Heat Transfer Through Refractory-Lined Gasifier Vessel

Walls: develop empirical heat flow/thermal conductivity models

for multi-component refractory-1 ined gasifier walls suitable for

use in the design of commercial refractory linings for coal gasification vessels.

• Development of Valves Compatible with Gasifier Plant Conditions:

develop and establish the mechanical integrity of families of valves

compatible with operating conditions encountered in the various

coal gasification processes: discover and describe new problem

areas, if any; provide data required for optimization so as to

minimize plant costs and maximize reliability and maintainability.

Acknowledgements

The authors acknowledge the assistance of many individuals who

provided data and reviewed ideas, budgets and data. Dr. John H. Smith,

25
National Bureau of Standards, provided valuable data on failure analyses

Mr. James Sims, Mr. Fred Ems, and Mr. Bruce Bell, all of TRW, provided

ideas on functional relations in performance assurance and reviewed

the manuscript. Mrs. Evelyn Halili, TRW, prepared data on conditions

encountered in coal conversion plants.

2k
References

"A Report on Improving the Productivity of Electrical Powerplants ,

Office of Energy Conversion; Energy Resource Development.

Prepared by FEA Interagency Task Group on Powerplant Reliability.

March, 1975.

C. Fink, G. Curran and J. Sudbury, "CO2 Acceptor Process Pilot

Plant - 1975." Paper presented at Seventh Synthetic Pipeline Gas

Symposium, Chicago, October 27, 1975, Available from AGA, Arlington,

Virginia.

W. W. Bodle and K. C. Vyas, "Clean Fuels from Coal," Oil and Gas

Journal , August 1974.

F. C. Olds, "Materials for Tomorrow's Energy Conversion Systems,"

Power Engineering , March 1976.

A. 0. Schaefer, C. H. Samans, M. A. Howes, S. Bhattacharyya, E. R.

Bangs, V. L. Hill, and F. C. Chang, "MPC Report for 1975." Prepared under ERDA contract E (49-1 8) -1 784, January 20, 1976.

Private communication; John Smith, Institute for Materials Research,

National Bureau of Standards, April 1976.

W. T. Long, J. D. Salazar and F. C. Kleager, "Results of

Demonstration of a Reliability Assessment Methodology Using Two Coal

Conversion Plant Models," Final Report, June 6, 1975. Prepared by

Kaman Sciences Corporation under ERDA contract 14-32-0001-1788.

25
DISCUSSION

D. Livaccari, Coal con : You mentioned that there are coal gasification

projects in some foreign countries. Has there been any effort to

obtain data from these foreign sources?

H. E. Frankel : Yes, efforts have been made to get this information.

However, you must remember that we are in competition with these people;

therefore, they are reluctant to share their data with us. The Lurgi

process is by far the major industrial process used in Europe. I can

cite an example that may shed some light on the reliability of this

process. In the southwestern United States, the El Paso consortium

is going to build plants to produce 250 million cubic feet of synthetic

gas per day. In order to do this using the Lurgi process, 34 plants

would have to be built. Only 27 plants (each producing 10 million cubic

feet) would be on line at any given time. The additional seven plants

are a reserve or redundant feature. When close to one-fourth of the

total plants in a system are inoperative at any one time, I would

consider the reliability of the plant to be rather poor.

26
ECONOMICS OF FAILURES IN ENERGY GENERATION SYSTEMS

Melvin E. Lapides

Nuclear Systems & Materials Division

Electric Power Research Institute

Palo Alto, California

?UDStract: Capital equipment costs and efficiency of fuel

utilization are well recognized criteria in the selection of

new electrical generation capacity. The service reliability

of the equipment, as measured by some term which reflects

both the productivity of the investment and the consequential

cost impacts of failure is an equally important, albeit

somewhat more elusive, consideration. The purpose of this

paper is to illustrate what forms of 'failure' can be

encountered with utility generation equipment and what the

consequential impact of these 'failures' is on the cost of

electrical generation. This background material, which is

specifically developed for large, baseload generation units,

is then used to describe some suggested orientations for

failure prevention in advanced technology systems.

The economics of equipment failures in utility generation

systems are reflected in the cost to the consumer of electric

generation. However, the impacts of the failure—and,

indeed, the definition of what constitutes a "failure" —must

be assessed in several ways that are dependent on the nature

of the generation unit and of the system in which it exists.

The issue is further complicated because the economic impact

will vary significantly depending on when the failure

prognosis occurs; failure assessment during acquisition

planning is a different situation than true failure during

operations

.

To unravel this fairly complex introduction for MFPG members,

it appears desirable to consider only a large (nominally

800 - 1300 MWe) generation unit intended for true baseload

operation. These are the type of units, based on either

coal or nuclear energy sources, that are expected to dominate

the new capacity market until about the year 2000. A utility

will begin the planning and acquisition phase for these

units some 10-15 years ahead of need time as defined by a

forecast of load and reserve margin requirements. This

single unit may represent from 6%-30% of the baseload

capacity owned by the utility when its operation is initiated.

27
Procurement decisions concerning new generating facility

additions are usually based on evaluations that determine

the lowest overall cost of producing electricity. Initial

cost, estimated capacity factor, fuel cost and operation and

maintenance cost are expressed by an equation of the form:

^ 1000 X A X B , „ , ^ = 8760 X

^ ^ ^0 ^

Where: = Generation cost in mills/kwh

A = Annual levelized fixed charge rate

(typically 15% - 17%)

B = Capital cost of the unit in $/kw

F = Fuel cost in mills/kwh

O & M = Operation and Maintenance cost in mills/kwh

Cp = Unit capacity factor

Figure 1, a brief parametric study based on equation 1,

illustrates the relation between capacity factor and generation cost for a range of equipment and fuel cost combinations

believed to be of future interest. The data are normalized

to a capacity factor of 0.8.

A utility nominally selects a new baseload unit addition

anticipating that it will provide the lowest achievable

incremental generation costs for its system. Theoretically,

it would like to run this unit "all the time" at full-rated

power (CF = 1.0). However, this ideal situation cannot be

met. Scheduled maintenance or modification time must be

considered; equipment malfunctions will occur; excessive

first costs may be associated with high levels of redundancy

needed to mitigate the impact of malfunctions. In addition,

the utility may anticipate discretionary power reductions

such as load following. Thus, the target capacity factor

for large baseload units is normally in the range of 0.75 to

0.9 (without provision for load following). Accordingly,

the utility will plan a major scheduled outage for preventive

maintenance, on the order of once a year, ideally at a time

when minimum demand exists. Assuming that the utility has

selected a nominal target value capacity factor of 0.8, a

failure can be defined as any equipment malfunction, or

excessive maintenance time, or regulatory issue mandating

modification which will prevent this value from being

achieved. This may appear to be an odd definition of

failure; but it leads to the correct emphasis on productivity

of an investment in generating capacity which is the concern

28
of the utility at this point. There are circumstances where

true equipment failures can be avoided by higher frequency

of maintenance; there are other circumstances where equipment

failures can be repaired without loss of generating capacity.

In classical reliability analyses all failures might be

given equal weight. Following these cases through to their

productivity impact, as measured by capacity factor, provides the more balanced view which is required. Figure 1

permits a direct evaluation of the cost of failures in the

aforementioned context. Because the generation cost of

current design and future plants appears dominated by capital

cost, the impact of capacity factor variation is obviously

quite large. Typically, a 10 point capacity factor variation will have a consequential impact of approximately 10%

on total generation costs.

Utility procurement evaluation interests focus on determining: the relative capacity factor values for ranking

generation alternatives; what failure causes are applicable

to each alternative; and finally, what relation exists

between first cost adders and the prospects for failuremitigation. Some of these questions are easier to answer

than others. However, before considering them in further

detail, it is appropriate to consider alternate dimensions

of the economic impact of failure.

The approximate situation that a utility faces in its

acquisition program is suggested by the pattern of capacity

additions in response to increasing customer demand shown as

Figure 2. When the new generation unit is first brought on

line it may provide a higher degree of reserve margin than

actually required in the system. At this time, (point A

)

the utility might be able to run the unit below its nominal

capacity factor without excessive penalty. Later, (point B)

when the unit becomes fully committed, an unanticipated

outage mandates that replacement power be acquired. The

added economic impact of failure now becomes the cost

differential which may exist between purchased and generated

power. The purchase premium (which results because systems

rarely have lowest cost generation output available as

surplus) might be from 2-4 times the purchasers own cost of

generation. The actual cost for a day's outage of a 1000-MWe

unit in this case could easily amount to a half million

dollars (assuming a cost of 20 mills/kwh for baseload generation) . So the cost of replacement power is the second

important dimension of failure economics. It usually becomes

dominant when the loss of the unit cannot be accommodated by

the owners system reserve.

29
A related case is a failure to bring the new unit on line at

the scheduled time. For a one-year delay, the extreme

result might be that the consequential cost of power purchases is 30%~50% of the unit capital cost. In addition,

the delay will probably increase unit capital cost by some

5%-10%; the reason for this being that the time-dependent

charges (e.g., interest during construction, escalation)

currently account for of the order of 30-50% of the plant

capital cost.

The preceding examples illustrate how failure to achieve

performance on a timely basis yields extremely large consequential costs in the electric utility industry. The

factors noted exert a major influence on the character of

major programs in which utilities can participate and on the

rate at which specific developments will penetrate the

utility market. The role of failure prevention disciplines,

which is of more immediate interest to MFPG members, can be

assessed by reconsidered utility deliberations in the context

of Equation 1. The utility would like to know: a) what

capacity factor should be applied over the total service

life of the unit (nominally 30-40 years) , and b) is it

reasonable to assume that the capacity factor will follow an

orderly predictable pattern, typically with provision for an

initial maturing phase, if the system is adequately maintained? On first principles, these questions focus on

deterioration modes which might foreshorten service life and

on the reliability and maintainability of the operating

system.

Coal-fired units, including advanced approaches such as

combined cycle options, are not generally thought of as

containing major service life foreshortening elements. The

most critical items in this regard are turbomachinery

,

wherein extremely long duration outages would be dictated

should major blading or rotor damage occur. There are many

steam turbine assessment programs underway on this basis.

These include as examples, stress corrosion behavior of

turbomachinery materials in the presence of trace impurities

in steam, moisture impingement effects, and cyclic fatigue

behavior; all as a means of establishing the least deleterious operating modes. Presumably direct-fired turbines

will require analogous efforts as extensions of present

activities for smaller-size peaking units.

*A foreshortened service life would normally be reflected in

an increase in the term 'A' in Equation 1. 'A' includes

depreciation.

30
The utility's capability to assess the unit capacity factor

is nowhere near as good as it should be. There is much

folklore as well as a growing body of technical literature

on the subject (1,2) which cannot be easily encapsulated for

this paper. However, a brief review of some salient issues

may be of interest. Figure 3, a plot of the cumulative

lifetime capacity factor of domestic nuclear generation

units, is a point of departure. The units represented range

from 200 MWe to 1000 MWe, have an 'average' service life of

approximately four years and an age distribution covering

approximately 1-14 years. What is immediately evident is

that an 'average' value does not offer a good description of

the situation. Instead, a wide distribution of performance

exists. There are good units which meet target expectations.

There are also poor performers. When discrimination studies

are performed the reasons for the spread do not turn out to

be easy simplifications. The agfe or the size of the unit,

for example, are perhaps less important than the perception

of value some 10-15 years prior to operation - or the ability

to predict a current regulatory climate from this same

distant vantage point. Thinking a moment about our own

capability to forecast economic and political climates on a

similar time scale, it seems difficult to fault anyone for

having missed the right (now) trade-off between first cost

and maintainability or redundancy. The same assessment

applies to regulatory issues, the fairly exclusive domain,

until recently, of nuclear units.

The technical results of the discrimination study can best

be likened to a complex 'learning experience.' Typically,

various 'campaigns' are required to solve those significant

engineering problems revealed only through operating experience. Concurrently, the utility is acquiring the information

needed to plan and implement maintenance or to diagnose malfunctions. The picture is admittedly 'fuzzy' because several

units with the same ills may have been committed while a

'campaign' was in process and because the transfer of operating experience in and among suppliers is not easily accomplished. Nevertheless, a maturity trend can be identified

when sufficient statistics become available. Figure 3,

which shows evidence of performance improvement following

the experience of first refueling, is representative.

At least a partial apology to MFPG members interested in

coal gasification is in order for the use of nuclear statistics for illustration; (in part because of the author's

background, as well as the pragmatics of more readily available codified data) . But, in fact, the conditions are

reasonably representative of what any new generation introduction might anticipate—and, at least at the aggregate

level, the performance of present large, coal-fired capacity

51
is not notably different than that for nuclear units (Figure

4) . One reason for this similarity is that all generation

units have many elements more or less in common--and, perhaps

to the surprise of some, it is these common elements which

are responsible for much of the capacity loss encountered.

The approximate historical situation for the locales of

nuclear capacity loss shown as Table 1 illustrates this

point

.

Also, at the risk of overgeneralizing , the orientation for

those interested in failure prevention in advanced systems

can also be extracted from either of the trend illustrations.

The essential goals of failure prevention are to get the

performance distribution function to be as high as practicable with the lowest mean deviation as fast as possible.

To do this, it is obviously necessary to emphasize high

reliability equipments and high standards of production

quality control. But, particularly in the case of the

aforementioned common equipments, one is invariably already

dealing with items which have achieved such stature (as

evidenced by the statistical mean-time-between failures

(MTBF) which they can be assigned.) So, the thrust here is

to reduce the maintenance time required, to provide the

information which permits the most economic spares and

replacement policy to be determined, and to provide the

technical basis for mitigating the infrequent high impact

outage which might occur. Good in-service failure precursor

instrumentation is an example of what is needed in the

latter case. For those subsystems where 'campaigns' might

be anticipated, it is again obviously necessary to insure

that the initial design implementation reflects the best

levels of technology available. But, it is equally important

to provide a sound technical basis for diagnosis and high

creditability modification and retrofit for in-service

equipment as rapidly as possible.

Many of you will recognize that the preceding comments imply

accent on the maintainability aspects of product performance

optimization (3) rather than exclusively on those reliability

approaches which emphasize MTBF per se. Perhaps the most

significant reasons for this assertion is again an economic

consideration; in this case, the amount of capital which is

placed 'at risk' in a new generation technology before

mature operating experience is acquired. This point is made

graphically by Figure 5, a representative study of the

status of units entering service as a function of calendar

time for a fixed construction term and schedule of manufacturing capability build-up. What is most significant is

the very large amount of capital which must be committed

before any statistically significant, long-term operating

experience is available to verify the investment judgment.

32
One can think of many ways to try and warp this situation,

but it invariably turns out that such exposure is inherent

in any approach which aims at making an appreciable impact

on the nation's electrical generation capability. Given

such circumstances, the capability for rapid, incisive

analysis of operating experience and feedback to retrofit,

design and operating actions is perhaps the highest leverage

tool for investment justification available.

References

1 . A Report on Improving the Productivity of Electrical

Power Plants , FEA Interagency Task Group on Power Plant

Reliability, May, 1975.

2. Lapides, M. and Zebroski, E., "Use of Nuclear Plant

Operating Experience to Guide Productivity Improvement

Programs," EPRI Special Report SR-26R, November, 1975.

3. "Maintainability Prediction," MIL Handbook-4 72 , May 24,

1966.

53
1.30

0.90

' ' ' ' '

0.5 0.6 0.7 0.8 0.9

Unit Capacity Factor

Figure 1 Plot of Relative Cost of Electric Generation

Versus Capacity Factor (Cp )

; Normalized to Cp = 0.8

3h
i

Capacity Addition(s)

Calendar Year

Figure 2 Typical Pattern of Utility Generation

Capacity Additions

35
56
100

i 60

CD Q.

Output

Factor

Availability

Factor

Fossil Units

Nuclear Units

80 — Capacity

Factor

40 — 2.

3.

NOTES

33 Nuclear Units > 1 year old

and >100 MWe (data cumulative

as of 7/75)

81 Fossil Units >600 MWe (data

cumulative through 1974)

Fossil Units use EEI availability

definition ~3% higher than NRC

20

1 10 20 50

Percent Plants Greater Than Ordinate

90

Figure 4 Comparison Plot of Cumulative Lifetime Performance

Factors for Large Nuclear and Fossil Units

57
200

180

160

140

120

Unit Distribution by Stage and Year (1985-2000)

2 Years for Design

4 Years for Construction

Units Entering Design each Year:

(First, Second, Third, etc.)

2 2 4 4 8 8 10 10 15

Constant each Year Thereafter

c

STAGE: YEAR 2000

168 UNITS IN AND

PAST DESIGN STAGE

TOTAL UNITS:

UNITS IN YEAR OF STAGE

12

34

5

OPERA TION

78

15

15

10108

CONSTRUCT

60

15

15

1515

DESIGN

30

15

15

100

(UE

3

80

60

40

20

0

1985 1990 1995 2000

Figure 5 Representative Illustration of Build-up of New

Generation Capacity

38
DURATION

ITEM (hours) % TOTAL

Forced Outage

(Equipment Malfunction)

Turbine/Generator 140 4.7

Condenser 124 4.2

Steam Generator 189 6.3

Pumps 60 2.0

Valves 132 4.4

Vessel & Core 75 2.5

Plant Electrical Distribution 30 1.0

All Other 310 10.4

SUBTOTAL 1060 35.5

Scheduled Outage

Maintenance 280 9.4

'Refueling' 1500 50.2

Training & Administration 30 1.0

SUBTOTAL 1810 60.6

Regulatory 116 3.9

TOTAL 2986 100.0

Availability Factor (Based on One Year Operation Between Refueling)

8760 + 1 500

Partial Power Reductions (Approximate)

Output Factor Multiplier

to Availability

Fuel Defect Related 0.95

Equipment Failure Related 0.98

Regulatory Issues 0.96

Load-Following 0.99

Time to Come to Full Power 0.99

All Other & Unaccounted 0.97

OUTPUT FACTOR (PRODUCT) 0.85

Capacity Factor = Availability x Output Factor

71% X 0.85 = 60%

Table 1 Representative Average Outage Duration and Partial

Power Reductions in Nuclear Units Through June 1975

39
DISCUSSION

S. S. Canja, ERDA, Fossil Energy : I have been looking at some of the

FEA reports on electrical utilities. It seems that over the last 3

or 4 years the capacity or availability of new power plants has been

decreasing, especially in nuclear power plants. Can you explain why

that is occurring?

M. Lapides : I think that is a misconception. I do not think the availability of nuclear units has been decreasing. The availability of

fossil units certainly has, for good and obvious reasons. Nuclear

power plant availability has been improving quite steadily over the

last few years.

S. S. Canja : What incentive does the electrical utility industry

have to improve its capacity when, as you say, if there is an outage,

a utility simply buys additional power from another utility and passes

the costs on to the customer?

M. Lapides : In the late 1960's, I don't think the utility industry

had any great motivation to build "high reliability equipment", meaning

equipment that would theoretically be available 90 to 100% of the

time between maintenance outages and could run at 100% capacity when

it was available. The reason for the lack of improvement in the nuclear

power plant industry is as follows. The nuclear power plant was a high cost generator. If one went out, the utility could turn to a cheaper coal-fired generating plant. Concerning fossil fueled plants,

in the late 1960's and very early 1970's, a utility might be operating

a 200 megawatt plant. In order to increase capacity the utility would

buy a new unit that might have a capacity of 1,000 megawatts, or five

times the capacity of the older plant. With such large reserve

capacities, there was little concern for high reliability. Since

1973, conditions have changed. The rate of increased demand is slowing

down, the size of the generating unit is nearly constant, utilities

are strapped for cash, and they are, of course, aware of the need for

energy conservation. They have a very strong motivation now that

they never had before. We look for a 10% reliability improvement in

the next 10 years in existing plants. That would be equivalent to

three billion dollars that utilities do not have to spend. This

magnitude of savings is very good motivation. I do not want to defend

the utilities, nor do I want to sound glib, but I do not think it is

fair to make a 1975 retrospective judgement on plant efficiencies for

plants built based on decisions made in 1965.

1+0
DEMONSTRATION OF A RELIABILITY METHODOLOGY

USING TWO COAL CONVERSION PLANT MODELS

John R. Hoffman

W. Tierce Long

R. Larry Williams

Kaman Sciences Corporation

P.O. Box 74 6 3

Colorado Springs, Colorado 80933

Abstract: In 1975 the Office of Fossil Energy sponsored

a research program to demonstrate the use of a reliability methodology for modeling process flow in coal

conversion plants. The methodology was applied to the

Institute of Gas Technology HYGAS and the FMC Corporation

COED pilot plants. The methodology, called GO, had

previously been successfully applied to a variety of

complex systems involving electronic, hydraulic and

mechanical subsystems. Other applications of GO have

included the human interfaces, many of which are common

to several subsystems and necessary for proper system

operation. This paper presents a brief introduction to

the GO methodology and an overview of its application

to coal gasification plants.

Key words: Coal gasification; GO reliability methodology.

Coal conversion plants are extremely complex, consisting

of thousands of process elements with their associated

monitoring and control instrumentation. As conceptual

designs are formulated, converted into design specifications, construction is completed and plants enter

into operation, continuously updated reliability assessments are necessary to insure that plant reliability

goals are achieved and maintained. A highly desirable

attribute of a reliability assessment methodology is

the capability to model accurately the operation of a

coal conversion plant, where there is a high degree of

correlation between drawings and schematics and the

assessment model. Such a methodology would also provide

for rapid revisions in the assessment model in keeping

with design changes and proposed engineering change

orders. It would permit concurrent reliability assessment

of these changes as they are proposed.

i+1
Over a period of 15 years a reliability methodology

called GO has been developed and successfully applied

to a variety of systems involving complex electronic,

electrical, hydraulic and mechanical systems including

their human interfaces. The GO methodology possesses

the attributes previously mentioned. The primary

motivation in the development of GO was to produce a

computer routine which could, with a minimum of scientific

labor, quickly, economically and comprehensively analyze

the reliability and safety of complex hydraulic, pneumatic

and electromechanical networks involving hundreds of

components having two and often three or more modes of

operation. Using this generalized approach the computer

program, rather than the analyst as in the fault tree

or equation writing techniques, systematically creates

and retains the various event combinations bearing

on both the central problem and all other significant

system operational modes. Because the logic, other

than the component interactions, is handled automatically,

significant savings in scientific labor are achieved,

and increased knowledge of system responses is obtained.

The GO program is an event tree procedure. Components

are identified by their input signals, output signals,

and probabilities of operation in different modes

(success, premature and failure). The GO chart is a

diagram of component interactions through the signal

paths. The modeling required includes selection of the

proper standard GO component to represent the physical

components and the identification of signal paths.

This modeling is direct and immediate since the chart

can be drawn in one-to-one correspondence with the

schematic, almost as an overlay. Currently there are

11 standard GO components which are used in modeling.

Others are available for special applications.

The fundamental steps in a GO analysis are shown in

Figure 1. The analyst working with system schematics,

wiring diagrams, drawings, etc. constructs the GO

chart. From the GO chart an input deck is derived, the

data is processed and the results listed. For the

moment I am going to skip over a step-by-step discussion

of GO chart development and show you an example of one

section of the HYGAS pilot plant.

Figure 2 shows a schematic of the HYGAS methanation

section. Figure 3 is a GO chart for the same section.

There is an almost one-to-one correspondence between

the schematic and the GO chart with each major system

element being modeled by a GO component. At first

glance Figures 2 and 3 may appear to be extremely

h2
complex but I assure you that it is relatively simple,

particularly when compared with the task of trying to

write an equation for the system.

Note in Figure 2 the large number of valves with their

associated sensor and control systems. A brief discussion

of this combination of valve and sensor will demonstrate

that the GO chart is rather simple and easy to use and

will also demonstrate how the detail of the modeling

can be expanded to the degree desired.

Figure 4 shows a schematic of a valve controlled by a

sensor with the flow as indicated. A GO chart for this

simple combination is also shown where two Type 1

components are used to model the sensor and the valve.

Signal 1 represents the flow of the material. Signal 2

represents the function of the sensor and signal 3

represents the function of the valve. In this discussion

let us assume that we are dealing with three time

periods. If the sensor functions properly, signal 2

will be generated in time period 1; likewise if the

valve functions properly signal 3 will also be generated

in time period 1, which also indicates that both the

sensor and valve are functioning. If this is the case,

the material flow should be allowed to proceed. This

is accomplished by the Type 10 component, an "and"

gate, i.e., signal 4 which will occur in time period 1

now represents the continuing material flow. This

could have been modeled in slightly different fashion

by putting the sensor and valve in series with the

process flow but our experience has shown that if we

follow the schematic it becomes easier to check that

all components are modeled and it is also easier to

explain to people who are not familiar with GO.

Let us take the example one step further and assume

that if the sensor fails a warning light goes on in the

control room and an operator is dispatched to the valve

and operates it by a handwheel in accordance with

instructions received via telephone or two-way radio.

During this operation the sensor is repaired. How do

we model this back-up mode? The GO chart on the right

of Figure 4 shows one approach. Signal 2 indicates the

state of the sensor. This is fed into a Type 9 component

representing a switch in the annunciation light circuit.

Note that the main input into the Type 9 component is

signal 3 representing the availability of power. The

failure of the sensor triggers the switch allowing

power to the warning light. The warning light is noted

and if an operator is available signal 5 effectively
triggers the operator who then goes to the valve and

operates it. Signal 7 representing the operator and

signal 2 representing properly functioning sensor are

fed into a Type 2 "or" gate. If either signal 7 or

signal 2 is present the valve will be actuated and we

obtain signal 10 representing the material flow.

When the back-up mode is introduced the system timing

can be modeled so that signal 7 will occur in time

period 2. The effect of this treatment is to obtain

signal 10 in time period 1 representing automatic

operation and in time period 2 representing operation

in the back-up mode.

A model such as this could be used to conduct experiments

to determine the level of operator availability

required to achieve some level of successful operation.

Another point should be noted, the communication net

between the control room and the operator has not been

modeled nor is the warning circuit modeled in much

detail. If additional detail is required the modifications can be easily and quickly added to the basic

model

.

Time does not permit a detailed discussion of other

examples. Suffice it to say that when we examined the

schematics of the two gasification pilot plants for

ERDA we did not find any insurmountable problems in

modeling them with GO. This is not to say that GO is a

perfect modeling device. I doubt if such a thing

exists, but it does have features which permit expanded

evaluations over those generally available with fault

tree or equation writing.

With this brief background let us now turn to results

obtained in the ERDA study. Starting with failure rate

data for the various elements the reliability for each

component for one hour, 10 hours, 100 hours, etc., were

calculated. Using these reliabilities as inputs to the

GO model the probability of operating for T hours was

calculated. A plot of this information is shown in

Figure 5.

Figure 5 shows three basic uses of GO results. First,

the area under the curve can be integrated to determine

the mean time to failure of the total system. In this

case the MTTF was about 47 hours. This low MTTF is a

direct result of using an arbitrary failure rate of

10~2 per hour for a critical non-redundant hydrogen

plant. We have been criticized by some people in

industry for showing such low MTTF. However, our

kk
report specifically states that the 10 was our

assumption. We find it necessary to repeat that we

were not attempting to evaluate the reliability of any

specific plant - only to demonstrate a methodology.

Specific analyses would use refined data.

The next use of the GO analysis is to establish the

sensitivity of total plant operations upon the reliability

of one critical element or subsystem. In this case we

chose the hydrogen plant and decreased its failure rate

to 10~3 and 10"^. The points plotted at 100 hours on

the abscissa indicate the results. The MTTFs associated

with the new failure rates are approximately 83 and 90

hours

.

GO was also used to evaluate a "start-up" and "continuous

operation". There is little difference in these modes,

although the continuous operation is slightly more

reliable than the start-up mode. Recalling the previous

example with the valve it is easy to see how various

operational modes can be evaluated.

GO can also be used to assist in the evaluation of continuous operation with various maintenance and repair

schemes. The basic evaluation is treated as a discretestate, discrete-time Markov process with GO being used

to develop input probabilities to the general transition

matrix.

In summary the project for OFE demonstrated that GO

models of the process flow of coal conversion plants

typified by HYGAS and COED are applicable and efficient.

It has been demonstrated that GO can model various

modes of operation such as start-up and continuous

operation. The model is also modular in that specific

subsystems can be easily omitted or added.

It has also been demonstrated that GO can be used as an

experimental tool to evaluate various hypotheses relating

to total system operation as a function of a single

component reliability change.

In conclusion, the completion of the OFE project within

a 10-week period which included significant time for

report preparation illustrates that GO can be applied

rapidly and economically to provide comprehensive

reliability and availability assessments of coal conversion plants.

^5
=GO CHART —GO DECK COMPUTER OUTPUT LISTINGS

Figure 1

COMPRESSOR

Figure 2

1+6
Figure 3

Figure 4

^7
240

T ( HOURS )

Figure 5
DISCUSSION

E. Passaglia, National Bureau of Standards : Certainly, techniques of

this kind must have been applied to other areas of sophisticated technology like that used in the Apollo space program. Can you comment on

other programs to which your technique has been applied?

J. R. Hoffman : I am not familiar with the work done on the Apollo.

We are modeling the scram system for a gas cooled reactor at Fort St.

Vrain for ERDA. At the Fort St. Vrain reactor we modeled about 15,000

components compared to about 300 components at the HYGAS plant. We

have found some problem areas that had not been indicated in other

analyses.

E. Passaglia : How do your results compare with the Rasmussen report?

J. R. Hoffman : We found nothing that would show that the Rasmussen

report was in error in any large degree. We have considered some things

that were not covered in the Rasmussen report, for example, operator

interactions with the system. The GO technique is a little different

from that generally used. Most NASA people that I have talked to are

not worried about reliability analysis because there are various ways

to circumvent the problem through design. One way is to overdesign.

But overdesign with too many redundant systems may lead to trouble by

causing premature shutdowns. We found that there were 13 different

ways to actuate the deceleration mechanism for the Mercury flights,

and in fact predicted prior to that flight that there was a reasonable

chance for failure in the automatic system. And in fact, this occurred

on one of the Mercury missions. The astronaut had to do everything by

hand during deceleration because the reliability was not adequate.

h9
CRITICAL MATERIALS PROBLEMS IN COAL CONVERSION

R. W. Staehle

Department of Metallurgical Engineering

The Ohio State University

Columbus, Ohio 43210

Abstract: The stability of engineering materials in coal conversion

systems is reviewed with respect to effects of specific chemical

species: carbon, sulfur, oxygen, hydrogen, chloride and other species.

These chemical species operate both at low temperatures and high temperatures to accelerate the deterioration of engineering materials.

These species participate both in general degradation as well as highly

localized attack such as stress corrosion cracking, dusting, intergranular attack and break away reaction phenomena. In addition to

the strictly chemical influences on the metals, the deterioration of

metals in the coal conversion systems is accelerated by erosion and

static and cyclic stresses which lead to stress corrosion cracking,

hydrogen embri ttlement and corrosion fatigue.

Introduction: We start this discussion with the first law of materials

application: "all engineering materials are unstable." Thus, the

primary efforts of design and materials engineers must be directed

toward delaying the inevitable deterioration of materials for sufficiently long times that the material will perform as desired for the

intended life of the equipment. A second law having as much validity

as the first for large engineering systems is: "The chain is as strong

as its weakest link." While the latter seems trite, arising as it

does out of someone's long forgotten book of sayings, nonetheless, it

is a conceptual cornerstone in the development of large engineering

systems. Unfortunately much of the development effort in new systems

is placed upon the novel and intriguing problems with little effort

given to what is commonly referred to as off the shelf or conventional

equipment.

Past history with the fossil and nuclear power industries shows that

most of the down time is associated with conventional equipment and

not with more exotic components. The implicit suggestion here is that

whatever development work is undertaken to construct large coal conversion systems should consider reliability of all components; action

Reprinted with permission from Critical Materials Problems in Energy

Production, edited by C. Stein, copyright Academic Press, 1976.

50
should be taken to raise the integrity of such equipment in proportion

to the consequences of its failure to the performance of the total

system.

The full scope of potential materials problems was considered at a meeting in April 1974 at Ohio State University on the subject:

"Materials Problems and Research Opportunities in Coal Conversion" (1).

This document should be carefully reviewed.

A second and related meeting was held to consider materials for MHD

applications: "NSF-OCR Engineering Workshop on MHD Materials" (2).

This is also an excellent volume and should be carefully reviewed.

In assessing the expected performance of structural materials in coal

conversion systems the approach is little different from that which

should be used in any system. One starts first by defining the chemical species which are an implicit part of the system. The second

question one asks concerns the operational influences including

temperature, pressure, flow, particle velocity, heat transfer, etc.

Having defined these one then moves to define acceptable materials or

to develop a materials testing program. Unfortunately the common

approach is to decide early on the materials of construction and then

forget the question of compatibility hoping, by closing ones eyes

sufficiently tightly, that any deleterious influence would somehow lie

pleasantly dormant for an infinite time.

With respect to the environmental species in coal conversion equipment,

these are not difficult to identify. They include primarily carbon,

hydrogen, nitrogen, oxygen, sulfur, and chlorine. Impurities such as

zinc, lead, tin, and others often are damaging but are unlikely.

Physical influences which are to be considered simultaneously with the

chemical influences include the following: temperature, time, thermal

cycling, erosion, stress, and stress cycling together with the

exacerbation of creep-fatigue and stress corrosion cracking.

The above have implied damage processes which are associated with

fracture or corrosion type phenomena. These phenomena may be abetted

by prolonged thermal influences on the structure and properties of

metals. For example, temper embri ttlement operates over an intermediate range of temperatures and affects low alloy steels of the type used

in pressure vessels and turbines; stainless steels sustain the sensitization phenomenon at a somewhat higher temperature range; and,

51
finally, high alloy ferritic materials age to produce an embrittling

Sigma phase.

Having now defined the major considerations in materials performance,

i.e., the chemical environments, physical influences, and the change

of the substrate with time, now consider what tools and resources are

available for describing boundary conditions within which satisfactory

performance might be expected. There are four separable categories.

The first resource is the large reservoir of empirical data obtained

from reasonably similar industrial systems. For example, there is

already a fund of information from low BTU coal gasification systems.

The petroleum, gas turbine, and chemical industries provide extensive

information.

Secondly, there are well developed procedures based on thermodynamic

analyses which can be used to predict regimes of stability of materials.

These diagrams for stability of materials in environments are utilized in various forms. One of the most common is the simple plot of

free energy of formation of a compound vs. temperature.

For the

M + 1/2 O2 = MO

the free energy of formation is plotted vs. temperature and the curves

for the formation of various metal oxides can be readily compared as

for Figure 1. Lower values of the free energy of formation indicate

the more stable oxides. Such comparative plots as in Figure 1 can be

developed for the formation of other compounds such as sulfides,

chlorides, carbides, nitrides, etc. all of which are of interest in

coal conversion technology.

A useful approach for assessing stability of alloys in high temperature

gases is to follow the pattern of Figure 2 where the partial pressures

of sulfur and oxygen are plotted with respect to the existence of

principal phases of the alloy species. Here regimes of stability of

chromium and nickel phases are identified from work by Quets and

Dresher (3). The broad range of stability of the protective Cr203 film

accounts for the stability of alloys which contain chromium as a major

alloying element. The general approach epitomized in Figure 2 has been

discussed by Rapp (4)

.

The comparably important diagrams for low temperature aqueous corrosion

processes are the Pourbaix diagrams (5, 6). These address the question

52
Figure 1. The standard free energy of formation

of many metal oxides as a function of temperature.

[From F.D. Richardson and J.H.E. Jeffes, substantially as in J. Iron Steel Inst. 160, 261 (1948)]

of stability of pure metals in aqueous solutions. Here important

reactions are considered, e.g.

Fe = Fe"^"^ + 2e (2)

Fe203 + H"^ = 2Fe'^^ + 3(0H') (3)

55
I I I

1 -30 -20 -10

OXYGEN PARTIAL PRESSURE, Log Po2(atm)

Figure 2. Superposition of Ni-S-0 and Cr-S-0

stability diagrams at 1200°C (3)

Equilibrium equations for these reactions are developed in terms of

the electrochemical potential and pH, and diagrams such as Figure 3

are developed for regimes of stability for various iron compounds.

For combinations of potential and pH where ions are stable corrosion

is expected; where the insoluble compounds are stable, corrosion is

reduced owing to the protective nature of insoluble compounds.

Figure 4 compares Pourbaix diagrams for aluminum in water and fused

sulfate salts. There is substantial similarity here which, to some

extent, is fortuitious but the general applicability of the diagrams

is clearly demonstrated for electrolytes in general.

A third approach to assessing the expected performance of materials

involves laboratory testing. Advanced approaches take their leads

from the diagrams of Figures 1-4 as modified by the expected engineering environments. These laboratory tests would measure general and

localized attack under carefully controlled conditions.

5h
'12 - Elemental Fe Fe+zHjO-HFeOz +3H*+2e E=049-009 pH

-I g _ No Corrosion Occurs Because Metal is Stoble

0 4 8 12 pH

Figure 3. Annotated potential -pH diagram for the

iron-water system at 24°C. The hatched regions

indicate zones of various reaction types: no hatching indicates that the metal will not corrode; fine

hatching means that the metal tends to corrode since

the ionic species are soluble; broad hatching shows

regions of insoluble product layers where passivity

should occur if the layers are protective. The

applicable equilibria with their corresponding pH and

potential dependencies are placed parallel to the respective lines. Regions are also noted where the

corrosion potential can exist depending upon the state

of aeration of aqueous solutions. Adapted from

Pourbaix.

Fourth, materials testing is conducted in pilot plant facilities and

compared with the predictions from laboratory tests.

Each of these four methods for developing an understanding of materials

performance produces its own feedback which suggests approaches,

analyses, and experiments on the other category.

55
Figure 4. Comparison of thermodynamic diagrams

of the stability of aluminum in water at left (a)

and in molten sulfates at right (b). The water

developed for 25°C and the other for 1000°C. The

reversal in location of acid and base regions arises

from conventions in the respective technologies.

The following discussion will emphasize problems associated with metallic materials. Problems of ceramic materials in coal conversion

systems have been dealt with by Wachtman et al (7). Unfortunately,

the corrosion behavior of ceramic materials has never been considered

in as much detail as metallic materials. The reason, of course, has

to do with the use of bulk of quantities of ceramic materials where

small amounts of corrosive activity is not so serious as it is for

metallic materials. However, only metallic materials can serve as a pressure boundary; thus, integrity still remains as the principal concern in performance.

The following is divided into brief discussions concerning each of the

chemical species; this is followed by comments on the change in substrate, physical influences, and a few commentaries on the so called

weak link problem.

I have divided the consideration of the chemical species into high and

low temperature circumstances. One is prone to think in the coal conversion circumstances that only the high temperature problem is at

56
issue, and a good deal of work is directed toward the resolution of

problems arising in high temperature operations. However, there are

inherently low temperature environments which can be equally or perhaps

even more debilitating. Such environments, for example, can occur in

scrubbers.

Finally, in an overall view Table 1 summarizes the occurrence of

failures of components in coal conversion units. This information was

prepared by Smith at the National Bureau of Standards and was reported

later in the ERDA newsletter "Materials and Components in Fossil Energy

Applications" (8).

Carbon: In high temperature gases carbon-containing gas molecules

produce two different kinds of phenomena depending upon whether the

gases are oxidizing or reducing.

In oxidizing conditions mild steels oxidize in dry CO2 environments

much as they do in oxygen. However, above about 500°C and especially

in the presence of small amounts of water the corrosion rate is greatly

accelerated. After an initial period where parabolic kinetics--

characteristic of adherent films--the protective quality of the films

breaks down and a rapid linear rate ensues (9, 10). Figure 5 shows

this phenomenon schematically and Figure 6 shows the post breakaway

rate as a function of water content and temperature. These conditions

are most pertinent to coal gasification. These rapid rates can be reduced by some alloying elements including silicon and by lowering the

water concentration.

In reducing environments carburizing conditions may occur and the metal

is attacked by two processes. One is simple carburization. Here the

surface is embrittled by the inward diffusion of carbon.

In atmospheres where reducing conditions prevail, more serious is the

phenomenon of "dusting" which has been reviewed by Hochman (11). The

mechanism of the dusting phenomenon is not well established but seems

to involve critical surface processes where CO decomposes with the next

stop being the inward diffusion of carbon. Particularly characteristic

of dusting is a peak in the attack in the range of 500 to 700°C depending upon the alloy and environment. Figures 7 and 8 from Hochman show

the effects of environment, temperature, and alloy composition on

dusting.

Dusting can be inhibited by adding sulfur species which seem to slow

the decomposition of CO molecules on the surface much the same as sulfur

57
TABLE I

TYPE OF INCIDENT BY FREQUENCY OF OCCURRENCE"

Type of Problem

. E o a> z r

P'ocess BCD

Significance of Incident

Sutfidation 22 20

Corrosion

sec

Erosion/ Wear

Fabricatton Detect

10 8

9 4

8 6

3 3

Carbonization 3 1

Design 5 5 Thermal 3 3

Stress

Other 2 2

Metal Dusting 1 1

Refractory 1 1

Material Selection or O.C. Unknown

1 1

18

3 3

3 1

To Particular Process

ni Thermocouple critical for

control

(2) Slurry grid - complete

shutdovA^n ni Seveie and continuing

problems with thermo- couple lube and heater

coit not catastrophic but

severely limits life of parts Unknown

Great causes shutdown and

expensive repair - all CI cracking

Expansion bellows Water Lines

Great - short life, shutdown

Not critical - repair during maintenance

Critical - causes shutdown

Critical - causes shutdown

( 1 1 Valve residual

(2) Reducer stress m

welds- - shutdown

(3) Piping weld crack -

total shutdown

Great - this is the critical materials problem for the

clean coke process

(1) Quench pot - short life

(21 Bellows — total shutdown

(31 Heat exchanger — total shutdown

(4) Knife shouldn't be problem

(5) Sight glass - severe

safety hazard

Generally not a problem

S in environment prevents

Great significance — major

shutdown, long time shut- down, expensive repair

Great - shutdown plant

Great — total shutdown

Great — fire, total shutdown

To Coal Conversion Technology

Ma)or problem causing

short life

Expect to be the ma)Of prob lem determining life because

of high sulfur coal

Unknown - many critical

areas, possible catastrophic

GrcJi nearly alt systems

have Sfime areas where

possible - identify and

correct

Unknown - Identify areas

Great urgent problem of

seals on pumps

Great - short life, catastrophic shutdown

Unknown - review other systems to identify

critical regions

(1) Many similar quench

areas - critical

(2) Urgent problem - all systems

(3) Many similar areas - critical

(4) None

(51 Critical - all systems use

this

Identify critical areas Extremely rapid, catastrophic

failure when present

Highest significance - identify

critical areas, inspection, Q.C.

Requires constant alertness

Unknown

Unknown

Recommendations

Use coatings, better alloy, change environment

(2) Aloni/ed Fe Ni Cr alloys

are best now available

(1) Need detail diagnostic

failure analysis

(2) Need critical review of

all processes

(1) Carefully monitor environment

(21 Better material selection

(3) Some design change

possible

(II Change design/matenal

(2) Misalignment is cause

Bettor pump seals, filters, double seals

Strict attention to welding

procedures and residual

stresses

(11 Add S, water to envi ronment

(21 New alloy

(31 Redesign

(11 Redesign

(2) Redesign

(3) Redesign on basis of thermal stress

(4) None

(51 Redesign, new

material

( 1 ) Need better alloy

(21 Add small amounts of S

(31 Coatings (oxide, sulfide) may help

(1) Diagnostic Fail. Analysis

URGENT

(21 Need better refractory

(II Need high level of Q.C.

(II Diagnostic failure analysis needed

•Most failures tabulated here occurred in 1975 and 1976, with some earlier.

58
Figure 5. Schematic representation of breakaway

corrosion.

prevents other catalytic reactions at high temperatures. Hydrocarbon

gases also produce dusting but at higher temperatures. Water vapor and

ammonia appear also to inhibit the dusting.

At low temperatures carbon species contribute to acidifying the environment when CO2 dissolves in water to form carbonic acid. More virulent

is the stress corrosion cracking of mild steels which is caused by

carbonates and by dissolved CO (9, 10). Results are illustrated in

Table II and Figures 9 and 10 from references 12 and 13. The general

range of conditions where either of these environments cause accelerated

cracking has not been established.

Sulfur: At high temperatures sulfur-containing species seem to exert

three important effects. The first involves the so-called hot corrosion

59
1.3

I

1.4

l/T « 10-^

770 720 670 633 TEMPERATURE, K

500 600 700 800 900

Temperature

Figure 7. The reactivity of pure iron in pure CO,

5% Hp-CO and 10% H,-CO environments.

60
Figure 8. The reactivity of 316 stainless steel in

pure CO, 5% H„-CO, and 10% H„-CO environments.

Current Density, mA /cm

Cothodic Anodic o

o § 8

o

O

0

°0°o

o O

u O >

E

.5|8

I I 1 I I © KXO mV nTMn'

(?) 20 mV min

'

rr-T

% Reduction in Area

at Frocture

Figure 9. Polarization curves

and stress corrosion test

results for mild steel in

IN Na^CO^ + IN NaHC03 at 90°C.

6X
TABLE II

Effect of the Amount and the Ratio of Gas Mixture on

Stress Corrosion Cracking of Mn-Steel (O.T.) at 18°C

in Moist CO/CO«

No. Partial Pressure

(kg/cm^)

Total Pressure

(kg/cm^)

Period Week

0

c

n4

c0

LU N2

1 26 -- -- CX) u nu

o

c 26 14 AY AY

J 26 14 60 1 uU AY AY AY

/l4 10 16 X X

5 10 16 74 100 X X X

6 5 18 77 100 X X

7 1 17 82 100 X X

8 0.1 16 84 100 0

9 0.01 16 84 100 0

10 26 1 73 100 X

11 26 0.2 74 100 X

X: Crack 0: No Crack

62
phenomena which involves attack of metals in environments which contain both sulfur and oxygen. This phenomenon has been extensively

investigated in connection with accelerated corrosion phenomenon in

gas turbine blades where sulfur is present in the fuel. The accelerative process seems to be associated with the formation of a molten

sulfate salt at the metal surface.

Figure 10 shows that the molten sulfate greatly accelerates the

corrosive attack on high nickel alloys (14). This attack can be substantially mitigated adding aluminum or chromium to the alloy in order

to form a protective film.

Figure 10. Comparison of the oxidation behavior of

the nickel -base super alloy B-1900 (Ni + 8Cr + Ti , 6A1

,

6Mo, 4Ta, lOCo, O.IC, 0.07Zi, O.OIB) with and without

Na^jSO, coating.

Figure 11 shows the beneficial effect of adding species which improve

the quality of the protective film (15).

65
Sulfur gases at high temperatures seem to attack high nickel alloys

rapidly along grain boundaries. For metals exposed to HpS environments,

they are protected generally by increasing the chromium concentration

as shown by Yamamoto et al in Figure 12. The beneficial effect of

chromium is to be expected here according to the thermodynamic prediction for Figure 2.

At lower temperatures and in aqueous solutions sulfur exerts two

important influences leading to accelerated attack—again depending

upon the state of oxidation of the sulfur. In the oxidized state dissolved SO2 acidifies the environment. Additionally. SO? raises the dewpoint to the range of 160°C depending upon the concentration of SO? The precipitated water with the SO2 now incorporated to produce HoSo/' is very corrosive. Figure 13 shows clearly this correlation between

^or^o^i-onTi^oVMl.'^^^ ' SO^-contaminated atmosphere and iT''

Time (Hrs)

Figure 11. Weight change versus time for the oxidation of Na2S04-coated (0.5 mg/fcm2) specimen of Ni-Al

and Ni-Cr-Al alloys as affected by the addition of

V, Mo, and W.

6k
CVJE

o

o>E

c

oO

500

400

300

200

100

' 1

if

1 ' 1 Testing Time

^ • O lO.OOOmin. • ^\ 3,000min.

A 1 50 min.

0 Extrapolated

1 <

Value —

10 20 30

Chromium Contents ,wt %

Figure 12. Amount of corrosion products (weight gain)

of iron-chromium alloys at 600°C against chromium

content of alloys in hydrogen sulfide.

If the sulfur is present as H2S it substantially aggravates the stress

corrosion cracking of iron base alloys as shown in Figure 14; and as

the strength of the alloys is increased the tendency for SCC to occur

is increased. Further, H2S accelerates the entry of hydrogen in acid

environments and blistering often results.

Dissolved H^S decreases the corrosion resistance of iron. Together

with HCl there is a synergistic effect even at relatively low temperatures as shown in Figure 15 (18).

Hydrogen: At high temperatures the most insidious effect of hydrogen

is called hydrogen damage. The engineering data upon which hydrogen

damage is based is the Nelson curve shown in Figure 16 (19). This

figure defines the combination of temperature and pressure above which

a failure will occur for an iron base alloy. This phenomenon seems

essentially to result from the formation of methane molecules within

the metal and the subsequent formation of blisters. Hydrogen damage

65
80 100 120 140 160 180 200

Surface Temperature (®C)

Figure 13. Effect of surface temperature on

condensation and corrosion.

can be mitigated by adding chromium and molybdenum and as a result the

failure curve is raised to higher temperatures and pressures.

During thermal cycling of large vessels where hydrogen may have entered

the metal there is a further form of deterioration called "flaking."

This occurs when the surface temperature is rapidly reduced with the

result that the hydrogen is supersaturated. This resulting supersaturation causes hydrogen bubbles to precipitate and force metal flakes off

the surface.

In addition, another damage process which can occur at low temperatures

and high temperatures is called blistering. An example of blistering

is shown in Figure 17. Blistering essentially results from relatively

high hydrogen activities. These may result from the presence of

hydrogen sulfide or cyanide.

At lower temperatures, hydrogen enters the metal to cause stress

66
Steel

ChefTMcal cOTipoiiiion W) TVS

(kill UTS

(ksi) Hv

C Si Mn P s N Cr Cu Mo

HT 60 0 12 0 35 1 10 0 019 0 019 0 25 0 15 0 25 0 10 82 97 5 223 HT 70 0 1 1 0 30 0 95 0013 0 014 0 85 0 42 0 14 0 32 104 1 1

1

238 HT 80 0 M 0 36 1 03 0 010 0011 1 12 0 47 0 29 0 52 113 119 277

19

/ I

[

\

\ \HTf 0

\

K T6 3 \

TT, 7

10 50 100 500 5000 10 000 HjS conceniraiion (ppm)

Threshold derermined at 30 days on unnotched specimens loaded m bending

Environment* 0.5% acetic acid solution

Figure 14. Relationship between applied stress and H2S

concentration for initiation of cracking in various

grades of high-strength steel (after Ishizuka and Onishi).

corrosion cracking of steels. An early manifestation of this problem

in high strength steels especially associated with landing gears was

that of delayed failure. This phenomenon was extensively investigated

by Troiano (20). More recent work on high strength steels has shown

that the critical factor in the mechanism of crack propagation is

associated with the entry of hydrogen in the material (21). This

phenomenon is exacerbated as the strength of the alloy is increased.

The hydrogen can be derived either from water, gaseous hydrogen or

other materials such as H2S, HCl , and HBr. A comparison of the effects

of H2O, H2» and HoS is shown in Figure 18 from the work of Mclntyre

(21). Figure 15 has already shown that H2S accelerates SCC in lower

temperature regimes for relatively low alloy strengths. Two important

volumes summarize recent developments concerning effects of hydrogen

on mechanical properties (22,23).

67
MHgS

Figure 15. Dependence of steel corrosion on the H2S and

HCl content in the solution t = 25°C K-corrosion loss in

g.cm"^/6 hrs. 10"^, M-HCl and M-H2S. Concentration of

the components in the system, gram-mole/1.

1.400

1.200

*

a,- 1.000

400

I I I I

I

I I I

I

§P^CrjD. 5_Mp_§.teel

-~ J>XlQrJl 5 M^_5t£a!

2.25i;r^LQilo_stssL_

I I I I I I I I I 500 1,000 1,500 2,000 2,500 3,000 8,000 12,000

Hydrogen Partial Pressure, Lb/in*^ abs

Figure 16. Effect of temperature and hydrogen pressure

on the hydrogen damage failure of iron base alloys.

Alloys are "safe" below the lines shown and are subject

to failure above these lines. Effects of alloy additions

indicated. From Nelson (19).

68
METAL FRACTURES

3/8" THICK _J

CARBON STEEL

Figure 17. Hydrogen blister in a 9.5 mm thick A-283

carbon steel plate exposed to environment containing

H,S, HCN, NH.OH, and a trace of NaCl at 130°F.

Chloride: At high temperatures the halidation of metals may occur.

This general subject area has been recently reviewed by Rapp (24).

However, the concentration of halogen chemicals is not sufficient to

be a significant factor at high temperatures in coal gasification

environments.

At lower temperatures the effect of chloride ions on the stress corrosion cracking of austeni tic stainless steels is well known and has been

extensively discussed (25). It is not necessary here to further

elaborate except to point out the important interdependence of chloride

cracking on the oxygen concentration which is shown in Figure 19 (26).

Chloride also accelerates localized corrosion processes such as pitting

and crevice corrosion owing to the debilitation this ion has on the

passive films.

69
100

10

e

E 0 1

51?

0.01

0.001

0.0001

"T r

Hydrogen Sulphide Gas

at 1,000 mbar Pressure —A— A

Hydrogen Gas

at 1,000 mbar Pressure

10 20 30 40 50 60 70 80

Kj, (MNm-''^)

Figure 18. Crack velocity as

a function of stress intensity

for a 897 M39 steel at 29rK

in environments of hydrogen

sulfide, hydrogen, and 3.5%

NaCl

.

02 \

02

0.1

\

\

\

\

\

\

\

\\

LEGEND

O No Failure # Failure

•Z •t

Ql ^<

03

81-

,^z

03

Oi

10 Chloride, ppm100 1,000

Figure 19. Relationship between chloride and oxygen

content of alkaline phosphate

treated boiler water for stress

corrosion cracking of

austenitic stainless steel.

70
Oxygen: At high temperatures oxygen contributes to the oxidation of

metals and is also significant in combination with sulfur, carbon, and

hydrogen as discussed above. The high temperature oxidation of metals

has been extensively treated and will not be elaborated upon here

(27, 28).

At low temperatures oxygen exerts its influence primarily when it

dissolves in water. Referring to Figure 3 which shows the Pourbaix

diagram of iron, the line for the H2O/O2 equilibrium is shown near the

top and at potentials substantially higher than the H2O/O2 equilibrium.

This higher equilibrium potential for the H2O/O2 equilibrium is the

basis for oxygen raising the potential. The influence of oxygen in

exacerbating the chloride-SCC of stainless steel as shown in Figure 19

is directly related to raising the potential into a regime where SCC

can occur.

Other Species: Species such as molybdenum and vanadium have been

traditionally associated with the phenomenon of catastrophic oxidation

which was first studied by Fontana and Leslie (29). This phenomenon

has been more recently interpreted in terms of the effect that these

species exert on the equilibrium chemistry and the location of these

circumstances with respect to Pourbaix diagram stability.

Other low melting species such as lead, zinc, aluminum, and gallium may

accelerate damage to either grain boundary attack or a type of liquid

metal embrittlement. If substantial quantities of these species can

exist in metallic form such problems should be considered.

I have omitted consideration of effects of nitrogen since previous

experience suggests that it does not play a significant role relative

to the more aggressive reactions involving hydrogen, carbon, chlorine,

oxygen, and sulfur.

Physical Influences: The important physical influences in addition to

the chemical ones involve primarily the effects of stress and particles

as they contribute to wear or erosion.

Stress exerts its influence in a number of ways which vary depending

upon the temperature. At high temperatures stress is associated with

the phenomenon of creep rupture and environments may accelerate this

process although environmental influences on creep have not been

extensively studied.

71
As a variation on the subject of creep, the subject of creep fatigue

is receiving significant recent attention as it applies to pressure

vessels operating at elevated temperatures (30, 31). While creep

fatigue has been of primary interest to nuclear vessels, it will

certainly be of greater importance to pressure vessels used in coal

gasification. The problem embodied in the subject "creep fatigue"

involves the fact that cyclic loading superimposed upon a creep

situation accelerates the creep damage; conversely, long holding times

between stress cycles also exacerbate fatigue damage, i.e. increases

da/dN.

At low temperatures constant stress causes stress corrosion cracking,

and in the oscillating circumstances we have corrosion fatigue. Stress

corrosion cracking depends upon the synergistic interaction of numerous

factors; this interdependence is illustrated in Figure 20. If the

product is below an arbitrary constant value, SCC will not occur in a time less than the same value and at some point this time is long

enough to be effectively infinite. SCC can be eliminated if any of

the factors in the equation is zero or if several factors can be

reduced simultaneously.

Corrosion fatigue and stress corrosion cracking are part of the same

continuum as illustrated in Figure 21. These two phenomena, which are

ordinarily considered as separate, approach each other along the

coordinates of cyclic figuring and stress ratio. In the limit of a period which is long with respect to the time required for SCC to occur,

corrosion fatigue becomes stress corrosion cracking. On the other

hand, as the ratio of the minimum stress to the maximum stress approaches positive unity the condition of constant load is again approached.

With respect to the question of particle induced deterioration consideration should be directed toward two cases. One is the interaction

of particles on the wear process. This is particularly significant

relative to valves and seals which separate zones of different

pressures. There is presently very little information on this process

but it deserves careful consideration.

The second problem of erosive wear produced by high velocity particles

has been considered more extensively and is expected to be a major

issue especially in components such as cyclone separators and turbines.

With respect to particles, parameters of size, shape, strength, and

angle of impingement are critical. With respect to the substrate,

hardness and simultaneous corrosion processes are critical. Here,

again, this subject is just now being seriously considered by the

technical community and only generalities are available at present.

72
MAJOR ALLOYS

MINOR IMPURITIES

GRAIN BOUNDARY

MATRIX STRUCTURE

' ANISOTROPY

' GRAIN SIZE

/ ALLOY

VCOM POSITION

• OXIDIZING CONDITION

'SPECIFIC IONS •SOLVENT

•pH

INHIBITOR

•STATIC TENSILE SLOW STRAINING

CYCLIC -FREQUENCY

-PERIOD

- MEAN VALUE OF STRESS

- MINIMUM TO MAXIMUM

STRESS RATIO

(initiation) (propagation)

(^initiation) (^PROPAGATION )

see

Figure 20. Five factor relationship giving critical

components in stress corrosion cracking.

(+)

(-)

High Mean stress with Low Amplitude, (Approaches SCO WW'-'-

0 Mean Stress

HIGH CYCLIC FREQUENCY

APPROACHES sec AS MEAN STRESS

INCREASES AND AMPLITUDE DECREASES

LOW CYCLIC FREQUENCY

APPROACHES sec AS

PERIOD LENGTHENS

^ Low Cyclic Frequency, High Amplitude , Square Wave

Figure 21. Schematic diagram

showing how fatigue parameters

approach constant load conditions,

i.e., corrosion fatigue approaches

stress corrosion cracking.

T'3
The general problem of abrasive and erosive wear are discussed

generally in the volume from the Ohio State Conference (1).

Changes in Alloy Structure With Time: An implicit part of the performance of coal conversion equipment is its operation at relatively

higher temperatures for long times. These temperatures approach those

of interest to phenomena such as sensitization of stainless steels,

temper embrittlement and sigma phase formation depending upon the

alloys. The phenomenon of sensitization in metals has been extensively

studied and relationships for the development of the sensitized condition have been determined experimentally (32). Similarly, the

phenomenon of temper embrittlement has been extensively studied and the

conditions of alloy chemistry, temperature and time, again have been

generally developed (33, 34).

These time-dependent changes are important as they contribute to unexpected degradation at a later time in the operation of equipment. This

implies a particularly important mandate in the early testing of

materials: i.e. that these changed conditions should be evaluated

early in laboratory testing for any enhanced susceptibilities to failure which they may imply.

The Weak Link: As engineering systems become larger and operate under

progressively more punishing circumstances, the possibility of failure

of any of the components increases. Further, there is an increased

potential for failure owing to the fact that it becomes progressively

more expensive to conduct proof testing on large scale equipment.

There is a growing tendency to attempt predicting reliability without

going through the prototype stage. Such an approach is generally

disastrous but it seems to be the current procedure. Such an approach

in this area should be avoided.

Simply stated, the concern of this section is the following: when any

one component is shut down, the entire system is shut down; and the

length of time necessary to get back on stream depends on the time it

takes to repair the failed component. One of the most striking

examples occurs in the nuclear industry with the failure of condensers.

Condenser failures have contributed substantially to the downtime of

nuclear power plants. It would be thought that condensers are a part

of "standard engineering;" however, they are not and are frequently

subject to leaking. Failures also occur in steam turbines despite the

fondest hopes of their manufacturers. Again, these are supposed to be

standard items of commerce, but failures are all too frequent. When

the turbine or condenser fails the entire system must be stopped until

the offending equipment is repaired.

7k
In view of such past history, it seems appropriate that more careful

consideration be given to the possibility of such failures. Hopefully,

a more balanced approach to design and development would be taken for

these large systems.

Acknowledgements: It is a pleasure to acknowledge several contributions

to the development of the ideas in this paper. The suggestions to

use Table 1 I obtained from Dr. John Smith of the National Bureau of

Standards. I discussed the matter of contributions of ceramic

materials with Dr. Jack Wachtman also of the National Bureau of

Standards. Further, I am indebted to the National Science Foundation

and the former Office of Coal Research now of ERDA for its support of

the Ohio State Conference on Materials Problems and Research

Opportunities in Coal Conversion. Their financial support and

encouragement in organizing this meeting got me initially involved

in the subject. Finally, I would like to acknowledge the able assistance of Dr. Arun Agrawal , Mr. Gary Welch, and Ms. Catherine Ward in

helping with the manuscript.

References

1 . Materials Problems and Research Opportunities in Coal

Conversion , 16-18 April 1974, editor: R. W. Staehle,

Department of Metallurgical Engineering, The Ohio

State University.

2. NSF-OCR Engineering Workshop on MHD Materials , 20-22

November 1974, Massachusetts Institute of Technology,

editor: A. L. Bement, Energy Laboratory, Massachusetts

Institute of Technology, Cambridge, Massachusetts.

3. J. Quets and W. Dresher, Journal of Materials , March 1969.

4. R. A. Rapp, paper presented at the Agard Panel on Propulsion Energetics, October 13, 1969, Dayton, Ohio.

5. M. Pourbaix, Atlas Electrochemical Equilibria in Aqueous

Solutions , NACE, Houston, Texas (1966).

6. M. Pourbaix, Lectures on Electrochemical Corrosion , Plenum

Press, New York (1973).

7. J. B. Wachtman, S. J. Schneider, A. D. Franklin, "Role of

Ceramics in Energy Systems" presented at the ERDA/NSF

Workshop on Ceramics for Energy Applications, 24-25

November 1975.

75
8. ERDA Newsletter, Materials and Components in Fossil Energy

Applications, 1 April 1976.

9. Corrosion of Steels in CO2 , Proceedings of British Nuclear

Energy Society, International Conference at Reading University, 23-24 September 1974, editors: D. R. Holms,

R. B. Hill, and R. M. Wyatt, British Nuclear Energy Society,

1974.

10. J. M. Furgeson, J. C. P. Garrett, and B. Lloyd, from

reference 9.

11. R. F. Hochman, Catastrophic Deterioration of Metals at

High Temperature and Carbonatious Environments, Report of

Work to the National Association of Corrosion Engineers

under sponsorship of the NACE Research Committee.

12. M. Kowaka and S. Nagata, "Stress Corrosion Cracking of

Mild and Low Alloy Steels in CO - CO2 - H2O" Proceedings

of the Conference on Stress Corrosion Cracking and Hydro'gen

Embrittlement of Iron Base Alloys , NACE, 1977.

13. J. M. Sutcliffe, R. R. Fessler, W. K. Boyd, and R. N. Parkins

Corrosion 28, No. 8, pp. 313-320 (1972), NACE, Houston.

14. J. A. Goebel and F. S. Pettit, Metallurgical Transactions

Vol. I, p. 1943-1970.

15. J. A. Goebel, F. S. Pettit and G. W. Goward, Deposition

of Corrosion in Gas Turbines , editors: A. B. Hart and

A. J. B. Cutler, Wiley and Sons, New York, 1973.

16. K. Yamamoto, M. Izumiyama, and K. Nishino, "Corrosion of

Iron and Iron-Chromium Alloys By Hydrogen Sulfide,"

Proceedings of the 5th International Congress on Metallic

Corrosion , 1974.

17. M. Kowaka and H. Nagano, "The Mechanism of Sulfur Dewpoint

Corrosion," Proceedings of the 5th International Congress

on Metallic Corrosion , 1974.

18. R. Baronicek, "Corrosion of Steel in Solutions of Chlorides

and Sulfides" Proceedings of the 3rd International

Conference on Metallic Corrosion , Vol. I, 1968.

19. G. A. Nelson, Proceedings of American Petroleum Institute , 45 190 (1965).

76
20. A. R. Troiano, Trans. ASM , 52, 54 (1960).

21. P. Mclntyre, Stress Corrosion Cracking and Hydrogen

Embrittlement of Iron Base Alloys , editors: R. W. Staehle,

J. Hochmann, J. E. Slater, and R. D. McCright, to be

published by NACE, Houston, 1977.

22. I. M. Bernstein and A. W. Thompson, Hydrogen of Metals , ASM, 1974.

23. I. M. Bernstein and A. W. Thompson, Effect of Hydrogen

on Behavior of Materials , TSM, AIME, 1976.

24. R. A. Rapp and P. L. Daniels, "Halogen Corrosion of Metals"

Advances in Corrosion Science and Technology , Vol. 5, p 55-

172, Plenum Press.

25. R. W. Staehle and R. M. Latanision, Proceedings of

Conference on Fundamental Aspects of Stress Corrosion , p. 214, September 9-15, 1967, Columbus, Ohio.

26. W. L. Williams, Corrosion , 539t (1957).

27. K. Hauffe, Oxidation of Metals , Plenum Press, New York

(1965).

28. G. R. Bel ton and W. L. Worrell, Editors: Heterogeneous

Kinetics at Elevated Temperatures .

29. W. C. Leslie and M. G. Fontana, "Mechanism of the Rapid

Oxidation of High Temperature High Strength Alloys

Containing Molybdenum," Trans. ASM , 41, 1213-1247, (1949).

30. S. Manson, G. R. Halford, and M. H. Hirschber, "Symposium

on Design for Elevated Temperature Environment," American

Society for Mechanical Engineers, New York, 1971.

31. L. F. Coffin, Jr., Fracture, 1969 Proceedings , Second

International Conference on Fracture, Brighton, April 1969.

32. H. F. Ebling and M. A. Scheil, Advances in the Technology

of Stainless Steels and Related Alloys , ASTM-STP 369 , ASTM,

Philadelphia, Pennsylvania.

33. C.J. McMahon, "Strength of Grain Boundaries in Iron-Base

Alloys," Grain Boundaries in Engineering , Proceedings: 4th

Bolton Landing Conference, June 1974, Editors: J. L. Walter,

J. H. Westbrook, D. A. Woodford.

77
34. B. J. Schulz and C. J. McMahon, Temper Embrittlement of

Alloy Steels , ASTM STP 499, ASTM 1972, p. 104.

78
DISCUSSION

W. Netter, Lone Star Lafarge Company : You mentioned coating and shot

peening. Are these techniques good or bad?

R. W. Staehle : Those were some options that could be utilized for

amelioration. Shot peening is a very effective tool and greatly under

utilized, especially in the power industry. Unfortunately, at higher

temperatures the beneficial effects of shot peening anneal out. We

are restricted to using materials that the code lets us use. Unfortunately, many of the standard industrial alloys are very susceptible

to cracking. We are going to have to learn how to work within the code

and use more ameliorative procedures like coating and shot peening.

For example, using a chromate type surface coating in components of

the LMFBR's that contact sodium is valuable. It is now clear that

chromate is a very good inhibitor for caustic stress corrosion.

79
THE AGA-ERDA-MPC PROGRAM ON MATERIALS

FOR THE GASIFICATION OF COAL

Adolph O. Schaefer

The Metal Properties Council, Inc.

New York, New York 10017

Abstract: This paper will aim to present an overview of a large

program, a portion of which will be described by another speaker.

The roles of AGA, MPC, and ERDA and the various contributions of

their respective organizations will be described. The attack on the

problem, and its division into "Phases" will be explained. The scope

of each phase will be clarified. The plans for Phase V will then be

described at least as fully as in the latest work schedule. Plans of

MPC include ultimate publication of this work in a form and by an

organization which will make it possible for the book to be referenced

in scientific literature.

Key words: Aluminum alloys; aluminum bronzes; cast iron; coal

gasification; corrosion, diffusion coatings, erosion; field corrosion

tests; heat resistant steels; liquid immersion tests; nickel alloys;

pitting; refractories; steels; stress corrosion; t Itanium alloy s

,

I. INTRODUCTION

The AGA-ERDA-MPC Program for Materials for the Gasification of

Coal was developed in an Ad Hoc Task Group set up in Subcommittee 8

(Corrosion) of the Technical Advisory Committee of The Metal Properties Council, Inc. The importance of the subject was suggested by

Dr. Ab Flowers of the American Gas Assocation. The Task Group

was and is still chaired by Mr. William Hulsizer of The International

Nickel Co. , Inc. The Task Group started its deliberations in 1972.

In 1972 a program was formulated duly approved in accordance with

MPC practice. The American Gas Association agreed to finance it,

and a Contract was placed with the IIT Research Institute of Chicago in

1972.

80
As of January 1, 1975 the Energy Research and Development Administration assumed responsibility for most of the financing of the program,

the American Gas Association retaining a small portion of it, however.

The Technical Director of the Fossil Fuel Division, Dr. Henry E.

Frankel is ERDA's Technical Director for this program.

II. THE METAL PROPERTIES COUNCIL, INC.

The Metal Properties Council, Inc. is a not-for-profit corporation,

organized under the laws of the State of New York, and by whom it is

chartered. It was formed in 1966 to make it possible for companies,

associations, universities, and government agencies to pool their

resources, both technical and financial, to make available reliable

information on the properties of metals.

Much data on the properties of metals exists in the literature, and in

the several data banks which are available for this work. An unknown

quantity exists in company and institutional files. It is costly and timeconsuming to extract the data in the latter conditions, and it is also

sometimes difficult or impossible to appraise.

Testing programs are costly and time consuming, and the evaluation

and arrangement of information is perhaps the greatest problem of all,-

and the one which must be done by competent workers. It is aimed to

publish Metal Properties Council data only after analysis and evaluation

by experts, and also after review and approval by a group of representatives of varied interests and backgrounds. The work of the Council is

directed to specific areas of need as expressed by industry or government, and is carried out in a number of programs such as the one here

under discussion.

in. THE ORGANIZATION OF THE MPC TASK GROUP

The Metal Properties Council, Inc. is an effective organization for

accomplishment in its field because it offers a unique combination of a

strongly busine s

s -oriented Board of Directors, and a Technical

Advisory Committee of the best experts in industry. A low-overhead

small staff operation efficiently manages the programs of the Council

utilizing all funds given to the Council as quickly and efficiently as

possible.

The Technical Advisory Committee has a number of technical subcommittees as well as task groups reporting to it. One of these.

Subcommittee 8, is responsible for those projects of the Council which

are concerned with corrosion. Since it has been in existence under

81
Subcommittee 8, the Task Group on Materials for the Gasification of

Coal has grown to a total membership of 92, and it truly represents all

elements of interest in designing, building, and operating pilot plants

and the succeeding production units for the stated purpose,

IV. THE PROBLEM IS DIVIDED INTO PHASES

It has been found to be helpful to divide this large program into at

least five phases, which may be designated as follows.

Phase I - Gaseous Corrosion - Laboratory Tests

II - Exposure Tests in Pilot Plants

III - Aqueous Corrosion - Laboratory Tests

IV - Erosion-Corrosion - Laboratory Tests

V - Engineering Properties of Materials

The procedure which was followed in developing programs for all of

the phases which have been activated so far is indentical in all cases.

After planning the work to be done in the Phase Group, and obtaining

the necessary approval from Subcommittee 8 and the Technical Advisory Committee, inquiries were sent out to a number of laboratories,

and proposals were received from those prepared to undertake this

work. These proposals were reviewed by the Task Group. In some

cases visits were made to inspect the facilities and to meet the

personnel of the most responsive bidders. Contracts were subsequently negotiated with those bidders considered by the Group to offer the

best technical combinations. Contracts for Phases I to IV were

awarded to the Illinois Institute of Technology Research Institute.

Notice of award of Contract has been issued to Southwest Research

Institute for the work planned so far for Phase V.

It is understood that another speaker will describe the programs being

conducted at IIT Research Institute for Phases I to IV. The remainder

of this paper will describe the work that is being done on Phase V.

V. PHASE V. ENGINEERING PROPERTIES OF PROMISING

CANDIDATE MATERIALS - DATA SOLICITATION

The Sub Section for Phase V was assigned the task of developing the

information on materials of construction needed by engineers. Phases

I to IV are screening a number of candidate materials. Phase V will

work on the successful candidate materials as revealed by Phase I to

IV. Mention should be made of another Sub Section of the Task Group

on Materials for the Gasification of Coal which relates to all Phases

82
of the program. This Sub Section which does not bear an identifying

number is charged with the selection of materials for test. It is an

important factor in planning the work and in reviewing the claims of all

materials suggested for inclusion in the Program. It is chaired by

Mr. J. M. Bates of the Union Carbide Corp,

The Sub Section for Phase V conducted during 1974 a search for data on

the properties of seven alloys which were at that time considered to be

promising. A number of companies, as a result of solicitation by The

Metal Properties Council, submitted information from their files.

Meetings of the Sub Section have been held with engineers to determine

what information is needed. Initially, that requested may be divided

into three categories - physical properties, mechanical properties, and

general characteristics. The information desired must be carefully

identified and characterized. It is essential that the product form,

complete method of manufacture, dimensions, location and orientation

of test specimens be known. The test data desired should permit

statistical evaluation. It is sometimes most important to be aware of

the range of properties to be expected in materials, as they are available commercially. There follow the properties on which data was

solicited in 1974.

Alloy 800

Type 310 Stainless Steel

Type 314 Stainless Steel

Rolled Alloys 330

HK - 40

HK - 40 - 3 percent Si

50 Cr - 50 Ni.

Physical Properties

1.

2.

3.

4.

5.

6.

7.

Melting Point (or Range)

Specific Heat

Thermal Expansion (Coefficients)

Thermal Conductivity (Coefficients)

Density

Moduli of Elasticity

Poisson's Ratio

Mechanical Properties

1. Tensile Properties, temperatures up to 1850F

2. Creep and Creep-Rupture Properties, temperatures up

to 1850F

83
3. Impact Strength (CV), temperatures up to 1850F

4. Fatigue Strength (several frequencies),

temperatures up to 1850F

General Characteristics

1. Weldability - Physical & Mechanical Properties

of Weld

2. Castability - Forgeability

3. Machineability

4. Stability

5. Effectiveness of Surface Treatment (Aluminizing,

Coatings , etc. )

Response to the solicitation has resulted in some information which has

been put into the hands of MPC's analyst, Dr, George V. Smith. It is

apparent that available data is not adequate. Isolated, one-heat data,

unsupported by characterization of the material, does not enable the

engineer to design effectively. It was never anticipated, of course

that there would be available from existing files the information needed

for materials for the gasification of coal on the effects of the hostile

environment on the mechanical properties of the materials to be utilized

MPC's close relationship with the ASME Committee for the Code on

Boilers and Pressure Vessels indicates that there will be a continuing

need for more data as experience is gained, changes are made in

design, and new materials for construction become available. The

important accomplishment to be sought in the conduct of Phase V is to

bring to the design engineer a valid body of data supporting certain

values of those properties deemed essential. It is hoped that MPC's

long experience with the Boiler and Pressure Vessel Code will facilitate

this desired end.

Mention should be made of the fact that refractories are being subjected

to exposure tests in pilot plants. The program that is reported here

will most certainly expand as the screening and pilot plant exposures

indicate the value of materials not included in the Phase V tests at this

time. It is possible that additional tests will need to be planned on such

materials as weldments, coatings, etc.

VI PHASE V. ENGINEERING PROPERTIES OF PROMISING

CANDIDATE MATERIALS. THE TESTING PROGRAM

A. Objective

The objective of the Testing Program of Phase V is to generate engin81+
eering data on materials which are likely candidates for use in the

construction of plants for the gasification of coal. These data include

both physical and mechanical properties of the materials in coal

gasification environments. Final details of the work schedule for this

program are currently being worked out. This report of the current

concept of the program may ultimately be modified in details.

B . General Specifications

1. Materials The materials to be tested have been slightly

increased in number over those for which data was solicited. They

have been divided into groups for convenience in test layout (Table I).

The mechanical and physical property data specified is to be determined for the materials in both Group I and Group II. In addition, selected

data will be determined for welded joints produced with the materials

in Group I only.

Materials will comply with the applicable ASTM Standards. All

materials will be identified by heat number, manufacturing history,

product form, size, and chemical composition. All materials will be

characterized metallographically by representative photomicrographs.

Representative hardness tests will be made and recorded of all

materials in the state in which they are tested.

At least three lots (heats) of each material will be procured and tested

as specified below. Three specimens will be tested for each condition

of test unless otherwise specified.

All welding materials to be used will conform to AWS and ASME standards. All welding filler materials will conform as closely as possible

to the chemical composition of the base metal. Welding procedures

and operators will be qualified in compliance with the ASME code for

pressure vessels to ensure weld integrity and uniformity. All weldments will be fully radiographed and radiographs retained.

All materials and welding processes will be approved for use by the

MPC Sub Section which includes the ERDA Technical Director or his

representative.

2. Environment - The chemical composition (in mole percent)

of test Coal Gasification Atmosphere (CGA) decided upon for the Phase

V tests is shown in Table II.

85
C. Tasks

1. Mechanical Tests

In general, a full set of tests conducted in air is required to serve as a

base line for the data developed in the CGA environment. Specimens

will be pre-exposed to the CGA at 1000 psi for 1000 hours at various

temperatures. Subsequent tests at various temperatures and in prescribed atmospheres shall be conducted as described under each type

of test. The contractor is required to have the capability of conducting

all tests at a maximum of 2000F if it is subsequently decided to be

necessary.

All tests are to be carried out in accordance with applicable ASTM

specifications, utilizing standard specimens.

a) Tension Tests

Triplicate specimens from one lot of each material in Group I together

with the weldments made from the same lot from Group I will be tested

in the condition of the metal as received and in the conditions after

exposure in air and in the CGA environment as indicated in Table I. For each test specimen the properties to be determined are (1) yield

strength, (2) ultimate tensile strength, (3) percent elongation, and

(4) reduction in area to fracture.

The various conditions for which data shall be generated are listed in

the Table I. All pre-exposures in the CGA environment will be

accomplished at 1000 psi for 1000 hours while the exposures in air are

to be conducted at atmospheric pressure for 1000 hours. The tension

tests will be run at atmospheric pressure. The effects of various preexposure treatments on the microstructure will be documented. In

addition, corrosion penetration resulting from the various pre-exposures

will be documented from inspection of broken tension test specimens.

Tension tests of pre-exposed specimens will be made without removal

of any scale.

b) Impact Tests

Charpy V-notch tests will be conducted in triplicate for the same

materials for which tension tests are conducted. The results will be

reported as fracture impact energy in foot pounds, lateral expansion,

and percent shear. The pre-exposure and test matrix for the impact

tests shall be the same as that shown in Table I for the tension tests,

except that all Charpy tests will be conducted in air and at room

96
temperature.

c) Stress Rupture Tests

Replicate stress rupture tests will be conducted on all lots of material

in Group I and Group II and the weldments in both air and the CGA

environment. Initial tests will determine the stresses required for

rupture in 100, 300, and 1000 hours of exposure in all materials.

Subsequently, 10, 000 hour tests will be conducted on the four most

rupture-resistant materials. Tests will be conducted at 1200F, 1500F,

and 1850F in air at atmospheric pressure and in the CGA environment

at 1000 psi using 0. 357 inch diameter smooth round specimens.

9 Complete creep curves will be developed for each test together with

tables of stress, rupture time, elongation, reduction in area and

minimum creep rate.

d) Fatigue Tests

Low cycle fatigue tests will be conducted at 1200F, 1500F, and 1850F

in air at atmospheric pressure and in CGA environment at 1000 psi.

The specimen geometry and exact loading cycle will be determined by

the contractor and approved by the monitoring MPC sub section.

Since the combined effects of creep and fatigue greatly affect the

number of cycles to failure in low cycle fatigue at elevated temperatures, it will be required to initially screen several materials to

determine the cyclic hold time at which the creep effect saturates. This

initial screening program will use specimens from one lot of Alloy 800,

one lot of Type 310 stainless steel, and one lot of HK-40.

2. Physical Property Determinations

The following physical properties will be determined by ASTM

established methods for three lots of each material (see Table IV).

Vn. CONCLUSION

Recognition must be given to the fact that representatives of at least

75 companies have shared in the formulation of this program; and will

continue, as their contribution, to take part in the monitoring of the

work as it proceeds. Finally, they will appraise and evaluate the

results so that the final report will represent the combined thinking of

a majority of those who may be expected to participate in this new -old

industry, the gasification of coal.

87
Obviously this program might be expanded as results indicate the

advantages of other materials, as pilot plant operations indicate

operating environments significantly different from those chosen for

test at this time. We are assured of new and significant data, critically evaluated which cannot help but be of value in our current efforts to

assure our supply of energy.

88
TABLE I

Phase V

List of Alloys for Initial Testing Program

Group I Alloy 800

Alloy 800, Alonized

Type 310 Stainless Steel

Type 310 Stainless Steel, Alonized

HK-40

50 Cr - 50 Ni

Group II Type 309 Stainless Steel

Type 314 Stainless Steel

RA-330

HK-40-3 Si

TABLE n

Chemical Composition (mole percent) Coal Gasification

Atmosphere Phase V

CO2 - 12 percent

CO - 18 percent

H2 - 24 percent

CH4 - 5 percent

NH3 - 1 percent

H2S - 0, 5 percent

- Balance

89
C

o H

o

in

O 00

00 '—1

80,

1200

80,

1500

80,

1850

80

1200 1500

lo50

CGA

/\ /\ */\

Air XX X X XXX

0) o

H

^

1200 1500 1o

n

A

1850

1200 )1500 )

1850) 1200 1500 1850

Environment

None

Air

(atmospheric

pre s

sure

CGA

(1000

psi)

Material

As

Received

Pre

-exposed

1000

hrs.

Pre

-exposed

(1000

hrs. )

90
TABLE IV

Physical Properties

Phase V

Melting Point (Range)

Specific Heat

Thermal Expansion (room

temperature to ZOOOOp)

Thermal Conductivity (room

temperature to 2000°F)

Density

Moduli of Elasticity (up to 2000°F)

Poisson's Ratio (up to 2000°F)

Emis sivity

91
TABLE V

Task Group on Materials for the

Gasification of Coal

Numbers of Members - April, 1976

The Task Group 91

Phase 1 22 Phase 4 24

2a 29 5 16

2b 16 6 15

3 19

Steering Committee 14

TABLE VI

AGA-MPC-ERDA PROGRAM

on Materials for the Gasification

of Coal

Phase I Gaseous Corrosion

Ila Pilot Plant Tests - Metals

lib Pilot Plant Tests - Refractories

III Aqueous Corrosion

IV Erosion-Corrosion

V Engineering Properties

VI Special Problems Rotating Parts

92
DISCUSSION

G. M. Ugiansky, National Bureau of Standards : In our work we have seen

tremendous differences in the mechanical properties and the mode of

failure at different strain rates. Is any consideration being given

to testing these materials at various strain rates?

A. 0. Schaefer : Yes, but we think that in the work we are doing now,

strain rate should not be a variable. We are watching your work with

considerable interest. Incidently, we are purchasing double quantities

of material so that this fully characterized material can be tested at

various strain rates if such tests are indicated by programs such as

yo urs

.

D. Canonico, Oak Ridge National Laboratory : You mentioned that we are

concerned with internals in this program, and they are not part of the

code. But do you foresee, from a reliability point of view, that we

are going to have to set standards for materials used in coal conversion

processes that take into consideration the environments to which these

materials are subjected?

A. 0. Schaefer : Yes, I do. We hope the basis of such codes will be

reliable information. We need to get the information fast enough so that these codes will be developed on a sound basis.

D. Canonico : I just wanted to make sure we were not on different

tracks. We are considering that indeed someday we will have some sort

of standards even for internals to insure reliability.

93

SESSION II

FAILURE

ANALYSIS

CHAIRMAN: E. E. KLAUS,

THE PENNSYLVANIA STATE UNIVERSITY

FAILURE ANALYSIS OF COMPONENTS FROM COAL-GAS IFI CAT I ON PILOT PLANTS

S. Greenberg and K. Nates an

Argonne National Laboratory

Argonne, Illinois 60439

Abstract: Construction materials in coal-gasification pilot plants are

subjected to a variety of corrosive/erosive environments, ranging from

liquids and solids at relatively low temperatures to gas and solid mixtures at high temperatures and pressures. Component failures may be

directly attributed to interactions between the materials and the

corrosive /erosive environment. Two corrosion failures that have been

examined are discussed in detail: (1) Inconel 702 thermocouple sheath

exposed to a multicomponent gas environment at 2000°F and 1200 psi, and

(2) Types 304 and 316 stainless steel instrument tubing containing

superheated steam-oxygen mixtures at 600 °F and 1200 psi. The failures

were examined in detail using optical metallography, scanning-electron

microscopy, and electron-microprobe techniques as well as chemical analses and nondestructive testing methods. The failure of the thermocouple

sheath was attributed to internal oxidation of chromium and aluminum

present in Inconel 702. The failure of the instrument tubing was associated with chloride stress-corrosion cracking. Details of the analyses

and possible solutions to prevent such failures in the future will be

presented. In addition, other ANL investigations of gasification plant

components are summarized.

Key words: Coal-gasification plant-component failure; HYGAS plant;

Synthane plant, stress-corrosion cracking; internal oxidation; scanningelectron microscope and electron-microprobe techniques.

An early step in the program to use the nation's considerable coal

supply in the form of clean gaseous fuel is the design and construction

of a series of coal- gasification pilot plants. As these pilot plants

continue to come on line, materials-related problems are becoming evident. These problems must be understood and solved before the demonstration plants are reliable for long-term operation in hostile environments, i.e., high temperature and pressure, corrosive chemicals, ana

abrasive solid, liquid, and gaseous media.

At Argonne National Laboratory we are engaged in a cooperative effort

with various pilot plants to examine failed and unfailed components

after removal from service. As a result of our examinations and analyses, we expect to be able to recommend changes in materials and/or operating conditions that will lead to improved performance. In addition.

97
through timely and widespread dissemination of results, we hope to make

all pilot-plant operators aware of generic problems and so minimize

repetition of problems. Since February 19 75, twelve Investigations have

been made of failures and related materials problems at the HYGAS plant

In Chicago and the Synthane plant In Bruceton, Pennsylvania (Table I).

In the present paper, we will discuss two of the HYGAS Investigations In

detail and summarize several others.

I. HYGAS Thermocouple Sheath

An Inconel 702 sheathed thermocouple assembly that was exposed to a

multlcomponent gas environment at 2000°F and 1000 psl In the steamoxygen gaslfler was severely embrittled and cracked after approximately

3-4 months of service. The composition of the gas that was present In

the vicinity of the thermocouple sheath Is shown In Table II. Chemical

analysis showed that the sheathing contained a sulfur concentration of

0.010 wt% (within the maximum specified for Inconel 702) and an oxygen

concentration of 0.784 wt% (significantly higher than the specifications

for the alloy). Chemical analysis of acid soluble and Insoluble fractions demonstrated that the former is predominantly a nickel-rich phase

and the latter consists of chromium, manganese, and aluminum. Formation

of stable oxides (Cr203, AI2O3, MnO , etc.) in the sheathing material Is

a distinct possibility in view of the high oxygen concentration and the

acid insoluble composition. Chemical analysis of the ceramic packing in

the thermocouple assembly showed that magnesium was the major constituent.

X-ray diffraction patterns of the thermocouple sheathing material and

the ceramic packing were made to Identify the type of phases present In

the materials. The powder patterns of the sheathing indicated predominantly nickel (cubic structure) and lines corresponding to Cr308,

Cr203, Cr30Lj(noncublc structure). Only traces of chromium sulfate were

evident. The powder patterns of the ceramic packing showed that the

material was predominantly MgO with traces of Mg(0H)2. Optical microscopy showed that the tubes exposed in the gaslfler had significant precipitation of a second phase.

Fracture and metallographically polished surfaces of the tube were

examined by means of the scanning-electron microscope (SEM) and analyzed

using the SEM in the energy-dispersive X-ray mode. The matrix phase was

identified as nickel with small amounts of Fe, Cr, and Al. The second

phase was found to be chromium rich, and some aluminum was also detected

in the polished specimens.

To establish the composition of second-phase particles, an electronmlcroprobe analysis was performed. From this analysis, it was shown

that the matrix phase was nickel and the second-phase particles were

chromium and aluminum oxides. Although extensive examination of the

tube wall was conducted to determine the presence of sulfur, none was

98
detected. The composition of the second phase, determined in four

locations of the sheathing, is listed in Table III. The quantitative

analysis shows that the second-phase regions are predominantly chromium

oxides with a small concentration of aluminum oxide.

The results of the analyses presented indicate that the Inconel 702

thermocouple sheathing had undergone internal oxidation of chromium and

aluminum in the alloy during its service in the steam-oxygen gasifier.

The oxidation characteristics of Ni-Cr alloys have been extensively

studied by a number of investigators (-'-"-^^and their results indicate

that the process of oxidation of these alloys is a strong function of

the chromium concentration of the alloy and temperature. For alloys

containing <10% chromium, the oxidation process leads to NiO and

NiCr20i^ at the surface and an internal subscale of Cr203. In alloys

containing >20% chromium, the oxidation process at 1100°C results in

the formation of a continuous layer of Cr20 3 on the surface of the

alloy. The Cr20 3 layer is protective in nature and any additional oxidation is significantly lowered due to the slowness of the oxygen diffusion rate through the oxide layer. The chromium concentration

required for external scale protection of the alloy increases with a

decrease in temperature, requiring '^30% at 800°C. In the chromium

concentration range of 10 to 20% and at a temperature of 1100 °C

('^'2000°F) , the alloy is in the transition region between internal oxidation and external protective scale formation.

Wagner(^) has proposed that the transition from internal to exclusive

external oxidation should occur when the solute content of the alloy is

sufficient to form a critical volume fraction of internal oxide precipitate at the reaction front. The volume fraction of Cr203,

v . . , , for the Ni-Cr system can be defined as follows: critical

V . . = N° a ^ /2V , , , (1) critical Cr Cr20 3/ alloy'

where is the mole fraction of chromium in the bulk alloy, V^^^

q

and V^2ioy molar volumes of the oxide and alloy, ^

^ respectively, and a is an enrichment coefficient. The value of a is

determined by the diffusion rates of chromium and oxygen in the alloy.

The volume fraction of Cr20 3 phase in the nickel matrix determined in

the failed sheathing using an Image Analyzing Computer Company

Quantimet 720 yields values in the range of 28 to 34%. Using

Nqj. % 0.199 (corresponding to ^^^15. 6 wt% Cr in Inconel 702), V^^ q

= 29.2, and ^^n^y = 6.6 in Eq. (1) yields a value of 0.71 for a.^ ^The

insertion of this value of a in Eq. (1) and calculation of the volume

fraction of Cr203 phase in Ni-20 wt% Cr alloy yield a value of 0.42.

This value should correspond to the critical volume fraction at 1100°C,

since the Ni-20 wt% Cr alloy oxidizes with the formation of an external

scale.

99
The Inconel 702 thermocouple sheathing exposed in the steam-oxygen

gasifier at 1100°C was found to be internally oxidized. The oxidation

products were identified as Cr203 and AI2O3 using optical and scanningelectron microscopy, electron microprobe and X-ray diffraction techniques, and chemical analysis. The internal oxidation of the alloy can

be prevented by increasing the less noble solute content (i.e., chromium) to a level that exceeds a critical composition whereupon a compact protective layer of solute element oxide is formed at the external

surface. This necessitates selection of a nickel-base alloy with

>20 wt% chromium or an alloy such as Type 310 stainless steel that is

inherently superior in resistance to oxidation. Type 310 stainless

steel was substituted for the Inconel 702 and has performed satisfactorily. Use of a nitrogen purge may be contributing to the satisfactory performance.

II. HYGAS Instrument Tubing

Types 304 and 316 stainless steel instrument tubing containing superheated steam-oxygen mixtures at 600°F and 1200 psig failed after brief

(hours to days) service. Failures varied from small pinhole leaks to

massive tube rupture.

Metallographic examination revealed that cracking originated at the

inside surfaces of the tubes and was mixed intergranular and transgranular. Chemical analysis of boiler feed water indicated erratic

chloride control. Concentrations of 2.4 and 0.1 ppm were observed.

Analysis of the pipe insulation showed that it met nuclear specifications for stainless steel pipe insulation. Energy- dispersive X-ray

analysis using the SEM showed the presence of chloride in the scale of

the Type 316 stainless steel process piping associated with the instrument tubing, but chloride was not detected in the inside surfaces of

the instrument tubing. This is not considered surprising in view of

the relatively high detection limit of the analytical technique and the

fact that the process piping was exposed to a much greater volume of

fluid than the instrument tubing.

The method of plant operation led to the conclusion that failure was

associated with chloride stress-corrosion cracking. When the plant is

down, the steam system is shut off, thus permitting condensation and

possible air in- leakage. On start-up, operating pressure is achieved

more rapidly than operating temperature, a condition which also promotes condensation. In fact, due to the length of the lines, it is

probable that continuous refluxing takes place in these lines during

plant operation. At 1200 psig, the saturation temperature is 569° F.

These operating conditions are conducive to intermittent locally high

chloride concentrations.

100
In studies (5) in support of nuclear- fueled superheaters, a variety of

alloys were exposed under stress to superheated steam generated from

water containing 1.5 ppm chloride, oxygen, and hydrogen. Maximum temperatures varied from 560 to 1250° F, and the temperature was cycled to

produce condensation. Austenitic stainless steels failed by transgranular or a combination of trans granular and intergranular cracking.

A ferritic stainless steel (Type 406) and high nickel alloys did not

fail.

The HYGAS components under investigation operated under similar,

although probably less severe conditions. Hydrogen is probably not

present but is not believed necessary for the observed failures.

Oxygen may not be present in all lines.

Based upon these results and the studies referred to above, Incoloy 800

or Inconel 600 are more suitable materials of construction. Incoloy

800 was substituted for 18-8 stainless steel and has performed satisfactorily in excess of 500 h.

The Type 316 stainless steel process line is considered to be vulnerable, particularly in those areas where condensation can take place,

e.g., in horizontal runs. A surveillance program is under way, but to

date no incipient cracking has been observed.

HI. Other ANL Investigations

A. Type 304 Stainless Steel Purge Lines - HYGAS

These lines carry Chicago city water at 200° F and 1200 psi. They

failed by cracking upon startup. The failure was diagnosed as chloride

stress- corrosion cracking, and the results of metallographic examination were consistent with this hypothesis. The lines are incompletely

drained between runs and evaporation of the remaining water can result

in locally high concentrations of chloride upon start-up. (Chicago

city water contains about 10 ppm chloride.)

The problem could be alleviated by maintaining the lines always full of

water or using an ion exchanger to remove chloride (flow rate is very

low, gpm) . Based upon our recommendation with respect to the

instrument lines, the plant operator chose to substitute Incoloy 800

for the Type 304 stainless steel. Results to date are satisfactory.

B. Carbon Steel Coal Pretreatment Vessel Cooler - HYGAS

The central (water inlet) pipe was severely bowed and the pipe-toheader weld had cracked. Other pipes were less severely bowed. This

heat exchanger serves to maintain temperature of the exothermic reaction. Stress analysis indicated the failure was caused by buckling as

a result of excessive cooling of the failed pipe section. The

101
excessive cooling was the result of poor temperature distribution produced by the use of six coolers instead of the four for which the

process had been designed.

In an associated investigation of a failed thermocouple and thermocouple protection tube from the same vessel, temperatures much in

excess of the design temperature were demonstrated to have existed in

other parts of the vessel.

C. Type 321 Stainless Steel Bellows - HYGAS

This bellows, part of the start-up burner assembly, was perforated.

Metallographic examination revealed extensive melting had occurred.

Chemical, energy-dispersive X-ray and Auger electron analysis of

deposits found in the bellows demonstrated that coal products had

reached the interior of the bellcws.

D. Incoloy 800 Bellows - HYGAS

This bellows, part of the main gasifier transfer- line expansion joint,

was perforated. Incoloy 800 piping associated with the assembly was

cracked, particularly at welds. The failures may be associated with

sulfur attack but the investigation is only in the initial stages.

E. Incoloy 800 Thermocouple Protection Tubes and Pressure Taps - HYGAS

These tubes, from the ash agglomerating gasifier, suffered accelerated

wastage, apparently coincidentally with change to a high (^^3% in contrast with '^^0.5%) sulfur char feed. Chemical analysis of the scale

revealed a sulfur content of ^^14%. On the assumption that sulfur

attack is responsible for the observed wastage, the Incoloy 800 has

been replaced with higher chromium Types 310 and 446 stainless steel

alloys. The performance of these materials will be monitored.

F. Type 316 Stainless Steel Pipe to Type 304 Stainless Steel Flange

Weld - Syn thane

The initial purpose of the investigation was to determine the cause of

the cracked weld in the socket-welded assembly. This was determined to

be the result of mechanical stresses, on a weld that had inadequate

penetration.

In the course of the investigation, cracks were also observed in the

pipe and diagnosed as chloride stress-corrosion cracking. The source

of the chloride was the pressure testing fluid. This fluid was not

completely drained from the system and locally high chloride concentrations could be produced when the fluid evaporated and the system was

subsequently refilled. Chloride was detected on crack surfaces, inner

surface of the pipe, and weld socket.

102
Acknowledgments

This work was carried out imder the auspices of the Fossil Energy

Branch of ERDA. Many individuals in the Materials Science Division and

Chemical Engineering Division, in addition to the authors, participated

in the investigations. The work could not have been as successful as it has been without the complete and wholehearted cooperation of the

pilot-plant operators.

References

1. C. S. Giggins and F. S. Petti tt, Transactions of the AIME,

Vol. 245, p. 2495, 1969.

2. C. S. Giggins and F. S. Pettitt, Transactions of the AIME,

Vol. 245, p. 2509, 1969.

3. J. Moreau and J. Bernard, Compt. rend. Vol. 237, p. 1417, 1953.

4. C. Wagner, Z. Electrochem. Vol. 63, p. 772, 1959.

5. C. M. Spalaris, "Stainless Steel and High-nickel Alloys for Use in

Superheated Steam," pp. 260-288 of TID-8540, Reactor Technology:

Selected Reviews - 1964 (July 1964).

105
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TABLE II. Gas Composition (% by Volume) in the Vicinity of the

Failed Thermocouple Sheath in the Gasifier^

«2 20

H^O 50-51

CO 9-12

co^ 15-17

CH,

4

2

'^'O.l

The gas composition is that obtained by room- temperature

analysis using gas chromatography technique.

TABLE III. Microprobe Analysis of the Second Phase in Thermocouple

Sheathing (Concentrations in wt%)^

Location Cr Ni Al 0 (By difference)

ID 56.0 8.1 7.3 28.6

Center-ID 66.5 4.1 1.7 27.7

Center-OD 62.7 2.7 3.60 31.0

OD 43.3 8.1 16.2 32.4

The oxygen concentrations corresponding to CrO, Cr20 3, Cr0 3, and

AI2O3 are 23.5, 31.6, 48.0, and 47 wt%, respectively.

105
DISCUSSION

P. J. Birbara, Coalcon : When the stainless steel instrument lines were

replaced with Incoloy 800, there were no failures after 700 hours.

How long did it take for the stainless steel lines to fail?

S. Greenberg : The stainless steel lines failed in a matter of hours

to days.

106
EROSION PROBLEMS IN LETDOWN VALVES

J. J. Mueller

Battelle Columbus Laboratories

Columbus, Ohio 43201

Abstract: The coal-derived slurries associated with all types of

liquefaction processing present serious wear problems for many of

the system components. In particular, the throttling valves used to

let down the ash-containing slurry from the high processing pressure

to near-ambient pressure experience relatively short service life

as a result of erosive wear of the internal components. The wear

life of cemented carbide trim components in pilot facilities ranges

from only about 2 weeks to 2 months. Other components of the valve

body have lasted only a few days when not properly protected from

direct impingement by the rapidly moving slurry. Design modifications are continually being made to minimize the wear problem and

thereby lengthen the time between component changes. The design

of trim components is discussed and examples are presented of worn

components and some of the valve design modification which have

been evaluated. Wear of the critical cemented carbide trim

components is shown to occur by the mechanism of removal of the

soft metal matrix from between the hard, wear-resistant carbide

particles, and the associated pullout of the hard particles.

Improvement in the life of trim components is expected to come

with minimized metallic binder content or adoption of hard, singlephase ceramic materials.

Key Words: coal liquefaction, letdown valves, wear-resistant

cemented carbides, valve trim, wear problems.

Presentation: The present and projected shortage of petroleum has

prompted extensive development of the technology for converting

coal to useful forms of fuel by the liquefaction approach. In

addition to providing much needed fuels, this technology will also

yield desirable organic compounds for the chemicals industries.

The development of this technology in the United States was started

in the late forties by the Bureau of Mines at Louisiana, Missouri.

The purpose at that time was to demonstrate that American coals

could be processed into liquid fuels in a manner similar to that

done earlier in Germany. Despite considerable equipment difficulties

this goal was basically achieved, but because of the then ample sources

of petroleum the effort was discontinued. During the past decade,

however, the need for such technology has been expressed through the

establishment of several pilot and experimental facilities in the

United States.

107
All of the presently operating liquefaction facilities are experiencing

many of the equipment problems which were encountered in the first

demonstration plant. Pumps, seals, valves and piping are being worn

by the flowing coal-derived slurries which contain inorganic matter,

a large part of which is ash. The inorganic contaminants normally

constitute 5 to 15 percent of the coal.

The equipment component which suffers most from erosion by the ash is

the letdown valve through which the slurry passes from the zone of high

reaction pressure to one of near-ambient pressure. In Figure 1, which

shows a flow diagram of a solvent extraction process, the letdown valve

is located in the line between the dissolver and the gas-liquid

separator. At this point the coal has been fully reacted, and the

resulting slurry consists of dissolved coal products and gases and the

undissolved erosive agents which are held in suspension. The slurry is

typically at a pressure of 1000 to 3000 psi and at temperatures as high

as 600 to 800 F, Throttling control is required to maintain the large

drop of operating pressure during letdown.

Figure 2 shows the basic design of a typical valve used for slurry letdown. This type of valve has several desirable features over the many

other types and designs of valves available, many of which have been

tried. One important feature is that the stem and seat trim components

are replaceable. They can be removed without breaking a line connect*

ion by simply removing the bonnet. The flow direction, which is the

reverse of normal for such valves, allows the slurry to enter the stemcontaining chamber and to exit through the seat into the larger linesize opening. The expansion of the slurry resulting from volatiles

and dissolved gases is thereby more readily accommodated. The exiting

slurry does not have to change direction rapidly as would be the case

for flow in the opposite direction. Wear is common at surfaces which

force the change in direction under conditions of rapid flow.

The trim components of the valve which experience the highest flow

rates with associated direction change and turbulence undergo the most

severe problems of erosion. Figure 3 shows a typical trim set for

throttling control. The stem member may be gradually tapered or else

be cylindrical with a tapered flat to provide a changing cross section.

In operation, the stem is unseated and withdrawn until the appropriate

size of opening is obtained. The stem position during letdown changes

as wear and associated change in opening size occur.

Solution of the trim wear problem has been sought primarily through

changes in materials of construction, with relatively minor changes in

trim design in a given valve. The evolutionary changes in materials

have followed a trend from stainless steel to shock-hardened steel to

Stellite alloys to cast carbides and finally to the presently used

108
cemented carbides. Evolution in the cemented carbides was generally

from the machining grade of tungsten carbide with high cobalt binder

content to wear-resistant die grades and finally to specially designed

wear-resistant grades containing a more corrosion-resistant cobaltchromixxm binder alloy. With the change from metal alloys to the best

grades of cemented carbides the service life of trim components increased from a value of a few hours to up to as long as 2 months.

The most wear-resistant carbides have been found to be less tough, and

users have experienced a much higher rate of breakage during installation and operation. Stems break under bending loads resulting from

misalignment or particle jamming. Seats are broken as the result of

tensile stressing at the time of valve closure.

Figure 4 gives examples of the severity of wear that a coal slurry can

produce on alloy components within a relatively short time. The bulk

of such wear can occur over a period covering anywhere from hours to a few days of operation.

Figure 5 shows a carbide stem member from the H-Coal Pilot Plant in

Trenton, New Jersey. It has a typical life span of 2 weeks in letting

down a coal slurry from a pressure of 3000 psi. The tapered flat on

the 1/4-in. -diameter stem is grooved by wear to a depth of about 1/16

in. The groove pattern varies among stems. The corresponding seat

member undergoes comparatively little wear. The stem is believed to

experience the major wear because it forces the flowing slurry to reverse direction as it enters the trim set.

Figure 6 shows a stem obtained from the Solvent Refined Coal (SRC)

Pilot Plant in Wilsonville, Alabama. This stem is about 3/8 in. in

diameter and is shown after 2 months of seirvice in letting down coal

slurry from 2000 psi. The wear pattern is quite uniform, with fine

wear grooves which appear to relate to the initial pattern of grinding

lines. The wear of other replacement stems in the same valve, however,

is not always as uniform nor do they have the same length of service.

Figure 7 shows a similar stem member which exhibits nonuniform erosive

wear. Localized gouging occurred along the flow path, while undercutting in the form of a ring occurred at the junction of the cylindrical and angular sections. The irregular gouging is believed to result

from turbulence in the stream of slurry. It has been noted that the

seat member, which usually experiences little attack, is attacked and

gouged when the stem member is unevenly attacked. This could be expected under turbulent flow conditions. Figure 8 shows a third type

of erosive wear in the same type of stem member. The wear is in the

form of localized gouging on the cylindrical surface on the side

opposite the tapered flat, a location where there is usually no

apparent wear problem. The cause of this type of attack is not obvious.

109
The mechanism of wear of the cemented carbides has been tentatively

identified as resulting from erosion of the softer metal matrix from

between the hard carbide particles, and subsequent pullout and loss of

the hard particles. Figure 9 is a scanning electron micrograph of an

eroded surface of a fine-grained cemented carbide. The carbide particles stand well above the underlying metal matrix. The particles are

well defined in shape and have, in general, retained their sharp edges.

Figure 10 shows an eroded surface of a specimen containing some large

carbide particles. The absence of binder can be seen clearly at the

exposed surfaces of the large particles.

The wear problem in letdown valves is not solely restricted to erosion

of the surfaces of the trim components. One of the problems commonly

encountered occurs at the exit side of the trim set where slurry expands and sprays out against the walls of the valve. Since standard

designs of valves are used in the larger pilot operations, the exit

chambers are of a normal, moderately small size. The exiting slurry

strikes the walls with such high energy that it can erode through in

times as short as a few days.

The general approach to preventing this type of erosion problem has

been to incorporate a cylindrical sleeve of cemented carbide at the

exit of the trim set. The wear-resistant sleeve, which is of moderately small diameter, collimates the slurry and directs it axially into

the exit line. This works well, if no openings develop between the

sleeve and trim set which allow shunting flow between the sleeve and

valve body. The spray from this type of leak will also readily cut

through the alloy valve body at an accelerated rate. To prevent such

leaks, high pressure loadings are required between the sleeve and seat

member, and with the more brittle wear-resistant grades breakage can

occur, which permits a similar problem to appear. Figure 11 shows an

example of erosion of the exit side of a valve seat holder which

occurred following breakage of the adjoining carbide sleeve. The

broken surface of the sleeve caused the slurry to be directed back in

a direction reverse from which it came, thereby causing penetrating

attack of the seat holder and ultimately complete penetration of the

valve body.

An attempt was made to avoid the above problem of breakage by making

the sleeve extension integral with the seat member, thus eliminating

the fitup problem between two separate members and the need for application of an axial force. This, however, was not effectively evaluated

because of the occurrence of another already experienced problem. A

leak path developed between the carbide member and the seat holder

where a braze is used to join and seal the members. The location of

leakage is shown in Figure 12. The leak at that location occurs as

either the result of improper brazing or disruption of the braze caused

by the difference in thermal expansion rates of the components. Figure

110
13 shows the results of the leak on the back side of the assembly. The

stainless steel sleeve which surrounds the carbide extension has been

grossly penetrated, thereby allowing the slurry to attack the surrounding valve body.

The erosion problems experienced in letdown valves in coal liquefaction

service point up the need for development in at least two major areas,

namely (1) improvement in the basic materials from which trim components

are fabricated and (2) design of valves specifically for this type of

service with consideration given to the requirements of the trim

material involved. The apparent cause of erosive wear of the cemented

carbides presently used suggests that improvements in trim materials

will come through the use of hard, probably single-phase ceramic-type

materials without a soft binder present or with the binder content

significantly reduced. With this trend, the materials may become more

fragile and potentially unbrazable. The valves into which these new

materials will be incorporated will consequently have to be designed

to suit the requirements of those materials.

We acknowledge our appreciation of samples of worn trim supplied by

the H-Coal and SRC facilities in support of a program of trim materials

development sponsored by the Electric Power Research Institute and

monitored by Mr. Howard Lebowitz of that organization.

Ill
Raw coal

Coal

preparation

Slurry

mixer

Slurry pump

Solvent recycle

Gas-liquid

separation

Preheater

Slurry

Dissolver

Product slurry

Hydrogen recycle

Gas

Hydrogen

generator

Solvent recovery

Raw

Gas

Absorber

Filtration

Absorber

liquid I cycle I

Sulptiur Plant

Solvent refined coal Filter coke

to gaslfler

Sulpliur

FIGURE 1. FLOW DIAGRAM OF TYPICAL LIQUEFACTION PROCESS

112
115
FIGURE 5. WORN CARBIDE STEM MEMBER FROM H-COAL PILOT PLANT

11^
FIGURE 7. UNEVENLY WORN STEM MEMBER

115
FIGURE 8. LOCALIZED EROSION ON BACK SIDE OF STEM MEMBER

FIGURE 9. SCANNING ELECTRON MICROGRAPH OF WORN SURFACE

OF FINE-GRAIN CEMENTED CARBIDE

116
FIGURE 10. SCANNING ELECTRON MICROGRAPH OF WORN SURFACE OF CEMENTED

CARBIDE CONTAINING LARGE CARBIDE PARTICLES
FIGURE 12. SITE OF LEAKAGE BETWEEN SEAT AND HOLDER MEMBERS

FIGURE 13. RESULT OF LOCALIZED LEAKAGE BETWEEN SEAT

AND HOLDER MEMBERS

118
DISCUSSION

W. Netter, Lone Star Lafarge Company : Have you consulted with the

cemented carbide producer about particle size packing to minimize the

binder?

J. J. Mueller : We developed a wear test to enable us to evaluate some

straight ceramic type materials to be used as a short term immediate

fix. We believe that these will possibly work. Then in our own program

we will consider particle size.

W. Netter : What kind of ceramics have you been looking at?

J. J. Mueller : Zirconium diboride, high density boron carbide, high

density alumina, aluminum nitride, silicon nitride, some very high

quality bearing materials and others.

E. E. Klaus, The Pennsylvania State University : Would you describe

the wear test you developed?

J. J. Mueller : We tried to duplicate the conditions that the actual

letdown valve sees. We are working with a typical coal slurry, using

anthracene oil as a solvent for the unfiltered SRC product from Wilsonville. This product contained about 32% ash. We are using in this

system a cemented carbide orifice to direct a very fine slurry beam at

the end of a specimen and then we can evaluate for depth and type of

wear. We used a bellows type pump because we thought that the piston

pump would suffer erosion damage. This works very well except that in

a small system, if all the slurry is pumped out from the reservoir,

the bellows can blow itself up. We had good success with it and

succeeded in boring the straight machining grade carbide K3H to a depth

of 300 microinches in 45 minutes. We feel that we have a sucessful

test now for evaluating wear in materials.

R. Perkins, Lockheed, Palo Alto : Chromium carbide is quite widely used

as a coating and as a bulk material for sliding wear resistance. I am

interested in seeing its application in the slurry. Do you have any

feel from the work you have done as to why chromium carbide looks good?

What are the essential characteristics of a material that make it an

excellent wear resistant material? Is it just hardness, or is it a unique combination of hardness, modulus and toughness?

J. J. Mueller : I cannot answer you from the standpoint of properties.

The chromium cobalt matrix cemented carbides are made not by adding

cobalt and chromium but by adding cobalt and chromium carbide. The

amount of cobalt, I believe, is lower. The trend is toward a minimized,

soft matrix.

119
S. M. Wolf, ERDA : Have you considered using coatings of a single phase

ceramic deposited onto the commercially available cemented carbides,

and if so, would you tell me what type of coating characteristics -- such as thickness ~ you would be looking for?

J. J. Mueller : We considered using single phase ceramics, but we feel

there are solid materials that can work. I don't think there is a good

reason not to use them except that coatings have been tried, although

usually on too soft a substrate. This resulted in catastrophic erosion

of the trim when the coating breaks. As an example, stainless steel

trim was coated with tungsten carbide. When the coating was penetrated,

the stainless steel stem member wore out in about 2 to 5 hours.

S. M. Wolf : Have you any feel for the desired hardness of the surface

of the material?

J. J. Mueller : The general feeling is that the surface should be as

hard as possible, but then there will be problems with thermal shock

resistance and other properties. Perhaps Ian Wright can comment.

I. G. Wright, Battel le Columbus Laboratories : One of the factors that

seems to have been causing the high wear of the cemented carbides has

been the difference in hardness between the carbide phase and the

matrix. The matrix has been eaten out whereas the carbide has not been

attacked at all. We simply would require a uniform hardness of the

surface, as in a single phase material.

120
ERDA INFORMATION CENTER FOR FAILURE PREVENTION

IN FOSSIL ENERGY PLANTS

J. H. Smith and W. A. Willard

National Bureau of Standards

Washington, D.C. 20234

Abstract: The ERDA Fossil Energy Failure Prevention System is a centralized system for collecting, evaluating, and disseminating information about operating experiences and component failure experiences in

coal conversion pilot plants. The objectives of this program are to

assist plant operating and design personnel in preventing plant shutdowns and in extending the useful life and reliability of plant

components

.

Centralized coordination of the failure prevention activities will

ensure that adequate and accurate diagnostic failure analyses are

conducted and will enable the identification of significant and recurring problem areas common to many coal conversion pilot plants. This

will provide a means of sharing and exchanging information between

pilot plants about component failure problems and successful corrective

measures to prevent future problems.

The National Bureau of Standards is responsible for collecting and

evaluating all detailed information from the pilot plants and from

laboratories conducting diagnostic failure analyses. This information

is stored and catalogued according to coal conversion process, material

type, failure category, and component type so that the information is

readily accessible. The information will be made available to operating and design personnel through direct contact with the Failure

Prevention Information Center and through published reports describing

specific problem areas and recommended corrective measures in coal

conversion pilot plants.

Kei^words: Coal conversion pilot plants; computerized data system;

failure analysis; failure prevention; fossil energy; information

retrieval

.

The major function of the ERDA Fossil Energy Failure Prevention Program

will be to coordinate all the failure prevention, failure analyses and

research programs now underway at Argonne National Laboratory, IITRI,

Oak Ridge National Laboratory, various pilot plants, etc. The purpose

will be to ensure: 1) that adequate and accurate diagnostic failure

analyses are conducted, 2) that significant problem areas are identified, 3) that corrective measure and/or development efforts required

are identified. These programs will be accomplished by collecting

121
information on component failures, material evaluations, research

projects, etc.; the evaluation of this data for completeness and

accuracy; and the dissemination of this information to the users. An

overall view of how the program functions is shown by the information

flow diagram (Fig. 1). It is expected that the information from this

program will be useful in avoiding unexpected plant shutdowns, in

extending the life of plant components and in the conservation of

materials of construction.

The Failure Prevention Data Center will serve as the centralized base

for the collection, evaluation, and dissemination of information on

operating experiences and component failures from all pilot plants,

process development units and future production plants.

Information Collection . Information will be gathered from many sources

(Table I) . The ERDA Materials and Component Failure Reports are sent

to the Materials and Component Division of ERDA by the plants' operating

managers. These reports are the key to an effective failure avoidance

program since they can be used to identify recurring and particularly

troublesome problem areas. The plant operating manager will make the

decision to initiate a failure analysis of the failed component. These

analyses can be performed at company laboratories or sent to ERDA

designated research laboratories. The plant operator may decide against

doing an analysis due to a lack of time, money or interest. To help

alleviate some of the expenses involved in doing necessary failure

analyses, ERDA has supplied funds to several research laboratories to

assist the pilot plants. Argonne National Laboratory, Oak Ridge

National Laboratory, Sandia Laboratory are the designated organizations

which will perform failure analyses. Detailed failure analyses reports

are the essential keystone of the failure prevention system. They are

essential in building up the data base needed to improve component

reliability and performance.

Information Evaluation . All of the failure analysis reports from the

various laboratories are evaluated at the National Bureau of Standards

for completeness, accuracy of diagnosis and correctness of the data.

Analyses are performed by specialists in areas of metals, ceramics,

erosion, corrosion, etc. Once all of this material has been collected

a failure mode analysis can be conducted to identify significant

problem areas. Table 2 presents some of the problem areas which have

been uncovered to date. As expected the major problem areas are with

corrosion and erosion. The hostile environments associated with the

coal conversion processes and the necessity of moving coal slurries

have led to many operation problems.

Information Dissemination . All of the information collected and

analyzed must be made available to the users rapidly and in a suitable

format. A brief description of the operation of the ERDA Failure

Prevention Data Center will show how this function is performed. All

122
the information items mentioned in Table I that are received at the

data center are assigned an identification number. This number is

recorded in a logbook along with a short description of the item. The

item is analyzed for completeness and accuracy and a detailed technical

abstract is prepared. The item is classified, for cross-indexing

purposes, into several categories, such as coal conversion process,

type of material, component, failure mode, author, (as shown in

Table 3). The original report is then filed by information number into

a master file. Initially the procedure was to type the information on

5x8 cards and cross-filed by the information in a manual retrieval

system. This procedure is inadequate to handle a large volume of

information. Therefore, the information is being transferred onto a

computerized (CCA Model 204) data base management system which will

enable information to be more readily available for failure mode

analysis and will ease the dissemination of information to the users.

The most important function of this data center is to get pertinent

information into the hands of people who can use it, in a useful form

and in time to be of value. Some of the methods to be used for information dissemination are shown in Table 4. As recurring problem areas

are uncovered reports will be written and sent to interested users to

alert them of the problem. Through technical meetings, publications in

the ERDA Newsletter and in technical journals, information from the

data centers will be disseminated to a wide range of interested users.

The ERDA Failure Prevention Data Center has only just gotten underway.

Additional information is being received continuously on component

failures and material problems so that the data base is being enlarged.

The sharing of operating experience between all the pilot plants arid

process development will significantly reduce the time required for

these plants to reach full operation and to establish which materials

and components will perform satisfactorily in the coal conversion

environments. This information will permit designers to design more

efficient, dependable plants and plant operating personnel to improve

the operation of the plants and minimize downtime. This program will

enable the ERDA Fossil Energy program to reduce the time required to

get production plants on-stream and start producing significant amounts

of energy in gaseous and liquid form from coal.

125
Failure Avoidance:

Information Flow Diagram

Plant Failure Incident

t

Immediate Failure Report to

ERDA - Mat'l & Comp. Div.

No Failure

Analysis

r

(hbs)

ERDA

Newsletter

Open

Literature

& Meetings

Report Evaluation

I

Data Center

I

Information Dissemination

i X J r3

Diagnostic

Failure Report

Open Literature

MPC

Mfg. Lit.

Plant Operations

Manager

Design Engineers

Tech. Evaluation

Contractors

Figure 1

12 U
Table 1

-INFORMATION GATHERING-

-SOURCES-

-ERDA MATERIALS AND COMPONENT

FAILURE REPORTS

-DIAGNOSTIC FAILURE ANALYSIS REPORTS

BY DESIGNATED LABORATORIES

-SERVICE EXPERIENCE OF OPERATING

PLANT MANAGERS

-PUBLISHED LITERATURE AND

MANUFACTURERS DATA

-SPONSORED RESEARCH PROJECTS

-TECHNICAL SOCIETIES

-METALS PROPERTY COUNCIL

-NACE

-AIME

-ASM

125
Table 2

PROBLEM AREAS

HIGH TEMPERATURE SULFIDATION

CHLORIDE STRESS-CORROSION CRACKING IN

STAINLESS STEELS

EROSION

THERMAL FATIGUE/THERMAL STRESSES

CARBONIZATION

FABRICATION DEFECTS

CORROSION-CAUSTICMETAL DUSTING

DESIGN

IMPROPER MATERIAL SPECIFICATION/QUALITY

CONTROL

126
Table 3

-INFORMATION WILL BE CROSS INDEXED TO INCLUDE

-COAL CONVERSION PROCESS

-TYPE OF COMPONENT

-TYPE OF MATERIAL

-FAILURE CATEGORY

-INFORMATION SOURCE

127
Table 4

-INFORMATION DISSEMINATIONREPORTS DESCRIBING SIGNIFICANT PROBLEM AREAS

AND CORRECTIVE MEASURES

PERSON-TO-PERSON COMMUNICATION WITH

WORKING PERSONNEL

PUBLICATION IN THE ERDA MATERIALS AND

COMPONENTS NEWSLETTER

PUBLIC TECHNICAL MEETINGS

PUBLICATION IN OPEN TECHNICAL LITERATURE

128
DISCUSSION

D. Livaccari, Coal con : How can I get access to your data file? Can I make a phone call and obtain information on a particular problem?

J. H. Smith : That is a good question. We hope to get some thoughts

from people like you as to the form in which this data would be most

useful. Right now, all we have done is to abstract and cross-index

the information so we can find it. What we want to have is a quick

retrieval system so that the people who need the information can call

us directly and we can give an immediate answer covering everything in

our files on that particular subject. Further down the line we will

be writing essentially interpretive reports that describe certain

problem areas. These reports will probably be published in the ERDA

Newsletter. I would like to solicit comments as to what kind of information is needed, in what form it can best be used and on what time

scale it would be needed. I think with this information we could then

mold our system better to serve you at the early stages of your design

and materials evaluation.

D. Livaccari : Well, I think that if we could call in and talk to you

people that would be a big help to us.

S. M. Wolf, ERDA : I think this type of information is very useful.

Are you also planning to incorporate in your data bank information from

accelerated engineering testing programs such as those at IITRI and

those that Schaefer described yesterday?

J. H. Smith : Yes.

D. M. Bailey, The Lummus Company : Getting this information down to

the operating facilities as soon as possible is going to be of great

significance. We all don't want to reinvent the wheel. In the Synthane

plant, we have already worn out most of our pumps, nozzles, etc.

L. G. Samuels, SRC Pilot Plant, Ft. Lewis : One of our problems is that

we are constantly besieged by people who want the same information.

We cannot report our new information because of so many requests for

the old information.

J. H. Smith : This is an extremely good point. How do you suggest Lnat

we bypass or eliminate some of these requests?

L. G. Samuels : I would suggest that the information be sent directly

into ERDA and let them disseminate it.

J. H. Smith : All of our information comes through Frankel 's office.

We are not trying to set up another system.

129
L. G. Samuels : In addition, we have to prepare a very detailed monthly

report.

J. H. Smith : These reports have been one of our best sources of information.

150
STEEL PLANT COKE-OVENS:

AN ENERGY CONVERSION PROCESS WITH WARPAGE PROBLEMS

H. W. Lownie, Jr. and A. 0. Hoffman

Battelle Columbus Laboratories

505 King Avenue

Columbus, Ohio 43201

Abstract: A brief discussion of the warpage problems existing in the

armour of steel plant coke-ovens and the proposed research to develop

upgraded designs/materials to eliminate these problems.

When Professor Ling became aware of the research Battelle is doing on

the metallic components of by-product coke-oven batteries, he expressed

an interest in having a paper by Battelle at this Symposium. Our research is still in the early stages, but with the interest of this

group in coal-conversion systems, you may be interested in the failure

problems we have found and how we plan to overcome them. There may in

the future be a relationship between these problems, and their solutions, and the problems being encountered in new coal-conversion processes.

Long before there was an interest in coal conversion or coal gasification processes, there existed batch, low- temperature and high- temperature processes for coal distillation or coal carbonization. In particular, the high- temperature by-product coking process is alive and

well today, producing blast-furnace and foundry coke from 85 million

tons of coal per year. Each ton of coal used also produces about

10,000 SCF of gas having a heating value between 500 and 600 BTU/SCF,

plus tars, oils, and ammonia chemicals.

Coke ovens typically measure about 18 inches wide by 10 to 20 feet tall

and 40 to 50 feet long. Usually about 25 to 80 ovens are stacked side

by side (like books on a shelf) to share common separating walls that

contain flues for heating the coals to coking temperature (about

2000 F). A coke battery of 25 to 80 ovens is essentially an arrangement of high-conductivity silica brick, plus insulating brick, held

together with steel tie rods, buckstays, and other structural parts.

Battelle 's interest is in the metallic armour on these batteries, with

particular emphasis on the end-closure equipment. Members of this audience may be interested in the fact that this batch process is 90 to

95 percent thermally efficient, with the probability that this percentage can be improved.

Because coke ovens produce solid product in a batch operation, each end

of the 12,000 or more coke ovens is closed by a heavy refractory- lined

151
removeable steel or cast iron door. After the coal in a particular

oven has been coked, the doors on each end are removed so that the incandescent coke can be pushed from the oven into a railroad car. For

the next charge, the doors are latched back onto each oven. The seal

is a flexible stainless steel strip pressing against the cast iron

frame on each oven. These seals leak and release hydrocarbon particulates and gases into the atmosphere. Our first research effort was directed towards improving the sealing of these doors against the metallic armour of each end closure.

In June of 1974, Battelle's Columbus Laboratories was awarded a research contract to "Study Concepts for Minimizing Emissions from CokeOven Door Seals". This contract was funded jointly by the Control Systems Laboratory of EPA and by the American Iron and Steel Institute.

One of the tasks in this completed first-stage study was to "define the

problem". To complete this task we made field measurements and did

field testing plus laboratory experiments. It was found that the primary cause of the leakage was the degree of warpage that has occurred

on most (if not all) of the 25,000 or more cast iron jambs in everyday

operation. In addition it was found that the metal contact seals were

not flexible enough to adjust to the degree of out-of-plane warpage of

the jambs. Given warpage and relatively inflexible seals, the result

is gaps or openings in the sealing system, resulting in leakage from

the ovens. Table I is an example of the warpage found on operating

jambs

.

Table I

AN EXAMPLE OF THE DEGREE OF INWARD AND OUTWARD BOWING (OUT OF PLANE) OF

JAMBS ON COKE-OVEN END CLOSURES AS REFERENCED TO THE JAMB CORNERS (Numbers are in 32nd 's of an inch. A minus 5, for example, is 5/32 inward

bowing)

Left Side Right Side

Measurement

Oven Number Oven Number

Location

1 2 3 4 1 2 3 4

Top 0 0 0 0 0 0 0 0

Quarter Point -5 0

- 22 -12 -3 -1 -15 -10

Middle +1 1 -8 -8 +4 +3 -12 -2

Quarter Point -1 0 -8 -2 +8 +5 -9 +4

Bottom 0 0 0 0 0 0 0 0

The recommendations made by Battelle as the result of this preliminary

study were:

1. More-flexible and more-heat- resistant metal seals should be developed further in a follow-on program.

152
2. Design work should be preceded by experimental effort to analyze

the temperature distribution and thermal-stress patterns in existing systems and designs. These analyses would serve as valuable

input to the design and material-selection process.

3. Because the basic emission-causing problem is the distortion that

has occurred at operating jambs, the factors causing this problem

should be analyzed quantitatively. A technical analysis should indicate what steps can be taken in design and materials to develop

a more dimensionally stable jamb for both new coke-oven batteries

and replacement of some jambs at existing batteries.

The American Iron and Steel Institute and its member companies, and the

EPA accepted these recommendations and asked Battelle-Columbus to submit a research proposal to complete the follow-on project. This proposal has been submitted and includes:

o Interaction between a detailed mathematical modeling, physical modeling, and field experimentation program, leading to

o Full-scale unit design and testing of parts, and

o Fabrication, installation, and field testing of new designs for

jambs and seals.

It is possible that the analytical portion of this proposed project may

be useful in the materials problems that may surface in the development

of other coal-conversion processes.

153
DISCUSSION

J. Kelly, Rolled Alloys, Inc. : It is my understanding that people make

ingot molds out of gray iron rather than nodular iron because the gray

iron warps less. Has that been considered or studied?

A. 0. Hoffman : It is part of our analysis to find out if this is true.

We don't have enough information at present. There are only a few

nodular cast iron jambs in our system, and they have only been in use

for a short time, so we don't know if they are showing a warpage pattern

similar to that of gray cast iron.

J. Kelly : And, more in line with my company's interests, what coefficient of expansion would be required in the stainless steel spring?

A. 0. Hoffman : As low as possible, depending on how it is fastened.

The most important part to us is its strength at temperature.

J. Kelly : What sort of temperatures?

A. 0. Hoffman : We expect that these seals may hit 900°F at times when

an oven is left on without coal in it.

J. Kelly : Then you could almost use a martensitic steel.

A. 0. Hoffman: Possibly.
SESSION III

RELATED

MATERIALS

RESEARCH

CHAIRMAN: F. F. LING,

RENSSELAER POLYTECHNIC INSTITUTE

SELECTION OF MATERIALS

USED IN COAL GASIFICATION PLANTS

M. A. H. Howes

IIT Research Institute

10 West 35 Street

Chicago, Illinois 60616

1. INTRODUCTION

Early review of the projected environments of coal

gasification pilot plants clearly showed that the temperatures, pressures, and gas compositions in the different

components of the plants were extremely hostile. There was

no literature or any real experience with the behavior of

materials of construction in such hostile environments . In

1972 the American Gas Association saw the need for some reliable data on the corrosion behavior of alloys (and ceramics) of construction in the projected environments of

pilot plants. The AGA initiated this work with the Metal

Properties Council whose Task Group on Materials for Coal

; Gasification developed a well-planned series of experimental programs to gather the needed data. Beginning in

1975 ERDA assumed the funding of the programs through a

contract with MPC. The work is subcontracted to IIT Research Institute in Chicago and is being regularly monitored by the appropriate subcommittees of the Metal Properties Council.

The major areas of materials degradation in coal gasification equipment, along with some of the environments,

are summarized in Table 1. It is apparent from this chart

that unless the "right" materials are selected for construction of the equipment, one may be faced with frequent

shutdowns for repairs . During the limited experience with

the operating pilot plants most of these problem areas in

coal gasification equipment have been observed. The most

severe conditions exist, of course, in the main gasifier

and the transfer lines which see high temperature, high

pressure, corrosive gases, and high-velocity char and ash

particles which cause severe erosion. There is very little

information in the literature related to high temperature,

high pressure erosion. Another area of concern is the

severe corrosion of alloys in the aqueous quench tower system. Here again, there are no data in the literature to

draw from.

137
Based on these considerations, the American Gas Association and ERDA initiated a five-phase experimental program. The first phase is to screen alloys in laboratory

tests in a high temperature, high pressure gaseous environment typically found in the gasifier. The second phase is

a comprehensive one in that all materials of construction,

both metals and ceramics, are to be suspended in selected

locations of each of the pilot plants for varying amounts

of time and the results to be compared with appropriate results from each of the other three phases . The third phase

is concerned with the screening of alloys of construction

in the environment expected in the aqueous quench tower

systems with and without inhibitors in the environment.

The fourth phase is a complex version of Phase I in that

the best alloys from Phase I will be examined for high temperature, high pressure erosion/corrosion resistance in the

environment containing the gasifier gas as well as high

concentrations of char, ash, and dolomite particles moving

against the samples at high velocities. The fifth and final phase is being organized to collect reliable design

engineering data on the best alloys and ceramics found in

the first four phases

.

2. PHASE I - HIGH TEMPERATURE AND PRESSURE

GASEOUS CORROSION

This phase involves laboratory corrosion testing for

exposure times up to 5000 hr, primarily in an atmosphere

typical of that which would exist in a gasifier but containing three different hydrogen sulfide levels at temperatures of 900°, 1500°, and 1800°F and at a pressure of 1000

psi

.

Two reactors were designed and built to operate at a

pressure of 1500 psi with a temperature capability of

2000°F. The reactor is surrounded by a pressure vessel

with a controlled argon pressure so that the differential

pressure across the reactor wall is only a few pounds per

square inch. The specimens are spaced on a sample tree,

and the tree is suspended from a ceramic tube which also

forms part of the gas circulation system. A circulating

fan, driven by a magnetic drive unit, causes efficient interaction of gas with the metal surface. The gas flow is

arranged so as to obtain a change of gas volume every 8

min

.

The specimens are 1 x 1 x 0.25 in. coupons. After exposure these samples were cut and metallographically polished and etched. Measurements were made of the scale and

penetration. From the data, calculations were made to

138
express corrosion rates in terms of percent loss of sound

metal in inches per year.

Reproducibility tests were carried out in both reactors using all-309 specimens and also a six-alloy series.

The results show that, statistically, it makes no difference to the corrosion result which reactor is used or which

portion on the tree is selected for test

.

To date about 31 tests have been completed. New alloys now being tested include cast and wrought high chromium alloys, cobalt-base alloys, and stabilized high chromium

stainless . Future plans include corrosion effects on weldments and on refractories

.

3. PHASE II - PILOT PLANT EXPOSURE TESTS

OF METALS AND REFRACTORIES

The laboratory tests planned in the laboratory phases

will be corroborated with exposures of alloys and ceramics

in various test locations in four of the pilot plants constructed for coal gasification. The cumulative exposure

durations are planned approximately at one month, three

months, and six months. It is expected that comparison of

the laboratory test data with results of the pilot plant

exposures will give a high level of confidence for the corrosion rates of all the alloys and ceramics.

It should be pointed out that all the alloys selected

for exposures in Phase II have a logical counterpart in one

of the laboratory phases . It should also be noted that the

metallic samples are in the form of corrosion coupons,

welded coupons, and stressed coupons. After the samples

are exposed in each location for a specified duration of

time, they will be examined metallographically and otherwise in the same manner as in Phase I, III, or IV.

The pilot plants involved in this program are Hygas,

Consol, Synthane, and Bigas

.

The sample racks were specifically designed for each

location and welded in place. The main requirements are

rigidity and minimum interference with gas flow in the component .

To date, exposures for only a limited number of pilot

plant tree locations have been completed. These test locations are at the Consol and Hygas plants. With such limited corrosion results available as yet, an extensive correlation of laboratory and pilot plant data is not possible.

139
but the two sets, in general, compare well thus far. Significant differences have been observed in a few cases in

high- temperature locations at Consol. These differences in

corrosion behavior can be attributed to a complex corrosion

environment in the pilot plant, and resolving them will require additional corrosion data from both laboratory and

pilot plant.

4. PHASE III - AQUEOUS CORROSION IN QUENCH TOWER SYSTEMS

Hot gases coming out of the gasifier are quenched in

order to remove most of the harmful impurities. Here the

temperatures can reach 475°F and pressures up to 1250 psi.

The gases contain major impurities such as H2S, NH3, SO2,

HCN, oils, tar acids, and chlorides. In this environment,

one can anticipate general and pitting corrosion, crevice

corrosion, stress corrosion, weld cracking, and hydrogen

embrittlement

.

To determine the required corrosion data in the proper

environment several autoclaves are employed. Plain and Ubend samples (welded and nonwelded) are suspended in the

gas phase, placed at the gas-liquid interface, and immersed

in the liquid. The data recorded include weight change,

maximum pit depth, stress corrosion susceptibility, etc.

The initial group of alloys selected for Task I indicated that all these alloys cannot be tested in a single

test chamber at the same time. The 316L lining from the

reactor also interfered with some of the test alloys. The

lining is now Teflon coated and seems to be inert to the

test materials. After many experiments, it was finally

possible to group the alloys in such a way as to eliminate

the interference.

Statistical analysis of the data indicated that, because of the strong correlation existing between the variables, it would not be possible to uniquely identify the

corrosion potential of each variable. To determine the effect of these variables, a statistically designed experiment was recommended by the MPC Phase III Committee.

In Task II of this phase, a statistically designed

test series was started. This is a modified subset of the

experimental design suggested by IITRI to the MPC Committee.

Basically it is a series of 50 hr and 150 hr tests intended

to uniquely determine the individual and interaction effects of the various components in environments, some of

which correspond to the Task I environments 2J, 2H, etc.

Initially, only four steels will be tested, and these carbon steel and stainless steels 304, 316, and 410.

Iho
5. PHASE IV - EROSION/CORROSION TESTING

In parts of the gasifier where gas velocities are appreciable, erosion may also become a problem. This effect

may be important in cyclones, transfer lines, valves, and

other areas. Laboratory tests are planned which include

combined erosion/corrosion testing for periods of 50, 100,

and 1000 hr in a Phase I gas atmosphere. Temperatures of

1500 and 1800°F will be used at atmospheric and 1500 psi

pressures with erodents of char, ash, or dolomite.

Three reactors are in various stages of construction.

The atmospheric pressure equipment is completed, and tests

have commenced. The high pressure equipment is expected to

be completed in the near future

.

6. SUMMARY

A large number of materials of construction are being

evaluated for their resistance to different environments

expected in various components of coal gasification pilot

plants . Several alloys have been found to be promising for

application in the high-temperature, high-sulfur environment. The pilot plant exposure tests are now well under

way with test coupons installed in four plants and plans

made to include three others . Results are now available

from the aqueous program, and a statistically designed test

sequence is now being commenced. The erosion/corrosion

test program is in the early stages, and three reactors are

under construction. When the data become available and

their reliability and long-term reproducibility characterized, the information will be an invaluable aid in designing and costing commercial coal gasification plants.

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DISCUSSION

D. W. Short, Lawrence Livermore Laboratory : In the results from your

aqueous corrosion tests, you found that there was a greater corrosion

rate in the lab tests than in the pilot plant tests. Did you look at

the effect of galvanic coupling?

M. A. H. Howes : The difference in the results came about because

conditions in the pilot plant were quite different from those in the

laboratory. The conditions are enumerated in the table of results.

They are quite a lot more severe in the laboratory, mainly because of

differences in pH.

G. M. Ugiansky, National Bureau of Standards : Have you seen any cases

of stress corrosion cracking in any of your specimens either in the

lab or in the pilot plants?

M, A. H. Howes : As you know we do have U-bend specimens in three phases

of the program and so far we have not seen any evidence of stress corrosion. The information we are getting from the U-bends, particularly

the welded U-bends, at the moment is principally the difference in

corrosive attack around the welds and the heat affected zones.

R. De Angel is. University of Kentucky : Have you compared any of your

corrosion rate data with data in the literature on the same alloys to

see what the effect of the environment is?

M. A. H. Howes : Yes, we have done a fairly thorough literature survey

to compare the other data that are available with ours, but the other

data seem to be so far removed from the coal gasification environment

that we really can't make a meaningful comparison.

S. M. Wolf, ERDA : You mentioned you were planning to do mechanistic

evaluations as well. How are these evaluations coming along, particularly in the transient stages of corrosion, since you indicated that

erosion-corrosion attack may be more significant than erosion itself?

M. A. H. Howes : These studies really haven't started. We have done

a few experiments on the samples that we have, but it was only at a recent meeting that the scheme was laid out. We have a matrix now

that covers all four phases. Specimens of about eight materials will

be compared from the plants and laboratory studies.

D. Canonico, Oak Ridge National Laboratory : I noticed that some of

the U-bend specimens were tested at very high temperatures. Therefore,

would you not expect relaxation? And if there is relaxation, what

good are the tests?

1U3
M. A. H. Howes : Exactly. That's what we said for a long time. The

U-bend specimens are of particular value in phase three in the aqueous

corrosion study. They should be in any of the lower temperature

portions of the plant. I've always questioned putting U-bends in the

gasifier section. The answer always comes back that it is the welded

specimens that we are interested in because what we want to see is

what happens to the weld after it is stressed and then exposed to the

environment. I think it is of some value because it does give us an

indication of the corrosion on the heat affected zones and on the weld

metals themselves. U-bends probably don't have to be used -- the

specimens could be straight.

11+1+
PARTICLE EROSION MEASUREMENTS ON METALS AT ELEVATED TEMPERATURES

L. K. Ives, J. P. Young, and A. W. Ruff

National Bureau of Standards

Washington, D.C, 20234

Abstract: Measurements of the erosive wear of metals resulting from

impact by abrasive particles under reactive environmental conditions

are being conducted. Specimens of several stainless steel and nickel

alloys have been exposed to a gas stream containing abrasive particles.

The particle flux, angle of attack, particle velocity, particle size,

surface temperature and other significant variables were controlled.

Different types of abrasives were used including AI2O2, Si02, SiC and

pumice. Two different erosion test apparatus have been developed and

used to obtain particle velocities from 10 to 90 m/s and temperatures

up to 1000°C. Different gaseous atmospheres have been established

during the erosion exposures. Weight loss measurements and penetration

depth measurements were conducted on the specimens after exposure.

Multiple alloy specimen packages were used in some experiments to obtain

relative erosion data. Erosion rates were determined in the temperature

range of 25 to 1000° C. Erosion depended on particle velocity over the

range V to V , increased with particle size, increased with particle

hardaess, and was maximum for an angle of attack around 20°. The

effects of temperature and environment vary in a complicated way among

the different alloys.

Key words: Abrasive particles, erosion, erosive wear, metals,

oxidation, wear.

Introduction : Studies of metal wear by erosion under various conditions

have been conducted [1-6] at room temperature and in a few cases at

elevated temperatures [7,8]. Industrial applications, for example in

the petrochemical industry and in new industries such as coal gasification [9], require data on metal erosion under conditions of high temperature and reactive environments. Much of that information still needs

to be acquired. Erosion of metals at room temperature has been found

to depend on particle velocity in the range v to v [1,2]. The angular

dependence of erosion exhibits a peak at about 20° angle of attack [1,4]

and the effects of different particle sizes have been investigated

[2,5]. Erosion can either increase or decrease with increasing temperature [7,8] depending on the metal and the atmosphere. The mechanisms

of erosion have been studied using single particle impact techniques

[10]. The present paper describes recent erosion measurements conducted

on metals at room and elevated temperatures up to 1000°C in different

gaseous atmospheres.
Experimental : Two different erosion testing apparatus have been used

in the present work. One system was based on an instrument developed

previously at this laboratory [11]. That instrument had been used

principally to determine the durability of coatings.* Considerable

attention was paid during its development toward achieving reproducibility of operation. Modifications introduced in the current program

have been designed to extend the operating capabilities to elevated

temperatures while maintaining that reproducibility. A schematic

diagram of the system is shown in Fig. 1. In order to obtain data at

elevated temperatures, the metal specimens were heated directly by

passage of a dc current through them during erosion testing. Current

values up to 200 A at 10 V were used to reach an operating temperature

of 500°C and above. The metal specimen size was typically 3 cm long

X 1 cm wide x 0.5 mm thick. Battery clips (gold plated) were used to

achieve electrical contact at each end of the specimen during heating.

A thermocouple pressed in contact with the underside of the specimen

was used to determine the test temperature. The propellent gas -particle

mixture was also heated. After injection of abrasive particles, the

mixture passed through an eight foot length of 1.6 mm inside diameter

stainless steel tubing that was heated by the passage of up to 60 A ac

current along its length. The gas-abrasive particle mixture was

discharged through a right angle tungsten carbide nozzle, 0.5 mm inside

diameter. The exit gas temperature was adjusted so that the specimen

temperature did not change during the test although it may have been as

low as 300°C at high flow rates when the specimen was maintained at

500°C. The propellent gas used in the tests reported here was 99.9%

CO2. The exposure time during each test was 2 minutes. Table 1 lists

some of the characteristics of this test apparatus.

Table 1

Range of Operating Parameters for Roberts Erosion Unit

Gas: C02,02,CO, mixtures

Particle sizes: 5 to 50 ym (0.5 mm nozzle)

5 to 150 ym (1.25 mm nozzle)

Gas Pressure: 20-70 psig (0.14 - 0.49 MPa)

Particle velocity: 10-60-m/s

Solids concentration: 0.5 to 3 g/1

2 Particle flux: 0.5 to 3 g/cm -s Specimen tenperature : ambient to 500°C+

ItRoberts Jet Abrader, Kameras Instruments. This instrument is identified only for the purpose of adequately specifying the experimental

procedure used.
The second erosion system has been described previously [12] and

permitted test temperatures of 1000°C to be achieved. Briefly, a

propane -oxygen-air burner was used to direct a stream of hot combustion

gases containing entrained abrasive particles down a 41an tube to impact

on the specimen. The stream was approximately 2 cm in diameter. By

changing the oxygen and propane flows, the composition of the gases

impinging on the specimen could be varied. When oxygen was supplied in

excess of the amount needed for complete combustion, an atmosphere composed of N^, and was produced. When excess propane was

introduced, CO, and hydrocarbons were obtained in addition to the

above gases. Test times were usually 60 minutes. Table 2 describes

the operating features of this unit.

Table 2

Range of Operating Parameters for High Temperature Erosion Unit

Gas: Combustion gases; air

Particles: ^'^2^'5'

Particle sizes: 50-200 ym

Particle velocity: 10-90 m/s

Solids concentration: 0.005 to 0.02 g/1

2 Particle flux: 0.04 g/cm -s Specimen temperature: ambient to 1000°C

Table 3

Parameters of Abrasive Particles Used in Erosion Tests

Type Size Hardness

(ym) (HK@25°C)

Sic 150 2500

AI2O3 5 2100

AI2O3 50 2100

5-50 820

F-Pumice 5-100 560

4F-Pumice 5-50 560

The abrasives used in the tests reported here are listed in Table 3.

Room temperature hardness values are listed. The ^^2^3 abrasives are

metallographic polishing grade material having a narrow size distribution. A collection of the 5ym Al20_ particles is shown in Fig. 2. The

particles passed only once through the system and were then discarded.

The particle velocity was measured using the rotating disk, time-of1U7
flight method [13]. Velocity measurements were conducted at the test

temperatures

.

Weight loss values were determined by direct weighing after exposure

and cleaning. Microscopic inspection of the surface indicated whether

particle adhesion to the specimen was significant. If so, attempts

were made to mechanically remove the adherent particles by light brushing. Since scale formation occurred at elevated temperatures, it was

difficult to remove all adherent abrasive and yet not affect surface

scale. Dimensional measurements of erosion crater depth and of specimen

thickness loss were made using microscopic or micrometer methods with a

precision of the order of ±1 to 10 ym depending on surface roughness.

Examination of the eroded surfaces was conducted using optical and

scanning electron microscope (SEM) methods.

Results

Studies at 25°C and 500°C: Examples of isolated particle impacts are

shown in Fig. 3 after a low flux exposure of an SAE 52100 steel specimen. The rim of each erosion crater consists of exposed material that

has been deformed plastically and which is susceptible to removal on

subsequent particle inpacts. That material is also more susceptible

to attack in a chemically reactive environment. Measurements have been

conducted at room temperature using the modified Roberts unit with

different abrasive particle velocities. Relative weight loss and penetration measurements on 304 stainless steel are shown in Fig. 4 for 90°

(normal) incidence, using two sizes of ^^2^z P^^^i^-'-^^* erosion

loss depends on the velocity raised to about the 2.8 power in these

tests. In general, we find that erosion is proportional to velocity in

the range of v to v at room temperature. A greater erosion loss is

seen here for the larger particles, 50ym ^^2^z' comparison between

weight loss and penetration distance is usually complicated by such

factors as erosion beam geometry changes when the abrasive type and size

are changed. It is preferable to use the same erosion measure when

comparing different metals.

The relative weight loss as a function of angle of attack a, the angle

between the specimen surface and the incident particle stream, has been

determined for 304 stainless steel at both 25°C and 500°C. The particle

flow and velocity were maintained constant as the specimens were exposed

at different angles to the particle stream. At 25°C a peak erosion loss

occurs at about 20° followed by a gradual decrease as the angle is

increased up to 90°. The angle dependence of erosion at 500°C is different. The low angle peak occurs at about 10°, followed by a rapid

decrease and then little change occurs in the range 40-70°. The loss

appears to increase again as 90° impingement is approached. At 500°C

oxidation is more rapid than at room temperature, hence, the incident

abrasive particles experience a different surface condition. The

increased relative loss at 90° may be connected with the known erosion

characteristics of brittle materials where the peak loss occurs at

ihQ
normal incidence. The oxide film or scale probably behaves in a more

brittle manner than the ductile underlying metal.

A group of eight different alloys have been examined at 25°C and 500°C

using this apparatus. Results on the erosion loss of the alloys using

two different sizes of Al20^ particles are shown in Table 4. The particle velocity was 30 m/s at 45° angle of attack using propellent.

Table 4

Erosion Measurements on Alloys Using Two Sizes of

Al^O^ Particles at 30 m/s and 45° Incidence

Wt. Loss(mg)/Wt.Abr. (g) Penetration(ym)/Wt .Abr. (g)

Alloy

Type

25°C 500°C 25°C 500°C

5 ym 50 ym 5 ym 50 ym 5 ym 50 ym 5 ym 50 ym

18Ni-250MS 0 08 0, 12 0. 04 0, 95 10 9 0 5 16

AISI 446 0. 05 0, 05 0 01 0. 20 10 6 0 6 11

AISI 304 0 05 0. 47 0 02 0. 26 7 26 0 2 12

AISI 316 0 04 0. 10 0 01 0. 21 7 9 0 8 13

AISI 310 0 03 0. 09 0. 02 0. 20 5 9 0 8 13

Incoloy 800 0 06 0. 32 0 01 0. 26 8 20 0 4 18

Inconel 601 0. 06 0. 30 <0. 01 0, 19 8 20 0 4 14

Inconel 671 0 02 0. 11 0. 01 0. 15 4 9 0 4 13

Both relative weight loss and penetration are shown. It is clear that

erosion increases significantly with particle size at both temperatures

and for all alloys. This size effect is particularly large for the

500°C tests where a decreased erosion loss is seen for all alloys for

the 5 ym particles (relative to 25°C) . Apparently the developing oxide

scale on the surface offers significant protection but only for the

small particle size. The data at 500°C using 50 ym size particles

varies among the alloys in comparison with the 25°C results. At 500°C

the alloys having larger chromium content in general show the least

erosion loss (although exceptions are present). Oxide thicknesses

measured on specimen cross sections after testing at 500°C for 2 minutes

ranged from about 2ym down to less than 0.5 ym, depending on the alloy.

More data needs to be acquired at other exposure conditions of velocity,

particle size, and environment before definitive conclusions can be

reached concerning relative material erosion rates.

A comparison between the results obtained with different abrasives is

shown in Table 5. The data refer to 304 stainless steel in air at

lh9
Table 5

Erosion Measurements on 304 Stainless Steel Using Different

Abrasives at 30 m/s and 45° Incidence

Wt. Loss (mg)/ Penetration (ym)/

Wt. Abr. (g) Wt. Abr. (g)

Abrasive 25°C 500°C 25°C 500°C

(Size)

AI2O2 0.5 0.2 7 0.2

(5 ym)

Al^O^ 0.47 0.26 26 12

(50 ym)

Pumice 4F 0.21 0.04 29 2.7

(5-50 ym)

Pumice F 0.10 0.03 8 1.7

(5-100 ym)

Silica 0.50 0.21 45 12

(5-50 ym)

30 m/s particle velocity at two temperatures, 25°C and 500°C. The increased erosion loss for 50 ym ^^2^], ^^l^tive to 5 ym ^^2^2) P^^^i^^^^

is apparent. The two grades of pumice show somewhat reduced losses

relative to 50 ym Al20_ that are probably associated with the reduced

hardness value. However, a detailed study of these and other data shows

that factors other than abrasive hardness are significant. These

include "cutting efficiency" at elevated temperatures, tendency to fracture, hardness at temperature, etc. Such details can only by understood

as a result of comprehensive studies of the various abrasives. Another

relevant abrasive characteristic is the tendency for certain abrasives

to sinter to the eroded surface and hence offer protection.

Studies of the effect of surface hardness of the metal on erosion resistance are underway. The results of one series of tests are shown in

Fig. 5 using SiO^ abrasive and type 18Ni-250MS steel hardened to different levels. Relatively little effect on erosion rate is seen as the

metal hardness varies; that observation has been reported previously by

others [14].

Studies at 1000°C : Experiments conducted in the second erosion system

have used either 150 ym size SiC abrasive or 50 ym ^^2^'^ particles.

Two different types of experiments were conducted. In one, multiple

alloy specimen packages were used in order to obtain data on relative

erosion for the alloys. In the other, a single alloy specimen was used

for each test. Figure 6 shows an exanple of a multiple alloy specimen

package after exposure in the test unit at 1000°C for 60 minutes using

150
150 ym SiC particles at a velocity of 50 m/s. Excess oxygen conditions

were maintained during the test. Each specimen in the package was 0.5

mm thick and was fabricated to have two surfaces exposed to the particle

stream at angles of 90° and 45°. Fiducial marks were placed on each

specimen surface in order to measure the dimensional loss after testing

One other edge, not exposed to the abrasive particles but exposed to the

heated atmosphere, provided information on the oxidation process. While

this specimen design provides an opportunity for obtaining relative data

between the alloy samples in the same atmosphere, there can be interferences between neighboring specimens in the package, particularly if the

erosion rates differ greatly. In Fig. 6 the specimens in Inconel 601,

671 and 310 stainless steel exhibit the least erosion. On cooling to

room temperature the oxide scale spalled from the 304 stainless steel

specimen. Little or no spalling occurred on the other alloys.

Erosion data obtained from two tests using the multiple specimen package

under different environmental conditions are shown in Table 6.

Table 6

Erosion Measurements on Alloys at 1020°C in Combustion

Gases at Approximately 55 m/s Using 150 ym SiC Particles

Equivalent Wt. Loss (mg)/Wt. Abrasive (g)

Excess Oxygen Excess Propane

Alloy

Type

90° 45° 90° 45°

AISI 446 0 41 0 35 0 73 1 1

AISI 304 0 59 0 37 1 6 1 5

AISI 316 1 2 1 3

AISI 310 0 32 0 28 0 58 0 64

Incoloy 800 0 42 0 32 0. 56 0 64

Inconel 601 0. 29 0 24 0, 23 0. 49

Inconel 671 0 26 0 28 0. 15 0. 25

1. Typical Analysis: 02=13%, 00^=10%, n^=64%, H^0=13°^

2. Typical Analysis: H2=8%, C0=12%, H20=17%, C02=5%

N2=52%, Other=6l.

Examination of the results in the excess oxygen atmosphere indicate a

small difference between the 45° and 90° surface erosion losses. However, under excess propane combustion conditions a greater difference

develops between the erosion rates at these two angles. The increased

loss at 45° associated with the ductile behavior is clear under excess

propane conditions. The difference in erosion rate among the different

metals is also more apparent under those conditions. The most resistant

151
alloys appear to be those containing larger chromium concentrations.

That same characteristic appears to apply in more strongly oxidizing atmospheres. An example o£ the surface conditions that develop at 1000°

C

after erosion is shown in Fig. 7a for 310 stainless steel exposed under

excess oxygen conditions. Much roughening due to impact damage is evident on the surface and some abrasive particles (or fragments) are seen

imbedded in the specimen. A cross section through this specimen is shown

in Fig. 7b and indicates the oxide film present.

Summary

1. Two sets of test apparatus have been developed and applied to erosion

measurements on metals in the temperature range of 25°C to 1000°C. The

atmosphere, particle size and velocity, specimen orientation and other

significant variables can be controlled.

2. Significant effects on the erosion rates of the metals studied are

attributed to the oxide film or scale that forms on the surface. The

chromium content of the alloy is one important parameter.

3. Abrasive hardness is a significant factor in erosion rate although

other abrasive characteristics may be equally important. Hardness

for a given alloy may not be an important parameter.

4. The maximum rate of erosion occurs at angles of 10° to 20° at temperatures up to 500° C, suggesting that cutting processes are a prominent

metal removal mechanism.

Acknowledgements

This study was partially supported by the Energy Research and Development

Administration/Fossil Energy and their support is gratefully aclonowledged. Many useful discussions concerning these studies were held with

5. Wiederhom, D. E. Roberts, E. Passaglia, and others at NBS to whom

the authors are indebted.

152
REFERENCES

1. Neilson, J. H. and Gilchrist, A., "Erosion by a Stream of Solid

Particles," Wear, Vol. 11, 1968, pp. 111-122.

2. Goodwin, J. E. , Sage, W. , and Tilly, G. P., "Study of Erosion by

Solid Particles," Proc. Inst. Mech. Engrs. (London), Vol. 184, 1969,

pp. 279-292.

3. Kleis, I. R. , "Problems der Bestimmung des Straheverscheisses bei

Metallen," Wear, Vol., 13, 199 (1969).

4. Sheldon, G. L., "Similarities and Differences in the Erosion Behavior

of Materials," Trans. ASME, Vol. 92, 1970, pp. 619-626.

5. Finnie, I., "Some Observations on the Erosion of Ductile Metals,"

Wear, Vol. 19, 1972, p. 81-90.

6. Tilly, G. P., "A Two Stage Mechanism of Ductile Erosion," Wear,

Vol. 23, 1973, pp. 87-96.

7. Tilly, G. P., "Erosion Caused by Airborne Particles," Wear, Vol. 14,

1969, pp. 63-79.

8. Smeltzer, C. E., Gulden, M. E. , and Compton, W. A., "Mechanism of

Metal Removal by Impacting Dust Particles," Trans. ASME, Vol. 92^,

1970, pp. 639-654.

9. "Workshop on Materials Problems and Research Opportunities in Coal

Conversion: Conclusions and Recommendations," Staehle, R. W.

,

Director, Ohio State University, April 16, 1974.

10. Hutchings, I. M. and Winter, R. E., "Particle Erosion of Ductile

Metals: A Mechanism of Material Removal," Wear, Vol. 27^, 1974,

pp. 121-128.

11. Roberts, A. G., "Improved NBS Abrasive Jet Method for Measuring

Abrasion Resistance of Coatings," ASTM Bulletin No. 244, 1960,

pp. 48-51.

12. Wiederhom, S. M. and Roberts, D. E., "A Technique to Investigate

High Temperature Erosion of Refractories," Bull. Am. Ceram, Soc.

,

Vol. 55, 1976, pp. 185-189.

13. Ruff, A. W. and Ives L. K. , "Measurement of Solid Particle Velocity

in Erosive Wear," Wear, Vol. 35, 1975, pp. 195-199.

14. Finnie, I., Wolak, J., and Kabil, Y. , "Erosion of Metals by Solid

Particles," Journal of Materials, Vol. No. 3. 1967, pp. 682-700.

155
Fig. 1 Schematic representation of

the modified Roberts erosion apparatus.
— 2|ni

I .^^,y

^

Fig. 3 Erosion impact craters on steel surface.

o> E — 0

a>

if) >

•& inO

_i

<

We

.01 -

3U4 SS

5 g/min

90° angle

25°C, COj

O ^5 um AUO • a50 vm AT^i

_L _L

20 30 40 60

Velocity (m/s)

100

10

c

CL

>o<

80 100

Fig. 4 Velocity dependence of erosion

loss at 25°C for two particle sizes.

155
E

5

>o

<

1.5

0.5 -

250 MS steel

v= 17 m/s

5 g/min

25° C.

5-50um

CO,

Wf. Loss

Pen.

35 40 45

Hardness

50

(HRC)

200 I,

150 I

o

100

- 50

c

CL

2>

>o

<

55

Fig. 5 Variation o£ erosion loss for different

hardness levels in type 18Ni-250MS steel.

Fig. 6 Multiple alloy specimen package after erosion test

at 1000°C. Two exposed surfaces 45° and 90°, are shoMi.

156
Fig. 7

Surface of 310 stainless steel after erosion test at 1010°C.

Cross section of specimen showing oxide film and erosion craters.

157
DISCUSSION

I. G. Wright, Battelle Columbus Laboratories : Can you tell me the size

range of the particles used in the jet abraser test?

L. K. Ives : These were commercial abrasive materials used for

polishing. I believe the size range was fairly narrow, but I don't

have data on the exact size range.

I. G. Wright : What was the most convenient method you found for

measuring the depth of penetration?

L. K. Ives : We simply focused a measuring microscope on the bottom

of the depression and then on the upper surface and determined the

difference.

158
HIGH-TEMPERATURE CORROSION

K. Natesan

Materials Science Division

Argonne National Laboratory

Argonne, Illinois 60439

Abstract: Materials considered for application in the high-temperature

gaseous environments that are present in various coal-gasification

processes must possess good structural integrity at elevated temperatures and inherent resistance to the corrosive atmospheres. A

thermodynamic approach has been developed to characterize the gas

environment in different pilot plant coal-gasification processes.

The analysis is used to examine the thermodynamic stability of ironand nickel-base alloys in these process environments. The results

show that the sulfur and oxygen potentials in all processes are in a

region where chromium oxide will be thermodynamically stable. In the

absence of a continuous oxide layer, sulfidation of the alloys is expected which can lead to severe corrosion rates, particularly when

liquid nickel sulfides are formed. It is concluded that a protective

Cr203 layer is essential for an effective application of these alloys

in coal-conversion processes.

INTRODUCTION

Much of our knowledge concerning the high temperature corrosion behavior of commercial iron- and nickel-base alloys is derived from

studies of high-purity metals and simple alloys in well-characterized

binary and ternary gas mixtures. Even though the results from the

simple experiments aid in the establishment of the relative corrosion

behavior of different metals, the usefulness of such information in

the prediction of the corrosion rates of multicomponent alloys in

complex gas environments is very limited. Studies on fundamental

processes such as oxidation, carburization, sulfidation, and nitridation are generally conducted over a relatively short time period with

the objectives to identify the most stable phases formed and to determine the mechanism and rate-limiting step for the process. Thermodynamic considerations have been used to rationalize the experimental

observations in terms of the reaction potential of the gas species , at the temperature and pressure of interest. Gulbransen and Jansson^

have reviewed the thermodynamic analysis of product phase stability

for metals in 2 component reactive gases, e.g., SO2 + SO3, H2 + H2S,

CO + CO2, and H2 + H2O, by means of what is commonly known as Ellingham

diagrams. These diagrams depict the stability of the condensed phases

for a given metal as a function of thermodynamic activities of the two

reactive gaseous components. A similar approach for the evaluation of

159
the corrosion behavior of metals in multicomponent gas mixtures is

usually limited to the determination of stable compound (s) that are

formed as a result of exposure of the metal to the gas mixture.

The combustion gas composition in coal-conversion processes generally

depends on the type of process and feed stock analysis in addition to

operating temperature and pressure. The gas mixtures usually consist

of CO, CO2, H2, H2O, CH4, H2S, and NH3; as a result, the simultaneous

presence of reactive elements such as 0, C, H, N, and S needs to be

considered in the evaluation of the material behavior in the gas environment. The room- temperature compositions of the gas mixtures

that are anticipated in different pilot plant processes are

listed in Table I. (2) ^he compositions given are based on the use of

low-sulfur coal in the processes. Also given in the table is the composition selected by the Metals Properties Council (MPC) for use in

the experimental research programs for the corrosion evaluation. C-^)

It is evident that the processes can have a wide variation in the gas

composition and therefore, materials performance in different processes

is not expected to be the same even for identical conditions of temperature and pressure. It is also evident that in order to cover the

entire spectrum of gas composition variation, the experimental program

will be time consuming and expensive, especially if long-term corrosion rates under high pressure conditions are required.

GAS COMPOSITION CHARACTERIZATION

When studying reaction kinetics or reaction equilibria between complex

gases and condensed phases, the chemical potential of the reacting

elements C, 0, H, and S needs to be established and their competing

interactions with the alloys must be considered. For this purpose,

a computer program was developed by which the equilibrium gas partial

pressures could be evaluated at elevated temperatures for a given roomtemperature composition. For a gas system that consists of CO, CO2,

H2, H2O, CH^, H2S, and NH3, the following gas equilibria may be written:

(1)

C + O2 = CO2 (2)

C + = CH (3)

C + ^S^ = CS (A)

c + S^ = cs^ (5)

160
CO

1o

Xi

4Jrt

!3

COQi

CO

CO

(UO

o

u

P-i c

o

•H

4J

COO

•H

M-l •H

CO

tabO

1 iH

cd o

O o

CLJ CD

CDo

•Hu

CO > COo

•H

COo

•H

4—

i

•H

COo

so

CO

to

(U 4J

CO

CO M

CU tH

CO H

CU t3

J •H

CU iH

r-t CO CO

CD U 00

U

CO o

PQ

Uni

CNl CO CN cn

CM CO

t o

o

CN in o

ON CN CN

^£5 cn

COo

CO C30 CN

uO

CN CN

in

CN

o o

o o O

o

o

o

o

CO

o o

o o O CO

o

o

CO o

o

o o

O LO

CM

•H r-v

CD CNO CN-vfOC/3 fO&o IXlUOIXl CNCNW^--'

o cj) ffl tn s PL, H

l6l
(6)

H2 + "2^2" ^^2^ (7)

2^2 = ' (0)

(9)

¥2 + °2

= (10)

1 3

2^2 + 2«2

= (11)

CU + -2^2 COS (.12)

+|h2= NH3 (13)

where K^,... are equilibrium constants, a^ is carbon activity, and Vco*

Pc02' • '^1^^ the partial pressures of CO, C02,...etc. The equilibrium

constants for the reactions (1) through (13) are given by

K. = exp (-AF^/RT), for j = 1 through 13 (14)

where

R = gas constant, 1.987 cal/mole °K

T = absolute temperature,

and

AFj = free-energy change for the j th reaction, cal/mole.

In a given complex gas mixture, the total number of gram-atoms of

carbon (EC), sulfur (ES) , oxygen (EO) , hydrogen (EH), and nitrogen

(EN), were obtained from the sum of the gas species present.

For the initial mixture:

1 1

162
i i

(M/iH)/iv)/ivr'(s), EH. = 2 ''''

1

1 X

i

l\ ' (h^hJ (19)

1

where n is the number of moles of the gas indicated by the subscript.

For the mixture at elevated temperature:

'^f = \0, ^ \0 + ^CH, + \S ^ ^CS, \0S ^20)

2 4 2

TM£ - ^\ ^ \o ^"co^ \o + "so - ^"soj ^"sOj ^ "cos

"so,"'" "cos (23)

If the total number of moles of the gas species CO, CO2, CH^ , S,

•••etc., is denoted by Zn, the partial pressure of any species j

is given by

n. P. = P (25)

J In

where P is the total pressure in the system. Since the respective

values of EC, EO, EH, ES, and EN in the initial and final states are

the same, it can be written

EC.if= EC^ (26)

163
zo. = zo

1 (27)

ZH^ = ZH^ (28)

ZS_j^ = ZS^ (29)

ZN^ = ZN^ (30)

P = Zp^ (j ^ CO, C02,...etc.) (31)

Equations 26-30 along with the total pressure relationship given by

equation 31 comprise a set of nonlinear equations that were simultaneously solved with a digital computer to obtain the gas compositions

at elevated temperatures. Table II lists the values of p02> PS2> ^^'^ carbon activity a^,, calculated for the gas mixtures given in Table I

for different coal-gasification processes. The results show that at

a temperature of 1000°C, the oxygen partial pressures range from

7.2 X lO"-'-''' to 4.5 X lO"-*-^ atm and sulfur pressures from 8.4 x lO"-*-^ to

6.1 x 10"^ atm in these processes. The results also indicate that the

MFC selected gas composition (with 0.1% H2S) is approximately the same

as that anticipated in the Synthane coal-conversion process.

The sulfur partial pressures calculated in these processes can be used

to evaluate the sulfidation behavior of materials in the gas environment.

In the absence of a protective oxide, the calculated sulfur pressures

(or PH2S/PH2) different processes can be superimposed on the

isocorrosion-rate curves for austenitic stainless steels reported in

the literature. (3) Such a comparison is shown in Fig. 1. The values

of PH2S/PH2 ^^-^ processes except C02-Acceptor are in the range

1.8 x 10~3 to 4.6 X 10""3 and are insensitive to temperature. Under

these conditions, the steel should corrode probably at a rate of 20

to 100 mil per year at a temperature of 800°C. The PH2S/pH2 ^^tio

calculated for the C02-Acceptor process is in the range 4 x 10"^ to

6 X 10~^ and this should result in a negligible sulfidation attack of

the steels. At a temperature of 980°C ('^^1800°F) , the metal protection

by the formation of Cr203 layer on the steel surface is minimized due

to formation and subsequent vaporization of Cr03. Under these conditions, the MFC program at IIT Research Institute reported a sulfur

corrosion rate of '^^125 mils/1000 h for Types 304 and 316 stainless

steel which is in agreement with the values predicted from this analysis.

CORROSION BEHAVIOR IN FROCESS-GAS ENVIRONMENT

The oxidation behavior of Fe-Cr and Ni-Cr alloys show that Cr203 will

be a thermodynamically stable oxide at all chromium concentrations in

the alloy. Under these conditions, the simultaneous presence of O2

and S2 should be considered in evaluating the alloy behavior. Figures

16^
i 00 rH CM in CM

•H tH CM ON 0 rH Q CO 0 0 0 0 0 0 c

•H

COcO

•H

4-t •HW in in CO ro in O CJ rH rH rH rH rH rH

CI. 0 1 1 1 1 1 1 a 0 0 0 0 o • 0 e rH rH rH rH u C/D u O PM CO X X X X X

CO

o II CO CM CM rH <r CO

CD

H

00 <r CM rH <r

o CU iw fa

CO

u

iH CM CM CM C^ rH CM

cC CM CM CM CM CM CM

•H iH 1 1 1 1 1 1 •U 3 CM g 0 0 0 0 0 0 C CO 0 u iH iH rH rH rH rH

0) 1 PL, CO

4-1

XX

X

X

oo

hJ <r 00 vO CXD in CM

d 4:: CM <!• rH o •u •H&

cd

C_) CO

(U rH <f vj- <t CM CO

13 CO

u iH 0 0 0 0 C CO CO 0 0 0 0 0 0

CO 0)0 0 0 0 0 0 0 0 3

i«

iH 0

•H

U 0 CM 0 0 0

•u 0 rH rH rH C3^ rH

CO 0 1 1 1 1 1 1 C 0 0 0 0

cu •H CM

G rH rH rH rH rH rH

M-l r-\ •H P-i CO

X

X

XX

CO II

o CO CM 00 0 rH rH

bO

H

u 1 iH CX3 rH CM o rH

CO0

CO CJ

cu

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165
2 and 3 show the Ellingham diagrams for Fe-Cr-O-S and Ni-Cr-O-S

systems at 1200°K ('^^1700°F) along with the calculated partial pressures

of oxygen and sulfur in different coal-conversion processes. The open

symbols in these figures are the calculated pressures for the gas

compositions listed in Table I and the closed symbols are for a

concentration of 1.0 vol. % in the process gas environment. The

analysis shows that chromium oxide is thermodynamically stable in

Ni-base alloys and that the oxides in Fe-base alloys will be a mixture

of iron and chromium oxides. The effect of an increase in the sulfur

concentration in the coal feedstock (Appalachian coal in contrast

to Western coals) is to shift the process gas compositions in the

direction of increasing PS2« Under such conditions, there exists

a distinct possibility for the formation of Fe- and Ni-sulfides. Since

the sulfide layers are not protective in nature and the growth rates

of sulfide layers are orders of magnitude larger than the oxide layers,

the corrosion rates of these alloys may become prohibitively large.

Furthermore, in the case of Ni-Cr alloys, an increase in sulfur potential in the gas environment can lead to formation of Ni sulfides that

are liquids at this temperature and can result in catastrophic corrosion rates. Therefore, an effective utilization of Fe-Cr and Ni-Cr

alloys requires that a protective Cr203 layer be established upon

exposure of the materials to coal-gasification environment. Even

though Cr203 is thermodynamically stable at all chromium concentrations

in Ni-Cr alloys, a large chromium content in the alloy is required

for the oxidation process to change from internal oxidation to formation

of an external protective layer. The chromium concentration that is

required for the external scale formation is a function of temperature

and oxygen potential in the environment and these functional relationships are yet to be established. It has been reported that a value

of 20-25 wt % Cr in the alloy is necessary for the application of

Ni-Cr alloy at 900°C and 0.1 atm oxygen pressure.

Extensive high-temperature corrosion studies are being conducted at

Argonne National Laboratory to evaluate the behavior of commercial

iron- and nickel-base alloys in a complex multicomponent gas environment with a wide variation in composition. Experiments are also planned

on high-purity Fe-Cr-Ni alloys in ternary and multicomponent gas

environments to understand the corrosion mechanisms under different

conditions. Microstructural evaluations and thermal cycling effects

form a large part of our investigations. The effect of the corrosiveerosive environment on the stability of the protective layers will

also be evaluated.

REFERENCES

1. E. A. Gulbransen and S. A. Jansson, "High-Temperature Metallic

Corrosion of Sulfur and its Compounds," ed. Z. A. Foroulis, The

Electrochemical Society, New York, 1970, p. 3.

166
A. J. MacNab, Workshop on Materials Problems and Research Opportunities in Coal Conversion, Vol. Ill, Ohio State University,

Columbus, Ohio, April 16-18, 1974, p. 33.

E. B. Backensto and J. W. Sjoberg, NACE Corrosion, Vol. 15, p. 125

1959.

High-Temperature Corrosion-Erosion Program, Illinois Institute of

Technology Research Institute, Chicago, Illinois, 1975-1976.

C. S. Giggins and F. S. Pet tit, Trans. Met. Soc. AIME, 245,

1969, p. 2495.

167
TEMPERATURE ."F

, 400 600 800 1000 1200 1400 1600 1800

I tr ~i 1 1 1 1 1 i-i

icr^ I I I

I

I I I I I 200 400 600 800 1000

TEMPERATURE ,*»C

Fig. 1. Superimpositlon of Sulfur Potentials in Pilot-plant Processes on Isocorrosion-rate Curves for Austenitic Stainless

Steel.

168
log Pq^^o^^^)

I200"K

Fe-Cr-O-S

LOW SULFUR 1% H2S

o

0

o

HYGAS

CO2 ACCEPTOR

SYNTHANE

BATTELLE-UC

BIGAS

MPC

Fig. 2. Thermochemistry of Fe-Cr-O-S System at 1200°K. The gas

environments in pilot-plant processes are indicated by different

symbols.

169
-44 -40 -36 -32 -28 -24 - 20 -16 -12 - 8 - 4 0

0

-5

E

-'0

cvj-15

o> _20

-25

30

Ni SULFIDES (C)

Cr SULFIDES

\ acr =0.

PURE Cr1200 K

Ni-Cr-O-S

LOW SULFUR l7o H2S

o

V

0

o

HYGAS

CO2 ACCEPTOR

SYNTHANE

BATTELLE-UC

BIGAS

MPC

Fig. 3. Thermochemistry of Ni-Cr-O-S System at 1200°K. The gas

environments in pilot-plant processes are indicated by different

S3mibols

.

170
DISCUSSION

A. J. Mac Nab, C. F. Braun and Company : I would like to compliment Nat

on this work. This kind of analysis is badly needed. The fact that

he has suggested getting away from just the Y-direction study and going

in the X-axis is also a fine approach. As you rightly pointed out, we

are working with only one gas composition and that may not be too

meaningful. There are different gases, different types of coal, and

different operating conditions, all of which are going to affect gas

composition. Would it not be possible to complement what you are doing

with a process-type study to pick out gas compositions that could occur

in commercial units. It would be nice, if possible, to narrow down the

number of different compositions. The charts showing corrosion rates

and the thermodynamic cutoff data with the gas compositions from the

different plants looked like the data published by Backensto. They are

a little controversial at this time in regard to the validity of the

corrosion rates. There are now considerably lower values for sulfiding

rates from the petroleum industry.

K. Natesan : I don't mean to indicate that that is absolute data. The

one thing I wanted to point out was that with 0.1% and 1% H2S, the

C type 304 and 316 stainless steels measured 125 mils corrosion in 1000

hours. That is right in the same ball park as the data show at 1500°F.

The curves may be shifted a little either way, but the approach is

there. How effectively it is used depends on the feedback from the

plant to the researchers.

171
DEVELOPMENT OF NONDESTRUCTIVE EVALUATION

METHODS FOR COAL-CONVERSION SYSTEMS*

W. A. Ellingson, G. C Stanton, and N. P. Lapinski

Materials Science Division

Argonne National Laboratory

Argonne, Illinois 60439

Abstract: Coal-conversion processes require the handling and containment of high pressure, high temperature, corrosive and erosive gases and

liquids often containing particulate loadings. These severe environments cause materials failures that reduce successful and long-time

operation of coal-conversion systems. The determination of the material

and component response and development calls for proper nondestructive

examination methods, equipment, and techniques. This paper briefly

describes the nondestructive development efforts in high-temperature,

wall-thickness measurements for in situ erosion data, passive infrared imaging applications for thermal profiles? gamma radiographic applications for crack and erosion detection and acoustic methods for

failure prediction.

Key v7ords: Nondestructive evaluation; coal gasification; ultrasonic

inspection; infrared imaging; refractory liners.

Nondestructive evaluation (NDE) methods for coal-conversion systems must

of necessity encompass a broad spectrum of applicable technology.

Transfer lines, for example, may be refractory lined or unlined, depending upon the requirements of the location, i.e., composition, temperature, and pressure of the flow. Preoperational inspection and online monitoring systems that measure the material response of materials

systems require different nondestructive examination approaches. In

nonref ractory-lined transfer lines, ultrasonic pulse-echo systems can be

developed to measure wall thinning caused by erosion/corrosion at high

temperature. However, the porosity of a refractory, acoustic impedance

of a refractory/steel interface, and poor acoustic transfer properties

do not allow ultrasonic pulse-echo methods to be used on refractorylined components typical of coal-conversion process systems. Gamma

radiography or passive infrared imaging with appropriate thermal models

is necessary to determine the material response and/or structural integrity of refractory-layered structures. In addition, some components

such as the lock-hopper or pressure let-down valves have a high initial

cost and are time consuming to replace. Nondestructive evaluation

172
methods to assist in determining the optimum time for replacement of

such components are of value. The broad-based ERDA/FE sponsored nondestructive evaluation development program at Argonne National Laboratory is designed to address the above areas.

The ultrasonic monitoring of the erosion of high-temperature steel

transfer lines requires a waveguide design that must consider: (a)

signal-to-noise ratio, (b) energy transfer, (c) material attenuation,

(d) appropriate interface geometry (including attachment mechanism)

,

and (e) a satisfactory cooling mechanism. These considerations have

led to a delay-line design that will shortly be employed on several

coal-conversion pilot plants. A schematic of the delay-line design and

associated temperature decay curve is shown in Fig. 1. Ultrasonic

thickness measurements require a reflection at the inner and outer

wall surfaces to determine the time of flight of the pulse and hence

the wall thickness. A typical amplitude decay of the back-wall reflection is shown in Fig. 2. This is a critical reflection because

part of the ultrasonic system is triggered by the back-wall amplitude,

and an unsatisfactory amplitude would cause the system to fail.

A complete material wall-thickness measurement system using this delayline design is being implemented to monitor real-time erosion of the

main coal feed line of the Synthane coal-gasification plant. Figure 3

shows the coal feed elbow and array of 31 transducers that will be

used to establish real-time erosion. A large number of transducers

are required on this initial system for a complete mapping of the

erosion pattern on this critical component. Clearly, such a large

number of transducer sites is not required in all applications, and

methods have been developed that will allow the ultrasonic delay line

to be attached to existing piping for in-place monitoring.

Gamma radiography has been shown to be capable of clearly visualizing

the bore of refractory-lined transfer lines. Figure 4 shows a doublewall gamma radiograph taken with ^ "^Cobalt and Eastman Kodak Type AA

film. The dark bore region is sharp, and thus time sequential images

could be used for erosion-rate measurements. Figure 5 is a schematic

diagram of the transfer line showing the refractory thickness and

bore diameter for the double-wall radiograph. The refractory in this

case is KAOTAB, which is a high-density cast-alumina refractory with

a density of ^150 Ib/ft^.

The high temperatures and high pressures of most gasification systems

have also demanded the use of refractory-lined pressure vessels. The

most common methods used to install refractories are gunning or

casting. The protective refractory lining is usually monolithic or

layered with low-density insulation covered by a high-density hot face.

These refractory-steel structures are used with or without watercooling jackets. Schematic diagrams of typical dry-wall and watercooled wall pressure vessel sections are shown in Figs. 6 and 7.

175
Thermal cycling and the resultant moisture condensation during start-up

and shutdown can cause degradation and cracking of the refractory.

This can result in sufficient refractory spalling to expose so that

the steel shell would be exposed to high temperature and pressure. The

thickness of the installed refractory and the uniformity of the refractory density is important for long duration runs. Gamma radiography

has been shown to be a viable method to not only locate cracks but

also to map refractory thickness variations. Figure 8 is a plot of

normalized radiographic film density as a function of refractory thickness for KAOTAB refractory (of uniform density) on a 3/4-in. steel

plate. The data were normalized by means of a steel step wedge and

the characteristic amplitude transmission-exposure (t-E) curve for

Eastman Kodak AA radiography film (see insert on Fig. 8). In the

linear range of the t-E curve, the density D can be related to the

exposure E as follows:

D = Y log E - D , (1)

where

D = photographic film density,

Y = slope of line curve,

n ^ '

E = exposure = IT,

I = intensity,

and

T = time of the exposure.

The results of the photographic density versus refractory thickness

were verified by a field application on the Battelle-Columbus coalgasification process development plant.

Additional work is being conducted on the use of remote thermal-sensing

and pattern-recognition techniques through the use of passive infrared

imaging systems to obtain thermal profiles on critical components.

Expansion bellows, necessary in long, high-temperature transfer lines,

are in dynamic states of design, and full field thermal mapping is

useful in determining design effectiveness, i.e., indicate particulate

buildup, erosion, or gas by-pass flows. Figure 9 shows the general

exterior geometry of an expansion bellows and a typical real-time

isothermographic image. Such images are being obtained by the use of
a commercially available AGA Model 750 portable infrared scanning

camera that produces a complete image in 40 ms . The use of patternrecognition methods by means of digital computers will be employed

to compare the thermal patterns generated by particle erosion.

Other work is also being conducted on acoustic emission as a means

of detecting crack initiation and propagation in refractory-layered

vessels

.

175
I 2 3 DISTANCE FROM PLATE

4

(IN.)

5- MHZ

6- MM DIAMETER

LONGITUDINAL WAVE TRANSDUCER

Fig. 1. Air-cooled Waveguide and Temperature Decay

Curve with Block Diagram of Instrumentation.

176
Fig. 3. Line Drawing of Coal Feei-line Replica.

Waveguides are axially staggered ±30° to cover a

60° cross-sectional sector.

177
T
TYPICAL GASIFIER REACTOR

WALL CROSS-SECTION

(AIR COOLED)

(b)

MONOLITHIC HIGH DENSITY

764 ALUMINA CASTABLE REFRACTORY MONEL

CLADDING

Fig. 6. Schematic Diagrams of Typical Dry-wall (Air

Cooled) Refractory-lined Pressure Vessels. (a) Twocomponent refractory and (b) monolithic refractory.

179
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180
Fig. 9. Infrared Thermal Profiling of Bellows Expansion Joint of Bellows Expansion Joint of CO2 Acceptor Coal-gasification Pilot Plant,

(a) Conventional photo of bellows expansion joint, (b) iso thermogram

image of bellows expansion joint, level at 199 °C, and (c) composite

thermal profile map of expansion joint.

181
DISCUSSION

E. R. Fuller, Jr., National Bureau of Standards : Are you planning to

use the acoustic emission spectrum analysis technique instead of ultrasonics to monitor erosion of the elbow joints?

W. A. Ellingson : We are planning to use this technique to monitor

erosion in the cyclone. One of the problems when mapping the cyclone

wall thickness is knowing whether the bore is concentric. An apparent

wall thinning may have been due to a nonconcentric bore rather than

erosion.

182
POTENTIAL MATERIALS PROBLEMS

IN COAL GASIFICATION SYSTEMS

A. M. Hall

Battelle

Columbus Laboratories

Columbus, Ohio 43201

Abstract: Potential problems with structural materials in those coal

gasification systems designed to produce a make gas for conversion to

pipeline quality gas are discussed. The following problem areas are

covered: corrosion and erosion/ corrosion; wear and abrasion; hydrogen

effects; creep and creep-rupture; temper embrittlement of steel; thermal fatigue; component design and manufacture; material quality; and

assembly of components and equipment. Both metallic and ceramic

materials are discussed in terms of these potential problem areas.

Key words: Abrasion; ceramics; coal gasification; component design;

corrosion; creep; creep-rupture; erosion/ corrosion; fracture toughness; hydrogen attack; hydrogen effects; hydrogen stress cracking;

material quality; metallic materials; refractories; stress raisers;

structural materials; temper embrittlement; thermal fatigue; wear;

welding

.

The objective of this presentation is to highlight structural materials

problems that are being, or may be, encountered in coal gasification

plants. Our interest, however, is not in all types of plants but is

directed entirely at those plants that are designed to use the advanced

processes currently under development to produce a synthesis gas suitable for conversion to pipeline quality gas.

These processes differ considerably among themselves as to chemistry,

operating conditions, and component and equipment design. Nonetheless, they have much in common and some general statements can be made

regarding materials and equipment problem areas. First, it is clear

that process conditions are unique and, in a number of process steps,

the environments experienced by the structural materials are extremely

severe. Again, equipment and component failures seldom are ascrlbable

exclusively to the material; they usually involve other factors such

as component design, operating conditions, component manufacture, and

equipment fabrication, or a combination thereof.

METALLIC MATERIALS: For convenience, we will separate problems involving metallic materials from those involving ceramics, and we will discuss them by phenomenological category starting with corrosion.

185
Corrosion and Erosion/Corrosion: No unusual or severe corrosion problems are to be expected in the handling, storage and preparation of

the coal to be consumed in the plant, unless unsuitable materials are

selected. For example, if an overzealous contractor constructed coal

pretreatment equipment of austenitic stainless steel instead of carbon

steel, he might invite chloride stress-corrosion cracking because

moisture would be present and coal contains chlorides.

The greatest opportunity for corrosion appears to be elevated-temperature attack of exposed penetrations in such equipment as gasifiers,

regenerators and combustors. The attack is likely to take the form of

oxidation, sulfidation, carburization or combinations thereof, depending on the composition of the environment. Whenever the atmosphere is

turbulent and contains particulate matter, the situation will be complicated by the added phenomenon of erosion which will work hand-inglove with corrosion to promote material deterioration. The problem

is one of material and/or coating selection coupled with design aspects aimed at reducing turbulence. Coatings to be considered in such

cases would be abrasion-resistant types capable of withstanding high

temperatures

.

The erosion factor probably becomes more pronounced in the case of the

exposed metallic components of valves for transfer lines and let-down

systems . These assemblies will handle streams heavily laden with particulates often at very high temperatures. Careful material selection

and clever value design are required to alleviate the likely problems.

Equipment for wet scrubbing and quenching of the product gas from the

gasifier constitutes another locale for potential corrosion problems,

the nature and severity of which will depend on the composition of the

gas and the materials of construction and perhaps on the design and

construction of the equipment. It could be stress-corrosion cracking,

pitting corrosion, crevice corrosion, general corrosion, or even galvanic corrosion.

Wear and Abrasion: Lines handling dry or slurried coal may be subject to wear and abrasion. The same holds for the valves used in

such lines, for the controlled-rate feed devices used to inject coal

into gasifiers and combustors, and for the pumps that handle slurries.

The ensuing problems should be resolvable by proper material selection,

component design, equipment selection, or alteration of operating

conditions

.

For example, as to equipment selection, plunger- and piston-type reciprocating pumps are preferred for handling slurries. Liquid-end parts

are quickly and easily replaced. Centrifugal pumps are impractical for

transporting slurries at high pressures because of the large number of

wear parts and close tolerances required.

181^
As to materials, standard gray cast-iron components may be unsatisfactory and white irons may be required; or, structural steels may have to

be replaced by abrasion-resistant (AR) grades. Again, ceramics or rubber may be superior to metallic materials or coatings for certain components .

Hydrogen Effects: Economic considerations strongly favor use of structural carbon or low-alloy steel for the principal structural elements

of the gasifier, such as the shell, heads, nozzles, and internal jackets or coils. However, during operation, the internal gaseous environment will gain access to the ID surfaces of these components either by

diffusing through the refractory lining or by penetrating cracks in the

refractory. Thus, to prevent corrosion of the steel by condensed vapors the temperature of the shell must be maintained above the dew

point of the process stream. At the same time, to avoid excessive

scaling, sulfidation, and degradation by hydrogen as well as loss in

strength, the shell should be held to a moderate temperature, i.e., in

the order of 600 F. The major contributors to hydrogen problems would

be the H2 and H2S in the internal atmosphere, while H2S would be the

sulfidizing reagent.

Of course, the steel shell may be internally coated with an epoxy or

other organic material to protect it from corrosion by condensates, or

it may be clad, lined, or overlaid with a corrosion-resistant alloy

such as stainless steel.

Superficially, it would appear that the situation regarding the steel

components is well in hand. However, even though these components' may

be coated or clad, hydrogen will be able to enter them at the temperatures and over the time periods they are expected to experience in

service. Moreover, the interaction of hydrogen and steel at high pressures in the temperature regime of 450 to 600 F or so is not well documented and is a matter of great concern because of the danger of unexpected catastrophic failures.

Problems resulting from dissolved hydrogen that could be encountered in

shell and duct components are: (1) loss in tensile ductility on cooldown to room temperature, (2) hydrogen stress cracking that may occur

on cooling to room temperature during a shutdown, (3) blistering, and

(4) hydrogen attack which results in decarburization with attendant

loss in strength and formation of internal fissures, cracks and sometimes blisters. In coal gasification the concern over degradation of

structural components by hydrogen is both with the effect of hydrogen

at temperature and, perhaps more importantly, with the events that

could occur on cooling down to room temperature during a shutdown.

These types of questions are now under investigation, but the area requires much more research than is now underway.

185
Other Phenomena: Creep-rupture failures, or failures caused by excessive creep without rupture, should not occur in load-carrying components under normal conditions. They would not be operating in the creep

regime. However, failure of a section of refractory lining in, for examle, a high-pressure gasifier undoubtedly would trigger these failure

mechanisms in the steel shell by exposing the metal to the high temperature of the internal environment. A way to reduce the potential damage is to coat the steel shell with temperature indicating paint, to

place thermocouples at strategic locations on the shell, or to monitor

the shell's temperature with a scanning infrared thermocouple, and

have water hoses available to cool the shell when a runaway overtemperaturing situation is indicated.

Carbon and low-alloy steels used in combustors, gasifiers, and regenerators may gradually become brittle during long-time service at

operating temperature. The petroleum industry has become concerned

about the problem of aging or temper embrittlement of chromiummolybdenum steels during service for long periods at intermediate temperatures. The industry uses this type of steel in many heavy wall

reactors where resistance to hydrogen attack and high elevated-temperature strength are required. Research on the phenomenon is in the

early stages.

Thermal fatigue is another problem that may arise. However, it is far

more likely to be encountered in process demonstration units than in

full-scale commercial operations because the former experience a great

many more start-ups and shut-downs than the latter. Thus, although

thermal fatigue failures are frustrating, their prevalence in process

demonstration units is not necessarily indicative of performance under

full-scale conditions.

CERAMIC MATERIALS: Coal-gasification processes currently being investigated will place severe demands on the refractory linings of gasifiers as well as those of combustors, regenerators, cyclones, and connecting piping. It is these materials that must withstand the brunt of

the corrosiveness, erosiveness, and general reactivity of the hot,

high-velocity, high-pressure, particulate-laden process gas stream.

The severest condition is considered to be in the gasifier.

The refractory problem is compounded by the fact that there are no

closely analogous applications. Thus, considerable extrapolation from

state-of-the-art experience is required to meet the coal-gasification

situation. The nearest analogs seem to be the secondary reformer in

the manufacture of ammonia, ethylene pyrolysis, blast furnaces for

production of iron, and the cyclonic boiler. These operations encompass various combinations of gas reactivity, gas velocity, erosion,

pressure, and temperature but none combine reducing conditions, high

pressures, high temperatures, high velocities, and erosion—the conditions that distinguish the gasifier environment. Therefore, many

186
questions arise with respect to the performance of refractories in the

unique and severe environment of the gasifier. It is clear that much

needs to be learned about the performance of refractories in coal gasification environments. The same goes for insulating materials. Some

specific problem areas are as follows:

(1) Chemical interaction between refractories and

the CO, H2, H2O, H2S, char, and unreacted coal

in the atmosphere

(2) Effect of hydrogen on the properties of insulating materials

(3) Erosion of refractories by steam and solids in

the atmosphere

(4) Effect of impurities on the properties of refractories and insulating materials operating

in reducing environments

(5) Spalling and disintegration of refractories

(6) Compatibility of refractories with coal ash,

including slagging, penetration of the refractory, and alteration of the refractory's

properties

(7) Effect of acid condensation on the integrity

of refractories and insulating materials

(8) Reliability of thermal-physical property data

for candidate refractory and insulating

materials

DESIGN, MANUFACTURE AND ASSEMBLY: As has been noted, intelligent and

innovative design can alleviate or even solve materials and equipment

performance problems. On the other hand, faulty design can do the opposite. For example, designing mechanical notches into a load-carrying structure is intolerable. Likewise, overdesign may be selfdefeating; for instance, increasing wall thickness may increase thermal gradients and hence, transient stresses. Again, a structure which

is to be assembled by welding should be so designed and not treated as

monolithic. Likewise, castings should be designed to take into account

the constraints of the casting process, rather than being designed according to concepts based on manufacture by forging or machining.

In the manufacture of critical components, steps should be taken to

insure that the quality of the material used is high enough to provide

adequate fracture toughness. In this regard, in structural steels.

187
important considerations include: minimum adequate carbon content;

low sulfur content; chemical homogeneity; low nonmetallic inclusion

count; and good quality surfaces.

Assembling components into a structure, especially a structure so massive and demanding as a full-scale pressurized gasifier, is a critically important activity. Such a vessel may be as much as 250 feet

high by 30 feet in diameter and weigh 3000 tons.

For the metallic components the job is accomplished principally by

welding. Careful planning and close supervision are required. Among

other things, every precaution must be taken to insure that assembly

operations do not promote structural failure. This means close attention to details even to such seeming trivia as avoiding arc strikes,

avoiding nicking and gouging of surfaces, avoiding rough welds and excessive crowns on welds, and a host of other actions that produce

stress-raising notches in the structure which, in turn, may become

points of origin of catastrophic failures.

Finally, another area fraught with potentially catastrophic problems

should be noted. It is the refractory linings for such equipment as

combustors, gasifiers, regenerators, and connecting ductwork. As

indicated earlier, collapse of sections of such linings may bring

about failure of the pressure-containing metallic piping or shell by

creep buckling or creep rupture. The cause of such a collapse could

well lie in improper installation of the refractory. For most installations, castable refractories will be used. Great attention must be

directed to supporting them and anchoring them in place.

188
SESSION IV

MATERIALS PROBLEMS

IN COAL CONVERSION

PILOT PLANTS

CHAIRMAN: H. E. FRANKEL,

ENER6Y RESEARCH AND

DEVELOPMENT ADMINISTRATION

LOW DUCTILITY, HIGH TEMPERATURE FAILURE OF AUSTENITIC MATERIALS

F. B. Hamel

Gulf Science and Technology Company

Pittsburgh, Pennsylvania 15230

Gulf Oil Corporation is actively engaged in coal conversion research and

development with a Solvent Refined Coal (SRC) process pilot plant in

Tacoma, Washington, and laboratory studies at J^rriam, Kansas and

Harmarville, Pennsylvania. They are also conducting pilot plant development of the Catalytic Coal Liquefaction (CCL) process at Harmarville,

Pennsylvania

.

An interesting and pertinent problem that we have seen several times

involves low ductility intergranular fracture of austenitic alloys

operating in the 1100 to 1200 °F temperature range.

One specific problem that confronted us was a crack that developed in a

ten inch Incoloy 800 type 2 transfer pipeline. Incidentally, this piece

of piping was made of rolled plate that was manufactured in England. It

was shipped to a fabricator in France who rolled it into pipe sections

and welded it. It went to another fabricator in France for fabricating

into a piping detail. From there it went to a unit in Spain.

This pipeline operated at about 1200 °F under 400 psig in a clean

environment --that is, little or no sulfur was present. There were

essentially no contaminants in the system. The temperature was too high

for the presence of chlorides, but the fracture was obviously brittle.

The fracture passed through parent material - -not weld material. We

worked at solving this problem for five years. It was concluded that

the cracking was caused by a strain aging phenomenon which led to low

ductility at high temperatures. We had similar low ductility intergranular fractures occurring in Types 304, 316 and 321 stainless steel

that had been operating in the 1100 to 1200°F range.

A modest research effort testing prestrained specimens has shown that a

10% prestrained specimen aged for 1000 hours can be notch sensitive and

fail with less than 5% elongation. The cause of failure was identified

as prestrain followed by loading at temperature. The failure mechanism

has been characterized as strain age embrittlement . There is formation

of a precipitate and there is grain boundary depletion. Solution

annealing after all fabrication has been an effective corrective measure.

It seems that this is the kind of problem that we are going to have in

the coal conversion industry when working with austenitic materials at

high temperature.

191
THE SRC PLANT

Larry G. Samuels

Supervisor of Engineering & Ifeintenance

Tacoma, Washington 98327

Plant Background

The SRC (solvent refined coal) plant at Tacoma, Washington is a 50 tpd

(feed rate) pilot plant located on Fort Lewis, Washington. The plant

was originally financed by The Office of Coal Research, Department of

Interior. It is presently funded by ERDA and operated by The Pittsburg

& Midway Coal Mining Co. , a Gulf subsidiary. The process design was

developed by The Pittsburg & Midway Coal Mining Co. and the initial

plant design was by Steams-Roger Corporation. Construction was by

The Rust Engineering Company under the direction of The Pittsburg &

Midway Coal Mining Co.

Construction began July, 1972 and was conpleted in the sunrner of 1974.

The first coal was introduced September 30, 1974. The first year of

operation was spent making material balance runs at different conditions

of reaction flow, residence time, pressure, and temperature and sorting

out other reaction area parameters. In September, 1975 a concerted

effort to produce 3,000 tons of SRC for a bum test was begun. The

first four months of this production run resulted in approximately 100

tons per month production due to mechanical problems in the filtration

area and processing problems in the solvent fractionation areas. During

February, 1976 approximately 500 tons of SRC was produced and during

March production amounted to about 400 tons. Improvement, to 500 or

600 tons per month now seons possible.

Process Description

In the process, coal is dried and pulverized to about 70 percent through

200 mesh. The coal is then blended with a solvent derived from the process at a solvent to coal ratio of approximately 1.5/ 1. The solvent/

coal slurry is then mixed with hydrogen and fed through a preheater

to a dissolver v^ich provides sufficient contact time at approximately

1,500 psig and 850 F to ccmplete the reaction.

In the reaction, hydrogen (about 2 percent by weight of the MAF coal)

adds to the coal molecule, which dissolves in the solvent. After reaction, the coal solution is let down in pressure and fed to a pressure

precoat filter operating at approximatelv 150 psig and 450°F to remove

the ash. Flash gases are scrubbed to remove H2S and a portion is recycled. The cake frcm the filter is dried to recover solvent in an indirect fired rotary dryer.

The solution of SRC coal product and solvent is fed to a vacuum flash

unit operating at 600 F and approximately 3 psia. Solvent is recovered

and fractionated for use in the process. The heavy ends (process sol192
vent) is used for slurrying with feed coal vMle the middle cut (wash

solvent) is used for washing on the pressure filter. Light ends frcm

the pilot plant are disposed of through local contractors. The molten

SRC product fron the bottom of the vacuum flash drum is solidified by

cooling on a flaking belt.

Other facilities at the pilot plant include a hydrogen generator which

is a conventional steam-methane reforming unit. Desulfurization of

recycle gas is acccmplished by absorption in a diethanolamine scrubber,

is converted to elemental sulfur using a Stretford process.

The plant is also eq\iipped for slurry recycle frcm the flash step before filtration back to the slurry blend tank. This is expected to

render product as liquid rather than solid at ambient conditions.

The SRC product has aJieating value of approximately 16,000 Btu/lb and

solidifies around 350 i''. The SRC product contains 0.1-.2 percent ash

and 0.6-0.8 percent sulfur, depending on t3^e of coal fed.

Problem Areas Encountered to Date

(1) Slurry preheater feed pump valve erosion. This was solved using

200 chrome spherical valves instead of spring loaded hemispherical

valves

.

(2) Raw coal feed chute pluggage when feeding wet coal. Solved by

changing plant chutes , air locks , etc . . (3) Early concern because of high erosion rates of 347SS reaction area

piping has diminished to the point of being inperceptable with

ultrasonic gaging equipment.

(4) Erosion of reaction area tungsten carbide letdown valve trim every

15 to 30 days of operation remains a problem to be addressed before cctmiercial scale-up.

(5) Overstressing of high pressure-high teiperature slurry to air exchangers was solved by removing this mit from service and replacing it with water quench, flowing directly into the slurry.

(6) High-temperature, pressure filtration has caused the most problems,

but we are confident we now have most of these problems solved on

the pilot plant level. Comnercial size scale-up of these units

still poses many potential problems, including capital and maintenance cost.

(7) Coking of the vacuum flash preheater and downstream piping has b^en

minimized by removing light ends prior to preheating and vacuum

flashing

.

(8) Product solidification problems have been eliminated, however there

are now serious product dusting problems to solve.

(9) Pump and pump seal life has been greatly inproved but much work

remains to be done in this area.

(10) Mineral residue drying to recover solvent frcm the filter cake discharge is a severe operational problem and the disposal of the

dry mineral residue is an even worse problem due to its pyrophoric

nature and the potential pollution hazard due to contained phenol

195
and sulfur.

A Challenge to Manufacturers

Manufacturers and others may help develop this process by being willing to do the unusual in terms of design, delivery, and in seme cases

initial pricing of their special product.

Those of us on the energy crisis "firing line" need, fron manufacturers,

quick solutions to "hairy" problems, even if it is on a very small scale

and in fact may be unprofitable and seemingly undesirable business.

When this, or seme other process, is cctimercialized , those with foresight enough to have been willing to help, (I mean really help by giving our needs priority in your production and R&D shops) will be at

the top of the recomnended vendor's list. More importantly, they will

be in a position to provide workable equipment based on first hand knowledge of the process. Gaining further knowledge through participation

in early synthetic fuels problems is the most econonical and logical

approach to fulfill the mission of this group, the Mechanical Fail\jres

Prevention Group.

I believe I speak for the entire coal conversion industry when I say,

we welcone all the help we can get, but be prepared to perform (and

perform quickly) before a proposal is made. Vhea a $20 million plant

is idle with a problem, we can't wait 42 weeks for a $5,000 solution.

By providing quick action and delivery, manufacturers may gain invaluable insight into a new industry. A few "handsprings" by an engineering force and/or a production department can accoiplish as much as

50 super-salesmen working night and day.

19U
HIGH BTU GASIFICATION PILOT PLANT EXPERIENCE

A. J. Mac Nab

C. F. Braun & Co

Alhambra, California 91802

In developing a process from laboratory to commercialization

the usual justification for a pilot plant stage is to

demonstrate continuous, integrated process feasibility.

Process considerations therefore receive top priority.

Secondary benefits include the gathering of process

information for operational control and for scale up to

commercial size. Materials performance usually takes a low

Order priority and is of concern only as it affects the

safety or operability of the pilot plant. Pilot plant

construction therefore tends to be expedient and self

Serving and does not necessarily reflect the best or even

i^easonable materials selections for commercial plants.

Such is the case with the high Btu gasification pilot plants.

In a few areas where the environments are particularly

severe the best materials selections presently available

have been made. Thus, in a sense, these selections can be

regarded as feasibility studies. But so far there has been

no attempt to operate the units to establish operational

limits on materials or to determine the long term outlook

for materials life. Indeed the incentive to do so may be

lost if the present materials perform well and do not

significantly affect the capital investment for a commercial

unit. That is to say the next plants built, either

demonstration or commercial units will copy the pilot plant

materials of construction and the limitations will be

learned by experience.

The above discussion covers events that are fairly normal

throughout industry, but are an essential background to the

following discussion on pilot plant materials failures.

reliability: The significance of any pilot plant component

failure must be valued against its reliability requirements

in commercial service. There are three main aspects of

reliability, (1) Safety, (2) Operability, and (3) Economics.

195
While all three items are of utmost concern in any

successful commercial venture, primary and mandatory

attention must go to safety. Component failures that

endanger personnel or property cannot be tolerated.

Engineering practices concerning the design and operation of

most components in this category are, of course, governed

by law as reflected in the various Codes.

Even so, there are unpredictable events that can occur which

lead to hazardous situations. For example, an entirely new

mode of failure previously unrecognized, or, failure of a

minor component which triggers a series of events leading

to disaster. Pilot plant component failures of this type

are of course completely accidental but have the morbid

compensation that they occur only once preventing larger and

possibly more numerous occurrences.

Component failures that interfere with operability receive

prompt attention although the solution in a pilot plant

tends to be more expedient than optimum. The economics of

component reliability is harder to define. Component size,

replacement cost, frequency of repair or replacement,

effect on plant operation, predictability of failure and so

on, are all factors that need to be taken into account in

assessing the economic impact of a failure.

PILOT PLANT FAILURES: In the light of the above discussion

then it should be clear that any pilot plant component

failure must be carefully analysed to determine the long

term consequences. The following questions must be asked,

is the component of commercial significance ?

has the proper material been used ?

has the component been used properly or exposed

to meaningful environments ?

Very often the answer to these questions are obvious and an

immediate decision can be made with regard to the

disposition of the problem. But there will also be

situations which are not as readily resolved and which

require the best judgement of experienced operators,

materials engineers and materials scientists. It is in

dealing with problems of this type that the failure

196
reporting and analysis systems discussed in this conference

can be extremely useful. The dissemination of materials

performance information to all concerned with development of

these plants at this time is of particular importance in

view of the National goals at stake. Economic competition

frequently prevents private industry from revealing pilot

plant information, except where safety is concerned.

Matters relating to safety however should be, and are,

openly discussed. It might be argued then that in matters

of national economy affecting us all, the same attitude

should be taken. The only problem appears to be at a plant

level where initial recognition of a problem is vital to the

system. Or, conversely can we afford to investigate every

failure

.

PILOT PLANT EXPERIENCE: Up to the present time only two of

the pilot plants have operated under self-sustaining

conditions. The IGT Hygas pilot plant has been in operation

since 1971, and the Consol CO2 Acceptor pilot plant since

1972. The total operating time is of course fctr less than

the calender years, probably around several thousand hours

a year, and the time at actual operating conditions much

less than that. So while it can be said that in general

there have been no major safety problems in those plants,

the time frame only allows us to discuss short-term effects.

The long-term effects of corrosion or cumulative exposure

have yet to be evaluated.

However this is not insignificant. The plants have been

subjected to extraordinary cyclic conditions under high

pressures of hydrogen without adverse effect so far. This

improves our confidence in the present designs.

Numerous component failures have been reported for both

plants, some of which involved severe mechanical or

environmental effects. In almost every case there has been

an available solution, or the problem does not relate to

commercial operation. For example, severe sulfiding of the

Consol recycle gas heaters has been a serious operating and

economic problem in the pilot plant. However, the recycling

of sulfide containing raw gas through such heaters is a

pilot plant feature only. The information obtained is

useful but may not have serious implication in a commercial

design.

197
Failure of stainless steel by stress corrosion cracking

has been reported in minor components at both plants. This

is a well known problem throughout industry and in most

cases can be eliminated by proper design or materials

selection. Occasionally, unpredictable chloride ion

contamination occurs that must be traced down and

eliminated. As indicated above, however, not all the usual

options are available to pilot plant designers and failures

of this type can be expected.

SUMMARY : Pilot plant component failures require careful

analysis to maximize the information on materials

performance. The key to any successful system of analysis

would seem to be at the plant where problem recognition is

needed

.

198
ACCEPTOR PROCESS

C. A. Schulz

Conoco Coal Development Company

Library, Pennsylvania 15129

I represent Conoco Coal Development Company and am involved with the

Consol CO2 Acceptor Pilot Plant at Rapid City, South Dakota.

To understand the metallurgical and mechanical problems, a brief description of the process might be helpful.

The CO2 Acceptor Process, a fluidized bed system to convert lignite or

subbituminous coal- to pipeline gas, is undergoing testing in a 40-ton

per day, $10,000,000 pilot plant at Rapid City, South Dakota. The

demonstration program is being carried out by Conoco Coal Development

Conpany under a contract with ERDA and the American Gas Association.

A schematic diagram of the CO2 Acceptor Process is shown in Figure 1.

There are two fluidized bed reactors, a gasifier, and a regenerator

which operate at a pressure of 150 psig. Lignite or subbituminous coal

is fed to the bottom of the gasifier where, after rapid hydrodevolatilization, gasification of fixed carbon with steam occurs. The gasifier temperature is in the range of 1480°F to 1550°F. Heat for the

gasification reactions is supplied by a circulating stream of limebearing material called acceptor. The acceptor, which can be either

limestone or dolomite, supplies heat needed for gasification by the

exothermic CO2 acceptor reaction.

CaO + CO^

^

CaCO,

L b {IVY')

AH = -76,200 Btu/Mol.

The CO2 Acceptor reaction is reversed in the regenerator at about 1850°F

where heat is supplied by burning the residual char from the gasifier

with air. Ash is removed from the regenerator by elutriation and

collected via an external cyclone and lockhopper system. Seals between

the gasifier and regenerator are maintained by purged standlegs or

solids.

Since the acceptor loses reactivity to the CO2 acceptor reaction as it

circulates between the reactors, some of the circulating inventory

purposely is withdrawn from the gasifier and replaced with fresh stone

makeup. The makeup is added to the acceptor which is returning to the

regenerator

.

199
The above describes the essence of the process. Necessary auxiliaries

and process steps not shown include a coal preheater, pressured coal

feed lockhoppers, gas cleanup and quench system, and a methanation step,

wherein the CO and H2 are converted to methane (CH^)

.

To date we have had a total of 33 runs. The most recent one was a very

successful 12 -day run under full control at full design conditions.

The run included a 10 -day period making a high Btu gas --most of it

above 900 Btu/cu ft. The run was terminated when a small piece of

refractory lodged in a control valve.

Many of the earlier runs were aborted because of mechanical and metallurgical failures. As one can readily see, we are dealing with aggressive atmospheres, at high temperatures, along with a potential erosive

condition because of the solids that are present.

A brief list of some of the hardware and metallurgical problems that

cause stoppage would include:

(1) Cracking and spalling of refractories in the reactors.

(2) Lockhopper valve failures. Seal areas become scratched and

permit flow of gases.

(3) Loss of internal cyclone in the gasifier due to a weld failure.

(4) Failure of solid transfer line control valves.

(5) Erosion of solids transfer lines, particularly in the area of

expansion joints.

(6) Stress -corrosion failure of cold expansion joints.

(7) Carburization and sulfidization attacks on gasifier heater

coils.

The last mentioned item was a frequent cause of run failure in earlier

runs. The furnace coils are in a recycle system which is a pilot plant

requirement only. Subsequently, we have changed metallurgy, reduced

temperature, added a sulfur removal system, and also added an oxidant

(steam) to the quench gasifier recycle stream.

200
FIGURE 1

201
CONSOL PILOT PLANT MATERIALS PROBLEMS

J. F. Leterle

Continental Oil Company

Ponca City, Oklahoma 74601

Abstract: Recycle gas heaters suffered severe sulfidic corrosion of

Incoloy 800 tubes prior to desul furi zing the gas stream with a ZnO

system. In a sulfur free recycle gas stream 321SS and Incoloy 800

tubes encountered rapid pitting attack by metal dusting until 50%

steam was introduced into the recycle gas stream. Large vertical

cracks in the inner castable refractory liner of the gasifier and

regenerator vessels occurred because a light weight insulation between the refractory and the vessel shell lacked strength to support

the refractory layers when the system was pressurized. Erosion of

the expansion joints of an inner liner of a transfer line pneumatically carrying solids and the stress corrosion cracking of the 304SS

expansion bellows of the outer pipe are other problems experienced.

Key words: Erosion; metal dusting; process vessel refractoryinsulation design; stress corrosion cracking; sulfidic corrosion.

The chief materials problems encountered with the operation of the

Consol CO2 Acceptor Coal Gasification Pilot Plant have been:

.sulfidic corrosion

.carburization - "metal dusting"

. refractory-i nsul ation fai 1 ures

.erosion

.stress corrosion cracking

A brief description of the essential aspects of these problems

follows:

Sulfidic Corrosion

The most severe corrosion problems have occurred in Incoloy 800

recycle gas heater coils operating in the vicinity of 1500°F and

higher. The principal form of sulfur corrodents have been H2S and

to a lesser degree SO2 and COS. The normal level of H2S is about

500 ppm with concentrations up to several times this level at some

occasions such as during start-up periods. Thick layers of metallic

sulfides form on tube walls within 150 hours operating time and have

occasionally caused complete tube blockage. Liquid nickel sulfides

202
have formed in higher temperature zones of heaters and have been

carried downstream, solidified and agglomerated into chunks and balls

in lower temperature locations.

To control this problem sulfur was eliminated in the recycle gas

streams by the installation of a ZnO desulfurizer system.

Carburization - Metal Dusting

With the virtually complete removal of sulfur from the gasifier recycle gases severe pitting attack of the recycle gas heater type

321SS and Incoloy 800 tubes was experienced by the metal dusting

reaction. This attack was chiefly in the 800-1200°F temperature

range. During normal operation with char and steam in the gasifier,

the recycle gas downstream of the desulfurizer contains 13% CO, 10%

CO2, 6% N2, 60% H2, and 11% CH4. The problem was solved by adding

steam to the recycle gas in an amount equal to about 50% of the

whole.

Refractory - Insulation Failure

The lignite gasifier vessel and acceptor regenerator vessel were

originally lined with 7 to 17 inches of J-M superex block insulation

and then 3 inches of low density castable insulating refractory

A. P. Green VSL-50 and finally 3 inches of a harder higher density

castable A. P. Green KS4V. Large vertical cracks developed in the

cast layers because the block insulation did not have sufficient

compressive strength to support the castable layers when the system

was pressurized. The cracks permitted channeling and gas flow within

the insulation blocks thereby causing excessive heat loss to the

vessel shells. Corrective measures were the replacement of the

diatomaceous silica block insulation with higher crushing strength

castable and vapor stops of high density hard-face castable were

installed at several levels to prevent bottom- to-top circulation

paths within the insulation thickness.

Erosion

Piping which carries solids at high temperatures consists of an outer

steel pipe, an inner alloy liner with the annular space between the

two filled with vacuum packed ceramic fiber insulation and

diatomaceous silica insulation. Thermal expansion of the inner tube

is accommodated by an enlarged end section bel 1 -and-spigot type slip

joint. Severe erosion of the inner tube occurs if there is misalignment of the tube at flanged joints and at the slip joints because of

flow turbulence at these locations. Metal spray and plasma arc spray

of chromium carbide and nickel aluminide coatings of the slip joint

areas provided marginal improvement. Hardface weld overlay with

Stellite 12 of the slip joints and close attention to alignment have

203
greatly reduced erosion problems. A new ceramic lined slip joint was

recently installed and work is in progress on the design and fabrication of a new solids line completely lined with formed ceramic

shapes. The velocity in this line is now maintained at about 50

ft/sec, previously the velocity ranged up to 100 ft/sec.

Stress Corrosion Cracking

The expansion joints in the outer carbon steel solids handling pipe

were 304SS bellows type design. Several of the stainless steel

bellows have failed through chloride stress corrosion cracking. The

original 304SS expansion joints are being replaced with solution

annealed Incoloy 825 expansion bellows which should minimize this

problem.

These have been the chief problems experienced in the pilot plant

operation. In a commercial size unit heat loss consideraitions

would not require recycle gas heaters or such exotic insulation

designs. This would minimize many of the problems briefly described

in these introductory remarks.

20k
THE SYNTHANE COAL TO GAS PILOT PLANT

Robert Lewis

Synthane Coal to Gas Pilot Plant

Pittsburgh, Pennsylvania 15213

The Synthane plant is the only pilot plant in the United States that is

100% government funded. Furthermore, the Synthane process is a government developed process. The Government, however, does not operate the

plant. It is operated by the Lummus Company under contract to the

Government. There is one other unique feature of the Synthane plant -- in the early days, it was the only plant that had full time government

personnel

.

The plant has been in a debugging, startup type operation for approximately ten to twelve months. We have started up and operated all

utilities and the coal handling and grinding system. The coal feeding

system, the char handling system, and the filtration system have been

operated. Coal has been fed to the gasifier, fluid beds have been

established and maintained, and some coal feed rates have been measured.

Various useful data have been obtained. Coal has been successfully

removed from the gasifier through the char handling system. Coal has

not yet been ignited and we therefore have not tested the gas cleanup

system under process conditions.

We have had various kinds of failures during the past twelve months,

despite the fact that we have yet to produce any process gas. The

failures can be categorized into two general types- -those that are

primarily related to the coal gasification process, and those that are

not specifically related to coal gasification and involve materials or

equipment common to other industrial or manufacturing operations.

Failures in the first category have been limited to only a part of the

plant since there are many portions of the plant that have not yet seen

process conditions. We had a major problem with a leak at the welded

gaskets at the gasifier main body flange. We had an internal stainless

steel head deform under excessive pressure in the gasifier itself.

This head served as a diaphragm to give us, in effect, two vessels in

one. We have had a number of erosion problems with slurry pumps,

mixing Venturis, spray nozzles, agitators, piping, etc., in coal slurry

handling facilities and we have had some minor instrument problems,

although most of these belong in the second category.

Failures of conventional industrial equipment not specifically related

to the coal gasification process have been numerous. There were 29

types of instrument failures involving perhaps 50 to 100 individual

205
instruments. Most of the other problems relate to rotating equipment

that does not handle coal or gasification products, and consist of

mechanical seal failures, cracked and broken pump casings and blower

casings. There were difficulties with our large four- stage carbon

dioxide conpressors , such as valve leakage and excessive wear on pistons

and piston rings. We have had problems with overloading of motors on

various pieces of equipment. We had a broken chain on our raw coal

bucket elevator and on our char conveyor. There were numerous problems

with explosion doors opening prematurely on a dry coal dust collector.

We had packing failures on the rotating leaf vacuum filters. There was

a major failure in the low pressure gas holder revolving around inproper

functioning of the piston and rupturing of the diaphragm.

I do not think that the second category failures should be glossed over

because they occur with standard industrial items. It is my unsubstantiated and very subjective opinion that the number and variety of this

type of failure are greater than they used to be when process units were

started up. This relates to problems of quality of material and equipment, and can be attributed in part to misapplications, problems with

procurement, rigid adherence to the principle of low bidder, poor

vendor quality control, and lack of appropriate guidelines for field

storage and handling during construction and startup.

Gasification pilot plant failures are difficult to anticipate. The best

ways to avoid or alleviate most of them were not available at the time

the pilot plant was engineered and constructed. I refer specifically

to the need for improved communications, centralization of information,

greater distribution of information and more interplay between those

engaged in projects where these problems tend to occur. Many people

are trying hard to improve the situation and I am happy to see that

there have been some positive steps taken along those lines. There are

several things that could be done. One is to establish a priority

system. When we need 316L stainless steel tubing, for exanple, we have

to compete on the open market. We have no special priorities because

we are government funded.

I would like to add that these last comments about improved communications are not intended to be critical. I believe meetings and symposia such as this are an effort to cope with this problem and should be

encouraged. I also know that there have been difficulties in attempting

to inplement some of these concepts. Further efforts along these lines

should pay dividends, particularly in view of the large expenditures

being planned for the near future.

206
I

PANEL DISCUSSION

Chairman: Henry E. Frankel , ERDA, Fossil Energy

Panel Members: Fred B. Hamel , Gulf Science and Technology Company

Larry G. Samuels, SRC Pilot Plant

Adrian J. Mac Nab, C. F. Braun and Company

Carl A. Schulz, Conoco Coal Development Company

Jene F. Leterle, Continental Oil Company

Robert Lewis, ERDA, Synthane Pilot Plant

F. B. Hamel : I was listening to some of the talks yesterday about

reliability and how reliability could be designed into plants. The oil

industry is very concerned with reliability. Several years ago I was

involved with a decision to go to an integrated refining installation.

We knew we could obtain 95% reliability or availability in a given unit

without too much trouble. Our management people wanted the plant

designed to be able to run for four years with a one-month shutdown.

This looks like 98% availability. But you fast come to the conclusion

that from a design, construction and operational basis, there is only

one thing to be done--do everything possible to get 100% reliability

during the operating interval. In order to have 100% reliability, all

components in a system must be working right. Obviously, some of these

components will malfunction at times. Most of my work has been involved

in correcting these malfunctions. A malfunction must be corrected as

quickly as possible on an emergency basis. There is no other way of

getting reasonably good availability.

When we try a new process, we like to have a turn around--that is, a period when the equipment is shut down and examined. We try to run at

least six months before turn around. If everything is going well, we

will stretch it out to a year or maybe two. We don't go for a fouryear turn around with an unfamiliar process. We want 100% reliability

for the operating interval before a turn around and that becomes the

objective of our engineering work. Basically, this is the kind of

philosophy we use.

L. G. Samuels : I assumed that there were going to be some manufacturers

and vendors of equipment here, and from looking at the registration 1 ist,

I see only three or four. I believe we have to have more participation

from these groups if we are ever going to solve the energy crisis. We

have had some outstanding examples of research papers presented this

week, but they are not of much immediate value to someone like myself

who faces immediate problems everyday in the plant.

To give you a little insight into what I am talking about I would like

to describe part of a typical two-week period at the SRC plant. We

discovered that there was a leak in one of the wash solvent overhead

I

207
condensers. We quickly determined that the thin 1 inch diameter, 8 foot

long carbon steel tubes on the air cooled condensor were leaking at the

inlet tube sheet, and further inspection disclosed that all 76 tubes

were very thin at the inlet tube sheet and that they would have to be

replaced. It was Friday afternoon. We have 64 operators, 16 on each of

four shifts, we have about 40 maintenance personnel plus perhaps 20 or

25 technical people. When the plant is not running, we feel the taxpayers are not getting their money's worth. So we quickly called Tulsa

where the exchanger had been made and we found out that we could get

some thin carbon steel tubes made up on Saturday and air freight them

from Tulsa to Tacoma. We inquired about 304 and 316 stainless

steel, but it would take 4 to 6 weeks or longer for the stainless steel

tubes, so we ordered carbon steel tubes and began arranging for a crane

to remove the exchanger for retubing. About Tuesday of the following

week, we had it down off the roof, retubed, and back up on the roof.

But just as that was finished, we discovered that the apparatus that

drys the mineral residue that is filtered out of the coal was coked up.

It takes about three days of jackhammer work to decoke this 36 inch

diameter, 40 ft. long vessel. Further, we had 1100 feet of chain in the

dryer that we added to rub on the sides to forestall this coking. These

had broken loose and become matted. So three days of jackhammer work

and 1100 feet of chain later, we thought we were going to run, but just

as that was being completed, the wash solvent column sprung a leak.

This is a 30 inch diameter carbon steel vessel, 3/8 inch thick, which

operates at 10 to 15 psi and 600°F. It is rated at 75 psi and 750°F

because we did not know the operating conditions when the plant was

built. The plant inspector examined the column with an ultrasonic

tester and decided that it was going to take many large patches to

repair it. Again it was Friday--the plates were rolled in anticipation

of applying several half circle patches around this column on Saturday

and Sunday. On further investigation we found there were large craters,

and by that I mean craters up to 2" in diameter. We also discovered

general corrosion in at least one square foot of every tray in this

column. On Saturday we decided to remove the trays and overlay the

column from the inside, but by Monday, that became impractical because,

as we started to remove the trays, we found that all the tray supports

and downcomer supports had corroded off. On Tuesday, it was decided

that we were going to replace the top 18 feet of this column. We

initially decided to replace the column with 316 stainless steel, but

finally decided on 316L because the column was to be welded to part of

the original carbon steel column. Fortunately, the material was available from a local fabricator. The old section was cut out and the new

section was fabricated, installed, pressure tested, inspected, recoated

and back in operation in four days.

The basis for the 316L selection was an article in Metals Handbook

concerning naphthenic acid corrosion. Now our lab had not been able to

verify that we have naphthenic acid corrosion, but it looks like a perfect textbook example. The condensor tubes that I first mentioned

208
should have been 316 stainless steel also, but there wasn't any 316

available. So we used carbon steel because we feel that it is more

important to keep the pilot plant running then to determine which

materials give best performance. We must strive to get as much information as possible from the pilot plant with what is available, not

waiting for what we can get next month or next year. Direct contacts

with some of the people in this room would be a big start in the right

direction.

H. E. Frankel : You mentioned that you saw very few vendors present at

this meeting. This, indeed, highlights a major problem facing the

whole coal conversion industry. The fact is, there really is not a commercial coal conversion industry. It is not worthwhile for vendors

to make specialized pieces of equipment. We are just going to have to

bear with this situation for many, many years until an industry does

come on stream.

A. J. Mac Nab : Of the failures about which we have heard so far, there

are only a few that I feel are directly significant in the development

of commercial gasification processes. Very often a material is used in

a system simply because it is available at the time it is needed. Sometimes it is deliberately put in, but the process situation changes. The

operating conditions are not as the designer was told. Minor component

failures are going to occur, and they are going to occur on commercial

systems. That type of failure to me is not terribly important in a pilot plant as long as we understand why it happened and it can be

corrected in a commercial design.

A problem that needs attention involves the failure reporting systems

and failure analysis systems. The weakest link in the chain is the

reporting at plant level. That is not to say that we don't have

competent people at the plant level, we certainly do. But, very often

they are not metallurgists or they are not familiar with the full gamut

of metallurgical problems and therefore could often overlook a significant piece of information. If we are leaving the reporting of the

failure to the first observer, he can classify it as not important or

important as it strikes him at that time. For instance, an internal

failure in a reactor could be dismissed as a routine mechanical problem

such as a poor weld, whereas in fact, a component may have a fatigue

life 1/3 below the expected level for that material under unexposed

conditions. This is an important piece of information but it is

neglected.

C. A. Schulz : In line with Adrian's remarks, gas recycle heater failures are not really significant except for historical interest because

gas recycle heaters will not be needed in the commercial plant.

H. E. Frankel : So far in this session, we have just discussed our

failures. There have been some notable successes. Perhaps Carl can

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address himself to some of the pieces of equipment and components that

have been successful , These are perhaps more important than the

failures.

C. A. Schulz : We have had a lot of successes. We have a solids control

butterfly type valve that has operated successfully for about 5000 hours

at 1850°F with dolomite--a very hard sol id--passing through it. Our

pressure vessels themselves have never been attacked despite the refractory failures. We have a cyclone in the gasifier that performed

satisfactorily for 5000 hours in a corrosive and erosive environment.

It even fell to the bottom of the gasifier once because of a failure in

a weld in the discharge pipe, but it survived. There are many good

things that can be proven in pilot plants, and perhaps we could learn

from the surviving components as well as from the failures.

R. Lewis : It appears to me that we are being let down by many of the

vendors who are supplying shoddy equipment and lousy workmanship, and

failing to meet even promised deliveries. I do not like to take the

position that American industry is not what it used to be, but we have

a pretty strong feeling that when you buy something, you do not get

what you thought you were going to get. We have had a lot of trouble

with slurry pumps and slurry pipelines. When you start asking

questions, however, you find that there are solutions to many of these

problems. We found that Black Mesa pumps a coal slurry about 300 miles

with positive displacement pumps. They do not have any problems. Even

in industry, there is not the kind of feedback there should be.

L. G. Samuels : One of our initial problems was pumping slurries with

positive displacement pumps. The pump was designed for 2400 pounds of

pressure at about 200 or 300°F, but we were only operating at about

1500 pounds. These spring loaded hemispherical valves would erode in

a matter of hours. These valves cost about $200 apiece and we were

going through about 12 per set every other day. We kept going back to

the vendor who gave us good service. But everything he sent was worse

than what we had. Finally, after we had exhausted every means available to us that the vendor could suggest, we called IGT (Institute of

Gas Technology, Chicago). They suggested putting a 2 3/4 inch diameter

chrome ball in the valves. In less than a day, we had these $35 balls

that you could buy off the shelf installed and those pumps operate for

months now without maintenance. There was interchange between government contractors.

R. Lewis : You are also backing up my point about some of the vendor

problems

.

C. A. Schulz : Bob, you point out something. You are three miles from

me. We were the developers of the world's first pipeline. All the

technology of Black Mesa came from Library, PA. You should have

consulted with us.

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R. Lewis : Carl, we talked to you, but the problem was that the

designers did not talk to you. The slurry system was designed four or

five years ago by a big engineering company who said they knew how to

design a coal handling system. Our slurry pumps are recommended by

everybody you talk to--they are standard slurry pumps.

C. A. Schulz : Larry, that is a mud pump that your vendor recommended.

I am sorry that you had so much trouble with your pumps. We learned

about the ball valve some ten years ago. Specifying a pumping system

is a complex problem. You have to know something about the hydraulics

of the system, the slurry concentration, the size consists, the carrier,

etc. I do not think the vendor has that process know-how.

R. Lewis : Sometimes an apparently insignificant and unnoticed design

change, usually in the interest of saving a few cents, can wreak havoc

with a system. As an example, we had a $100,000 four-stage reciprocating conventional compressor to pump carbon dioxide. We suffered

repeated failures with the unloaders. It took four weeks to determine

that the problem was that the gasket material had been replaced with an

inferior material. Problems of this type are very hard to diagnose.

C. A. Schulz : Your point about equipment manufacturers and fabricators

is a very valid one. I think that integrity has gone out of the

fabricating business. We recently built an addition to our CO2 Acceptor

Plant. We decided to spend the extra money to sit down with the vendor

to make sure he really understood the specifications. We also spent

a lot of time and money visiting the plant to make sure that everything

functioned properly. It was worthwhile to spend the extra money and

manpower because this pilot plant is the only one in many years that

worked properly from the beginning.

S. S. Canja, ERDA : I am ERDA's Systems Reliability Engineer. I work on

the staff of Dr. White, the Assistant Administrator for Fossil Energy.

We are in a very infantile stage in reliability quality assurance in

fossil energy programs. Dr. Frankel has begun the work in the area of

materials and failures. He and I are to work together in developing

what we call a performance assurance system. When we talk about performance assurance, we are not in any way trying to develop processes. We

are trying to reflect on all of the activity necessary to assure ourselves that we are going to have a working system at the lowest possible

cost. The primary elements of a performance assurance system as we see

it are a rel iabil ity program and a maintainability program. We feel

that by beginning performance assurance procedures in the process

development unit (PDU) stage, maybe we can predict some of the problems

that may arise in the pilot plant and in the demonstration plant. One

of the problem areas in the coal conversion industry is a lack of

standardization. Everybody today seems to design a pilot plant independently of everyone else. It would seem to be appropriate to provide

designers with information as to what components operate with a high

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degree of reliability at a good cost, etc. For instance, wouldn't it

be reasonable to have several plants using the same kind of pulverizers?

When there are problems, repair parts would be more plentiful. Problems

could be predicted from the experience of others. So we feel that

standardization is a very important element in our total program.

Life cycle cost--we are looking at this from the standpoint of what it

costs to operate equipment, not how many tons of coal go in and how

many BTU's of gas come out. This is not a performance assurance

problem; it is a processor's problem. We are also concerned with the

service life prediction--how long the various elements of the plant

will continue to function properly. That is a very quick overview of

the total performance assurance system that we would like to formalize

and enable the ERDA program managers and project managers in fossil

energy to apply to their contracts.

In order to get a performance assurance program underway, we talked to

our program/project managers and we were told by many of them that

reliability was already written into our contracts. In order to see

if this was really true, we screened 280 contracts. We identified 45

contracts that were prime candidates for performance assurance. These

contracts were for late PDU plants, pilot plants, and demonstration

plants. Only one contract had an appreciable number of elements

concerning performance assurance. Seven referred in some way to

reliability or quality assurance and some stated that there will be a reliable process. The remaining 37 contracts did not even have the

word reliability in any part of the work statement. Most of ERDA's

request for proposals had no provisions for reliability, quality

assurance, availability, etc. ERDA is now beginning to realize that in

order to get quality, reliability and performance assurance into its

programs, it is going to have to pay for them. Finally, there are not

in existence at this time any formal procedures, specifications, or any

other program elements which will act as a guide for performance

assurance within the fossil energy milieu. Performance assurance has

proven itself in the Department of Defense and NASA. I have been

directed to prepare some performance assurance provisions to be included

in future contracts. We are preparing interim specifications and

procedures to formalize the program. We must develop our own procedures

because often those developed by other agencies are not suitable. Some

of the discussion we heard this morning indicates that we are attacking

our problems on a piecemeal basis. We must apply some techniques of

failure prediction in the early stages of design.

Another subject that I would like to discuss is the possibility of

fossil energy programs joining what is known as "GIDEP". GIDEP is the

Government-Industry Data Exchange Program. It was originally started

by the Department of Defense (Navy) in 1959. The ERDA fossil energy

program has been invited to join at no cost. If we join GIDEP, the

program should complement the data collecting program at the National

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Bureau of Standards. Right now, GIDEP is primarily electronics

oriented, but there is much information on materials and components

that is common to fossil energy programs. GIDEP is willing to create

whatever categories of data that are needed and Dr. Smith is currently

working on a program to identify these categories of information and

how we would put them into a data retrieval system like this. The

whole point of GIDEP is the possibility of our using it instead of

creating a separate system that would cost us many hundreds of thousands

of dollars when this one is free. Two of the data banks in GIDEP are

the failure rate and failure experience data banks. You can join only

one bank if you wish, but you still have, as a user, access to any of

the other data banks. I think that the most compelling reason for

joining GIDEP is cost avoidance.

A. J. Mac Nab : The overall problem seems to be that we are trying to

upgrade the quality of standard industry. Things like weld-procedure

qualification, welder certification, etc., are standard procedures and

should not present a problem in gasification. In other words, there

is no reason at this time to demand any additional quality over what

we already have in other industries. What must be decided is how far

should one go in gasification in improving quality assurance and quality

control at every level of operation from design through the vendors and

in the reporting of information.

F. B. Hamel : Frankly, Mr. Canja, your remarks frighten me somewhat.

If we implement the programs that you are talking about, I think that

we would double the cost of the R&D programs. The documentation that

implements a performance assurance system is gigantic. There is one

major technical problem that we have in common with the space people;

that is, building one-of-a-kind of something. Reliability data cannot

be obtained on one-of-a-kind equipment. It is high time we recognized

the prime purpose of pilot plants and demonstration units. It is not

to develop hardware, it is to prove that we have a process that will

work. We make changes in our Tacoma plant every day. We feel that the

implementation of a performance assurance program to improve the

operability of a demonstration unit which was not intended to run all

the time anyway would be a waste of time and money. Some of our equipment was bought with the recognition that the plant in Tacoma was not

going to run forever. It has a finite life. We have to keep this kind

of thing in mind. Of the many failure analyses discussed at this meeting, very few will prove to be of any significance in the development

of equipment for commercial plants.

I agree that we need better technical information retrieval systems in

our industry. I am heavily involved with technical information

retrieval in my company. We all are fighting this thing.

To implement a performance program, there is the problem of working with

nationally accepted standards (most of which are accepted by OSHA) and

215
then there are government regulations that tell us we have to buy from

the lowest bidder. As soon as we write a special standard we raise the

price. But I defy you to show me, on something you have never built

before, how you can show any payoff in doing anything but the lowest

cost job that you can do.

0. Decker, Mechanical Technology, Inc. : I did not think the purpose

of pilot plants was just to prove the process.

F. B. Hamel : I was oversimplifying an issue.

E

.

B. Bel 1 , TRW : Once an extensive data base is established, equipment

and plant availabilities can be calculated. This data base can be

developed from pilot plants and demonstration plants, and in some cases

from PDU's. When we have this data base, we can apply computer

techniques to put redundance in a system to improve availability and

reliability. It is imperative that this data base be established as

soon as possible.

F. B. Hamel : My experience in the oil refinery business indicates that

most failures are one-of-a-kind. It is hard to establish a meaningful

data base from these one-of-a-kind failures.

E. B. Bell : If in fact over a period of time you are able to standardize some of the equipment in your plants, then maybe you wouldn't see

as many one-of-a-kind failures.

F. B. Hamel : Standardization is a good idea, but very difficult to

implement. For instance, several years ago we tried to standardize

heat exchanger sizes. It did not work out because if you needed an

exchanger just slightly larger than one standard size, you would not

be willing to pay for the next larger standard size which would

probably be much larger than needed.

R. Lewis : The statement was made earlier, and I generally agree with

it, that pilot plants are basically built to demonstrate that process

chemistry is valid and is capable of being scaled up to a commercial

size installation. The hardware that most of the pilot plants have is

basically commercial, off-the-shelf hardware. Now when it comes to

scale-up to demonstration and full scale plants, it is an altogether

different ball game, and here is where you get into questions of

standardization. We do not do many things in our pilot plants that

you are going to do on a commercial scale. We are grinding 5 tons of

coal a day in a little hammer mill, a standard conventional piece of

equipment. Now, no commercial gasification plant is going to have

equipment like that. I know there are people who are looking at ways

of handling 20,000 tons of coal, so the reliability factor on my little

5 ton a day coal mill is irrelevant. All I want to do is run the equipment long enough to get some coal in the gasifier and gasify it. I do

21k
not care what I have to do to grind that coal. The situation is similar

with heat exchangers, cooling towers, etc. Our problem is that we have

been working now for close to a year and we have not made any gas yet.

The reason we have not is because we cannot get past this commercial

hardware we bought and get it to work long enough to put some coal in

the gasifier.

E. Passaglia, National Bureau of Standards : I think Bob Lewis hit on

the key point with respect to materials reliability in pilot plants.

Clearly a pilot plant is designed to study the process because you want

to know if you are going to make money or not. However, when the

materials reliability question prevents you from getting your operating

data or prevents you from getting it on time, then I think you are in

trouble. I do not know if we are in trouble with respect to these coal

gasification plants. Are we having more troubles with coal gasification

plants, particularly with the standard equipment, than one would

normally have in a pilot plant in the oil industry? Bob, you seem to

feel that you do. Others of you may not. If we are, why, and what

can we do about it? Mr. Canja's program might help.

There is a related comment that I am prompted to make contrasting the

results of this particular meeting with the meeting that was held in

Columbus just about two years ago —the workshop on coal gasification.

At that meeting, materials people were being asked to consider what

kind of materials problems were likely to arise in coal gasification

systems. People hypothesized, on the bases of their experience and on

the kinds of atmospheres that the metals and ceramics were supposed to

be experiencing in these plants, that the main problems would be

erosion and corrosion. Based on results we have to date, those predictions are very largely borne out as would have been expected. From what

people are saying at this meeting, the problems seem now to be concentrated in areas where the materials people thought the problems were

solved--such as coal buckets and slurry pumps. Are these problems

unique to the coal gasification pilot plants? Are we experiencing the

same kind of thing we would experience in plants in other industries?

A. J. Mac Nab : There have been an unusual number of failures in

standard equipment on the pilot systems from what we have seen so far,

and the operating times are short. But this is really tied in, to some

extent, with the fact that they are pilot plants. I believe it has to

do with the economic incentive, the monetary value of pilot plants.

There is not much money invested in them, the budgets are usually fairly

tight, and they spring out of process development groups without a big

engineering organization backing up the design information that is

transferred between them and contractors. You get what you pay for.

Contractors take a lot of blame for plant quality, whereas in fact, a lot of shortcomings are due to poor specifications. A customer

frequently does not say what he wants. It is the nature of pilot plant

construction to have something less than the big guns working on the job

because of the economic incentive.

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C. A. Schuiz : I think that the petroleum industry is experiencing the

same problem as we are with ordinary standard equipment. Our pilot

plants are different from theirs in that they are much larger. Our

plants are unique mostly because we are handling solids.

S. S. Canja : It has been alleged that performance assurance adds at

least 507o to the cost of a project. Performance assurance cost the

U.S. Government about 14% of the total cost of putting a man on the

moon. Now, remember that we were really concerned about his health and

safety. We calculate the cost of the desired performance assurance in

the coal conversion industry to be 3 to 5%.

I am distressed by the fact that people tell me pilot plants are to

prove out a process. What was the purpose of the process development

unit? Well, to prove out a process. What was the purpose of the

demonstration plant? Well, to prove out the process on a bigger scale.

The question is, when do you start looking at components? When do you

start designing them with scale-up in mind? One of the problems in

the electrical utilities industry is scale-up. There are more problems

on a 600 megawatt and above generating plant than anticipated because

of the scale-up problem. But I think if you start scaling up from PDU

to pilot plant to demonstration plant, then the next step to a commercial plant will be easier.

R. Lewis : I agree with Carl in regard to the size of our pilot plants

vis-a-vis the petroleum industry. These pilot plants are really not

pilot plants at all. They are misnamed. Somebody arbitrarily said a PDU is up to 10 tons a day, and a pilot plant is up to about 200 tons

a day. We are talking about coal input now, and a demonstration plant

is a single train of a commercial -sized unit. Now, we are not really

going through all of these steps. Most of the large pilot plants have

70 to 100 tons a day capacity. These plants are scale-ups from the

PDU's on the order of 200 times. Probably the next size which is the

demonstration unit is a scale-up of 200 times more. Our pilot plants

are pretty substantial operations and very little of our equipment is

designed specifically for use in a coal gasification plant. Most of

the equipment consists of things like standard heat exchangers,

standard piping, etc., that are all bought commercially. We cannot

prove the feasibility of the process in the pilot plants because of

continuing problems with this standard, off-the-shelf equipment.

A. J. Mac Nab : Standardization has come up a couple of times and, as

Bob has pointed out, both pilot plants and commercial plants are built

using standardized piping, valves, pumps, etc. Standardization often

leads us into trouble. In order to pick a standard size or standard

piece of equipment, we oversize or undersize and create problems. This

can be as much of a pain as having nonstandardized equipment.

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C. A. Schuiz : Specification standards have progressed from the overly

elaborate bookshelf size volumes that were formerly used in the petroleum industry to the almost nonexistent ones currently in use for the

coal conversion systems. I do not propose that we go back to the

elaborate procedures once used, but a definite upgrading of current

specification standards is needed.

0. Decker : Why, in a pilot plant, can't you both demonstrate the

process and at the same time run parallel programs to develop critical

components so that by the time you get to a 2500 ton a day demonstration

plant, you will have equipment that gives the kind of service you need?

R. Lewis : We had this in mind when we designed our compressor. One of

the requirements was that it must be capable of being scaled up.

F. B. Hamel : That is terrific. But we have seen problems in just

doubling the size of a machine.

0. Decker : I think the Synthane Plant is looking at this problem in

just the right way.

F. B. Hamel : If the process does not work, the equipment is not needed,

so my point is that the process is governing.

0. Decker : Government contractors possibly have an advantage that

commercial companies do not enjoy. That is, they have more flexibility.

They can have programs to develop equipment while studying a process.

I am suggesting that ERDA should consider equipment development when

issuing contracts.

H. E. Frankel : You have to remember that every single pilot plant was

designed, and indeed built, long before such things as performance

assurance or reliability were considered. So let's not fault the

pilot plant for trying to prove a process. What we are trying to do is

to get as much information as possible from an existing pilot plant.

The demonstration plants that are at least 6 or 7 years away have time

for the instituting of this philosophy. I happen to be in agreement

with the performance assurance philosophy as you well know. We are all

taking pot shots at the pilot plant. I think they have done a good

job. What we are trying to do is make them aware that, while they are

trying to prove a process, they are also proving out materials, good,

bad, or indifferent.

R. Lewis : Materials yes, Henry, but not so much equipment.

H. E. Frankel : That is true.

L. G. Samuels : Our biggest problem with standardization is that we are

forced to purchase equipment from the lowest bidder. Similar equipment

217
from two different manufacturers may do the same job, but the parts,

fittings, etc., probably will not be interchangeable forcing us to

stock items for each. So, although standardization is nice, our

necessity of dealing with the low bidder does not allow us to take

advantage of it.

Another problem with the low bidder is that you may not be able to

buy equipment you are familiar with and that you know works properly.

The low bidder may say his equipment works, but our experience indicates

that that is not always true.

0. Decker : We must not forget the fact that equipment will be needed

for demonstration plants that is not available today.

R. Lewis : Adrian Mac Nab's Company, C. F. Braun, is very deeply

involved with that problem. They are looking at various systems,

schemes, equipment, etc., which could be used on very large scale

operations

.

E. B. Bell : In terms of equipment operating times, how do you schedule

maintenance in a plant if you do not have a pretty decent handle as to

the life or operating time of the equipment? And if you keep good

records of operating times on equipment and these records indicate that

the operating times are inadequate, I think this would be a very strong

case for not buying from the same vendor or not buying from the low

bidder. Without this information, you do not have the handle to apply

leverage to change contractors or to get a more expensive piece of

equipment if the cheaper equipment does not perform properly.

R. Lewis : That is awfully hard to prove.

C. A. Schulz : They hang you on minor changes and variables. You have

a pump that does not work, so you go back to the vendor. It turns out

that you said you were going to use a 30% concentration but, in fact,

you ran a 35% concentration through the pump. The change in concentration may have nothing to do with the failure, but the vendor will

claim you are using the pump out of specifications.

E. B. Bell : Are you saying that you are operating out of specs?

R. Lewis : We are not building a million units all alike on an assembly

line. These are research and development installations. If 5 years ago

we said we were probably going to run with a 30% concentration, and now

we find out that the process works a little better with 35%, that is

hardly operating out of specs.

E. B. Bell : I still do not see how you can approach a good maintenance

program without a good knowledge of equipment operating times.

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R. Lewis : We do not do any maintenance, we are doing repairs all the

time.

F. P. Williamson, Panhandle Eastern Pipe Line Company : We want to build

a coal gasification plant in Wyoming and it is going to cost us about

a billion dollars. We are looking at the Lurgi technology and I would

like to have the people here give me some advice. How can I insure

that, after my contractor has done the detailed engineering and

supposedly guaranteed that things will operate properly, when I push

the button six years from now, the project is going to work. I cannot

take a year or two to debug it like we do on the pilot plants.

R. Lewis : You ask that man to give you a half a floor in his engineering building and you put about 20 or 30 people in there and you

watch everything that he does.

F. P. Williamson : In other words, you check his engineering effort?

R. Lewis : You look over his shoulder at everything he does. That is

the only way you are going to be sure that the job is done right.

C. A. Schulz : Do not assign the young, green engineer to oversee the

project. You need someone with experience in there.

A. J. Mac Nab : Every customer comes in asking for the moon, and when

he finds out what it costs, he backs off rapidly.

F. P. Williamson : Well, that is the problem. You wrestle with how

much money you spend before you push the button versus how much money

you spend after you push the button.

R. Lewis : There is a calculated risk involved. How much risk are you

willing to take and how much are you willing to pay to minimize it?

F. P. Williamson : These are all good points. I agree that you need to

put the effort in to monitor your engineering contractor because he has

people working on the project who are really not familiar with it.

One other point, we need to get mechanical engineers involved in evaluating equipment bids and equipment specifications to make sure we are

getting the right piece of hardware to do the job.

L. G. Samuels : I am a mechanical engineer. We are sitting here batting

back and forth the purpose of pilot plants. Every morning at the

9:00 a.m. meeting at our plant, there is a big argument about what the

purpose of the pilot plant should be--to prove the process or prove

machinery. Someone asked if we are operating out of specs? Yes, we

are. The SRC plant was designed for a 3 to 1 solvent to coal ratio,

but we proved that the process will work with 1 1/2 to 1. That cuts

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the size of the next plant way down. We built the plant with two

dissolvers with four foot thick walls. These are very expensive vessels.

Even for the pilot plant, they cost about $200,000 apiece. Now we are

operating with one half of one, which means that we have saved 3/4

of the cost of the dissolvers. We have a preheater to heat the slurry

to about 800°F at 1000 lbs pressure. Right now we are operating the

preheater with half the coils insulated, which cuts down the cost of

the unit. We are doing more than proving a process--we are cutting down

the cost of plants and proving out machinery.

Somebody said that private companies like Gulf cannot run research and

development programs like the Government, but we are trying to develop

concurrently other equipment in the plant. We are trying to do basic

research right in our plant to develop a different kind of filter with

no moving parts.

Since last September, we have been under a mandate to produce 3,000 tons

of SRC. Some of us thought we could not do it, but our management said

we were going to do it and we are half way there. We are running our

pilot plant like a production plant.

D. Livaccari, Coal con : I wonder how much money is lost in pilot plant

down time that could possibly have been saved by a simple alert system

among pilot plants. We have heard some discussion about the poor

quality of American equipment. The function of quality assurance is to

put quality in the equipment that you buy.

R. Lewis : I do not quite see how you can put quality in the equipment

you buy by quality assurance when you are forced to buy the cheapest

thing on the market.

D. Livaccari : I disagree that you are forced to buy. You are forced

to evaluate costs, but you are also forced to evaluate a vendor's

expertise, experience, engineering, etc.

R. Lewis : No, sir. If you are buying a conventional item, you must

take the low bid.

R. Perkins, Lockheed, Palo Alto : Another change is taking place in

American industry that I have not heard mentioned here. We in the aircraft industry have become painfully aware of this change. Years ago,

you could get either a materials producer or an equipment producer to

do anything if you paid him for it. But today, chances are he will say

no. There is a danger in assuming you can get an improved quality

product or an improved material by simply paying more for it. We are

being forced in many cases to even go out of this country to buy

materials because the producers of materials in this country say there

is not enough profit involved. A manufacturer producing pumps by the

thousands will not be willing to change his basic production procedures.

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A. J. Mac Nab : Very good point, Roger. We are buying a large amount

of steel these days from Japan. One of the things that impresses us about the Japanese is that they implement their research. You cannot

ignore that, to say nothing about their cost and delivery times. Temper

embrittlement , for example, is much talked about and worked on in this

country, but the producers do not do much about it.

F. B. Hamel : You must remember that you get what you pay for. If you

put a much greater technical effort into any of these plans, there will

be a major return in quality. The big problem is to justify the higher

costs of quality to management.

S. S. Canja : I do not really feel that I have to defend performance

assurance because, as I said, DoD and NASA have been using this

scientific technical approach to develop good quality material for

many, many years. I am delighted to have had the kind of controversial

discussion that we had today. We do not want to sell the whole program

to pilot plants, but if we can start doing little things day by day in

performance assurance, I think that whenever we built commercial plants,

we will have improved reliability. So we ask everyone to keep an open

mind—do not close your mind to performance assurance.

H. E. Frankel : I am really gratified by this morning's discussion.

We have heard many problems associated with pilot plants. It also has

to be recognized, and I think it has been brought out strongly, that

the basic and prime purpose of the pilot plant is not to prove materials

or components, but processes. But, hopefully by meetings such as this,

what materials and component information that has been developed can be

gathered and used in the design of demonstration plants. I think this

meeting has been eminently successful and it is one of the most

productive meetings I have attended in many years.

221
MECHANICAL FAILURES PREVENTION GROUP

24th MEETING

Prevention of Failures In Coal Conversion Systems

List of

W. Abbott

Battelle

505 King Avenue

Columbus, OH 43201

R. J. Anderson

Battelle

505 King Avenue

Columbus, OH 43201

D. M. Bailey

The Lummus Company

Synthane Pilot Plant

P. 0. Box 18076

Pleasant Hills, PA 15236

M. M. Bailey

NASA/Lewis Research Center

2100 Brooke Park Road

Cleveland, OH 44135

R. J. Basile

Exxon Res. § Eng. Company

P. 0. Box 101

Florham Park, NJ 07932

E. B. Bell

TRW Systems ^ Energy

7600 Col shire Drive

McLean, VA 22101

P. J. Birbara

Coalcon

One Penn Plaza

New York, NY 10001

C. W. Boquist

Argonne National Lab

9700 S. Cass Avenue

Argonne, IL 60439

Registrants

H. C. Burnett

Metallurgy Division

National Bureau of Standards

Washington, DC 20234

S. S. Canja

ERDA Fossil Energy

20 Massachusetts Avenue, NW

Washington, DC 20545

D. Canonico

Oak Ridge National Lab

P. 0. Box X

Oak Ridge, TO 37830

R. Cherry

Battelle

505 King Avenue

Columbus, OH 43201

G. P. Cooper

Consolidation Coal Conpany

3300 One Oliver Plaza

Pittsburgh, PA 15222

S. L. Cooper

Union Carbide

Linde Division

P. 0. Box 44

Tonawanda, NY 14150

R. De Angelis

University of Kentucky

Dept. of Metallurgical Eng.

Lexington, KY 40506

0. Decker

Mechanical Technology, Inc.

968 Albany-Shaker Road

Latham, NY 12110

222
D. Dubis

ERDA, Synthane Pilot Plant

2304 Cassidy Drive

Bethel Park, PA 15102

W. A. Ellingson

Argonne National Lab

9700 S. Cass Avenue

Argonne, XL 60439

A. Fo Ems

TRW Systems § Energy

7600 Colshire Drive

McLean, VA 22101

H. F. Feldmann

Battelle

505 King Avenue

Columbus, OH 43201

J. W. Flannery

The Int'l Nickel Co, Inc.

One New York Plaza

New York, NY 10004

P. M. Fleming

Metallurgy Division

National Bureau o£ Standards

Washington, DC 20234

J. K. Floess

G. E. Company

Chemical Processes Branch

P. 0. Box 8

Schenectady, NY 12301

H. E. Frankel

ERDA Fossil Energy

20 Massachusetts AA/enue, NW

Washington, DC 20545

E, R. Fuller, Jr.

National Bureau o£ Standards

Building 223, Room A- 35

5

Washington, DC 20234

D. J. Gaertner

Gulf Science ^ Tech.

P. 0. Drawer 2038

Pittsburgh, PA 15230

R. G. Gillis

Embassy of Australia

1601 Massachusetts Avenue, NW

Washington, DC 20036

R. M. Grayson

Steams-Roger, Inc.

Homer City, PA 15748

S. Greenberg

Argonne National Lab

9700 S. Cass Avenue

Argonne, IL 60439

V. Griffiths

Montana College of Mineral

Science § Tech.

Butte, MI 59701

M. A. Hagan

Jet Propulsion Lab

4800 Oak Grove Drive

Pasadena, CA 91103

A. M. Hall

Battelle

505 King Avenue

Columbus, OH 43201

F. Hamel

Gulf Science § Tech. Company

P. 0. Drawer 2038

Pittsburgh, PA 15230

P. Henry

Peoples Gas Light § Coke Co.

122 S. Michigan Ave., Room 1725

Chicago, IL 60603

A. 0. Hoffman

Battelle

505 King Avenue

Columbus, OH 43201

223
J. R. Hoffman

Kaman Science Corporation

1500 Garden of the Gods Road

P. 0. Box 7463

Colorado Springs, CO 80933

M. A. H. Howes

IIT Research Institute

10 W. 35th Street

Chicago, XL 60616

L. K. Ives

I^tallurgy Division

National Bureau of Standards

Washington, DC 20234

C. Jackson

Battelle

505 King Avenue

Columbus, OH 43201

C. E. Johnson

Metallurgy Division

National Bureau of Standards

Washington, DC 20234

L. Katz

Babcock ^ Wilcox

20 S. Van Buren Avenue

Barberton, OH 44203

J. A. Kaye

Stearns-Roger, Inc.

Homer City, PA 15748

J. Kelly

Rolled Alloys, Inc.

5311 Concord Avenue

Detroit, MI 48211

H. K. Keswani

Gulf Res. ^ Development Co.

P. 0. Drawer 2038

Pittsburgh, PA 15230

Y. Kita

Nippon Steel USA, Inc.

200 Park Avenue, Suite 5310

New York, NY 10017

E. E. Klaus

The Pennsylvania State Univers

133 Chemical Eng. Building

University Park, PA 16802

R. L. Klebe

Stellite Division

Cabot Corporation

1020 Park Avenue

Kokomo, IN 46901

J. R. Lane

National Academy of Sciences

Washington, DC 20410

M. Lapides

Electric Power Res. Institute

Building 3412, Hillium Avenue

P. 0. Box 10412

Palo Alto, CA 94304

N. P. Lapinski

Argonne National Lab

9700 S. Cass Avenue

Argonne, IL 60439

J. F. Leterle

Conoco

Box 1267

Ponca City, OK 74601

A. V. Levy

Lawrence Berkeley Lab

Building 62, Room 351

Berkeley, CA 94720

R. Lewis

ERDA Fossil Energy

4800 Forbes Avenue

Pittsburgh, PA 15213

22k
F. F. Ling

Rensselaer Polytechnic Institute

Troy, NY 12181

D. Livaccari

Coalcon

One Penn Plaza

New York, NY 10001

T. Long

Kaman Sciences Corporation

1500 Garden o£ the Gods Road

P. Oo Box 7463

Colorado Springs, CO 80933

H. W. Lownie, Jr.

Battel le

505 King Avenue

Columbus, OH 43201

A. J. Mac Nab

C. F. Braun and Company

1000 S. Freemont

Alhambra, CA 91802

R. E. Maringer

Battelle

505 King Avenue

Columbus, OH 43201

W. R. Martin

Oak Ridge National Lab

Metals § Ceramics Division

Oak Ridge, TN 37830

N. A. Matthews

Bureau o£ Mines

2401 E Street, NW

Washington, DC 20034

D. E. McCabe

Westinghouse R § D Center

Beulah Road

Pittsburgh, PA 15235

R. L. McCafferty

Gulf R § D Company

P. 0. Drawer 2038

Pittsburgh, PA 15230

R. W. McClung

Oak Ridge National Lab

P. 0. Box X

Oak Ridge, TO 37830

R. L. McCray

Illinois Coal Gasif. Group

122 S. f4ichigan Avenue, Suite 2014

Chicago, IL 60603

R. Merrill

COGAS Development Co.

P. 0. Box 8

Princeton, NJ 08540

M. Miller

Fairchild Stratos Division

1800 Rosecrans Avenue

Manhattan Beach, CA 90266

R. S. Miller

Office of Naval Research

800 North Quincy Street

Arlington, VA 22217

D. Milligan

Hydrocarbon Research, Inc.

334 Madison Avenue

Morristown, NJ 07960

E. R. Mokros

Consulting Eng. Service

315 W. Prospect Avenue

Appleton, WI 54911

A. B. Mowry

Fairchild Stratos Division

1800 Rosecrans Avenue

Manhattan Beach, CA 90266

J. J. Mueller

Battelle

505 King Avenue

Columbus, OH 43201

K. Natesan

Argonne National Lab

9700 S. Cass Avenue

Argonne, IL 60439

225
W. Netter

Lone Star Lafarge Company

Suite 220, Bldg. 18

Koger Executive Center

Norfolk, VA 23502

J. J. Nowak

Dravo Corporation

One Oliver Plaza

Pittsburgh, PA 15222

M. S. Nutkis

Exxon Res. § Eng. Company

P. 0. Box 51

Linden, NJ 07036

J. R. Ogren

TRW Systems ^ Energy

7600 Col shire Drive

McLean, VA 22101

W. Orchard

Institute o£ Gas Tech.

3424 S. State Street

Chicago, IL 60616

E. Passaglia

Institute for Materials Research

National Bureau of Standards

Washington, DC 20234

R. Perkins

Lockheed- -Palo Alto Research Labs

3251 Hanover

Palo Alto, CA 94304

D. E. Price

Columbia Gas

1600 Dublin Road

Columbus, OH 43215

R. A. Rapp

Ohio State University

116 W. 19th Avenue

Columbus, OH 43210

D. Roach

Battelle

505 King Avenue

Columbus, OH 43201

G. S. Rosenberg

Argonne National Lab

Building 335

Argonne, IL 60439

A. W. Ruff

Metallurgy Division

National Bureau of Standards

Washington, DC 20234

L. G. Samuels

P ^ M Coal Mining Conpany

Gulf Mineral Resources

Box 199

Dipont, WA 98327

A. Saule

Dravo Corporation

One Oliver Plaza

Pittsburgh, PA 15222

A. 0. Schaefer

The Metal Properties Council, Inc.

345 East 47th Street

New York, NY 10017

F. Schmidt, Jr.

EI DuPont De Nemours § Company

ETL-Building 304, A311

Wilmington, DE 19898

C. A. Schulz

Conoco, Research Division

Library, PA 15129

R. Seidl

All is -Chalmers

P. 0. Box 512

Dept 3320/GE

Milwaukee, WI 53201

226
T. R. Shives

Metallurgy Division

National Bureau of Standards

Washington, DC 20234

D. W. Short

Lawrence Livermore Lab

P. 0. Box 808

Livermore, CA 94550

W. L. Silence

Stell ite Division

Cabot Corporation

1020 W. Park Avenue

Kokomo, IN 46901

E. N. Skinner

Consultant - Inco

114 Atlantic Avenue

Pt. Pleasant Beach, NJ 08742

L. L. Sluzalis

Stearns -Roger, Inc.

P. 0. Box 5888

Denver, CO 80217

C. 0. Smith

University of Detroit

4001 W. McNichols

Detroit, MI 48221

J. H. Smith

Metallurgy Division

National Bureau of Standards

Washington, DC 20234

R. W. Staehle

Ohio State University

119 West 19th Avenue

Columbus, OH 43210

G. C. Stanton

Argonne National Lab

9700 S. Cass Avenue

Argonne, IL 60439

T. M. Stastny

Exxon Res. ^ Eng. Company

P. 0. Box 101

Florham Park, NJ 07932

J. E. Stem

NASA/Goddard Space Flight Center

MS Code 325

Greenbelt, MD 20771

W. C. Stitzel

Armco Steel Corp. Res. Center

703 Curtis Street

Middletown, OH 45043

B. Thielbahr

ERDA/Conservation

20 Massachusetts Avenue

Washington, DC 20545

A. M. Tiemey

Fairchild Stratos Division

1800 Rosecrans Avenue

Manhattan Beach, CA 90266

G. Ugiansky

Metallurgy Division

National Bureau of Standards

Washington, DC 20234

J. W. Unverferth

Chevron Research

576 Standard Avenue

Richmond, CA 94802

R. W. Weeks

Argonne National Lab

9700 S. Cass Avenue

Argonne, IL 60439

A. J. West, Jr.

Sandia Labs

Box 969

Livemore, CA 94550

W. A. Willard

Metallurgy Division

National Bureau of Standards

Washington, DC 20234

227
R. L. Williams

Kaman Sciences Corporation

P. 0. Box 7463

Colorado Springs, CO 80933

F. P. Williamson

Panhandle Eastern Pipe Line Co.

P. 0. Box 1642

Houston, TX: 77001

G. Wilson

HRI Eng., Inc

8420 NW 52nd Street

Miami, FL 33166

S. M. Wolf

ERDA

Division of Physical Res.

J- 309

Washington, DC 20545

S. Wolosin

Curt is s -Wright Corporation

One Rotary Drive

Woodridge, NJ 07075

R. Wood

Battelle

505 King Avenue

Columbus, OH 43201

J. P. Young

Metallurgy Division

National Bureau of Standards

Washington, DC 20234
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1. Glossary of Terms AD 721 354

2. Proceedings of Meetings 1-9 (set of 5) AD 721 359

Meeting Nos. 1-5 Papers and discussion on failure

analysis and control.

Meeting No. 6 "Detection, Diagnosis and Prognosis",

December 6, 1968.

Meeting No. 7 "Failure Mechanisms as Identified

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March 27, 1969.

Meeting No. 8 "Critical Failure Problem Areas in

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June 25-26, 1969.

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"Identification and Prevention of Mechanical

Failures in Internal Combustion Engines"

July 8-9, 1970.

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October 19-20, 1970.

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"Advances in Decision-Making Processes

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January 25-26, 1971.

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"Failure Mechanisms: Corrosion"

April 14-15, 1971.

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"Mechanical Failure Prevention Through

Lubricating Oil Analysis"

November 2-4, 1971

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"Effects of Environment Upon Mechanical

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April 25-27, 1972.

11. Proceedings of Meeting No. 18 AD 772 082

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November 8-10, 1972.

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October 31 - November 2, 1973.

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May 8-10, 1974.

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NBS-1 14A (REV. 7-73)

U.S. DEPT. OF COMM. 1. PUBLICATION OR REPORT NO. 2. Gov't Accession

BIBLIOGRAPHIC DATA No. SHEET NBS SP-468

3. Recipient's Accession No.

4. TITLK AND SUBTITLH

Prevention of Failures in Coal Conversion Systems--Proceedings

of the 24th Meeting of the Mechanical Failures Prevention

Group

5. Publication Date

April 1977

6. Performing Organization Code

7. EDITORS

T. Robert Shives and William A. Willard

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No.

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Inst. for Matls.Res., NBS, Washington, DC 20234; ONR, Arlington,

VA NAUL, Warminster, ka ioy/4, rranKTora Arsenal,

Philadelphia, PA 19137; FAA, Washington, DC 20591; Battelle,

Columbus Labs, Columbus, OH 43201; ERDA, Washington, DC 20545

Ij. I ype 01 Report & Period

Covered

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

Library of Congress Catalog Card Number; 77-608043

16. ABSTRACT (A 200-word or less factual summary of most si^ificant information. If document includes a significant

bibliography or literature survey, mention it here.)

These Proceedings consist of a group of twenty submitted papers and discussions from

the 24th meeting of the Mechanical Failures Prevention Group which was held at

Battelle, Columbus Laboratories in Columbus, Ohio on April 21-23, 1976. Prevention

of failures in coal conversion systems is the central theme of the Proceedings. A

series of overview lectures dealing with reliability problems in coal conversion

systems, economics of failures in energy generating systems, corrosion, and gaps in

engineering data are presented. In addition, failure analysis, materials problems,

and related materials research are discussed.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons

)

Coal conversion; coal gasification; coal liquefaction; corrosion; failure analysis;

failure prevention; quality assurance; reliability

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