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NBS SPECIAL PUBLICATION 622

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

Prognosis: Contribution to the

Energy Challenge

MFPG

32nd Meeting
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards' was established by an act of Congress on March 3, 1901. The Bureau's overall goal is to strengthen and advance the Nation's science and technology

and facilitate their effective application for public benefit. To this end, the Bureau conducts

research and provides: (1) a basis for the Nation's physical measurement system, (2) scientific and technological services for industry and government, (3) a technical basis for equity in trade, and (4) technical services to promote public safety. The Bureau's technical work is per- formed by the National Measurement Laboratory, the National Engineering Laboratory, and

the Institute for Computer Sciences and Technology.

THE NATIONAL MEASUREMENT LABORATORY provides the national system of

physical and chemical and materials measurement; coordinates the system with measurement

systems of other nations and furnishes essential services leading to accurate and uniform

physical and chemical measurement throughout the Nation's scientific community, industry,

and commerce; conducts materials research leading to improved methods of measurement,

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institutions, and Government; provides advisory and research services to other Government

agencies; develops, produces, and distributes Standard Reference Materials; and provides

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Absolute Physical Quantities2 — Radiation Research — Thermodynamics and

Molecular Science — Analytical Chemistry — Materials Science. THE NATIONAL ENGINEERING LABORATORY provides technology and technical ser- vices to the public and private sectors to address national needs and to solve national problems; conducts research in engineering and applied science in support of these efforts; builds and maintains competence in the necessary disciplines required to carry out this research and technical service; develops engineering data and measurement capabilities;

provides engineering measurement traceability services; develops test methods and proposes

engineering standards and code changes; develops and proposes new engineering practices;

and develops and improves mechanisms to transfer results of its research to the ultimate user. The Laboratory consists of the following centers:

Applied Mathematics — Electronics and Electrical Engineering2 — Mechanical

Engineering and Process Technology2 — Building Technology — Fire Research —

Consumer Product Technology — Field Methods.

THE INSTITUTE FOR COMPUTER SCIENCES AND TECHNOLOGY conducts

research and provides scientific and technical services to aid Federal agencies in the selection, acquisition, application, and use of computer technology to improve effectiveness and

economy in Government operations in accordance with Public Law 89-306 (40 U.S.C. 759), relevant Executive Orders, and other directives; carries out this mission by managing the Federal Information Processing Standards Program, developing Federal ADP standards

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The Institute consists of the following centers:

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'Headquarters and Laboratories at Gaithersburg, MD, unless otherwise noted; mailing address Washington, DC 20234.

J Some divisions within the center are located at Boulder, CO 80303.
HA.TJONAL BUREAU

MFPG

or stahdards

LIBBART OCT 2 2 1981

Detection, Diagnosis and Prognosis: Contribution

to the Energy Challenge

Proceedings of the 32nd Meeting of the

Mechanical Failures Prevention Group,

held at the Inn at Santa Monica,

Santa Monica, California, October 7-9, 1980

Edited by

T. Robert Shives and William A. Willard

Center for Materials Science

National Measurement Laboratory

National Bureau of Standards

Washington, DC 20234

The 32nd meeting of the MFPG and these proceedings were sponsored b\

the Center lor Materials Science ol the National Bureau of Standards. Washington. DC 20234; the Office of Naval Research. Department ol the Navy, Arlington. VA 22217; the Naval Air Systems Command. A. J. Koury,

Washington. DC 20360; and the National Aeronautics and Space Administration, Goddard Space Flight Center, Greenbelt. MD 20771.

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

Issued October 1981
Library of Congress Catalog Card Number: 81-600125

National Bureau of Standards Speeial Publication 622

Nat. Bur. Stand. (U.S.). Spec. Publ. 622. 329 pages (Oct. 198!) CODEN: XNBSAV

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1981

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402

Price $8.00

(Add 25 percent for other than U.S. mailing)
FOREWORD

The 32nd meeting of the Mechanical Failures Prevention Group was held

October 7-9, 1980, at the Inn at Santa Monica in Santa Monica, California. The program, which focused on failure prevention in energy

related systems, was organized by the MFPG Detection, Diagnosis and

Prognosis Committee under the chairmanship of Robert R. Holden of the

Hughes Aircraft Company in Los Angeles. Appreciation is extended to

the committee, the session chairmen, and especially to the speakers

for an exceptional program. Gratitude is expressed to the Hughes

Aircraft Company for hosting the meeting.

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

of the National Bureau of Standards Fracture and Deformation Division

for their editing, organization and preparation of these proceedings,

and to Leonard C. Smith, also of the NBS Fracture and Deformation

Division, for photographic work. Most of the papers in the proceedings

are presented as submitted by the authors on camera ready copy. Some

moderate editorial changes were required.

Gratitude is expressed to Marian L. Slusser of the NBS Center for

Materials Science for handling financial matters.

HARRY C. BURNETT

Executive Secretary, MFPG

Center for Materials Science

National Bureau of Standards

III
TABLE OF CONTENTS

FOREWORD

SESSION I: ENERGY MANAGEMENT

1. Energy Management System. Kempt on Smith (no

manuscript submitted)

2. Statistical Analysis of Core Barrel Motion Orbits.

Ronald G. Canada* and James E. Jones

3. Acoustic Monitoring of Power Plant Valves.

J. W. Allen*, W. F. Hartman and J. C. Robinson

SESSION II: TECHNIQUES FOR DETECTION

1. Oil Debris Detection Progress. Thomas Tauber

2. Advanced Radioactive Engine Wear Analysis for

Filter Design and Evaluation. Gordon W. Jones

3. Oxygen Sensor for Automobile Combustion Control.

H. P. Wertheimer* and D. J. Romine

k. Detection, Diagnosis and Prognosis of Gas Turbine

Engine Health with the Use of Fibrescopes.

Robert M. McCord

SESSION III: BETTER AVAILABILITY

1. Integrated On-Board Detection, Diagnostic and

Prognostic System for Military Application.

Marquis W. Woody and Wsewolod Hnatczuk*

2. Progress with Pielstick Engine Diagnostics and

Experimental Results. A. Genot

3. An Energy Conservation Concept for Operating Machinery. Francois Envent*, Michael Cohill and Henry

Hegner

k. On-Board Instrumentation Techniques for the

Development of a Gas Turbine Engine for Truck

Applications. Paul D. Olivier (abstract only)

IV
5. Marine Ball/Roller Bearing Monitoring by Shock

Pulse Monitoring. Joseph P. Fischer, Donald S.

Schover* and David Board

126

SESSION IV: DIAGNOSTIC AND PROGNOSTIC TECHNIQUES

1. Conservation: Loss Prevention and Risk 139

Management. G. E. Gulbrandsen

2. Recent Experiences with Steam Turbine Disc 152

Cracking. Gerald A. Lamping

3. A Doppler Technique for Detecting and Locating l8l

Excessively Vibrating Blades in a Running

Turbine. R. L. Leon

k. IMACS Cost Savings Estimator - A Trade-Off 195

Analysis for a Built-in Monitoring System.

F. E. Bishop

5. Operating Experience with Advanced Computer 220

Based Surveillence System. S. Paul Mohan

(abstract only)

6. Mechanical and Aerothermal Diagnostics of 222

Turbomachinery. M. P. Boyce and P. J. Norris*

SESSION V: OPPORTUNITIES FOR DETECTION, DIAGNOSIS AND

PROGNOSIS IN THE ENERGY FIELD

1. Data Acquisition and Analysis in the DOE/NASA 257

Wind Energy Program. Harold E. Neustadter

2. Periodic Vibration Monitoring at the Synthane 2jk

Coal-Gasification Pilot Plant. J. T. McCabe

3. A Computerized Broken Blade Monitor for a Nuclear

Fuel Bundle. F. J. Sweeny, C. M. Smith* and

D. N. Fry (oral presentation only)

k. Description of "La Ranee" Tidal Power Plant. 289

Jean Rabaud

5. Detection, Diagnosis and Prognosis in Geothermal 310

Well Technology. A. F. Veneruso* and Hsi-Tien

Chang

V
APPENDIX

List of Registrants for the 32nd MFPG Meeting 323

MFPG Publications 327

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

VI
ABSTRACT

These proceedings consist of a group of 21 submitted entries (19 papers

and 2 abstracts) from the 32nd meeting of the Mechanical Failures Prevention Group which was held at the Inn at Santa Monica, Santa Monica,

California, October 7-9, 1980. The subject of the symposium was the

contribution of failure detection, diagnosis and prognosis to the

energy challenge. Areas of special emphasis included energy management,

techniques for failure detection in energy related systems, improved

detection and diagnostic availability for energy related systems, diagnostic and prognostic techniques for energy related systems, and opportunities for detection, diagnosis and prognosis in the energy field.

Key Words : Energy; energy conservation; failure detection; failure

diagnosis; failure prevention; monitoring techniques; prognosis;

sensors; wear; wear analysis.

UNITS AND SYMBOLS

Customary U.S. units and symbols appear in some of the papers in these

proceedings. The participants in the 32nd 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 the usage of the metric

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

NBS Special Publication, SP330, 1977 Edition, "The International System

of Units."

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

IEEE Standard Metric Practice (institute of Electrical and Electronics

Engineers, Inc., Standard 268-1979).

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. Views expressed by the

various authors are their own and do not necessarily represent those

of the National Bureau of Standards.

VII

SESSION I

ENERGY MANAGEMENT

Chairmen: A. Whittaker, Honeywell, Inc.

J. Philips, David Taylor Naval

Ship R&D Center

STATISTICAL ANALYSIS OF CORE BARREL MOTION ORBITS

Ronald G. Canada

James E. Jones

Technology for Energy Corporation

10770 Dutchtown Road

Knoxville, Tennessee 37922

Abstract: Excore neutron detectors have been widely used to

provide in-service monitoring of the mechanical motion of the

reactor core support barrel in pressurized water reactors. The

accepted procedure for determining core barrel motion (CBM)

involves analyzing small fluctuations in the output signals of the excore neutron detectors and relating part of these fluctuations to

the motion of the reactor core support barrel. This relationship

between detector signal fluctuation and core barrel movement is

non-trivial and statistical descriptors have been previously

developed to make determination of CBM root-mean-squared magnitudes

possible. This paper presents a new statistical descriptor, herein

called Core Barrel Orbits, which provides information about both

the magnitude and direction of core barrel motion. This analysis

can be used to determine the most probable locations for CBM and to

develop confidence limits on the maximum displacements which occur.

Use of this detailed analysis can lead to detection of potential

problems in the core barrel support or restraint mechanisms which

would occur only at certain directions.

Key Words: Core Barrel Motion; Neutron Detectors.; Reactor

Internals; Surveillance; Vibration.

Introduction: Excore neutron detectors have been widely used to

provide in-service monitoring of the mechanical motion of the

reactor core support barrel in pressurized water reactors (Ref.

1-4). The accepted procedure for determining core barrel motion

(CBM) involves analyzing small fluctuations in the output signals

of the excore neutron detectors and relating part of these

fluctuations to the motion of the reactor core support barrel.

This relationship between detector signal fluctuation and core barrel movement is non-trivial and statistical descriptors have

been developed (Ref. 5) to make determination of CBM possible.

These statistical descriptors are the cross- and auto-power

spectral densities and the amplitude probability distribution

3
functions of these fluctuations. These descriptors, although

adequate for determination of CBM magnitude, give little

information about the direction in which the core barrel moves. This paper presents a new statistical descriptor, herein called

Core Barrel Orbits, which provides this information.

CBM Determination

The core of a pressurized water reactor is contained within a cylindrical core barrel which is surrounded by a thermal shield, as illustrated in Figures 2.1 and 2.2. The core barrel is supported

at its top with the lower portion being free to move in a beam

mode, or cantilever fashion. In an operating reactor, movements of

the core barrel are induced primarily by random pressure fluctuations due to the turbulent flow of water in the downcomer and up

through the core. The frequency of this mechanical vibration is

governed primarily by the clamping force of the core barrel support

mechanism.

When a reactor is operating at power, the displacements of the core

barrel produce small variations in the number of neutrons escaping

from the core due to variations in the thickness of the water gap

between the core barrel and thermal shield, as illustrated in

Figure 2.3. These CBM induced variations are superimposed with

signals produced by effects not associated with CBM, such as reactivity fluctuations and statistical variations in the reaction rate

within the detector.

The problem of measuring CBM-induced responses reduces to

separating signal fluctuations due to CBM from the other effects

which are seen by these detectors. This may be accomplished by

realizing that diametrically opposite power range detectors will

see the same signal from beam mode CBM-induced phenomena, but

shifted in phase by 180 degrees. Making use of this realization, a cross power spectral density (CPSD) function may be constructed for

a cross-core detector pair with the corresponding phase and

coherence information used to establish a frequency band over which

CBM is occurring. A band-pass filter may then be employed to

reject signal components outside this frequency range. If CBM is

the dominant driving function over this frequency band (as

determined from the coherence and phase of cross-core detector

pairs), the band-limited signal is primarily the result of only core barrel movement (with some statistical noise). This signal can be assumed to be directly proportional to CBM provided the

system behaves in a linear fashion or if the signal fluctuations

are sufficiently small so that non-linear effects are negligible.
5
Figure 2.3 Representation of the Change in Water Gap Due to Core Barrel Motion

Experimental evidence has defended this linear assumption and a scale factor converting fractional detector response to mils motion

of the core support barrel has been calculated (Ref. 6) as:

n = 0.02 % detector change per mil (2.1)

Theoretical Considerations

The motion of the core barrel can be represented by a displacement

vector, D(t), between the center of motion and the time varying

position of the core barrel center, as illustrated by Figure 3.1.

Given a properly conditioned neutron detector signal, the fluctuation (Xj(t)) caused by this displacement is given by:

x.(t)= D(t),R3 (3.1)

J n

where n represents a conversion factor converting detector response

to mils motion (given by Equation 2.1) and Rj represents a unit

vector in the direction of the detector. Given N detectors,

Equation 3.1 leads to N equations (one equation for each detector)

6
Figure 3.1 Vector Representation of Core Barrel Motion

with only 2 unknown variables - the magnitude and the direction of

the displacement vector, D(t). This set of equations is solvable

for two or more detectors (provided at least two are linearly

independent). Therefore, given at least two neutron detectors

which are separated by an angle different than 180 degrees (to

insure independence), we may transform their time variant signals

into a time variant core barrel displacement (both magnitude and

direction). This provides the basis of the core barrel orbit

statistical descriptor.

Core Barrel Orbit Implementation

Most PWRs have four or six power range neutron detectors which are located as pairs of diametric (cross core) detectors (See Figure

2. IX To construct a core barrel orbit, all available detector

signals are band-limited so that signal components outside the beam

mode core barrel motion range are rejected. A time variant core barrel displacement is then computed from the simultaneous output

of all detectors by employing a least-squares fit to Equation 3.1.

If a large number of the resulting core barrel displacement vectors

are plotted together, a scatter plot similar to Figure 4.1 is

7
0.8 0.4 0.0 0.4

HORIZONTAL DISPLACEMENT IN MILS

0.8

Figure 4.1 Variation in Core Barrel Center Position Over a 5.0 Second Time Interval

produced. This figure clearly indicates the random nature of the core barrel motion since there is not an observable path the core barrel consistently follows. As a result of this random behavior,

describing the spatial characteristics of the CBM is a statistical problem. One approach for quantifying CBM that has

been used is the construction of a joint amplitude probability

distribution function, which describes the two dimensional

probability of the core barrel being in any given position. The

result of this approach, however, does not lend itself to easy

interpretation.

A more direct approach is to average all displacements which occur along any given direction and to compute the variance of these

displacements. When this average is calculated for all directions

and plotted, a plot similar to Figure 4.2 is obtained. The scattered data points in the figure represent the angular displacement

average while the smooth curve is a best fit to an elliptical path.

8
Figure k.2 Average Core Barrel Position and Best Fit Elliptical Path

If the standard deviation limits are also plotted for each direction, the resulting curves will represent the 63 percent confidence

path. This is defined as the path with which there is a 63 percent

confidence level that any given core barrel displacement will be

contained within. By a similar manner, one may obtain the path at

any desired confidence level.

Summary

Statistical descriptors are used to determine core barrel motion

from the signals of the ex-core neutron detectors. The descriptors

currently in use give little information about the directional

manner in which the core barrel moves. A new statistical

descriptor (core barrel motion orbits) is presented which allows

this information to be determined. The theoretical considerations

of this methodology are discussed as well as its implementation and

results. We feel that this new descriptor provides a significant

new tool for the analysis and understanding of core barrel motion.

9
Re f erence s

1. W. G. Pettus and R. L. Currie, "Monitoring Oconee I Internals with Neutron Noise Analysis", Trans. Am.

Nucl. Sec. J_9, 261 (1974).

2. D. N. Fry, R. C. Kryter, and J. C. Robinson, "On-Site

Diagnostics at Palisades Nuclear Power Station", paper

no. 27 of Proc. Symp. Power Plant Dynamics, Control, and

Testing, Knoxville, Tennessee (October 1973). Also Annals

Nucl. Energy 2, 341 ( 1975).

3. Federal Register announcement of "Regulatory Guide of Core

Barrel Motion Monitoring", Fed. Reg. 44 (126), (June 30, 1975),

p. 27508.

4. C. W. Mayo and R. L. Currie, "Neutron Noise Monitoring of

Pressurized Water Reactor Internal Vibrations" Proc. of the

Second Specialists Meeting on Reactor Noise. (Sept. 1977).

5. J. C. Robinson, J. W. Hardy, G. S. Shamblin, and C. L. Wolff,

"Monitoring of Core Support Barrel Motion in PWRs Using Ex-Core

Detectors" Proc. of the Second Specialists Meeting on Reactor

Noise. (Sept. 1977).

6. J. C. Robinson, F. Shahrokhi, and R. C. Kryter, "Inference of

Core Barrel Motion from Neutron Noise Spectral Density",

ORNL/NUREG/TM-100 (1977).

10
ACOUSTIC MONITORING OF POWER PLANT VALVES

J. W. Allen, W. F. Hartman and J. C. Robinson

Technology for Energy Corporation

10770 Dutchtown Road

Knoxville, Tennessee 37922

Abstract: Hydrodynamic related signals from pressurized water reactor

(PWR) feedwater control valves (FCVs) measured by a mini-computer based

monitoring system were able to predict and identify vibration levels and

cavitation conditions during plant transients. These results came from

a program sponsored by the Electric Power Research Institute (EPRI), the

overall objective being to increase nuclear power plant availability by

monitoring FCVs for failure mechanisms leading to plant shutdowns.

Acoustic emission and accel erometer signals, inlet water pressure, feedwater temperature and signals necessary to calculate water velocity were analyzed. The analyses determined that cavitation and high vibration

conditions occurred during certain operating conditions. These results

can be used by power plant operators to avoid operating conditions where

cavitation will occur.

Key words: Acoustic emissions; cavitation; feedwater control valve; pattern recognition; pressurized water reactor; remote surveillance.

INTRODUCTION

The Electric Power Research Institute is sponsoring research projects to

improve monitoring and diagnostic systems for power plant machinery.

The primary objective of these projects is to increase plant availability by developing systems that can detect failures early enough to warn operators of impending failures and inform maintenance personnel in ad- vance about the nature of the failure. Warnings will allow compensation

in advance for the eventual equipment shutdown, and information on the

nature of the failure will allow more effective planning and scheduling

of maintenance

.

One of the projects in this program is RP1246-1, "Acoustic Monitoring of

Power Plant Valves." The overall objective of the project was to

improve nuclear power plant availability, productivity and safety

through the application of advanced surveillance techniques to power

plant valves. The scope of work reported here concerns PWR Feedwater

Control Valve Monitoring and includes:

• A survey and classification of PWR feedwater control valve (FCV)

induced outages to determine likely failure modes which could be

monitored

11
• The development of analytic models for FCVs

• The design and construction of a remotely located, minicomputer

based system to monitor FCVs

• Installation of the monitoring system and data acquisition at

three PWR plants

• Evaluation of system performance and a conceptual design for a reduced system

SURVEY AND CLASSIFICATION OF FCV FAILURES

A survey was conducted with the intent of identifying the prominent

failure modes in FCVs. This survey utilized EPRI report NP-241,

"Assessment of Industry Valve Problems," in conjunction with License

Event Reports (LER) and communications with power plant personnel and

FCV vendors. As a result, six classifications of FCV problems and

failures were identified. These are:

• Controller Malfunction

-- Problems in this category are characterized by mechanical

failure of components or poor response of the FCV to normal

demands such as passivity when movement is expected and motion

which does not correspond to the demand given.

• Mechanical Breakdown

-- This category is characterized by structural degradation of

FCV components. This includes such items as stem failure,

trim cracking and air line breaking.

• Hydrodynamic Instability

-- This category is characterized by structural degradation

directly attributable to flow and FCV misbehavior due to particular flow instabilities. This includes cavitation

phenomena, sudden valve motion not related to controller

demand signals and water leakage.

© Electronic/Pneumatic Malfunction — This category is characterized by electrical and pneumatic

component problems and includes spurious signals to controller

components and breakdowns of components of an electrical

and/or pneumatic nature.

• Generic Design

1L1
-- This category is characterized by inadequate design of FCVs

for the ooeratinq conditions encountered. This includes items

such as under/oversized actuators or underdamped movement

characteristics.

® Human Error

-- This cateogory is characterized by misjudgments of the operator and improper repair.

The problem areas investigated in this report include controller malfunction, mechanical breakdown and hydrodynamic instability.

RESULTS AND CONCLUSIONS

The surveyed problems and failures of FCVs were listed and placed in one of the six classifications discussed above. The plant downtime asso- ciated with each failure was also included. The primary source of this

data is EPRI Report NP-241. The results are summarized in Table 1.

Table 1

SUMMARY OF SURVEY OF FCV FAILURES ________

Failure Category Incidents Forced Outages Downtime (days)

Control ler

- Mechanical 7 7 4.4

- Unknown 13 11 5.8

Mechanical 10 7 9.5

Hydrodynamic 5 4 3.6

Electronic/Pneumatic 14 5 4.7

Generic 2 2 70.0

Human _J3 _3 1.1

TOTALS 54 39 99.1

The following conclusions were made based on the survey results shown

above and the communications with plant personnel and vendors:

13
• Most of the mechanical problems in FCVs appear to be a result of

excessive vibrations and/or associated physical fatigue. This is

reflected by vendors who are now redesigning the FCV internal

structure and actuator damping features in order to reduce

excessive vibrations.

• Many problems are apparently due to stem packing tightness; i.e.,

if it is too loose, the FCV leaks but if it is too tight, the

stem is unable to move. Determining the proper tightness is

still more of an art than a science.

© The "unknown" controller problems could not be attributed

directly to water flow phenomena or spurious behavior of the

controller components.

o Many of the electronic malfunctions were on equipment mounted

directly onto the FCV topworks which are related to the control

signals (e.g., valve positioners, actuators, I/P transducers),

and were induced by excessive vibrations.

FCV ANALYTICAL MODELS

In order to assist in the design and development of the surveillance

system and aid in the interpretation of data, analytic models of the FCV

internal structures were developed and the FCV controller and internal

structures interaction with hydrodynamic phenomena were analyzed.

Controller

The controllers were typical 4-20 mA, three-element controllers using

feedwater flow/steam flow mismatch and steam generator level as the

controlling parameters. Figure 1 shows the flow of the control signals

and the normal components used. These components are usually a com- bination of (1) a low pass filter to eliminate spurious steam generator

level signals, (2) two integral-proportional filters, (3) a current to

pressure (I/P) transducer, (4) a stem positioner, and (5) a diaphragm or piston operated actuator.

Valve Internal Structure

Mechanical models of the FCV plug and trim were derived to determine

resonant frequencies that could be excited by hydrodynamic forces.

Finite element models were developed for a double globe stem- plug

assembly, a cylindrical stem-plug assembly, and an upper and lower trim.

These models determined the resonant frequencies of the dominant mode

shapes for the plug-stem assemblies clamped at the bonnet and for the

upper and lower trim. These are shown in Table 2.
15
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16
The notable features of these models are:

• The longitudinal resonant frequencies for the plug-stem

assemblies were both around 450 Hz.

• The cylindrical plug-stem assembly has a torsional resonance

around 43 Hz that was not seen in the double globe assembly.

o The valve trim structures had resonant frequencies greater than

4 kHz.

A further analysis of the torsional resonance in the cylindrical plugstem assembly for stem lengths not clamped at the bonnet determined that

resonant frequencies could vary from 11 to 19 Hz depending on length and

clearance assumptions.

Hydrodynamic Phenomena

The internal structure of the cylindrical plug modelled above was con- ducive to vortex shedding phenomena. Vortex shedding frequencies were determined which could create both torsional or longitudinal driving

forces for various flow rates through the valve. These are summarized

in Table 3.

TABLE 3

Vortex Shedding Frequencies for the

Cylindrical PI ug-Stem Assembly

Shedding Frequency (Hz)

Flow Rate (lbs/hr) a Longitudinal Torsional

3.5 x 106 30.5 15.3

3.2 x 106 28.0 14.0

2.7 x 106 27.5 13.8

2.3 x 10 6 19.8 9.9

1.9 x 106 16.4 8.4

1.5 x 106 13.4 6.7

a Rated 100% flow rate is 3.5 x 106 lbs/hr.

Cavitation in valves can occur on the exit side of the ports if the

water velocity becomes high enough to cause the vena-contracta pressure

to drop below the fluid vapor pressure. The vena-contracta pressure was

IT
calculated by assuming the ports act as a sudden contraction in a free

steam pi pe, i .e.

,

Pv = Po -

•

2 pCd 2 A

2

where in = Fluid flow rate

P = Fluid density

Po i i cc jti cum yJi c jjui c

A = Area of the port

Pv = Vena contracta pressure

and Cd = Discharge coefficient.

DESIGN AND CONSTRUCTION OF THE FCV SURVEILLANCE SYSTEM

A mini-computer based pattern recognition system was chosen for the FCV

monitoring. The system was designed to be moved to a plant site and set

up in a remote area where it would continuously monitor the FCV.

The design and construction of this FCV surveillance system was done in

three overlapping stages:

• Determination of key parameters, the signals required to monitor

them and the sensors required.

• Procurement and construction of a mini -computer based hardware

system.

• Development of data handling and pattern recognition algorithms.

A simplified block diagram of the finished system is shown in Figure 2.

Determination of Key Parameters, Signals and Sensors

The parameters important for monitoring the failure modes presented in

the survey were chosen using input from plant and vendor personnel and

engineering judgement. Following the selection of these parameters, the

signals or variables best describing them were chosen on the basis of

availability and simplicity. Special effort was made to include signals

already available in the plants; otherwise sensors were chosen to make

the measurement. A total of 19 signals were chosen of which six were already available. Table 4 summarizes the key parameters, sensors and

variables measured.

18
e

IONE ROL

PUTE E

O So O

UJ u r

I

(A

OC > o o

LL

UJ(A

tc

UJ V)

t- Z 3 <

< a <e z

_J 5 o

a o

o

19
Table 4

KEY PARAMETERS, SENSORS AND MEASURED VARIABLE

USED IN THE FCV SURVEILLANCE SYSTEM

Key Parameter Sensor(s) Measured Variable

Valve Demand and

Response

(Control ler)

Valve and Valve

Stem Vibration

(Mechanical

)

Pressure transducer3

Pressure transducer

Linear Variable

Differential Transformer (LVDT) b

Flow transmitter0

Flow transmitter0

Level transmitter0

Pressure transmitter0

Accel erometer3

Accel erometer

Control pressure to positioner

Actuator pressure

Stem position

Feedwater flow

Steam flow

Steam generator level

First stage turbine pressure

(nominal power level)

Valve stem-plug accelerations

Valve body accelerations

Valve Hydrodynamic

Character!

- sties

Rosette strain gauge^ Dynamic strain in valve stem

Acoustic emissions Acoustic emissions

Pressure transmitter0 Absolute outlet water pressure

Pressure transmitter6 Absolute inlet water pressure

RTD or thermocouple0 Feedwater temperature

Notes: a Sensor was mounted on two separate FCVs.

b Sensor was mounted on two separate FCVs except for the first

pi ant.

0 Sensor was available as a plant signal.

d Sensor was available for 2 of 3 plants.

e Sensor was available for 1 of 3 plants.

20
System Hardware Components

The hardware components were procured and built to support the desired

signal characteristics discussed below.

Development of Algorithms

The data handling algorithms can be placed in the following five

categories:

• Signal characterization

• Pattern recognition

• Data storage

• Data display

• Off-1 ine analyses

The signals were characterized by: (1) steady state or absolute (DC)

value, (2) root mean square (RMS) value of the noisy component over various frequency bandwidths, (3) power spectral density (PSD), and

(4) cross power spectral density (CPSD) with another signal. The CPSD

was displayed in terms of coherence and phase.

The pattern recognition algorithms were developed to operate in three

primary modes: (1) a learning mode to determine "normal" baseline

signal characteristics; (2) a tracking mode to survey for abnormal signal characteristics; and (3) a transient mode for non-steady state

operating conditions (e.g., power reductions). Data storage was developed to allow serial storage (for historical inspection) and to store

all abnormal measurements. Data display was developed to displav the

signal characteristics either graphically or numerically. Off-line

algorithms for in-depth analysis were developed as necessary.

INSTALLATION AND OPERATION OF THE MONITORING SYSTEM

The monitoring system was installed in three operating PWRs for about

100 days each.* The first plant had an FCV with a cylindrical plug and

diaphragm-operated actuator; the second plant had an FCV with a double

globe plug and diaphragm-operated actuator; and the third plant had a cylindrical plug with a piston-operated actuator.

*At the third plant, only 40 operating days were monitored.

21
Plant 1 had a chronic history of FCV problems including:

© Breaking stems

• Leakage through the stem packing

© Loss of control due to overtightened stem packing

© Significant stem and topworks torquing resulting in mounted

equipment failure.

Plant 2 had few problems with their FCVs and was chosen for comparison

purposes.

Plant 3 had moderate problems including:

© Leakage through the stem packing

© Loss of control due to overtightened stem packing

©Sudden, inexplicable rapid movements of the valve plug

Plant 3 was also a source of additional comparative information as a topworks changeout was done during the course of the monitoring

measurements.

Significant Results

Six major results were obtained from the data analysis.

© FCV stem and bonnet vibration levels were correlated with the

plants' historical problems; i.e., higher vibrations were measured

on those FCVs which had a history of trouble, particularly at high

frequencies

.

©All the FCVs showed strong vibrational peaks at various points in

a normal power transient.

© Tightening and loosening of the valve stem packing could be seen

in strain gauge and accelerometer data.

© Strain gauges detected significant valve stem torquing at one of

the plants.

• Conditions approaching cavitation were calculated, measured and

verified.

© Significant differences were seen before and after the valve topworks changeout of Plant 3.

22
FCV Vibration Levels

The vibrational data at higher frequencies revealed much higher stemplug and valve body vibrations for FCVs at Plants 1 and 3 than Plant 2.

The stem RMS accelerations at Plant 1 is nearly 47 g's over the frequency range 0-15 kHz (most of it over 3 kHz) whereas at Plant 3, the

two stem RMS accelerations were 5 and 10 g's and at Plant 2, they were

0.9 and 1.3 g's. Figures 3 and 4 show the FCV stem RMS accelerations

and integrated accelerations for each 1 kHz bandwidth at the three

plants.

FCV Vibrations During Power Transients

In some cases during power transients, several power levels could be

identified where vibrations were higher than they were at full power.

This phenomenon was particularly pronounced at Plant 2. Figure 5 shows

the RMS stem accelerations band-passed from 0-20 and 20-1000 Hz respectively for a startup at Plant 2.

There are evident vibrational peaks at power levels from ~ 4£)-50% and ~ 75-85% particularly in the higher frequency range. This phenomenon

was seen repeatedly during all transients and at the other plants.

FREQUENCY (Hi)

Figure 3. RMS Accelerations for the FCV Stem from 0 to 15 kHz

23
Figure 4. Integrated RMS Accelerations for the FCV Stem

from 0 to 15 kHz

100

POWER LEVEL %

Figure 5. RMS Vibrations of the Valve Stems from 20 to

1000 Hz During a Startup n% Plant 2

2k
Vibrations Related to FCV Stem Packing Tightness and Valve Torquing

At both Plants 1 and 2, stem vibration data was obtained which clearly

indicated when the stem packing was tightened. At Plant 1, this vibration was due to an excited torquing resonance of the stem-plug assembly

at about 14 Hz. Figure 6 shows the PSD of a strain gauge mounted 45° to

the stem axis on four separate days. The peak at 14 Hz increased dramatically until the stem packing was tightened when it reduced to nearly

its original level. The RMS value of this signal ranged from 38 yin/in

on the 28th day to 123 yin/in on the 48th day to 45 pin/in on the

51st day. The tightening of the stem packing was also observed at

Plant 2 by monitoring the stem accelerations.

Cavitation Parameters

Cavitation can occur whenever the water pressure falls below the liquid

vapor pressure. At Plant 3, calculations indicated cavitation

conditions. Figure 7 shows the vena contracta pressure and the liquid

vapor pressure for a transient to ~ 50% power and then back to 100%

power. There were several times when the vena contracta pressure fell

below the vapor pressure. This was reflected by the acoustic emissions

whose 100 to 400 kHz RMS value increased as the pressure difference between the vena contracta and liquid vapor pressure decreased (Figure 8),

This increase was attributed to the increasing water velocity through

the trim ports.

DAY 47

io 35

I 40 45—r

50

1 r~ 20 25 30

FREQUENCY (Hz) Figure 6. PSD of Stem Strain Gauge Showing Torguing Frequency

at 14 Hz and Effect of Stem Packing Tightening on Day 48

25
o

o

00

O.O O.I 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 I.O

TIME (DAYS)

Figure 7. Water Vapor Pressure and Vena Contracta Pressure

During a Power Transient

O O.l 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 I.O

TIME (DAYS)

Figure 8. Acoustics Emissions During a Power Transient

26
FCV Topworks Changeout at Plant 3

During the monitoring period at the third plant, the piston actuator was replaced with a different model. Four significant results were seen:

(1) there^was a large increase in the piston pressure; (2) the problem

with sudden unexplained stem motion disappeared (as of this writing);

(3) there was a corresponding significant increase in a mechanical

vibration resonance in the plug and stem assembly at ~ 900 Hz; and

(4) cavitation conditions appeared.

CONCLUSIONS AND DISCUSSION

Three of the significant results pertained to phenomena which could be

continuously monitored to assist plant operators in maintaining the FCV

integrity:

• FCV vibration resonances during plant transients

• Vibrations related to the tightness of the stem packing

• Detection of cavitation conditions.

The ability to calibrate and monitor these phenomena would allow operators to avoid those conditions where high vibrations and/or cavitation

may exist and to be able to determine when and/or how much to tighten

the stem packing. The other two results fell primarily into generic and

calibration design categories. Further investigation would need to be

done by the specific plants and/or vendors to affect the adverse

conditions.

EVALUATION OF THE FCV MONITORING SYSTEM AND THE CONCEPTUAL DESIGN FOR A

REDUCED SYSTEM

The FCV monitoring system was remotely located at three plant sites and

successfully measured and evaluated large amounts of data on a con- tinuous basis using customized measurement, storage and pattern recognition techniques. These algorithms formed the bases for determining the

significant results discussed above. The FCV surveillance system is a state-of-the-art on-line monitoring system developed to prevent unne- cessary plant outages.

The features designed for this system include the ability to:

• Alert the surveillance system operator to measured variables which

do not conform to the normal state of affairs

• Use pattern recognition techniques to establish baseline data

libraries and the expected ranges of the measured variables under

normal conditions

27
• Measure and store a large number of variables

• Perform in near real time operation

©Provide historical information for long term trends

© Perform when the plant is in both steady state and transient

operation modes.

The FCV surveillance system was designed to be general and flexible

enough so that adjustments could be made during the course of operation.

This was necessary because the nature of the signals chosen for monitoring was largely unknown. Therefore, it was necessary to use an overly large number of representative variables and trim down the number

as their effectiveness was evaluated. Among those variables which were

most useful in this evaluation were:

• The steady state, DC values of the signals

©Root Mean Square (RMS) values of the AC component of the signals

©The power spectral density (PSD) of the signals.

Several variables were found which were not of significant value. These

were:

©Some variables comprising the controller (steam generator level

and steam flow)

©Calculated time series variables for controller representation

© Low frequency power spectral densities (CPSDs) displayed as coherence and phase.

Concept of a Reduced System

The significant events which occurred suggest three functions which

could be monitored by a reduced system:

• Maintenance of proper stem packing tightness

© Avoidance of vibrational or torquing resonances during transient

and normal operations

© Maintenance of an adequate margin from incipient cavitation

conditions.

28
In addition, there was a lack of significant results concerning the

valve controller. Since known problems have occurred in the controller,

a fourth function should be considered:

• Assurance that positioner and actuator functions are performing as expected.

The required sensors for such a reduced system would be a subset of

those used in the general system described in the main report. These sensors are shown in Table 5. In addition to the above sensors, a "status" sensor should be chosen to indicate gross operational

conditions, e.g., power level.

Table 5

SENSORS REQUIRED FOR A REDUCED MONITORING SYSTEM

Sensor Location Function Monitored

Accel erometer Stem Packing, vibration

Accel erometer Bonnet Vibration

Acoustic emissions Bonnet Packing, vibration,

cavitation

Flow transmitter Feedwater line Cavitation

LVDT Stem Cavitation, controller

Pressure transmitter Inlet feedwater 1 ine Cavitation

Pressure transmitter Outlet feedwater line Cavitation

Pressure transducer Positioner pressure

1 ine

Control 1 er

Pressure transducer Actuator pressure line Control 1 er

Rosette strain gauge Stem Packing, vibration,

twi sting

Thermocouple/RTD Feedwater Line Cavitation

29
Microprocessors could be designed for the individual functions above.

In order to monitor all of the functions, a mi ni -computer designed for

field use in a non-optimal environment may be required. Furthermore,

the computer peripherals, sensors and signal conditioning, should also

be resistant to such environmental conditions as heat, dirt and non- routine maintenance.

30
SESSION M

TECHNIQUES FOR DETECTION

Chairmen: D. Fairchild, Fram Corporation

R. M. Whittier, Endcvco Corporation

OIL DEBRIS DETECTION PROGRESS

Dr. Thomas Tauber

TEDECO

(Technical Development Company)

24 E. Glenolden Avenue

Glenolden, Pennsylvania 19036

Abstract: For the last two years, the U.S. Army has been

testing an Advanced Oil Debris Monitoring System on a fleet

of 36 UH-1 helicopters at Fort Rucker, Alabama. To date,

approximately 25,000 flight hours have been logged. The

system has successfully detected all failures of oil-wetted

engine and transmission components, most of which were

missed by the conventional chip detectors and by SOAP.

These include transmission input quill and mast bearing

failures as well as engine No. 2, 3 and 21 bearing failures.

In all cases, the system has given early, unambiguous and

repeated failure alert. Component removal in early response

to these alerts has resulted in very limited or no secondary

damage. In some instances, only the affected component

required replacement.

Key words: Chip detectors; condition monitoring; failure

detection; helicopter diagnostics; oil debris; wear monitoring .

The benefits of improving existing wear debris monitoring

techniques are well-known and easily understood. For

instance, the U.S. Army estimates that 86% of all chip

lights in its helicopter fleet are erroneous and therefore

cause unnecessary mission aborts^). Despite a logistically

complex and expensive Condition Monitoring Program consisting of Spectrometric Oil Analysis, chip lights, filter

checks and pilot inputs, unnecessary component removals and

failures progressing to considerable debris and secondary

damage are a problem.

In 1978, the U.S. Army began testing an advanced debris

monitoring system at its Aviation School in Fort Rucker as

part of the so-called OLSAFE program. Initially involving

60 helicopters of its instrument flight training center, the

program originally had a different main objective. It was

designed to demonstrate that ultrafine filtration will

permit the extension of oil change intervals in the engine

33
from the current 100 to 1000 hours and in the transmission

from 300 to 1000 hours and thereby save the Army a considerable amount of Mil-L-23699 oil.

Previous experience on T-53 engines equipped with ultrafine

filters and with the General Electric T-700 engine with its

7-micron filter had indicated that Spectrometric Oil

Analysis becomes virtually ineffective. This is due to the

fact that these filters remove the recirculating fine debris

which gradually builds up as a failure progresses and which

otherwise could lead to SOAP indication.

Considering the low reliability of existing chip detectors,

the need for an improved oil debris detection system became

clear. The system which was eventually developed to meet

this need consists of

Full-flow chip detectors in engine and transmission

Pulsed chip detection system ("Zapper" or

"burn-off") throughout the aircraft

Separate cockpit indication parallel to and

redundant with existing chip light installation

FULL-FLOW CHIP DETECTION

In older installations, such as the T-53 engine and the UH-1

transmission, chip detectors are of the splash-type. This

means that they are located in the sump wall, usually with

no provision to ensure that wear debris is transported to

them. The magnetic attraction of the chip detector alone

cannot pull the debris from the corners of the sump. That

splash-type chip detectors are not very effective is illustrated by the fact that oil filters, coolers and oil lines

usually contain much more debris after a failure than the

chip detector.

The principle of full-flow debris monitoring places the chip

detector into the scavenge oil flow where the entire flow

can be intercepted. Figure 1 compares the splash-type chip

detector with a full-flow chip detector located in the pump

inlet screen. The oil, on its way to the pump, deposits the

debris in the screen where it is indicated by the chip

detector. A full-flow chip detector installation takes

advantage of the oil being the debris transporting agent, in

addition to its lubricating and cooling functions.

3k
In the OLSAFE program, the engine and transmission full-flow

chip detectors are located on the pressure side of the

scavenge pumps. Figure 2 shows the lube system schematic of

the T-53 engine with the location of the full-flow debris

monitor. The conventional chip detector is located in the

accessory gear box and its function is retained. The fullflow debris monitor, shown in Figure 3, is actually a centrifugal debris separator. The oil enters tangentially

into a cylindrical chamber and creates a vortex whose

centrifugal action separates the heavier wear debris from

the oil and deposits it on the chip detector at the bottom

of the chamber. The high debris capture efficiency of this

device is illustrated in Figure 4.

The transmission full-flow chip detector is shown in Figure

5. It replaces the disc-type filter located inside a transmission cavity. Since the disc filter also has the

function to protect an oil jet downstream, the chip detector

has an internal screen through which the oil flows back into

the transmission.

PULSED CHIP DETECTION SYSTEM

The majority of erroneous chip lights of conventional chip

detectors are caused by "wear fuzz". This fine debris is

the product of normal wear processes.

Pulsed chip detection systems are designed to suppress these

erroneous chip lights. This is accomplished by a current

pulse which discharges through the chip detector, melting

the contacts between the fine wear debris but leaving

larger, failure-related particles unaffected. This type

of chip detector also has come to be known as "Zapper" or

"burn-off" chip detector.

The engine and transmission, as well as the tail rotor and

intermediate gear box chip detectors in the OLSAFE program

are of the pulsed type. The necessary electronics are

located in the cockpit display panel which is shown in

Figure 6

.

For reasons of flight safety, the pulsed chip detection

system is completely redundant with the conventional chip

detection system of the aircraft. The cockpit display panel

originally had a manual pulse switching feature, as indicated in Figure 6. This allowed the pilot to initiate the

pulse. However, the program has shown that the failure

indication reliability is very high and all panels have

since been converted to the automatic mode. This means

that chip indications caused by fuzz or fine slivers are

suppressed automatically.

35
STATUS OF OLSAFE PROGRAM

As indicated previously, the major objectives of the program

are as follows:

Reduce no-cause component removals (engines,

transmissions, gear boxes)

Reduce mission aborts due to erroneous chip

lights

Increase oil change intervals from 100 (engine)

and 300 hours (transmission) to 1000 hours.

The program is currently configured as follows: 36 UH-1

helicopters belonging to the U.S. Army Flight Training

School at Ft. Rucker have been modified with improved debris

detection systems and ultrafine filters. This fleet logs

approximately 2000 hours per month and has attained a total

of about 25,000 flight hours. An additional control group

of eleven unmodified helicopters flies under identical conditions. The high-time aircraft in the test group has

approximately 1000 hours on engine and transmission. In the

control group, there is a high-time engine with 1700 hours

and a high-time transmission with 1300 hours.

In both groups, the oil is not changed until component overhaul. The condition of the oil is determined from samples

taken every 50 hours which are analyzed at the Naval Air

Propulsion Test Center (NAPTC) in Trenton, New Jersey. All

aircraft are also within the Spectrometric Oil Analysis

Program conducted at Ft. Rucker.

Following a chip light indication, the chip detector is

removed and replaced with a clean one. The contaminated

chip detector is- photographed and the debris analyzed at

the Joint Oil Analysis Program (JOAP) Center in Pensacola,

Florida. If the component is removed, the tear down

inspection results are carefully documented. In this way,

the information loop consisting of chip light/oil analysis/

debris analysis/tear down result is closed. This is one of

the major accomplishments of the program.

Approximately one year into the program it was realized that

some chip indications were caused by debris reintroduced

into the engine and transmission by inadequate design of the

bypass system on the ultrafine filters. This required substantial modification of the filters and of the engine fullflow debris monitor. To date , 22 aircraft have been retrofitted with the improved filters. Accordingly, data on

36
erroneous chip light indications cannot be considered

reliable at the present time.

RESULTS

The improved chip detection system has shown a 100% reliability in detecting failures of oil-wetted components.

Table 1 lists eight of the thirteen failures which have

occurred in the test group and for which tear down inspection records are available. It is interesting to note the

wide variety of failures. They include transmission mast

bearing, input quill bearing and gear failures, as well as

engine shaft bearing and accessory gear box bearing failures.

In all cases, the full-flow chip detectors provided early

and repeated warnings. Where the component was removed soon

after the start of indications, secondary damage was minimal.

None of these failures was detected by SOAP; only one was

indicated by the conventional chip detector. However, even

this indication was preceded by warning from the full-flow

chip detection system.

A typical engine failure is illustrated in Figure 7. The

failure was caused by a rotating No. 2 shaft bearing. Upon

removal, the outer bearing race was found to have. 006 inch

deep wear ridges. Otherwise, the bearing was in good condition. None of the other shaft bearings or any of the

accessory gear box components showed secondary damage. The

debris causing the indication is shown in Figure 8. It

should be noted that failures of this type which have been

thought to produce mostly fine debris have generally been

considered not detectable with chip detectors. This opinion

is clearly based on splash-type chip detectors which would

have had no chance to collect the small amount of debris

shown in Figure 8.

A second failure, this one in the transmission, is illustrated in Figure 9. This failure was caused by spalling of

the inner bearing in a triplex input quill set. The failure

had started long before the conversion of the aircraft.

Installation of the full-flow chip detector led to immediate

and repeated indications. When the transmission was removed,

there was considerable debris damage to bearings and gears,

as a result of the extensive operation with the failing

bearing prior to aircraft modification.

The debris from a transmission mast bearing failure is shown

in Figure 10. The transmission was equipped with the fullflow chip detector for a period of 301 hours. During that

time, there were eight chip lights. As a result of the

37
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38
extended operation with the failure in progress, there was

some debris damage. It is worth noting again that in the

UH-1 transmission a mast bearing failure is not reliably

indicated by the splash-type chip detector. The sun gear

and other components of the gear train collect much of the

debris on its way down into the sump. With the splash-type

chip detector off to the side of the transmission and somewhat above the sump floor, its capture efficiency is much

lower than that of the full-flow chip detector.

CONCLUSION

Despite the fact that the OLSAFE program has not been concluded, it has demonstrated that oil-wetted component

failures are indicated reliably and with long warning

periods by full-flow chip detectors. This points the way

to meeting a major program objective, namely the development

of unambiguous component removal criteria and elimination of

no-cause overhauls. During the remaining test time, determination of the frequency of erroneous chip lights will be

the main objective. This has not been possible due to the

filter reconfiguration mentioned earlier. The program has

further demonstrated that the oil change interval can be

extended safely.

Above all, the program has shown that full-flow debris

monitoring represents a significant improvement in Failure

Detection

.

ACKNOWLEDGMENTS

The author wishes to thank Wayne Hudgins of the Ft. Eustis

Applied Research and Technology Laboratories, Rhett Farrior

of the U.S. Army Aircraft Development Test Activity,

Ft. Rucker, Dick Lee of the Joint Oil Analysis Program,

Pensacola and Dominic Lubrano for valuable contributions

to this paper.

REFERENCE

1. D. P. Lubrano: "Field Experience Of Contamination

Effects And Diagnostic Effectiveness On Helicopter

Transmissions And Engines", 1977 Meeting of ASLE,

Atlanta, Ga

.

39
ko
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FIGURE 5: TRANSMISSION FULL-FLOW CHIP DETECTOR

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U8

ADVANCED RADIOACTIVE ENGINE WEAR ANALYSIS FOR

FILTER DESIGN AND EVALUATION

Gordon W. Jones

Fram Corporation

E. Providence, R.I. 02916

Abstract: Tests were performed to evaluate the effect of filtration on

the wear rates and particle size sensitivities of nine components within an engine. The wear measurement method used was a thin layer radioactive activation technique which had been proven in previous engine wear studies. In this test program, several advances were made in the wear analysis technique itself, which permitted measurements of one micrometer of wear on the components. These advances were primarily in

the test technique and data analysis areas.

The tests performed yielded results significant to filter design and

evaluation. The most important conclusion reached in regard to filtration was that particle wear sensitivity varied for different engine

components. This variability included different particle size sensitivities and different effects of filtration on the engine components.

This variation was used in the tests to demonstrate the different wear protection values of two filter media for several engine parts.

Key Words: Oil filter testing, oil filter design, radioactive wear

testing, engine wear analysis, particle size sensitivity, effect of

f iltration

.

The life blood of an engine is the oil used to lubricate it. As this

oil circulates through the engine, it insulates surfaces against wear.

In order to do this job effectively, the oil must be kept clean; this is

the function of the oil filter. How may we determine whether an oil

filter is protecting the oil and the engine? There are many bench test

procedures available for oil filters which have been written by manufacturers and technical societies. These procedures are valuable for

filter to filter comparisons, but they lack a direct correspondence to

actual engine protection in the field. The procedures cannot tell us whether a filter will prevent wear within an engine.

One method to evaluate the wear protection of a filter would be to measure the wear surfaces then measure what wear has occurred on engine

parts during a test by disassembling the engine. This would be a difficult and time consuming project. It would also introduce more variables

since when the relative positions of wearing components are changed, the wear rate also changes until the parts have broken in again. A better

50
measurement method would be one in which the engine need not be taken

apart for the measurements to be made. This is the advantage of radioactivity as a measurement tool; it penetrates the engine walls, permitting measurements of the parts inside.

This paper presents the results of a test program run on a diesel engine

to examine the effect of contaminant on its wear rates and the influence

of filtration on preventing this wear. The long range goal of the program was to determine methods which would allow more effective filter

design to meet the requirements of an engine.

The SPI-WearTM Method

The radioactive measurement method used in the tests was the SPI-Wear

technique devised by the SPIRE Corporation of Bedford, Massachusetts.

The method was developed to make measurements of surface wear in areas which are inaccessible or where conditions make physical measurement

methods impossible. The original application of the technique was to

measure the erosion of missile nosetips during atmospheric re-entry.

It permitted wear measurements to be made during the flight itself.

The measurement system consists of two parts, an activated volume of the

test component, and a gamma ray detector and readout instrument. The

detector measures the radiation being emitted by the activated material,

which is proportional to the depth of material remaining. This radiation measurement, or count rate, may be related to wear depth by a calibration curve.

The main advantage of this method as a measuring tool is the way in

which the radioactivity is used. The use of radioactivity as a wear measurement technique is not new, it has been used in many applications

in the past (1) (2) . Most previous uses relied on a bulk activation of

the test component in which a large volume of the part was made radioactive. This large amount of activated material caused the emission of

high radiation. This presented safety problems to the test personnel

and, because of the large activated volume, sensitivity to wear was

poor. In some techniques, the wear debris was monitored rather than

the part itself in order to increase sensitivity. This presumed that no radioactive material was lost between the occasion of wear and the measurement. The SPI-Wear method solves these problems by using a very

small amount of activity.

Activation of the wear measurement point is accomplished by bombarding

the area with a beam of high energy particles. These particles may be

alpha particles, protons, deuterons or helium-3, all of which are generated in a cyclotron. These high energy charged particles can activate most metals in common alloys. The beam can be controlled so that

it activates a very selective volume of the test specimen. This is con- trolled by varying the area and kinetic energy of the beam. The activated spot can be as small as 1.6 mm in diameter and as shallow as 7.6

ym. This allows a very small area to be monitored for wear with a high

51
8

degree of sensitivity. The limitations of this activation technique are

that the material can be activated and that the beam must reach the test

spot with no obstructions. The latter requirement necessitates the disassembly of the engine parts for activation. Once the activated parts

are installed, however, no further disassembly is required.

Since the technique can carefully control the site of the activation and

its intensity, it is possible to test several different wear points

within an engine at the same time. This is especially true if the com- ponents to be monitored are of different materials, leading to different

radiation spectra. In any case, when more than one spot is monitored at

a time, cross-talk is an important consideration. This may be minimized

through the location of the test elements, shielding of the detector, or through mathematical derivations during the data analysis. This ability

to monitor more than one test spot at a time permits several different

areas of an engine to be monitored under identical conditions.

Another advantage of this system is that it can produce depth measurements by relating radiation and wear depth through a calibration curve. This curve is generated through the careful wearing and measurement of a sample identical to that under test. These identical parts are irradiated at the same time so that their activation volumes and energies are

the same. The calibration part is then manually worn while being measured for depth of wear with a corresponding radiation count. These

points generate the calibration curve.

Previous Engine Testing Experience

The test program on a diesel engine described in this paper is the third

set of tests done by Fram and SPIRE using this technique. The previous

two test programs used an eight cylinder and a four cylinder gasoline

engine (3) . These tests were done to establish the applicability of the

SPI-Wear technique to engine wear measurements and to further refine

test methods so that the best possible data would be obtained in further testing. These tests showed that the SPI-Wear method could be used

to measure engine wear. They also demonstrated that multiple point mon- itoring was feasible provided careful fixturing and test controls were

used. Most of the problems which had to be resolved in these tests involved how the engine was run and how contaminant was introduced into

the engine. With the problems resolved, however, these tests demonstrated conclusively the value of the filter in preventing wear. Conclusions about the filter's role in wear prevention could also be drawn

from the results which showed a varying wear response for test components to different contaminant particle sizes. The results of these

previous test programs provided an excellent foundation for the diesel

engine tests and showed which paths new filter investigations should

take

52
The Diesel Test Program

This test program was undertaken to gain more information about filtration and its role in preventing engine wear. A primary goal of the program was to better define how a filter should be designed to protect an

engine. Based on past testing experience, a test schedule was drawn up

which called for monitoring nine different parts within a V-8 direct injection diesel engine for wear responses. The nine parts were:

1. oil ring lands

2. top compression ring surface

3. compression ring groove

4. intake valve sealing surface

5. fuel injection pump plunger

6. rocker arm bearing

7. wrist pin bearing

8. main bearing

9. connecting rod bearing

The tests performed were grouped under three main topics. The first

series was used to establish the engine wear rates with contamination in

the oil and the effect of filtration on these wear rates. The second

series investigated the effect of different particle sizes on engine

wear. The third test series investigated the comparative life and efficiency of two filter media types on the engine. In all, twenty different tests were run on the engine, with measurements of all nine points

taken after each test.

In previous testing, two main problems had been observed: the method of

introducing contaminant into the test engine and the method of maintaining test part to detector relationships. Previous findings had indicated that the best method of introducing contaminant was in a slurry

form directly into the lubricating oil system. In these tests, the test

contaminant (AC Fine Test Dust or fractions thereof) was mixed with a quantity of oil to form a slurry then pumped with a peristaltic pump to

the engine oil pump inlet at a controlled rate during testing. It was

found that this method offered the best repeatibility and eliminated

problems of contaminant agglomeration.

The problem of maintaining a constant relationship between the test part

and the detector is dealt with in two ways. Since all of the test com- ponents could move relative to the engine block, all had to be brought

to a reference position each time a measurement was made. Since all the

parts are mechanically tied to the engine crankshaft position, this was used as the reference to return all parts to their measuring position.

Each time measurements were made, the crankshaft was brought to the ref- erence position and pinned there. This insured that each part was in

the proper position for measurement.

53
The mounting of the detector itself is the second part of the problem.

The solution used was to prepare a detector mount bolted to the engine

block in each of the nine test locations. The detector was mounted in

a lead lined sleeve which insured that it would be attached to the en- gine in the proper position for each measurement. The lead sleeves also

helped minimize the problem of cross-talk between test locations by limiting the field of view of the detector to the test component at that

particular location.

Application of SPI-Wear to Diesel Testing

This set of tests was one of the most ambitious engine program applications for the SPI-Wear method. To be successful, a great deal of care

had to be taken in all phases of the method. Many new techniques were

designed so that errors were further minimized from previous testing,

making even finer measurements of wear possible. All of the planning

and new technique development of the SPI-Wear method for this program

was done by F. L. Milder of the SPIRE Corporation. Through his efforts,

the measurements taken during this program were the most accurate

possible

.

In this program, the SPI-Wear method was tailored and improved to meet

the requirements of wear measurements at nine different locations in

the engine. The program followed the basic outline of the method as described before, but used different techniques in many areas to improve

the data obtained.

The oil ring, compression ring, wrist pin bearing, piston, valve, rocker

arm bearing and the fuel injection pump plunger were all irradiated

using an alpha particle beam. The depths of activation ranged from 20

micrometers for the fuel injection pump plunger to 100 micrometers for

the compression ring. These depths of activation were sized for the

projected wear rate for each part. Each of the parts, with the exception of the valve, was irradiated with a 6.4 mm diameter spot in the

location projected to be the maximum wear point for that part. The

valve was irradiated over the full sealing surface.

A problem was encountered with the main and connecting rod bearings ac- tivation. Because of their material, a lead tin alloy, activation by

the particle beam method was not possible. The bearing material would

not activate sufficiently to overcome the signal produced by the iron

impurities in the surface of the bearing, which were also activated.

So that data could still be obtained from these two points, a different

activation technique was used. This involved the implanting of four

tin wires plated with ^Co into each bearing. The diameter of these

wires was 0.38 mm with the sides being plated for a length of approximately 0.25 mm. The four wires for each bearing were implanted in a 6.4 mm diameter area. These wires provided sufficient activity for

measurements to be made of these parts.

5h
One phase of the method which underwent the most scrutiny was the process of curve fitting for both the calibration curves and the radiation

spectra. Errors in these phases must be minimized to reduce errors in

the conversion from count rate to wear depth. For the calibration

curves, the fit was to a polynomial function of arbitrary order. The

order of the equation finally chosen was that which had the smallest

chi-square per degree of freedom while still being a physically reasonable curve. For the spectra curve fits, a peak or pair of peaks was chosen for each of the parts monitored. These peaks were then fitted

with a combination of two functions, one for background and a gaussian

for each peak. For both the calibration and spectra curves, errors were

determined and used in the final error margin calculations.

With nine irradiated spots within the engine, there was a question of

whether crosstalk would be a problem. To account for this effect, each

part was put into the engine, one at a time, and count rates were taken

at the monitoring points for all nine parts. These count rates gave the

amount of interference due to each spot at the monitoring points for the

other eight spots. In testing, it was found that there was a significant crosstalk between the main and connecting rod bearings and the

wrist pin bearing and compression ring. Because of the interference

matrix generated before testing, the actual strength values for these

components could be derived during the data analysis.

Tests and Results

The objectives of the test program were to determine the effectiveness

of filters in preventing engine wear and to determine directions which

future filter design and testing should take. To meet these objectives,

three sequences of tests were performed: wear with and without filtration, wear versus particle size, and wear versus filter media selection.

While analyzing the test data, it was found that the most significant

data regarding filtration was generated by three parts, the main bearing, the oil ring, and the wrist pin bearing. The rocker arm bearing,

piston ring groove, and the valve showed only a minor degree of wear during all the tests. 'The fuel injection pump plunger showed a significant wear, but this is not associated with lube oil contamination. The

compression ring showed a considerable amount of wear, but the test to

test scatter prevented the drawing of conclusions from any single test.

The data from the connecting rod bearing could not be used because one

of the implants broke free and migrated in the bearing surface. Because

of these results only the data from the main bearing, oil ring and wrist

pin bearing are reported and concluded upon in this paper.

In all the tests performed, an artificial contaminant (AC Fine Test Dust

or particle size fractions thereof) was used to accelerate wear rates.

These contaminants are representative of road dust which is the abrasive

contaminant likely to be present in the oil system. These contaminants

are also used in bench evaluation of filters. This provided a link

whereby the bench test results and the engine test results could be com55
pared. In all tests, the engine was run on a dynamometer using a load/

RPM cycle representative of on-highway service. Before any tests were

run, the new parts were allowed to break in during a run-in period of

six hours. Following this, initial readings were taken for all parts.

Wear Reduction through Filtration - the first test sequence run was to

evaluate filter wear prevention effectiveness. To do this, a comparison was made between the wear generated by injecting two grams of ACFTD

(0-80 micrometer) into the engine lube oil system with no filters present, and the wear generated by injecting twenty grams of ACFTD with

normal filters present in the system. These amounts of contaminant were

arrived at based on previous engine test results and an estimate of filter efficiency at 90%. The contaminant was added at a rate of 0.017

grams/min. for the no filter test and at 0.167 grams/min. for the filter

tests. The contaminant was injected in slurry form into the oil pump

inlet. Test duration was two hours with the engine run on a simulated

highway load/RPM cycle for the full time period.

The wear measurements produced in these tests reveal the effectiveness

of filters at preventing wear, but also raise other questions. The

greatest reduction in wear occurred with the oil ring. Here the use of

filtration reduced the wear rate by 96%. The wear reduction for the

main bearing was 86% and for the wrist pin bearing, 57%. These wear reduction figures also account for the difference in dust add rates.

The differences in wear rate reduction are indicative of the difference

in both the method of lubrication and the clearance between wearing sur- faces for each of these parts. The main bearing and wrist pin bearing

are pressure lubricated and see a higher oil flow rate than the oil

ring. This higher flow rate both subjects the parts to more particles

per unit time and tends to wash particles from the clearances. Despite

the filtering of particles, any particles present will probably have

many opportunities to cause wear. The oil ring sees low oil flow for

lubrication and washing, therefore any particles present would probably

be trapped allowing them to cause more wear. With filters present,

fewer particles will reach the oil ring because of reduced numbers and

low flow rates. The clearance between wearing surfaces will also influence wear rates; if particles can pass between the parts, there can

be little wear. This is more closely examined in the particle size sen- sitivity testing.

Particle Size Sensitivity - the next group of tests run were to determine if the engine parts were more sensitive in terms of wear to different contaminant particle size ranges. To do this, two gram samples

of particle size fractions of ACFTD were introduced into the lube oil

system, under the same conditions as in the previous study, with no filters present. The particle size ranges used were: 0-5 micrometer,

5-10 micrometer, 10-20 micrometer, 20-40 micrometer, 40-80 micrometer

and 80-200 micrometer. The 80-200 micrometer dust was derived from AC

Coarse Test Dust which is the same chemical composition as ACFTD but

with larger particles present (up to 200 micrometer) . This type of

56
testing is frequently used in the hydraulic industry to evaluate sensitivities of pumps, motors and seals, most notably in the work of

Oklahoma State University's Fluid Power Research Center (4) (5). This

testing is done to evaluate system filtration needs, and it seemed most

natural to extend it to another oil system, the lube system of an engine.

The test results were surprising. Rather than a uniform sensitivity to

all particle sizes, or a common maximum sensitivity for all parts which

might be expected, the measurements showed that the main bearing, wrist

pin bearing and oil ring were all sensitive to different particle sizes.

For the oil ring, its maximum sensitivity occurred with 5-10 micrometer

particles, for the main bearing 20-40 micrometer, and for the wrist pin

bearing 20-80 micrometer particles. This sensitivity to different particle sizes may be best explained by each of these parts having different clearances between wear surfaces. These clearances allow a particular size range to cause more damage than others, since the smaller

particles pass through causing little wear and the large particles cannot enter the clearances. What is not explained by this theory is that

the oil ring, which is the best protected by a filter, is the most sen- sitive to very small particles which would presumably pass through the

filter more easily. A possible explanation is that the grinding action

of both the oil pump and the oil ring itself gradually converts the

larger particles to particles in the sensitive size range for the oil

ring. Without the aid of filtration, the large particles become small,

increasing the wear rate with time. With filtration, these large particles are removed, lowering the concentration of critical particles over

the long run, resulting in lower overall wear.

Filter Media Comparison - in the automotive industry, there has been a trend toward extending service intervals for the engine. One method of

extending the life for a filter (life defined to a specified pressure

drop) is to use a more "open" filter medium. The more "open" medium 'is usually of lower efficiency in particle retention capability. For this

reason an evaluation was made comparing the wear rates with a "tight" versus "open" medium.

These tests were run differently from the preceeding tests. While previous tests were run using a set time period and contaminant addition,

the media comparison tests used the life of the filter as an end point.

To achieve this, the test was run and contaminant added until the filter

reached a differential pressure of 10 PSI, considered the end of the

filters effective life in this engine application. The contaminant used

was ACFTD with an add rate of 0.67 grams/min. The injection point and

method was the same as for previous testing. The two media chosen had

previously been run on this engine type in endurance testing and had ex- hibited a longer on-engine life for the open medium. These tests used no contaminant addition; only the contaminants formed by the engine itself

plugged the filters. Bench testing of these filters to the appropriate

57
specification with ACFTD could not, however, discriminate between the

two media.

The first result of the testing was that the open medium took 2.7 times

longer to plug than the tight medium. This agreed well with the results

of on-engine performance with no contaminant added. The amount of dust

added to plug the tight medium also agreed well with the bench test for

this medium type. However, there was no correlation between the bench

test of the open medium and its on-engine performance with or without

contaminant being added.

The wear measurements taken for these tests tell a significant story.

After normalizing for the different engine running times, it was determined that the wear rate for the wrist pin bearing increased by a factor

of 2.5 by using the open medium in place of the tight medium. For the

main bearing, the ratio was better than 3:1. The oil ring results did

not differ from one medium to the other, however. This result may seem incongruous until the results of the particle size sensitivity tests are examined. The oil ring is sensitive to a particle size range where neither filter medium has much effect, therefore there is little difference

in the wear rates. For the wrist pin and main bearings, their sensitivities lie in a range where the two media perform differently, consequently, there is a difference in wear rates.

These tests demonstrate the trade-off involved in extending service intervals through reduced filter performance. The more open medium does

allow a great increase in on-engine life but at the expense of increased

wear rates for any components whose sensitivity to particles lies in the

area where the media differ.

Conclusions

This test program was devised to investigate engine wear and the effect

of oil filtration on this wear. Three main objectives were part of this

investigation: wear reduction through filtration, wear versus particle

size and wear versus filter media selection. All tests were performed

on a diesel engine, using a radioactive wear measurement technique. To

maintain a controlled test and a reasonable test time, contaminants representative of the abrasive dust encountered by the engine in service were used to accelerate the wear rates. Since the primary function of

the filter is the removal of abrasive contaminant, their use is consistent with both actual engine conditions and the bench testing usually

done on filters.

Several significant conclusions may be drawn based on the results of

this testing.

1. The SPI-Wear method of wear measurement is an invaluable tool in the

investigation of wear processes. It permits multiple locations within

the engine to be measured and tested at the same time without any engine

58
disassembly other than the initial installations of irradiated parts.

Without this method, an investigation of this type would be extremely

difficult.

2. Filtration of the engine oil greatly reduces the wear experienced

by the engine parts. The reduction of wear due to abrasive action is

just one part of the picture, as evidenced by the different wear rate

reductions for different parts. If the primary failure mode for a com- ponent is through abrasive wear, however, the proper choice of filter

should prevent these failures.

3. Each component within an engine is sensitive to different particle

sizes. These differences probably stem from lubrication methods and

clearance differences. These differences in sensitivity complicate the

design of a filter for the entire system, since the increased cost and

service life penalty of a finer filter must be weighed against the cost

of repairing or replacing a component sensitive to the smaller part icles

.

4. Selection of a filter for a system on the basis of service interval

only may be a poor decision. The cost of increasing on engine filter

life is an increased wear rate for many of the engine parts.

In the long run, the useful life of the engine may be reduced as a con- sequence of trying to extend service intervals.

Future Filter Design and Testing - the results of the testing done here,

although they are the products of tests run on only one type of engine,

show the directions that filter design and testing should take in the

future. These directions will require a rethinking of current design

and testing practices to better reflect the true objective of filtration,

engine protection.

Design of Filters - because the primary function of the filter is engine

protection, the wear characteristics of the engine should be the basis

for the design of the filter. Past practices have largely been to me- chanically design a filter which will fit a space alloted it by the en- gine manufacturer. Selection of the specifications for filter performance is left to the engine manufacturer. With increased demands being

put on an engine for greater performance in a smaller, more fuel efficient package, the requirement for optimum filter performance will cer- tainly increase. In such a case, the engine itself must be used to determine the proper filtration design.

Using the entire engine for wear evaluations as was done here may not be

necessary. If a critical component in the engine could be identified,

then only this part need be measured to evaluate filtration needs. By

generating a particle size sensitivity spectrum for this critical com- ponent, the filter could be sized to meet the particle size retention

efficiency required to protect this part. Further filter evaluation

could then be done using a multi-pass type of testing, which uses parti59
cle size retention as a measure of the filter's efficiency. Further design development would then take the path of gaining maximum filter life

in a given envelope size while maintaining this protection level.

Testing of Filters - most current bench tests for filters use life and

efficiency measured in terms of volumetric or gravimetric contaminant

removal as a measure of the filter's value. These procedures frequently

do not reflect either actual engine filter life or whether the filter in

fact protects the engine. The results of the filter life testing performed here could show a way to modify bench tests to better reflect on- engine performance. The filter life using the bench contaminant in the

engine correlated well with actual engine performance using no contaminant. Yet the results did not correlate well with existing bench tests

using the same contaminant. Perhaps the solution may be as simple as using the engine oil pump in the test bench, since its particle modification capability may be causing the change in filter performance observed. Further testing will be necessary to examine this possibility.

The ideal bench test would be one that correlated directly with the

field performance, but this is not available in current procedures.

In the case of evaluating particle retention efficiency, a procedure is

available which measures this parameter. This procedure, if tied to the

particle size sensitivities of an engine would allow a good evaluation

of the engine protection potential of a filter.

The use of wear evaluation as a tool in the design and testing of filters will lead to the optimization of filters for engines. The end

result of this technology will be to reduce filter costs, increase the

protection of the engine by the filter, and consequently and most importantly, reduce the cost of operating the engine and increase reliability.

References

1. J. E. McClelland and S. M. Billett, "Filter Life versus Engine Wear".

Paper 650866 presented at SAE National Fuels and Lubricants Meeting,

Tulsa, November 1965.

2. J. J. Gumbleton, "Piston Ring and Cylinder Wear Measurements

Illustrate the Potential and Limitations of the Radioactive Technique."

SAE Trans., Vol. 70 (1962).

3. G. W. Jones, A. J. Armini, and N. C. Schoen, "Selective Radioactive

Tracers for Engine Wear Diagnosis and Filter Evaluation." Paper 780972

presented at SAE International Fuels and Lubricants Meeting, Toronto,

November 1978.

4. E. C. Fitch and G. E. Maroney, "A Fundamental Method for Establishing

Contaminant Tolerance Profiles for Pumps." Paper CI, Second Fluid Power

Symposium, BHRA, January 1971.

6o
5. W. T. Bonner and L. E. Bensch, "Hydraulic Motor Contaminant

Sensitivity Testing." Paper 74-40, BFPR Program, Fluid Power Research

Center, Stillwater, Okla. , 1974.

s

6i
OXYGEN SENSOR FOR AUTOMOBILE COMBUSTION CONTROL

H. P. Wertheiraer

Bendix Autolite Corporation

Fostoria, Ohio 44830

D. J. Romine

Bendix Autolite Corporation

Fostoria, Ohio 44830

"Three way" catalytic converters are effective in reducing automotive exhaust emissions of carbon monoxide, hydrocarbons, and oxides

of nitrogen, but only when the exhaust chemistry is near stoichiometry. The exhaust gas oxygen sensor makes possible a closed loop

fuel metering system to provide and maintain the required exhaust

gas chemistry entering the three way converter. The oxygen sensor

is a solid electrolyte galvanic cell which produces about one volt

when it is exposed to a "rich" exhaust mixture and near zero volts

when the exhaust is "lean". The sensor can signal the electronic control of the closed loop system whether the mixture is rich or lean,

thereby permitting the system to control at or near stoichiometry

.

The system of three way converter together with closed loop fuel metering permits meeting stringent exhaust emission standards while maintaining better fuel economy than would be provided by known alternatives.

Key words: Air-fuel ratio; Closed loop fuel metering system; Exhaust

emissions; Exhaust gas oxygen sensor; Exhaust gas recirculation;

Feedback; Oxidation catalyst; Oxygen partial pressure; Stoichiometric;

Three way catalytic converters; Zirconium dioxide.

Introduction

Since the 1968 model year (1966 in California) , government limits for

exhaust emissions have been in effect for all new cars sold in the United States. Initially, the limits applied to emissions of carbon monoxide (CO) and unburned hydrocarbons (HC) . A third exhaust gas constituent, oxides of nitrogen, was recognized as having an adverse impact

on air quality, and it was found that the control approaches for CO

and HC often caused an increase in emissions of oxides of nitrogen

(NOx) . Federal limits on oxides of nitrogen were applicable starting

with 1973 models. The standards, limiting the maximum amounts of each

pollutant to be emitted per vehicle mile, have been made progressively

more stringent. The vehicle manufacturers have responded by using many

emission control approaches to meet these standards. Generally, the

approaches can be classed into four generations.

62
The first generation, used for 1968 through 1972 models, combined

selective spark timing retard with lean (relative to uncontrolled

cars) air-fuel ratios. Improvements in the accuracy and distribution

of the fuel-air metering systems were needed and were developed during

this period. Some manufacturers used an approach in which the airfuel ratios were rich and an engine driven pump delivered air to the

exhaust ports, creating an afterburning effect when the air mixed with

the hot exhaust gases.

The standards for NOx spawned the second generation control systems. In

the 1973 and 1974 models controlled amounts of exhaust gas were routed

back to the engine intake. This exhaust gas served as an inert diluent

in the combustion process, lowering peak temperatures and thereby re- ducing emission of oxides of nitrogen. These exhaust gas recirculation

(EGR) systems were used in conjunction with the features of the first

generation.

Model year 1975 marked the advent of catalytic converters and the third

generation control systems. Catalytic converters, which served to

promote oxidation of CO and HC, required the use of unleaded fuel. The

converter based systems permitted retuning the engines to improve efficiency and driveability

The first of the fourth generation (closed loop) control approaches

appeared in some 1977 models sold in California. Three key developments led to a concept of a catalyst to deal with all three pollutants together with feedback control of air-fuel mixture. The three

developments were: (1) low cost, miniaturized electronics,

(2) "three-way" or oxidation/reduction catalysts, and (3) a means to sense oxygen in the exhaust.

Closed Loop Emission Control Systems

There were significant gains in fuel economy when converter based systems came into use in 1975 because spark timing and combustion chamber

design could be more nearly optimized for fuel efficiency. The 1980

standards (see Table 1) made it very difficult to maintain these gains

in efficiency. The 1981 standards, especially the lowered limit for

NOx, would surely have resulted in a step backwards for engine efficiency, if it had not been for technology that led to fourth generation

systems

The fourth generation systems utilize a catalyst that is known to

reduce the oxides of nitrogen in a reducing atmosphere and also to

oxidize the HC and CO in an oxidizing atmosphere. Both oxidation and

reduction are accomplished in a catalytic converter in atmosphere that

is neither net oxidizing nor reducing. This condition is achieved only

when the engine's fuel metering system is operated at stoichiometry

That is, the fuel metered must be precisely the amount that will be

completely oxidized by the air inducted.

63
TABLE 1 RECENT FEDERAL EXHAUST EMISSION

AND FUEL ECONOMY STANDARDS

YEAR HC CO NOx CAFE*

(g/mile) (g/mile) (g/mile) (miles/gal.)

1978 1.5 15 2.0 18

1979 1.5 15 2.0 19

1980 0.41 7 2.0 20

1981 0.41 3.4 1.0 22

1985 27.5

^Corporate Average Fuel Economy

Figure 1 illustrates the above-described behavior of oxidizing/reducing or "three-way" catalysts. Figure 2 shows how the use of such

a catalyst can affect the emissions from an engine at a typical operating point. Clearly, the emissions benefits of the three-way catalytic

converter are very significant, provided air-fuel ratio can be maintained near stoichiometry . An important added benefit of operating

near stoichiometry is apparent from Figure 3. Fuel consumption

approaches its minimum at air-fuel ratios near stoichiometry. The advantages of stoichiometric operation are many if air-fuel ratios are controlled

Figure 1. Three-way catalyst characteristics

6h
COz

o

CO

CO

LU

BEFORE

CATALYTIC CONVERTER

HC **\

coA /

/

\

\

• \ \

\

w • \/

J

1 ^-^\

NOx

•

' i i

10 12

i 14 j —1 1

i

' 16 18 20

A/F

STOICHIOMETRY

AFTER

CATALYTIC CONVERTER

A/F CATALYST

OPERATING

WINDOW

Figure 2. HC CO, and NOx emissions versus air-fuel ratio,

130 n

FUEL CONSUMPTION,

% OF MINIMUM 110~

105-

100 =

r~~l 1 1 1 1 1 1 1 1 10 11 12 13 14 15 16 17 18 19

AIR/FUEL RATIO

Figure 3. Fuel consumption versus air-fuel ratio

Conventional carburetors, as well as new carburetor concepts and

both electronic and mechanical fuel injection, have become highly refined and are capable of accuracy far in excess of what was available

in 1968. Nevertheless, engine transients, variations in ambient tem65
perature, humidity and altitude plus wear in service make it impracticable to achieve and maintain the air-fuel ratio control demanded by the

three-way catalyst. The solution to this dilemma is the closed loop

or feedback fuel metering system.

Figure 4 depicts the essentials of a fuel metering system employing

feedback from exhaust gas chemistry. In systems of this type, the oxygen sensor, which will be described in more detail in the following

section, behaves much like a switch. Whenever the exhaust chemistry

reflects an air-fuel ratio on the rich side of stoichiometry , the sensor produces an output of about 0.9 volt. Lean mixtures cause sensor output to drop to near zero.

ELECTRONIC

CONTROL BOX

Figure 4. Feedback emission control

The output of the sensor is fed to an electronic control, which interprets sensor outputs above 0.4 volt as indicating a rich mixture and

outputs below 0.4 volt as signifying that the mixture is lean from

stoichiometry. The electronic control in turn applies a signal to an actuator in the fuel metering system. Actuators may take several

forms, but the effect is always that a rich exhaust chemistry gives

rise to a correction to the fuel metering system causing a change to a leaner air-fuel ratio and conversely.

Among actuators used with carburetors are solenoids and stepper motors.

A solenoid can be incorporated in a carburetor so that when the solenoid is energized, a valve opens an air bleed passage causing the mix66
ture to go to a predetermined lean air-fuel ratio. De-energizing the

solenoid allows the mixture to go to a rich calibration. The solenoid

may then be pulsed at some frequency, and the duty cycle or percentage

of "On" time will determine how rich or lean the mixture will be. The

mixture is thus infinitely variable between the calibrated limits. Such

systems will respond to a rich signal from the sensor by changing the

duty cycle at a predetermined rate toward lean. When the sensor output

indicates lean, the direction of duty cycle change is reversed. This

concept is somewhat analogous to a temperature control with a thermostatic switch. The sensor is similar to the thermostat, and the rate

of change of duty cycle corresponds to the rate of heat input or re- moval .

All systems based on the switch like behavior of the oxygen sensor necessarily allow mixture to vary somewhat on both sides of stoichiometry. The requirements of the three-way catalyst are nevertheless

met very effectively by maintenance of the average mixture at or very

close to chemically correct. The three-way catalyst is often supplemented with a downstream oxidation catalyst. In this case air will be

pumped in between the two catalyst beds during some modes of operation.

Many variations of feedback systems have been implemented. Electronic

fuel injection is particularly well suited to closed loop operation

since response is fast and the injectors are the actuators. A number

of systems have been developed which combine closed loop fuel metering

control with electronic control of other engine parameters such as spark timing, EGR, and even idle speed. In all of these systems the

oxygen sensor is an essential component.

Operation and Principle of the Oxygen Sensor

Certain oxides have the ability to conduct electrical current by means

of very mobile oxygen ions. One of these oxides, zirconium dioxide, is

used as a solid electrolyte in a galvanic cell to sense the oxygen con- centration in automobile exhaust gas. Usually the zirconium dioxide

contains a small amount of yttrium oxide in order to reduce its electrical resistance and to provide high temperature structural stability.

The galvanic cell, Figure 5, consists of the solid oxide electrolyte

generally in tubular form which is coated on the inner and outer sur- faces with porous platinum electrodes. When the platinum surfaces are exposed to gases with different oxygen partial pressures, oxygen ions are formed on one electrode and migrate through the oxide electrolyte

from the region of higher to the region of lower oxygen concentration.

This establishes a voltage potential difference across the electrolyte,

the magnitude of which is defined by the Nernst equation.

Atmospheric oxygen is normally in contact with the inner electrode

in an automotive oxygen sensor. Ion flow is therefore in the direction

toward the outer electrode and the exhaust gas. Since the equilibrium

67
oxygen partial pressure in exhaust gas varies with normalized air-fuel

ratio as shown in Figure 6, calculations of theoretical voltage output

using the Nernst equation are possible. The family of curves shown in

Figure 7 result. The large abrupt change in the oxygen partial pressure

in the exhaust at stoichiometry and the resultant abrupt change in voltage produced by the voltaic cell make it usable as an oxygen sensor.

NERNST EQUATION

R j P02 (ATMOSPHERE)

EMF = — • LOG

4F P0 2 (EXHAUST)

P02 (ATMOSPHERE)

= .0496 T • LOG

P02 (EXHAUST)

R = UNIVERSAL GAS CONSTANT

T = ABSOLUTE TEMPERATURE

F = FARADAY CONSTANT

P02

= PARTIAL PRESSURE OF OXYGEN

ASSUMES ELECTRON OR HOLE CONDUCTIVITY CAN BE NEGLECTED

AS COMPARED TO THE OXYGEN ION CONDUCTIVITY

EMF METAL

INNER ELECTRODE

Figure 5. Oxygen sensor schematic

68
0

I

' ' '

I

' ' ' I

' ' ' I 0.80 0.84 0.92 1.0 1.08 1.18 1.2 NORMALIZED AIR/FUEL RATIO (=A)

Figure 6. Equilibrium oxygen partial pressure (log of psi) versus

air-fuel ratios

1100

1000

900

800-

700-

THEORETICAL 600 VOLTAGE

OUTPUT (mv) 500-

400-

300

200-

100-

370 C RICH • •LEAN

STOICHIOMETRIC

—I

1 1 1 1 1 1 r

0.8 0.84 0.88 0.92 0.96 1.0 1.04 1.08 1.12 1.16 NORMALIZED AIR/FUEL RATIO (=X)

Figure 7. Theoretical voltage output versus air-fuel ratio

69
When the exhaust gas is rich, the oxygen partial pressure is small and

the ion flow from the inner to outer electrode is large, resulting in

development of approximately 0.9 volt by the cell. A lean exhaust gas

with a large oxygen partial pressure inhibits the ion flow and results

in development of less than 50 millivolts by the cell. The electronic

control unit uses the voltage output as a signal to the carburetor or fuel injection system to decrease or increase the air-fuel ratios.

Examples of an oxygen sensor voltage trace on an oscilloscope are shown

in Figure 8. The traces were obtained when the sensor electrolyte tip was heated on a natural gas burner to temperatures of 350°C and 800°C

and the burner exhaust gas was switched through stoichiometry from rich

to lean and then back to rich. At 350°C the 970 millivolt rich and 35

millivolt lean outputs are typical. Also typical are the 800 millivolt

rich and 50 millivolt lean outputs at 800°C. Apparent on the traces are

the rapid voltage changes generally occurring in less than 100 milliseconds at 350°C and less than 50 milliseconds at 800°C. These fast

switch times assure the fuel control system is constantly updated as

to whether the exhaust gas is rich or lean.

1000 mv

0 mv

1 1 1

1 f1 1 1

1

-H-H- II 1 -H-H- -H-H- ++++- 1

~*\ I*- 100 i

L-R

350 C

- R-L

1000 mv

0 mv

-*\ k- 50 i

L R

800 C

R-L

Figure 8. Transient voltage switching curves of an oxygen sensor

70
The design features of a functional automotive oxygen sensor are shown

in Figure 9. The zirconium oxide electrolyte coated on the inside and

outside with platinum is protected from the exhaust gas by a layer of

magnesium aluminate spinel and an open fluted stainless steel shield.

Exhaust gas passes through the flutes in a swirling motion preventing

direct impingement on the electrolyte tip of the gas and solid particles

contained therein. The outer electrode is connected electrically

through the protective shield and a metal gasket to the electrically

grounded shell. Talc powder compressed between the electrolyte and the

shell provides a gas seal.

TERMINAL

REFERENCE AIR ENTRANCE

EXHAUST

GAS

TERMINAL

INSULATOR

•SPRING

CONTACT DISC

SHELL

Figure 9. Oxygen sensor cross section

Electrical contact with the inner platinum electrode is through a contact disc and spring to the terminal. A ceramic terminal insulator

prevents electrical shunts between the inner and outer electrodes. The

vented sleeve protects the inner components from mechanical shock and

contamination while allowing the entrance of air for sensor operation.

71
Automotive oxygen sensors of this design have proven themselves to be

durable under extreme operating conditions and are certified with the

Environmental Protection Agency for 50,000 miles.

Energy and Other Implications

A feedback controlled engine, operating near stoichiometry will run very close to the best efficiency point as shown previously. Further,

though EGR is still required in most applications, the amount of

recirculated exhaust gas can be kept below that which has much adverse

effect on efficiency. Similarly, spark timing can be maintained at or near the best efficiency setting for most operating conditions.

Thus, the three-way catalyst and closed loop, oxygen sensor based

approaches offer better fuel economy than currently practicable alternatives .

Another major benefit from the feedback approach is that the fuel

metering system becomes, in effect, self-tuning. Also, there is

little or no adverse effect from changes in ambient temperature or operation over a wide range of altitude. Many systems incorporate

self diagnosis which detects malfunction and alerts the driver to

have his vehicle serviced.

This fourth generation of emission control systems is seen to provide

not only improved fuel economy when a car is new, but the economy will

inherently be preserved over the life of the vehicle.

72
References

1. D.S.Eddy, "Physical Principles of the Zirconia Exhaust Gas Sensor,"

IEEE Trans. Veh. Technol., VT-23 , pp. 125-9 (1973).

2. C.T.Young and J. D. Bode, "Characteristics of ZrO„-Type Oxygen Sensors for Automotive Applications," SAE paper 790143, SAE Congress

and Exposition, Detroit, Michigan, February-March 1979

3. J.N.Reddy, "Applications of Automotive Sensors to Engine Control,"

SAE paper 780210, SAE Congress, Detroit, Michigan, February-March

1978.

4. T.W.Keranen and H . P . Wertheimer , "Spark Ignition Engine Control

Variables Study," SAE paper 730004, SAE Congress, Detroit, Michigan, January 1973,

5. D.L.Hittler, M. A. Boguslawski , L. P. Carrion, and R.K.Frank, "A

Microcomputer Emissions Control System," SAE SP90 (1980), Convergence '80, Dearborn, Michigan, September 1980.

6. H.Dueker, K.H.Friese, and W.D.Haecker, "Ceramic Aspects of the

Bosch Lambda-Sensor," SAE paper 750223, SAE Congress and

Exposition, Detroit, Michigan, February 1975 <

7. E.Hamann, H. Manger, and I.Steinke, "Lambda Sensor with Y„0^ - Stabilized ZrO^ - Ceramic for Application in Automotive Emission

Control Systems," SAE paper 770401, Congress and Exposition,

Detroit, Michigan, March 1977.

73
DETECTION, DIAGNOSIS AND PROGNOSIS OF

GAS TURBINE ENGINE HEALTH WITH THE USE OF FIBRESCOPES

ROBERT M. McCORD

United Technologies Corporation

Pratt & Whitney Aircraft Group

Government Products Division

West Palm Beach, Florida 33402

Abstract: The use of fibrescopes in determining the overall health condition of a turbine

engine has experienced tremendous growth in the past three years. The maintenance technician can now monitor the performance of each engine, and if the trend analysis signifies

structural degradation of gas path hardware, he no longer need remove the engine from service

for expensive disassembly to verify suspect damage. With the new developments in the use of

fibrescopes, he may now insert a fibrescope into the suspect area and verify that damage does

or does not exist and to what extent. Man-hour expenditure ratio for the two methods averages

about 160:1, and fuel savings per incident is normally 1000 gallons. This paper describes the

growth of fibrescopes over the past five years and their practically unlimited application in transportation, marine, energy production and agricultural equipment in the future.

Key words: Fibrescope; health condition; trend analysis; man-hour expenditure ratio; unlimited application.

Background

Disassembly to inspect gas turbine engines has been one of the biggest drivers in aircraft

maintenance support cost. At this time a majority of commercial engines and some military

applications have converted from the fixed time between overhaul (TBO) to the on-condition

maintenance (OCM) concept. But many critical parts, buried within the engine, still require

major teardown at certain prescribed maintenance intervals. This teardown ensures these

"buried" parts are capable of making the next inspection interval. Normally, a pre-maintenance operational check and a post-maintenance operational test run of the engine

is performed which consumes an average of 3000 gallons of jet fuel for each maintenance

inspection. During operational use of these engines, FOD, DOD and general parts deterioration occur on these "impossible" to inspect parts. Operational incidents, which could have been

detected if internal inspection techniques were available, are extremely costly on a multi-engine aircraft where an inflight abort is declared and tons of fuel are dumped to achieve a

safe landing, but to the single engine aircraft operation the result could be disastrous.

Having had first-hand experience with both fixed-cycle and on-condition maintenance for twelve years as a U.S. Air Force Propulsion Branch Chief, the author supports the OCM

concept. Personal interviews with experienced logisticians within Pratt & Whitney Aircraft

indicate a similar attitude in support of the OCM concept. Planning, scheduling and committing resources to maintain combat-ready aircraft around the world can be a logistics management nightmare if the manager elects to employ the fixed-cycle concept. Sudden changes in

7^
engine performance require immediate grounding of the aircraft and troubleshooting. Granted

that sudden failures, in some cases, cannot be predicted, the majority of those sudden failures

resulted from subtle performance changes that could have been detected, diagnosed, and

corrected had a diagnostics trend analysis system, coupled with newly developed nondestructive inspection equipment, been used. Spares provisioning, transportation and manpower

commitments can be predicted by the manager when he knows the exact health condition of

his operational assets regardless of global location.

Detection

One of the unique features of turbine engines is that their performance parameters, once

accurately established, vary only slightly from their initial values. The parameters that are

indicative of the gas path performance of a turbine engine include engine pressure ratio (EPR),

compressor speed (Nl and N2 rpm), fuel flow (Wf), and exhaust gas temperature (EGT).

There are numerous other terms used for these parameters, depending on the type engine and

manufacturer, but basically, these four or five signals will provide the input information

necessary for most engine condition monitoring programs. Normally, these parameters will not

vary on a specific turbine engine unless forced by an internal or external change. If one value

varies, variance in others can be predicted, and provided that the associated instrumentation

system or electronic engine monitoring system is not in error, this feature permits immediate

detection of the shift in performance. By plotting this information on a flight-to-flight basis

(Figure 1), subtle changes in the tracked performance parameters can be detected over a period of time. This shift in baseline performance gives the maintenance technician the

opportunity to remove the aircraft from the flying schedule before the failure occurs and

perform the necessary inspection and troubleshooting to pinpoint the deteriorated component.

Figures 2 and 3 identify major shifts in exhaust gas temperature and speed that is indicative of a damaged turbine. It is significant to note that in the majority of cases where potentially

serious damage was evident upon inspection, the engine was still performing within the

prescribed operational limits and would have failed before being pulled for performance loss.

Using a manual engine condition monitoring system to collect inflight engine data, the

Strategic Air Command of the U.S. Air Force has accrued an estimated annual cost avoidance

of $20 million in reduced hardware cost for the past 5 years.

75
Figure 1. Sample Engine Performance Evaluation Worksheet

76
Unit Aircraft No. Eng Pos Eng S/N: TSO/R

Figure 2. Sample Engine Performance Evaluation Worksheet

77
Unit. Aircraft No.

Eng Pos

_ FnqS/M- 631883 TgQ/R 2162

Figure 3. Sample Engine Performance Evaluation Worksheet

78
Current Applications

In conjunction with the trending program described in the previous paragraph, internal engine

inspection to detect deteriorating hardware is required to avoid inflight shutdown and

excessive secondary damage. Visual inspection is required since the trending plots do not

respond to these deteriorating components. The fibrescope (see Figure 4) is most widely used on the F100 engine which powers the F-15 and F-16 fighter aircraft. In addition to a regularly

scheduled inspection to observe turbine health (see Figures 5 and 6), the fibrescope is used to inspect many other engine components, thereby reducing the need for costly engine removal

and disassembly. In the past two years, the U.S. Air Force has realized an estimated cost avoidance of $50 million in reduced secondary hardware damage as a result of these inspections. In addition, 200 F100 engines have been removed from the aircraft prior to a major

component failure.

Figure 4. Fibrescope With Teaching Scope Attached

79
Figure 5. Actual Turbine Vane Damage

Other applications include combustion and turbine section inspection on the B-52 bomber

family, KC-135 tanker, C-141 cargo and F-lll fighter aircraft. On the commercial side, the

method used to inspect the F100 turbine was successfully adapted to the JT9D engine on the

747 aircraft and the PT6 engine installed in so many general aviation aircraft. With each new

idea, another application follows, and at the present time the growth potential is immeasurable.

80
Figure 6. Actual Turbine Vane Damage As Seen Through Fibrescope

Conclusion

As detection and diagnostic techniques become more advanced in the propulsion world,

inflight shutdowns should decrease proportionately — if the maintenance manager grows with

the technology and responds to the warning signals issued.

The challenge now must be that if this new equipment works so well on inspecting the internal

components of turbine engines, what action is being taken to inspect engine attaching mounts;

those inaccessible areas in the aircraft where corrosion and cracks occur; or in the fuel cells where holes are so difficult to find. In addition to aviation maintenance, an unlimited potential

application exists for inspecting the valve seats, cylinder walls and pistons of internal

combustion engines; inspecting weld joints inside of pipes; checking for corrosion and/or

obstructions inside of fluid or gas bearing tubing, etc.

We, as engineers and managers, in one of the largest energy consuming industries, must

concentrate on reducing the number of ground operational engine runs for troubleshooting and

test. We must never sacrifice safety, but we must develop and use new technology and

equipment to do the job without consuming fuel.

81

SESSION III

BETTER AVAILABILITY

Chairmen: R. A. Coulombe, Naval Ship

Engineering Center

J. A. George, Parks College

INTEGRATED ON-BOARD DETECTION

DIAGNOSTIC AND PROGNOSTIC SYSTEM FOR MILITARY APPLICATION

Marquis W. Woody

US Army Tank-Automotive Command

Warren, MI 48090

Wsewolod Hnatczuk

US Army Tank-Automotive Command

Warren, MI 48090

Abstract: Advanced electronic techniques are being applied by the US

Army to integrate on-board detection diagnosis and prognosis as an inte

gral part of a total combat vehicle subsystem integration effort. The

electronic system manages, controls and distributes electrical power in

combat vehicles and provides the system integration functions of communications, data processing and integrated controls and displays to the

subsystems. The subsystems include engine, electrical, fire control,

stabilization, intercoms and safety. The system enhances the RAM-D of

the combat vehicle by the inclusion of on-board diagnost ics /prognost ic

s

built-in-test and selected redundancy features. Electrical system

design and modification flexibility is improved.

The system integration techniques are described which include a shared

transmission medium called multiplex data bus, microcomputer control

and solid state power control. The core element hardware and software

design are discussed along with installation procedure for a baseline

Army combat vehicle. The interfacing of off-board test equipment with

an on-board multiplex bus system is discussed.

Key words: Electronic components; multiplexing techniques; on-board

diagnostics and prognostics; electrical power management; control and

distribution; total tank subsystem integration; MIL-STD-1553B multiplex

data bus; microcomputers; bus controllers; remote terminals; crew station terminals.

INTRODUCTION

The advanced technology systems approach for integrating all electric

power and information transfer within combat vehicles includes integrated on-board detection diagnosis and prognosis systems as a design

goal. The program is being performed under the title of Advanced

Techniques for Electrical Power Management, Control and Distribution

Systems (ATEPS) .

85
ATEPS is a technology thrust to introduce advanced electronic techniques

to meet the increasing combat vehicle power requirements impacts which

have increased electrical system complexity and reduced the reliability,

availability, maintainability and durability (RAM-D) and survivability

aspects. Concurrently, this trend has increased the information flow

in combat vehicles.

Five basic technical objectives were established for the ATEPS program:

reduction in vehicle wiring complexity; improved reliability, maintainability and survivability; reduction or elimination of combat vehicle

depot rebuild for the e lec t rica 1 /e lec t ronic system; improved crew effectiveness; and improved electrical system design and modification

flexibility. The ATEPS system requirements, analysis and conceptual

design of a tank-automotive vehicle information system was accomplished

in April 1977 by Systems Consultants, Inc. An ATEPS breadboard hardware system was designed and developed in FY78 by the Chrysler

Huntsville Electronics Division.

The brassboard hardware system was demonstrated sufficiently to warrant

advancement into an accelerated ATEPS prototype hardware development

program for vehicle installation. The vehicle selected for the ATEPS

prototype hardware program was a baseline XM1 tank.

SYSTEM DESCRIPTION

Figure 1 illustrates the total combat system integration potential of

the ATEPS concept. This system integration is achieved by the use of

digital multiplexing with microcomputer control, integrated controls and

displays and solid state power contro 1 / switching . Communication among

the combat vehicle subsystems is accomplished by means of a shared

transmission medium called a Multiplex Data Bus (MDB). Other key elements of the system are Bus Controllers (BC), Remote Terminals (RT) and

Crew Station Terminals (CST).

Figure 2 is an example showing the multiplex bus architecture. The

interconnection of the BC , RT and CST via the MDB is made through a slip ring which interfaces the hull and the turret data/power systems.

All data are transferred between the bus controller and various remote

and crew station terminals via the data bus section. The subsystems or Line-Replaceable Units (LRU) are interfaced with the ATEPS system

through RTs which are placed in zones of high wiring/component density.

Figure 3 shows how a typical ATEPS system might be installed in a tank.

The MDB is installed in a "ring" configuration and operates bidirectionally. If the MDB system is severed in one location, it continues to

operate in a normal manner by continuing the flow from both sides to the

point of rupture rather than in a continuous loop fashion. The MDB and

power leads are combined to form a hybrid cable assembly.

86
ENGINE CONTROL -»

FUEL SYSTEM MANAGEMENT *

ENGINE INSTRUMENTATION -a

CHARGING SYSTEM**

STARTING SYSTEM-*

FIRE CONTROL—

RANGE FINDER —

NIGHT SIGHTS

INTEGRATED

MULTIPLEX

SYSTEM

(redundant;

ELECTRICAL

POWER

* ^STABILIZATION CONTROL

< > FIRE AND NBC DETECTION

«* >- INTERCOM

-t * COMMUNICATIONS

-* «*• DIAGNOSTICS

* *- PROGNOSTICS * > DEMAND MAINTENANCE

> AMMO INVENTORY STATUS

FIGURE 1. TOTAL TANK SUBSYSTEM INTEGRATION POTENTIAL

MULTIPLEX BUS

TO/FROM

LRUs

TO/FROM-*

LRUs

MULTIPLEX BUS

TO/FROM *~ RT RT

LRUs

TO/FROM

LRUs

*• TO/FROM

LRUs

TO/FROM

LRUs

FIGURE 2. TYPICAL MULTIPLEX BUS ARCHITECTURE

87
88
The MDB was designed

triservice standard,

be low

in accordance with the requirements of the

MIL-STD-1 553B . Some of the bus features are listed

Bus Operation - Asynchronous

- Command /Re sponse

- Half Duplex

Word Types - Command

- Status

- Data

Modu lation - Serial Digital Pulse Code Modulation

Data Code - Manchester II Bi-Phase Level

- Bi-Polar

Transmission Bit Rate - 1.0 Megabit per Second

Word Size - 20 Bits

- 16 Bits plus Syn and Parity Bits

The bus controller controls the transfer of data over the MBD. It

consists of a central processor, bus interface logic and memory. The

central processor is a programable microcomputer which executes stored

programs such as operating programs, maintenance programs and self-test/

diagnostic routines. The prognostic routines could be added in future

ATEPS systems. The BC should be capable of performing all the functions

performed by a RT , if required. The overall BC functions are summarized

be 1 ow

- Maintains Bus Control

- Performs all Computations

- Performs all Systems Logic Decisions

- Fault Diagnostics and Malfunction Detection

- Displays Formatting and Processing

- Provides Status Information

- Verifies Data Transfer to/from Terminals

and . . . - Contains Systems Operational Programs

- Contains System Test Programs

- Contains Crew Advisory Service (Checkout Lists, etc.)

The remote terminals contain the electronics necessary to interface the

bus cable with the LRUs. It converts signals for transmission to the

BC and also decodes data from the BC. The solid state switches required

to connect power to the components are also located in the remote terminals. The output of the generating unit is distributed directly to

the RTs. This power is distributed as required by short cable lengths

to the LRUs. The overall RT functions are as follows:

89
- Conditions and Converts Input Data

- Multiplexes Input Data for Transfer to Data Bus

- Demultiplexes Output Data from Data Bus

- Drives and Protects Output Signals

- Recycles all Outputs Back to Data Bus for Verification

- Verifies Data Transmission to/from Bus Controller

- Performs Self-Test and Maintains Terminal Status

- Processes Data Utilizing Remote Microprocessor

The crew station terminals are the interface between the ATEPS system

and the crew. The following CST functions have been identified:

- Accepts Inputs from Crew Members (Illuminated Push Button

Switches

)

Display Control

Subsystem Control

Status Inputs

- Audio Input/Output

Converts Input to Digital

Converts Output to Audio

- Displays Discrete Status Lamps

Critical Status Information

Switch Functional Status

- Presents Status and Warning Information on Alpha-numeric Display (120 Characters, 6 Lines with 20 Characters Each)

All Subsystem Status

Maintenance Status

Test and Checkout Instructions

Subsystem Failure Indication

Crew Safety Warning

Displayed Data Available to all Terminals

The design utilizes an interactive or paging technique controlled by the

bus controller. Each crew member is provided with a crew station terminal. However, in current four-man crew applications, the loader only

has a panel interfaced with the multiplex data bus via a remote terminal.

Crew station terminals are designed to be internally identical, but have

unique custom front panels tailored to the specified requirement of its

operator. The integration of controls and displays in the crew station

terminals reduces the number of line replaceable unit components in the

conventional system. For example, the driver's CST replaces driver's

instrument panel, driver's master panel, master warning panel and

intercom box.

90
BUILT-IN TEST AND DIAGNOSTICS

ATEPS will contain all the measurement and stimulus capability to

perform self-diagnosis and fault isolation to the line replaceable unit

level on all the vehicle subsystems and to the printed circuit board

level on some of the subsystems. The effectiveness of the selfdiagnostics and fault isolation capabilities of ATEPS is dependent upon

the depth of incorporation of the multiplex system into the vehicle

subsystems

The response of the crew station terminal when interrogated by the bus

controller is checked for validity. This feature is used to verify

operation or isolate faults in the MDB cable assembly or the bus control

circuits in the terminals. The terminals contain built-in-test features

which allow measurement of inputs and outputs which are transmitted to

the BC microcomputer for verification or diagnosis. The CST functions

are tested by special diagnostic routines using the CST display to guide

the repairman.

The ATEPS concept lends itself extremely well to on-board diagnostics.

The major components, both hardware and software, are already in the

system except for addition of some sensors. Inputs from the sensors would be transmitted through the remote terminals, via the multiplex

data bus to the bus controller where they would be analyzed. Sensor's

output data would be checked as a result of either routine operation

commands from the BC or a symptom-oriented test selection from a CST.

After the BC performs all the necessary computations to determine

whether a malfunction has occurred, the resultant decision would be sent

to the appropriate CST for display and corrective action.

Diagnostics rationale, software and algorithms for most of the systems

have already been developed or will be developed prior to fielding of

ATEPS. The software and algorithms for diagnosing of spark and com- pression engines and associated accessories were developed under the

Simplified Test Equipment for Internal Combustion Engines (STE/ICE)

program by RCA, Burlington, MA for TARADCOM. The STE/ICE system has

been fielded and has proven to be extremely successful. Diagnosis capabilities for the AGT-1500 turbine engine and the electrical, stabilization, fire control and fire suppression systems in the turret were developed under the Simplified Test Equipment-Tracked Vehicle (STE-T)

by RCA, Burlington, MA for TARADCOM. STE-T is currently supporting the

XM1 tank during OT/DT III. Diagnostics for turret hydraulics, communication systems and on-board missile systems will be developed under the

Simplified Test Equipment-Expandable (STE-X) program and will be available in time to incorporate into ATEPS before it is fielded.

91
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92
PROGNOSTICS

The ATEPS concept provides for the incorporation of prognostics hardware in accordance with the block diagram of Figure 4. The principal

features are:

- EIA RS 232 Communication Port with Software

- MIL-STD-1553B Port for External Interface

- Extensive Data Logging and Analysis Capability

- Built-in Failure Analysis-Prediction-Detection-Correction

- Memory and Computing Capability for Trend Analysis

- Protocol to Interface External Computer, Bus Tester, Special

Crew Terminal for Data Acquisition

ATEPS is designed to access all the data base for any applicable vehicle. Low level multiplexing is available to condition, sample, convert

and filter a wide range of signals between 20 millivolts and 40 volts

with a response as great as 60 cps. The standard interface for the

digital and multiplex systems requires a minimum of circuitry to provide

special excitation and conditioning for special sensors that may be re- quired .

Nondestruct memory is provided to store indefinitely any measurements

or resultant calculations to provide a historical data base for any

trend analysis that may be requested. There is sufficient computing

capability available to do all but the most sophisticated algorithms

required for data analysis.

Any of these results may be processed for presentation either directly

to a crew station terminal, as accessed by bus monitor equipment, or using an EIA standard interface and to communicate with any data termina 1

.

The interface of prognostic monitoring with the ATEPS system will initially be limited to engine functions. The establishment of a prognostic test capability on combat vehicles will require definitive cost

effectiveness investigation and assessment of its contribution to improved readiness. Some of the combat vehicle systems to be considered

are as follows

- Transmission and Final Drive (Transmission, Tracks, Road

Wheels, Sprockets (Drive Wheels), Brakes)

- Power Plant

- Gun Tube and Breech

- Recoil Mount

- NBC

- Fire Control and Electronic Suites

- Autoloader

93
The TACOM prognostics program is developing around the hardware assets

of the Vehicle Monitoring System (VMS) project which was started in

1976 as a joint TARADCOM/DARPA project. Analysis of test data generated by this project has indicated considerable prognostic potential.

ATEPS BREADBOARD HARDWARE SYSTEM

The ATEPS breadboard hardware system provided capabilities for the

demonstration and evaluation of the multiplexing concept with integrated controls and displays for the hull electrical system, turret

electrical systems and engine monitor circuits of a combat vehicle.

The following items were demonstrated:

- Displays

- Engine (Sensors, Start-Up, Stop)

- Lighting (Service, IR, Combat Mode, Dome Lights)

- Stabilization (Power, Zero Balance, Moving/Stationary)

- Ballistics (Gun and Ammo Selection, Manual Entry, Firing/

Safety)

- Crew Safety (Fire Detection, NBC Detection, Smoke Grenades)

- Hardware Failures (Bilge Pump, Driver's Dome Light, Removal

of Te rmina 1

)

The concept for the Bus Controller was purely a breadboard function to

allow the use of an off-the-shelf microcomputer for the Central Processing Unit functions. The unit did perform the bus interface logic

for the data bus. The computer prototyping system (990/4) sent messages

to the Bus Controller rather than to the terminals directly. The hybrid

Multiplex Bus Cable assembly ran in a continuous loop between the six

terminals and the Bus Controller. This arrangement provided increased

reliability and a means to demonstrate that a single break in the cable

assembly would not disconnect any terminals from the Bus Controller and

that the entire system would still function.

ATEPS PROTOTYPE HARDWARE SYSTEM

The ATEPS Prototype Hardware system is being developed using the XM1

tank as a baseline for design, installation and test. The systems concept for the XM1 baseline tank implementation includes:

Dual Bus Controllers Hull Controller

Turret Controller

Imbedded SBP 9900 Microcomputer Within

Each Bus Controller

Vacuum Fluorescent Driver Gauges

Vacuum Fluorescent Alpha-Numeric Displays

New LED Illuminated Control Switches

Separate Digital Data Bus

Bus Control Computer

Crew Terminals

Intercom

9h
A hull LRU comparison between the ATEPS hardware and the XM1 hardware

that would be removed is as follows:

LRUs Added By ATEPS LRUs Removed By ATEPS

Right Front Remote Terminal

Left Front Remote Terminal

Power Pack Remote Terminal

Rear Remote Terminal

Driver's Crew Terminal Driver's Instrument Panel

Driver's Master Panel

Intercom Box

Hull Networks Box

Engine Control Unit

Fire Extinguisher Amplifier

The intercom box functions have been integrated into the crew terminals

The engine control unit function of the fuel management system has been

incorporated into the bus controller function. The reduction in wiring

has been initially estimated at 40%. The fire extinguisher system

receives power from ATEPS, however, the fire sensor signals are independent of the multiplex data bus. The fire extinguisher second shot

is bus controlled.

The turret prototype hardware system development includes a study and

analysis to define the system for design. The system will then be designed to the number of terminals and functions of each terminal. The

preliminary work indicates there would be four remote terminals and

two crew terminals. The design goal is to perform all electrical functions of the turret, the fire control functions and the stabilization

requirements

.

The gun/turret drive unit, line-of-sight unit, computer electronics

unit, commander's weapon station amplifier, gunner's control panel,

turret networks box and commander's panel will probably be replaced.

The gunner's primary sight may also be changed as the system is defined

The ATEPS system design provides significant benefits in the areas of

improved reliability, maintainability and flexibility. Some of the

improvements in each area are listed:

Re liability

- Protected Solid State Switches

- Less Cabling and Connectors

- Automatic Transmission Verification

- Redundancy Features

- Reduction in Electrical/Electronic LRUs

- Low Current Switches

- Less Relay Logic

BENEFITS

95
Maintainability

- Built-in Test Equipment (BITE)

- Automatic Failure Diagnosis

- Increased Status Visibility

- Reduction of Custom Cables and Improved Cable Accessibility

- Common Input/Output Circuit Boards

- Fewer Test Connectors

- Reduced Mean Time to Repair at Organizational and Direct Support Levels

Flexibility

- Ease of Adding Subsystems

- Interface Compatibility

- Reprogrammable Microcomputer for Operational Changes

It is also anticipated that ATEPS will significantly lower the life

cycle cost and possibly lower the acquisition cost of vehicles.

SUMMARY

The ATEPS technology offers a significant improvement potential for the

design of e lectrica 1 /e lectronic systems in combat vehicles. This

potential includes Product Improvement Programs (PIPs) and future Army

vehicle designs. Conceptual designs have been developed for expanding

the ATEPS technology to tactical and other combat vehicle weight

classes —XM2 (IFV) and an advanced self-propelled howitzer. Exploratory development tasks have been initiated to reduce the size of the

ATEPS Core Element electronics through the utilization of recent

advances in solid state technology and packaging techniques. Similar

developmental tasks are being formulated for a second generation MDB

using fiber optic technology with an extension of the technology to

include slip rings.

96
PROGRESS WITH PIELSTICK ENGINE

DIAGNOSTICS AND EXPERIMENTAL RESULTS

A. Genot

S.E.M.T.-Pielstick

2, Quai de Seine

93202 Saint-Denis, France

Abstract: In order to improve engine reliability and reduce maintenence

expenses on ships, S.E.M.T. has developed a monitoring and diagnostic

system for medium speed diesel engines used in marine propulsion or in

power plants. The Pielstick Engine Diagnostic system has been presented

at the 28th MFPG meeting. It automatically monitors wear of the piston

top ring, main bearing alignment and shell wear, pressure charging

circuit fouling condition and exhaust gas temperatures. A prototype

system was fitted onto an l8 cylinder propulsion engine of the container

ship M/V "RENOIR" which was commissioned in January 1978. This engine

has now operated for 12,000 hours. The present paper reports the re- sults obtained in the course of two years of operation of the system.

The information given by the P. E. D. system is compared with that

supplied by the servicing staff's routine inspections. This comparison

has led S. E. M. T. to undertake new laboratory research which will

concentrate on the problem of piston ring wear. The future improvements

contemplated for the P. E. D. system as a consequence of this initial

experience, as well as the necessity to have a better understanding of

and a better monitoring system for the energy balance of the power

stations, are explained.

Key words: Medium speed diesel engine; piston ring wear; crankshaft

bearing safety; turbocharging monitoring.

INTRODUCTION

The Pielstick Engine Diagnostic system presented at the 28th meeting of

the MFPG has been developed to improve the reliability and reduce the

maintenance costs of the medium speed diesel engines with outputs ranging from 3000 to 20,000 kW.

P. E. D. monitors wear of piston top rings, main bearing alignment and

shell wear, fouling conditions of the pressure charging system, and

exhaust gas temperature.

The prototype fitted aboard the container ship M/V "RENOIR" has been

operated for some 12,000 hours since January 1978.

In the course of these two years of operation, the P. E. D.'s indications have been compared to those obtained by conventional means.

97
The information and experience gained from this first prototype will be

used to develop an advanced system.

CRANKSHAFT MONITORING

The purpose of crankshaft monitoring is to prevent eventual failures in

the shafting, the main causes of which are the abnormal wear of a bearing or the misalignment of the driven machine (reducing gear or alternator) with respect to the engine.

In the absence of a monitoring system, the distance between the webs of

each crank are periodically measured for five angular positions of the

shaft with the engine stopped.

A safety system based on the reading of the bearing shell back temperature will permit the engine to be stopped before the crankshaft cracks

from overheating.

By using the P. E. D. system and measuring the vertical displacement of

the shaft in its bearings, we eliminate both the periodic inspections

and the heat alarm system.

A contact free displacement transducer is fitted in each main bearing

on the engine Vee axis (figure l). The signals received are analyzed

in terms of three characteristics: (a) peak-to-peak amplitude, (b) mean value, and (c) minimum lift of the crankshaft journal in the

bearings

.

Any change in amplitude (a) with respect to the value stored during sea trials triggers an alarm. In the same way, a deviation of (b) or (c)

values indicates a misalignment.

We have ascertained that sea roughness and the ship's cargo have little

influence on crankshaft movement (figure 2).

The amplitude (a) of the crankshaft vertical displacement increases in

a linear way, for instance, from 0.2 to 0.3^4 mm for main-bearing no. 5,

when the rotation speed increases from 350 to 500 rpm.

The influence of crankshaft bearing wear on crankshaft displacement

could be measured only in a main bearing of a 12 cylinder engine.

Aboard M/V "RENOIR" we observed that, except for two false alarms due

to pick-up connections, the bearings behaved normally. This was con- firmed by the continuous reading of the bearing temperature as well as by the periodic measurement of crankshaft deflection; all the parameters measured were stable.

The half bearings removed in the course of the semi-annual inspections were in perfect condition.

98
For now, we have not enough theoretical or experimental data about the

relationship between the measured values (a), (b) and (c) and the defects to be detected.

Should it be compared with bearing temperature monitoring, the displace

ment reading made with the P. E. D. system offers the advantage of giving information on the causes of anomalies and higher sensitivity. It

should allow the elimination of the periodic deflection readings, with,

however the disadvantage of being more onerous and more difficult to

keep in perfect working order.

PISTON RING WEAR MONITORING

The piston contains five to six rings of cast iron. They are coated

with a protective layer of chromium or copper. In some engines, one or two segments are of pure cast iron, without coating.

When the chromium layer protecting the top ring is worn off, the ring

deteriorates quickly. The piston must then be taken out and a new set

of piston rings fitted.

The purpose of the piston ring wear monitoring is to determine the

moment when the chromium layer of the top ring is worn off.

Inductive sensors are fitted in the engine cylinder liners, flush with

the cylinder wall and in such places that all piston rings successively

pass in front of them (figure h) . This allows the sensor to scan each

ring and to emit an output signal whose amplitude varies depending on both thickness and magnetic properties of the coating material.

Should one of the piston rings be of pure cast iron, it then is possibl

to measure the thickness of the coatings of other rings by comparing

the amplitude of the signals emitted at each ring passage.

Unfortunately, there is no non-coated ring in the PC2-5 engine and we therefore had to use the coppered first compression ring as reference.

Figure 5 shows such a ring after 1500 hours of operation. It may be

observed that no copper remains on the ring face, only in the grooves.

Such a ring produces, when passing in front of the sensor, a weaker

signal than that obtainable from a pure cast iron ring.

Figure 6 shows a chromium plated ring that is worn unevenly. This ring

had no chromium remaining along 2/3 of the face length, but the remaining third and the grooves were still coated.

In order to be able to use the values recorded on the engine, we measured, in the laboratory, the signals from various compression and top

rings from various cylinders on M/V "RENOIR". It has been observed

that, from the sensor standpoint, the wear on the second compression

99
ring may be considered to be evenly distributed.

The curve of figure 7 gives the mean chromium thickness in terms of

amplitude ratio between the signals obtained from both rings.

The dispersion around the mean value may reach +_ 30% which is explained

by the fact that the active surface of the sensor overlaps the ring face

and that, due to its wear, the chromium is no longer evenly distributed

on the ring. Larger signals are obtained from severely worn chromium

plated rings than from compression rings.

The "no more chromium" alarm shall therefore be tripped for an amplitude

ratio of l.lh and not 1.

The points plotted in figure 8 represent, for a four cylinder engine,

the mean value of 50 measurements made during a 100 hour period. It

may be observed that these values which are used to obtain the mean chromium thickness vary over a wide range because of a rotation of the

ring in its groove.

Figure 9 indicates the averaged thickness for about 1000 hours.

Figure 10 shows chromium distribution at the periphery of three piston

rings removed after U200 , 7200 and 10,000 hours of operation.

A comparison of figures reveals that in two out of three cases, there

are large differences between the mean thicknesses measured on the

removed piston rings and those read by the P. E. D. system.

We believe that this large difference results from an uneven rotation

of the ring on the piston. From our observation, the piston rotation

amplitude is short when the engine runs at constant speed and larger

when the engine is slowing down.

It's also possible that the ring is subject to an angular alternative

displacement so that the pick-up scans only a narrow band of the ring

for a longer or shorter time.

For the time being, the monitoring of piston ring chromium wear does

not work satisfactorily. We must go on with our research with regard

to piston rin,g rotation and decide if it would be possible to determine

the actual chromium wear by using two or three pick-ups per liner. We

also must try other types of smaller diameter, cheaper pick-ups. The

cost of the system becomes onerous when the number of pick-ups per

cylinder is increased.

TURBOCHARGING AND EXHAUST GAS TEMPERATURE

The constant cleanliness of the turbocharging system is important to

thermal efficiency as well as the lifetime of a number of engine com100
ponents such as the exhaust valves.

We have therefore incorporated into the P. E. D. system the means to

automatically make the measurements normally made by the conscious

users, i. e. , exhaust gas temperatures, air pressures and temperatures,

and turbocharger speeds.

Figure 3 shows the variation of the temperature average read at each

cylinder outlet and charge air pressure in terms of turbine speed or power rating.

These curves show the correlation of the various parameters. Washings

of turbine, compressor, and air cooler were more or less efficient,

since their characteristics remain stable sometimes, whereas they

deteriorate at other times.

The two mechanical interventions were more efficient, especially the

turbocharger inspection.

This stage of the P. E. D. shall be completed and improved in order to

determine the efficiency of the turbocharging system and, as far as possible, a more detailed analysis of the exhaust gas temperature.

HARDWARE PROBLEMS

We had to replace three pick-ups and one signal conditioning card out

of k6 measuring channels. On the data processing side, it is the prints

er which caused us trouble as it was not adapted to work in the engine

room ambiency.

Also, we observed three faulty indications because of defective contacts: two in microprocessor cards and another due to a faulty re- fitting of a pick-up connection after a main bearing inspection.

CONCLUSION

The P. E. D. system fitted on M/V "RENOIR" was only a prototype. It

shall be re-designed and improved not only because it does not work

satisfactorily with respect to its original purposes, but also because

the ship's users demand other information regarding fuel savings.

S.E.M.T. are going to pursue their research on piston ring wear and com- plete turbocharging monitoring in order to compute the efficiencies of

the system.

The monitoring of crankshaft displacement in bearings will be super

seded by 1/2 bearing temperature readings, but we shall pursue our re- search on crankshaft displacement using theoretical as well as experimental analyses.

101
We shall add to the P. E. D. the measurement of the output and of the

instantaneous consumption of fuel to help the captain determine the

ship's speed from an economical criterion.

102
CRANKSHAFT SENSOR

103
RENOIR: Influence of deplacement
105
106
107
108
109
110
Average measured chromium thickness

Figure 9.

Ill
112
AN ENERGY CONSERVATION CONCEPT FOR OPERATING MACHINERY

Francois Envent , Michael Cohill and Henry Hegner

ManTech International Corporation

2341 Jefferson Davis Highway

Arlington, VA. 22202

Abstract: Existing planned maintenance systems for complex machinery,

such as those used aboard ships and aircrafts, in power plants, and

processing plants, is viewed as time consuming and sometimes leads to

unnecessary maintenance actions being performed. Moreover, such maintenance practices have become expensive and are not effective to keep

complex machinery functioning with maximum efficiency.

In this paper, a conceptual approach to improving planned machinery ma- tenance as well as optimizing energy expenditures is described. This

concept, making wide use of color displays and interactive techniques,

represents a new practical solution to the implementation of an as- needed machinery maintenance, as opposed to the regularly scheduled

open and fix procedure mostly performed. The implementation of this

concept requires an on-line machinery monitoring system to detect equipment degradations. All performance monitoring and energy management

tasks will be coordinated from a central location called the Engineering

Maintenance Center (EMC)

.

This concept of machinery performance monitoring is discussed, highlighting such parameters as the functions to be performed by the EMC

and the role of the maintenance personnel. Scenarios are also presented to illustrate the EMC functions such as energy management, ma- chinery performance optimization, and detection, diagnosis and isolation

of faults.

The immediate benefits to be obtained from this application of a reliability centered maintenance are improved energy utilizaton and machinery performance, and decreased maintenance costs.

Key words: Machinery monitoring; Reliability Centered Maintenance;

Engineering Maintenance Center; Energy Conservation.

Introduction: As operating machinery maintenance becomes more diverse

and complex, their operating, maintenance, and performance monitoring

have become more difficult and costly. Development of modern maintenance monitoring techniques to provide machinery operating status,

levels of performance, failure detection and prediction, and determination of maintenance requirements based on Reliability Centered

Maintenance offers immediate benefits in improved energy utilization

and machinery performance, and decreased maintenance costs.

113
The objective of this concept is to highlight the need for development

of an automated system for monitoring operating machinery degradation/

failures with enough lead time to improve maintenance planning. With

machinery operating at its optimum, energy is conserved and equipment

availability is increased.

Approach: Existing planned machinery maintenance systems have been

based on the myth that machinery operates as expected or with a proven

life. Therefore, maintenance performed has sometimes been unnecessary.

There is additionally a lack of adequate information (historical data) on operating machinery conditions with little feedback to determine the cause of machinery breakdown.

The need to improve upon present machinery maintenance methods has initiated this conceptual approach centered around Reliability Centered

Maintenance (RCM) . This concept represents a new solution to machinery

maintenance that will be performed mostly on demand rather than regularly scheduled. Its implementation will also require an on-line monitor system to detect equipment degradation and direct maintenance personnel to appropriate equipment in a timely manner.

Reliability Centered Maintenance: A Reliability Centered Maintenance

System is by definition a maintenance concept of making operating ma- chinery more dependable. By monitoring critical machinery parameters, we can (1) conserve energy when running machinery in optimum conditions

(2) better plan shutting down and rework of machinery under stress (3)

improve safety conditions in machinery spaces and (4) the on-line ma- chinery monitoring system can aid in training of personnel.

Present maintenance procedures are structured as shown in Figure 1;

usually referring to preventative, corrective, and emergency maintenance.

This historic method of accomplishing planned maintenance relies upon

time based open-and-inspect procedures. This method does not allow for

the variable life of several equipments of the same model. Also, it

has been found that each open-and-inspect operation increases the

chance of future failure of .the equipment due to accidental improper

reassembling practices.

The next section will describe the concept for an Engineering Maintenance Center (EMC) where the human operator assisted by an on-line mon- itoring system will document machinery operation in a suitable format

to plan Reliability Centered Maintenance.

Engineering Maintenance Center Concept: The increase in size and com- plexity of operating machinery systems has necessitated the design of new on-line monitoring systems that can process large amounts of information. This new system had to be developed taking into consideration

the experience and limitations of a human operator. A digital computer

acts as the link between operator and machine. This link is implemented in software allowing for improved flexibility and upgrading

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115
capability. Also, the complexity of the machinery is handled by the

computer software which converts the multitude of machinery sensor inputs into data directly interpre table by the monitoring system operator.

The operator is only confronted with the data necessary for making a decision. The machinery operating data has to be presented to the operator in a format easily adapted to his level of expertise and understanding.

This operator oriented interface has been very successfully applied in

industry, and represents an answer to the control of increasingly

complex machinery. The same display principle has been adopted in the

EMC. The maintainer is responsible for the running condition of the

machinery. Such a duty requires the access to machinery parameters and

the knowledge of possible failure causes, to forecast a correct diagnosis. These requirements are easily achieved with the help of a com- puter where large amounts of information can be processed. A step-bystep computer aided procedure will guide the maintainer through the

complexity of the detection, diagnostic and prognostic phases.

The need of a monitoring system adapted to the operator might have

seemed unrealistic until the occurence of the well publicized accident

at the Three-Mile-Island (TMI) nuclear power plant. This accident illustrates the inherent problem with control rooms characterized by the

display of all the monitored parameters. Investigations from the

Nuclear Regulatory Commission (NRC) have indicated that this particular

accident was preventable. It seems that it all started as a series of

minor malfunctions which cascaded into a serious accident. It is

believed that human error is one of the major factors that contributed

to the event

.

In the future, it is safe to say that the complexity of machinery and

their controls will keep increasing, and more and more accidents are to

be expected due to human errors. This new methodology of the EMC re- places analog monitoring display devices with alphanumeric/graphic devices such as color cathode ray tubes (CRT) , and information displayed

is automatically limited to the minimum set of data necessary to the

operator for his present task. The EMC will be in charge of machinery

surveillance including the planning and carrying out of maintenance.

The use of a computer in the new maintenance methodology will allow for

efficient computer aided tasks such as training and inventory control.

Typical machinery failure scenarios could be designed in the system to

render the training more realistic and adapted to the level of the

trainee

.

The increasing complexity of operating machinery is being absorbed by a computer controlled interface whose function is to assist the maintainer

in its detection, diagnostic and prognostic task. The prognostic capability of the EMC is a unique function not attainable by today's

maintenance philosophy. It will cause a noticeable reduction in the

116
number of emergencies/catastrophic failures by optimizing the performance

of maintenance of machinery.

Computers and microprocessors constitute the needed technology to give

maintainer accurate and timely responses, as well as the capability of

processing large amounts of data. However, such an advantage would be

cancelled if the interface between computer and maintainer is too complex. The level of sophistication of monitoring techniques has been

rising at an accelerated pace while man has changed little. Therefore,

a special emphasis should be given to the conception of displays that are adapted to the operator instead of having the operator adapt to

fancy but ineffective displays.

Information on display techniques and major on-line monitoring systems

is described in the following section. These applications were developed from extensive industrial research in man-machine interface,

and reinforces the fact that the quality of the display determines the

maintainer's ability to successfully perform his search and identifying

tasks. Considerations for Alphanumeric/Graphic display devices for online machinery monitoring systems will be discussed also.

Man-Machine Interface : In order to successfully design display systems,

an appreciation for the role of man in the system and his human information-processing capability is required. The human factor is a function of several variables: (1) complexity of information displayed,

(2) operator tasks, (3) environmental factors, (4) operator characteristics, and (5) display characteristics.

The complexity of the information to be displayed and the operator's

tasks are usually predetermined and therefore, can not be controlled

when designing a display. Likewise, the environmental factors and

operator characteristics are virtually uncontrollable. However, in

order to generate an effective display, the designer must take into ac- count all these variables when solving the final one display characteristic .

The following sections will be concerned with the display characteristics

and their effects on human performance. These display characteristics

include: (1) display techniques, (2) coding techniques, (3) color selection, (4) density of information, (5) symbol size and resolution, and

(6) luminance.

Display Techniques : Display techniques deal with the manners in which

information is organized within the overall display. All displays can be categorized into four major groups: alphanumeric, graphic, representational and combinational, i.e., a mixture of two or all of the others.

Alphanumeric displays are most useful while performing diagnostic functions. They use strictly textual (alphanumeric) and numeric coding.

117
Search times will be longer due to the amount of detail on each display,

but this can be tolerated in light of the beneficial information re- ceived. However, there is no requirement for these displays to be

arranged in a purely columnar form. Related parameters may be oriented

on the screen in a logical manner to enhance search.

Graphic displays are usually used for prognostic functions. They include line or bar charts to indicate trending or historical information.

They are realatively clean and very easily understood.

Representational displays are most useful while controlling or monitoring a system. Symbols denoting major system components indicate, in

Figure 2, the overall functioning of a gas turbine power control system. Key parameters (e.g., temperature, pressure...) that affect overall system operations could also be displayed and used to evaluate performance .

Coding Techniques : In choosing coding technique, a designer must decide how to best code information to perform a given task. To accomplish

this, the designer must evaluate several factors, including: (1) space

available for coding, (2) type of information to be coded, (3) coding

function (i.e., alarm, identification) , and (4) visibility for coding,

i.e. resolution, contrast, luminance and illumination.

Coding techniques can be divided into five different methods: numeric,

shape, color, blink and textual (alphanumeric). In general, color

coding is very useful when searching or locating a class of object

which is most important. Color coding is described in more detail in

the next section. Textual, or alphanumeric, coding is most useful when

identification is desired; symbols/shapes are useful coding devices

when qualitative objectives are represented. Blinking is used almost

exclusively as an alarm or warning signal.

As few coding levels as absolutely necessary should be used to specify

levels within each code type; e.g., when using color coding it is rec- ommended that no more than eight colors be used. Increasing the coding levels beyond these recommended values will have an adverse effect

on the operator accuracy.

Color Selection : The most effective color display is one in which color

is used sparingly, only when needed, and where it uniquely conveys information that other codes can not or do not provide. The criteria for

selecting a specific set include: (1) maximun wave length separation,

(2) high color contrast, (3) high visibility in specific application,

(4) compatability of use with conventional meanings, (5) legibility and ease of reading, and (6) high saturation (i.e., the two colors labeled

pink and red have approximately the same hue but the red would be highly

saturated and the pink would be low in saturation or desaturated. Zero

saturation colors are black, gray and white)

.

118

Frame Density : Frame density involves determining how much data can be

placed on the screen before the amount begins to adversely affect the

operator's ability to perform his basic task. An analysis of existing

CRT displays that were qualitatively judged "good" revealed a loading

on the order of 15 percent. The remaining area constitutes "white

space" that is essential for clarity in any display. Furthermore, the

amount of variable data in these displays never exceeds 75 percent of

the total active area. The product of these limits dictates that no more than 18.75 percent of the screen should contain information of

continued interest to the operator.

Density within the display is also an important consideration. One

would like to know the maximum number of characters, the appropriate

symbol size, and proximity to other information areas.

Display Luminanc e: The appropriate overall or average luminance of any

display depends upon the viewing conditions, which include: (1) background luminance, (2) ambient illuminance, (3) symbol size, and (4) dis

play colors .

If the display is used in a dark room, and the observer is generally

dark adapted, then the display luminance should be between 10 and 100

foot-Lamberts. In lighted areas, or under normal room illuminance, the

display average brightness should be on the order of 100 foot-Lamberts.

The advantage of a brighter display is the improvement in visual acuity

of the eye. However, if the display is too "bright" for the given

viewing conditions, then the display appears as a glare source and is

quite annoying to the operator and generally fatiguing.

Existing On-Line Monitoring System Industry Experience, Honeywell/TDC

2000 (Ref: 8) : The TDC-2000 Basic Operating Center usually provides:

(1) Three color television-type monitors which, using a combination of

analog and digital methods, provide a variety of displays, including

overviews, group, loop, trending and alarm displays. All of these displays have been humanly engineered to best convey process control infor

mation to the operator, (2) a single keyboard with dedicated function

pushbuttons for each CRT monitor. These keyboards allow any person,

either operator or engineer, with a working knowledge of the process

and no knowledge of programming to be quickly trained to operate the

system, (3) the microprocessor and its associated circuitry, which permits communication along the Data Hiway with up to 63 devices located

as far as a mile away, allow the customization of displays to a particular process plant and provide security of operations through selfdiagnostic routines, (A) a cassette package which enables cassette load

ing and /or recording of data and displays. Once one Operator Station

has been configured, the redundant Operator Stations can quickly be

identically configured by loading the cassette. Information can be

stored on cassette for needs. A plant's system can be preconf igured on cassette to speed startup operations, (5) three-pen recorders which

allow hard copy recording of process variables located up to a mile

120
away, and

able logs,

auctions

.

(6) printers which print on command alarm logs, process varihistorical and real-time trending and other display reproTaylor/MOD III (Ref: 4 ): The MOD III process control system provides

flicker eliminating, high resolution P-39 phosphor, CRTs in combination

with a separate, full-color, CRT. The television- type monitors provide a variety of displays including overview, status, loop, and trending displays. Alarms appear on all displays as flashing, reverse-video

signals, highlighting the problem variable, and as flashing LEDs on the

page selector/alarm panel.

The system also provides a cassette package for recording, a nushbutton

keyboard, single loop microprocessor based controllers and printers.

In manufacturing and quality assurance, high reliability begins with

component quality but does not stop there. MOD III specifications include; (1) system designed to operate in high humidity and over a range

of 40°F to 12CfF, (2) CMOS integrated circuits for maximun noise immunity, (3) ceramic ICs, impervious to moisture damage and stable over wide temperature range, (4) non-corroding, gold-plated contacts on PC boards and bus connectors, (5) PC boards coated to prevent corrosion,

permit operation in high humidity, (6) long-life LEDs for system indicators, (7) f erroresonant power supply transformers for superior regulation, (8) semiautomatic backplane wiring with computer checkout to

eliminate wiring errors, (9) 169-hour burn-in to eliminate weak logic

components, and (10) 30-day burn-in of system and all spares.

Engineering Maintenance Center Functions : A description of anticipated

EMC functions are below. It is emphasized that all of these functions

will be software implemented. This software implementation of functions

will be mandatory to increase the versatility of the system by allowing

these functions to be added to, modified or deleted without requiring

a system reconfiguration. The EMC functions are: (1) energy conservation - (a) machinery performance optimization, (b) resource management,

(c) reliability centered maintenance, (d) inventory control. (2) an- cillary functions - (a) equipment status, (b) data base management,

(c) computer aided training, (d) system configuration, and (e) failure

mode analysis.

Engineering Maintenance Center Description: The EMC operation will be

centered around interactive techniques using terminals for input-output.

A printer or hard copy unit will be required for recording permanent

records of tasks such as alarm messages, machinery historical data, and

documenting maintainer's activity. CRT alphanumeric/graphic type displays will be used to evaluate machinery performance and to efficiently

perform the EMC functions. Figure 3 gives an example of an EMC arrangement .

121
122
The CRT displays selected for the EMC console will provide graphics for

diagrams and color for catching attention to status and other conditions

Color speeds identification, improves visualization and reduces response

time. The use of color enables the display of more information simultaneously which results in the surveillance of a greater number of critical parameters.

A typical example of a on-line machinery monitoring display is shown in

Figure 4.

Conclusions : Existing planned maintenance systems for operating machinery is viewed as time consuming, and sometimes leads to unnecessary

functions being performed. With operating machinery systems becoming

more complex and with a limited maintenance budget available, a catastrophic failure of machinery could have a staggering effect. A solution of these problems could be the implementation of an on-line monitoring system using modern color display techniques that could logically plan maintenance tasks in a reliability centered form. The re- sults of implementing such a maintenance system will be twofold: (1)

energy efficient machinery systems and (2) safer working environments

for the maintainers

.

REFERENCES

1. William R. McWhirter, Jr. et al, "A Shipboard Machinery Performance

Monitoring System Concept", DTNSRDC Report // PAS-78/30, February 1979,

Annapolis, MD.

2. "Upgrading of Engineering in the Wake of TMI Reactor Event",

Engineering Times, September 19 79, Vol. 1, No. 1, page 1.

3. Henry Marks, "An Evolutionary Look at Centralized Operations",

Honeywell publication, Report no. SY-05-02, Issue #2, Ft. Washington, PA

4. "MOD III Process Control System", Taylor Instrument publication,

Report no. 98172, July 1978, Rochester, NY.

5. M.J. Krebs, J.D. Wolf and J.H. Sandvig, "Color Display Design Guide"

Office of Naval Research, Report no. ONR-CR213-136-2F, October 1978.

6. Ben Shneiderman, "Human Factors Experiments in Designing Interactive

Systems", IEEE Computer, December 1979, pp 9-19.

7. Lawrence E. Tannas , Jr., and Walter F. Goede, "Flat-panel Displays:

a Critique", IEEE Spectrum, July 1978, pp 26-32.

8. "Total Distributed System"- TDC2000", Honeywell.

9. "CRT Display for Power Plants", M.M. Danchak, Combustion Engineering

Inc

.

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ON-BOARD INSTRUMENTATION TECHNIQUES FOR THE

DEVELOPMENT OF A GAS TURBINE ENGINE

FOR TRUCK APPLICATIONS

Paul D. Olivier

AiResearch Manufacturing Company of Arizona

Division of Garrett Corporation

Phoenix, Arizona 85OIO

Abstract

The development of a gas turbine engine for use in highway and off-road

trucks requires the implementation of considerable instrumentation techniques. The multitude of operational conditions that can be encountered

in the operation of a vehicle on the roads are very difficult to accu- rately simulate in a test cell. A test vehicle was outfitted with a large, on-line digital data system with multi-readout capability, as well as a multitude of script chart and analog instrumentation.

COMMENT

Mr. Olivier arranged to have the test vehicle driven from Phoenix to

Santa Monica for the MFPG Symposium and provided a demonstration of the

instrumentation. Editor

125
MARINE BALL/ROLLER BEARING MONITORING

BY SHOCK PULSE MONITORING

Joseph P. Fischer

American Steamship Company

3250 Marine Midland Center

Buffalo, N.Y. 14203

Donald S. Schover

GATX/GARD, INC.

7449 N. Natchez Avenue

Niles, Illinois 60648

David Board

SKF Industries, Inc.

1100 First Avenue

King of Prussia, PA 19406

Abstract: The American Steamship Company (ASC) (a subsidiary of GATX

Corporation) operates a fleet of modern self-unloading bulk carriers on

the Great Lakes. A group of these ships with similar drive trains have

experienced bearing failures in a 1740 Kw generator. GARD, INC., was charged with the task of evaluating available bearing monitoring techniques and equipment for their ability to detect and predict bearing

damage prior to destructive failure.

SKF Technology Services of SKF Industries, Inc. was called in as a con- sultant in the area of roller and ball bearing damage detection. They

have developed a production instrument (Automatic Shock Pulse Analyzer,

or ASPA) based on an advanced application of this technique. During

the summer and fall of 1979 a number of critical bearings were monitored

on three sister ships. Readings were correlated as to spectral energy

content and prototype ASPA readings. In this set of evaluation tests,

a bearing on one ship was classified as damaged. During maintenance and

repair operations that winter, the suspect bearing was removed and found

to have serious outer race damage.

During 1980, a production ASPA has been installed in one of three sister

ships (THE MV H LEE WHITE) and a log of five crucial bearings is being

kept.

When thoroughly proved out, further installations will be evaluated for

similar machinery in the fleet.

Key words: Automatic alarm of bearing malfunction; Marine Machinery

Bearings; Microprocessor based shock pulse analyzer; Multiplexing

bearing monitor channels; Prediction of bearing failure; Shock pulse

bearing monitoring.

126
The American Steamship Company (a subsidiary of GATX) operates a fleet

of 20 self-unloading dry bulk cargo vessels on the Great Lakes. These

ships range in length from 580 to 1,000 feet and, in cargo capacity,

from 10,800 to 66,000 tons. In three of these ships, propulsion

consists of two 3600 HP 20 cylinder diesel engines driving a single

propeller shaft and screw through clutches and a reduction gear set.

On these three ships, as seen in Figure l

s the layout of the power train

includes a large generator rigidly connected to the drive train of the

port engine. This 480 volt 3 phase 1740 kw generator provides

electrical power to the self-unloading conveyor system and the bow and

stern thrusters used in docking and restricted space maneuvering. The

after end of the generator shaft is connected to the port pinion gear

of the reduction set through a clutch. The generator rotor turns when- ever the port engine runs but is not used to generate electrical power

unless it is declutched from the reduction gears and operating at

synchronous shaft speed of 720 rpm. Thus, the generator rotor acts

only as a flywheel during most hours of engine running when traveling

between ports. Its use to generate electricity amounts to a very short

period of maneuvering time when entering or leaving dock facilities and

when unloading its cargo. Normally, unloading occupies a time span of

8 to 12 hours.

The forward end of the generator shaft is rigidly supported by the end

of the diesel engine drive shaft. The after end of the generator rotor

is supported by a ball bearing with the generator shaft coupled to the

input flange of the clutch. On two of the three ships having

essentially the same propulsion layout, seen in Figure 1, there have

been disastrous failures of the generator bearing. These failures have

proved very costly in terms of loss of vessel use and extensive repairs

to the generator.

GARD, INC., a subsidiary of GATX was requested to investigate the

feasibility of bearing failure prediction to mitigate this costly

failure mode. GARD surveyed the field of bearing monitoring consultants

and instrument suppliers for the latest and most promising instrument

approaches compatible with marine installations. The instrument had to

be reliable and simple enough to use by the operating engineers

employed on this class of vessel. The selected instrument had the

capability of monitoring multiple bearing sites through multiplexing

provisions. It was decided to monitor five locations on a trial basis

to evaluate both the technique and the instrument. These five locations

are shown in Figure 1. They consist of the generator bearing (the prime

monitored site) and the four pinion bearings of the reduction gear set.

These components are large double row spherical roller bearings

operating at engine shaft speeds ranging from approximately 900 rpm down

to 400 rpm in speed range. The pinion bearings are force-lubricated by

the reduction gear oiler system, while the generator bearing is lubricated by means of a low volume sump at the bottom of the bearing. The

sump oil level is frequently monitored and replenished. Maintenance

procedures for these vessels include frequent and periodic submission of

127
oil samples to several analysis facilities for reports on contamination

and evidence of metal debris. It has been recognized that this is not

practical as a quick response feedback on bearing condition since

failure can occur well within analysis response time.

The Automatic Shock Pulse Analyzer: The technology and instrument

chosen by GARD is the Automatic Shock Pulse Analyzer (ASPA) designed and

supplied by the SKF Technology Services Division of SKF Industries Inc..

The Mark IV analyzer shown in Figure 2 is based on the recognized

phenomena of bearing defect shock pulse generation but utilizes this

information in a more sophisticated statistical approach than several

other proponents of this technique. The original use of this concept

depended on monitoring only the peak amplitude of these pulses and

counting the number that exceeded a selected threshold value over a measured sample duration at a known shaft speed. The SKF approach

computes energy content for each shock pulse. All of these individual

pulse energy quantities are summed over a fixed sampling period. This

technique recognizes that some pulses have different durations than

other pulses of a similar peak amplitude and also takes into account the

many times that pulses of different peak amplitudes are partially

superimposed on each other. The method is microprocessor based and in

a very simple form is described in Figure 3.

The shock pulse approach depends on the generation of energy impulses

by the impact of balls or rollers on defects on the inner or outer

races, or defects in the ball or roller itself, or debris that may be

trapped within the bearing assembly. These shock pulses propagate outward in a spherical geometry modified by reflections within the complex

mechanical structure itself and can be detected almost anywhere within

reasonable range of the origin. A very favorable characteristic of

these pulses is that they are in the ultrasonic region of 20 kHz to

500 ^Hz and are thus well separated from the audible frequency range in

which much of the stray machinery noise can be found. The machinery

noise energy often masks the audible signals generated by the defective

bearing. Thus, shock pulse generation results in a signal that can reliably be discerned as bearing phenomena and permits the investigator

to discriminate against ambient machinery noise.

The transducers most commonly used are piezoelectric accelerometer type

sensors, appropriately matched to the mechanical impedance of the

propagating medium and the electrical characteristics of the shock pulse

analyzer. There are several practical techniques for satisfactorily

mounting transducers. A threaded stud is used in our application. The

shock pulses detected by the transducers excite a damped oscillatory

train at frequencies close to the natural resonance of the transducer.

The transducers employed resonate at approximately 37 Khz. Figure 3a

shows the rolling elements initiating spherical shock waves which

excite the sensor to generate damped trains superimposed on the lower

frequencies characteristic of machinery vibration mechanisms. A bandpass filter removes the unwanted frequencies leaving only the ultrasonic

128
trains of shock excited transducer ringing. These are then envelope

detected to produce a train of the shock pulse envelopes. The shock

pulse train is then digitized and the microprocessor in the analyzer

computes the total energy content of all pulses which occur during a controlled sampling period.

The system, as configured in the Mark IV, also controls the multiplexer

switching from one channel to the next and displays the results of each

data frame as compared to preset limits for "Caution" or "Replace"

warnings. The instrument has logic which calls for operator attention

when limits are exceeded. Both visual and audible alarms suitable to

the noise and activity environment of the typical ship's engine control room warn the control room attendants of abnormal conditions. Although

the Mark IV is capable of monitoring up to 8 groups of 31 channels each,

the trial installation by American Steamship Company on the Motor Vessel

H. LEE WHITE monitors only the 5 previously mentioned channels. In

order to set the threshold levels contained in the instrument's Read

Only Memory (ROM), it is necessary to measure typical acceptable bearing

performance at specified speeds for a sufficient period of time to

accumulate the statistics from which the "Caution" and "Replace"

thresholds are computed. These quantities, once stored in the ROM, are

the reference to which the warning decisions are made.

Evaluation Program: During the summer and fall of 1979, three ships of

the American Steamship Company fleet, having similar propulsion and

generator installations were visited. On these ships, transducers were mounted on the generator bearing housing shown in Figure 4 and on the

four reduction gear pinion locations as shown in Figure 5. A portable

battery powered prototype (the Mark III) was used to record shock pulse

energy levels to compare bearings from ship to ship. In addition, a spectrum analyzer accompanied these experiments to define the frequency

content of the shock pulse train. This spectral data was then used to

fault isolate the specific mechanical source of abnormal shock pulse

energy levels.

In the course of this program, the port forward pinion bearing on the MV

H. LEE WHITE was found to have significantly higher shock pulse energy

numbers than its counterpart on the starboard side or the rear pinion

bearings. The bearing was subsequently disassembled and examined.

Significant outer race damage was found to be present as shown in Figure

5. This bearing was replaced during the normal winter maintenance

season.

In 1980, the Mark IV was installed on the H. LEE WHITE and the crew was trained in making entries to a log. Behavior has been monitored over a period of 12 weeks to date. Normal cruising speed for this vessel is

roughly 15 miles per hour (statute miles are used on the Great Lakes)

at a propeller shaft speed of 120 rpm (corresponding to an engine crank

shaft speed of approximately 900 rpm). Early in the sailing season of

1980, the ship's operation was altered to a cruising propellor shaft

129
speed of approximately 103 rpm to conserve fuel. At the start of the season it was found that the forward starboard pinion bearing was exhibiting a shock pulse energy number 10 to 15 times higher than the

portside pinion bearings. Figure 6 shows the results of 7 weeks of data

logging of the 5 bearings at speeds of both 120 rpm and 103 rpm. Additionally, the generator bearing is monitored at its synchronous speed

of 720 rpm during power generation. Several interesting features can be

noted on examining the results. Channels 1, 2, 3, and 4, show very

consistent levels during the entire observation period for each

propeller speed recorded. This demonstrates the consistency of the

instrument and its ability to operate in the temperature, vibration and

moisture environment of Great Lakes commercial vessels. Probably the

most important aspect of information from this type of monitoring is seen in the slopes of these curves showing the trends of increased wear

during the period of observation. This is also holding true for channel

5 at its higher level than the other bearings (at least for the period

of observation). At one point, at 103 shaft rpm, its level increased

by 35% for a period of 6 hours. The reading then dropped back to its

previous level. This shows the sensitivity of the technique to what

probably was particulate contamination that entered the bearing and was subsequently flushed out during its operation. This bearing is being

closely monitored during the sailing season. Although the high level

does not, in this case, indicate a damaged bearing it is probably

warning that life for this bearing will be shorter than its neighbors

and that its energy trend should be closely monitored. If there is a significant increase in energy trend over a relatively short period of

time, this will indicate that this bearing should be replaced at the

earliest opportunity to avoid destructive failure.

Conclusion: The shock pulse energy monitoring technique as embodied in

the Mark IV Automatic Shock Pulse Analyzer has provided meaningful information on bearing condition. The bearing monitoring installation is

still in a period of operational evaluation. Pending the final results

of this trial period, the value of additional installations to appropriate fleet machinery will be determined.

130
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133
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136
SESSION IV

DIAGNOSTIC AND PROGNOSTIC

TECHNIQUES

Chairmen: J.

P 0

Anderson, Spectral Dynamics

Howard, Energy and Minerals

Research Company

CONSERVATION: LOSS PREVENTION AND RISK MANAGEMENT

G. E. Gulbrandsen

Philadelphia Manufacturers Mutual Insurance Company

Valley Forge, Pennsylvania 19482

Abstract: Many factors are involved in Risk Management and Property

Conservation. Loss prevention, predictive-preventive maintenance, cost of

money and insurance are just a few of the many. The subject of cost can be

further subdivided into real and subjective costs; the real cost of unexpected

losses and the subjective (though some feel real) cost of uncertainty. Today,

the intelligent management of all factors is of prime importance. With the

high costs of downtime and replacement parts, one can no longer rely on

previous methods.

In the 1970's some insurance companies which deal in industrial property coverages, i.e., turbine insurance, pressure vessel insurance, compressor insurance,

etc., have taken an active interest in the early detection of incipient faults.

This interest has led some of these insurance companies to purchase sophisticated electronic devices (Acoustic Emission Analyzers, FFT Spectrum Analyzers, Shock Pulse Analyzers, etc.) and to use these instruments to help the

Insureds conserve their assets. Property conservation, loss prevention, and

risk management have now combined their collective capabilities to ensure the

early detection of faults and maximum life of machines for the most

economical cost of these procedures and insurance coverages.

Key words: Acoustic Emission Analysis; Insurance; Loss Prevention; Modal

Analysis; Property Conservation; Risk Management; Shock Pulse Analysis;

Vibration Analysis.

In today's modern manufacturing and public utility facilities, risk management

has taken on a new meaning and importance. With the economic situation

being what it is, one must be aware of every possible avenue to save time,

money, and property. The plant manager and other management officers must

now know the meaning and importance of Risk Management and Loss Prevention.

To begin, we must define "risk management" and its associated elements. In a simple phrase, risk management is the treatment of loss exposures; loss

exposures, further, have three basic elements. They are:

1. The item must be subject to a decline or disappearance in value, i.e.,

subject to loss.

2. The item must be subject to causal forces which may cause a loss.

3. Extensive negative impact from a loss must be a possibility.

139
Item Subject to Loss

The term "loss" implies the decline in value or disappearance of an object or property. Be this the case, it is quite important in risk management that a thorough identification and evaluation be made of exactly what is subject to a

loss, and to what type of loss it is subject.

Items subject to loss can be simply categorized into (a) assets (things of value

owned) and (b) income (provided by these assets).

Causal Forces

Once we have identified objects subject to loss, we must now deal with what

exactly can bring about the adverse effect. We in the risk management and

insurance business call such an element a "peril." A peril is a potential cause

of a loss. Thus, an adverse event (a peril) may happen and create its

subsequent economic loss.

It is quite important to be aware and identify the perils associated with each

piece of property in one's care, custody, and control. We must identify what

equipment is subject to loss and find out the associated perils. A program of

peril identification can do this for us. As stated by Williams, Head, and

Glendenning, knowing what exactly is subject to loss and what types of losses

it is subject to must clearly be resolved before any method of risk management can be intelligently considered.

Perils may be grouped according to their origin as either natural, human,

and/or economic. Natural perils are familiar, such as fire, windstorm, hail,

flood, etc. Human perils may be considered as theft, riot, vandalism,

negligence, and the failure to satisfy an expressed obligation. Economic perils can be inflation, recession, technological advances, etc. There are, obviously,

many overlaps.

Keep in mind that perils are only a portion of loss exposures and that some

perils are not insurable. What is of great importance and significance,

however, is the problem of peril identification and analysis.

Potential Economic Impact

This final element of loss exposure is both the quantitative and logical sequel

to the other two. One must realize, however, that potential financial impact

is a relative rather than an absolute term. What would constitute a severe

financial impact to one party would not be as severe to another. Also, the

potential impact varies over a period of time for the same party.

LOSS EXPOSURES AND RISK

In risk management and insurance, the term risk is meant in practice to mean

any one of the following:

iko
1. The possibility or state of being exposed to loss.

2. The probability or chance of loss.

3. A peril.

4. A hazard.

5. The property or person exposed to damage or loss.

6. The potential losses that may be sustained.

7. Variation of these potential losses.

8. Uncertainty concerning loss.

Risk as the Possibility of Loss:

According to this usage, one faces the risk or possibility of a certain type of

loss. Those who use this definition claim that risk (possibility of loss) cannot

be measured. It either exists or it does not exist.

Risk as Chance of Loss ;

In this usage, it is the probability or chance of loss. The chance of loss is the

relative likelihood that a loss will occur within some stipulated time period.

Thus, risk can be measured and chance of loss can be stated to be between 0

and 1, zero maintaining that loss will not occur and 1 that loss is certain.

As an example, if risk is thus defined as the chance of loss, and the risk of a

turbine explosion during the next year is estimated to be 1/6, thus this would

mean that on the average, one would expect this type of loss to occur once in

every six years.

The chance of loss is an important element in pricing insurance, underwriting

insurance, and deciding whether to recommend insurance in a particular

situation.

Risk as a Peril : A less common but still frequent practice is to define risk as a cause of loss (a

peril). Examples of perils are fires, explosions, etc.

Risk as a Hazard : A hazard is a condition that creates or increases the chance of loss arising

from a particular peril. Hazards, therefore, are the real causes of loss in that

they cause the perils that cause the losses. Examples of hazards are

carelessness with property that may increase the chance of a certain loss, i.e.,

poor housekeeping, inadequate ventilation, improper storage of hazardous

materials, etc.

Risk as the Uncertainty Concerning Loss :

This may be the most important definition of risk. When the potential of loss

varies, or is believed to vary, a person is uncertain or doubtful about his ability

to predict the outcome of events. This definition then equates risk with a

Ikl
person's conscious awareness of a variation in what might happen. Because

two persons may have different information concerning the potential losses

and may interpret that information differently, their uncertainty can vary

greatly even though they are exposed to the same potential losses. An

example is the person who believes that only a few outcomes (differing very

little from each other) can occur. Another person facing the same facts and

situations may conclude that widely varying outcomes can occur. One may be

right or both may be wrong. The first person believes he or she can predict

the future fairly well; the risk is small. The second has little faith in his or her forecasting ability and the risk is great. This doubt concerning their

ability to predict the future is certainly an important concept because it influences many risk management and insurance decisions. Uncertainty is the

key word in the economic impacts of risk.

ECONOMIC COSTS OF RISK

A. H. VVillet, in his discussion of the economics of insurance, refers to the cost

of uncertainty arising out of:

1. The unexpected losses that do occur,

2. The uncertainty itself, even if there are no losses.

We all know the financial impacts of the cost of unexpected losses. When

unexpected losses occur, production ceases and the business flow is interrupted. The economic consequences are both direct and indirect. The cost of

repair or replacement of the damaged object can be considerable and the fact

that the end product is no longer available for sale also causes a cashflow

problem. In certain instances, valuable customers may be lost and never

regained.

The cost of uncertainty itself, however, can be considerable. The first cost of

uncertainty is the tendency to reduce the total satisfaction associated with a given economic status. This reduction may result from:

a) The diminishing marginal utility

b) Overestimating the chance of loss, and

c) Fear and worry

Another cause of uncertainty is its tendency to cause inefficiencies in the

utilization of existing capital and to retard development of new capital. As a

result, total production or potential of production is decreased. To explain,

let's assume that there is a given fixed amount of capital. With other things

being equal, the marginal productivity of this available capital in each industry

tends to decrease as the amount of capital committed to that industry

increases. Thus, this available capital is appropriated in an optimum way when

the marginal productivity in each industry is the same. If this were not so, total production could be increased by transferring capital from an industry

where the marginal productivity is least to one where it is greatest. Uncertainty disturbs this balance because relatively too many resources tend to flow

lk2
into the safe industries and society may have to live without the products that

could be developed from a risky industry. For example, could utilities have

attained their present productive status if each individual utility had to bear

the monetary losses due to accidents to their larger and larger turbogenerators? I think not. As stated by C. Arthur Williams, Jr., and Richard M.

Heins, in their book Risk Management and Insurance, "Within an industry, the

existence of uncertainty may affect the apportionment of capital among

firms; within a firm, it may affect the selection of the methods of production

and distribution."

To summarize, the cost of uncertainty, in addition to the unexpected actual

losses, are generally

a) a reduction in the total satisfaction because of the existence of

uncertainty and,

b) Less than optimum production, price levels, and price structures.

Five Steps in the Risk Management Process

1. Procedures and communications should be established throughout the

organization to allow for complete inventory and discovery of the

potential (pure) risks that may arise in the activities of their business

firm.

2. After identification of risks, the next important step is the proper

measurement of the losses associated with these risks.

3. Once the risk is identified and measured, the various alternative

solutions of risk management should be considered and a decision

made with respect to the best combination of solutions to be used in

attacking the problem.

4. After deciding among the alternative methods of risk treatment, the

risk administrator and appropriate management groups should establish means for effective implementation of the decisions made.

5. The results of the decisions made and implemented in the first four

steps must be monitored to evaluate the wisdom of these decisions

and to determine whether changing conditions should suggest different solutions.

Step No. 3 in the risk management process, meaning the identification and

measurement of the various alternative solutions of a risk management

problem, offers a number of various alternative solutions. Once the risk is identified and the amount of risk evaluated, we must decide how to live with

this risk. We can decide to avoid the risk. If we do this, the amount of risk is reduced to zero. If one does not engage in an activity that has the associated

risk, the risk does not exist. Thus, if a company decides not to manufacture an

item, and does not purchase the equipment that is needed for the manufacture

of that item, the risk is thus avoided.

Another way of attacking a problem is to transfer the risk to some other

party, that is, to buy insurance. When insurance is purchased, part of the risk

and financial burden is transferred to the insurer. Except for a certain

deductible amount, the risk has been transferred. Still another way of dealing

with this problem is to retain or bear the risk internally. In this case, if a loss

lh3
occurs, the company will bear the financial loss itself. This is similar in

consequences to ignoring the risk. The final alternative is to reduce the

chance of loss or to reduce its magnitude if it does occur. This, of course, is the fundamental premise of loss prevention.

Loss Prevention and Incipient Fault Detection

After the risk has been identified and measured, and the appropriate steps to

deal with it have been accomplished, one still has to deal with the fact that a machine will, in most probability, fail sometime in the future. If insurance has

been purchased, or if the risk has been partially or wholly retained by the

owner, it is quite important that some sort of loss prevention system be

implemented.

Property Conservation, Loss Prevention, and Predictive Analysis

In times of soft economies, as well as in times of fierce competition, it is historical for corporate management to worry more about the marketplace and

production than about loss prevention. Concern is frequently placed on

research and development for new products and the possible penetration into

untouched markets. Loss prevention (including predictive analysis) falls by the

wayside, for after all, there is insurance coverage on the plant and machines.

There may even be Business Interruption Insurance to cover lost profits for the

downtime suffered. But there is no insurance that will cover the situation in

which one of your salesman has to say, "we cannot deliver. ..our production

ceased due to the destruction of our turbine (or whatever)."

Property conservation and loss prevention are closely tied to many factors,

including your company's reputation or image in the business community,

efficiency, employee morale, and most importantly, to its ability to produce

and deliver its product day after day, consistently. A company's customers

may sympathize with the problem; but they have an obligation in turn, the

same as yours, to deliver their product.

As equipment and material costs continue to escalate and profit margins

decrease, plant management efforts must now be directed toward methods

that will ensure continued and uninterrupted production from their facilities.

The same risk management criteria and procedures which were used by a corporate risk manager must also be utilized by the plant engineer. For a "quiet night's sleep" and peace of mind, he must weigh the various risks

involved and the methods to deal with these risks. Predictive analysis is one way to deal with these risks.

Because of today's economic conditions and the high cost of everything

involved in production and repair, it is virtually impossible to charge enough

insurance premium to cover all losses. In many cases, small items costing

$10,000 five years ago costs over $35,000 today. One way of dealing with this

situation is for an insurance company to increase the deductible amount

applied to the policy. Thus, the insurance carrier has transferred back to the

ikh
Policyholder part of the "risk." In the past, a manufacturing company may

have been able to handle a number of $10,000 deductible nuisance losses, but it is not financially prepared today to handle the same number of $25,000 or even

$30,000 losses. The deductibles today are, in many cases, in the six figures,

which indicates the importance of having to evaluate the risks involved and

develop methods with which to deal with them effectively.

It is both unproductive and wasteful to schedule a machine for internal

inspection and dismantle for no reason other than "it's time to tear it apart."

Likewise, it is inefficient to "run it until it breaks." Both are present

philosophies of some large industrial corporations. What is needed is a blend

of scientific procedures and criteria which would allow a method of determining machinery health in order to best utilize available resources to

maximum benefit. It is a waste of precious oil to change it every 4,000 miles, on the other hand, it is also a waste of a good machine to let it run without an

oil change.

Modern electronics and creative engineers have given us some new tools with

which we can work. Among the fairly new analysis tools are "real-time

spectrum analyzers," "acoustic emission analyzers," "high-frequency shock

pulse analyzers," and "modal analysis systems."

Vibration analysis has been around for some years, basically since the days of

the hand-held vibration meters with tunable filters. They were good at

detecting unbalance and misalignment. Since then, however, the state of the

art has escalated almost exponentially with the advent of the Fast Fourier

(FFT) Real-Time Analyzer (RTA). The FFT RTA now allows us to peek at the

more esoteric frequencies and nuances of machine vibration in order to figure

out "what's going on." Figure 1 shows the setup using such a device to analyze

the vibrations emitting from a high-horsepower, multi-stage centrifugal compressor used as the main incoming air supply at an air reduction plant. The

loss of this compressor would not only be a large loss for the insurance carrier,

it would also be a burden for the company itself; it must supply another plant

which is dependent upon the various gases produced via pipeline.

In many cases, a replacement bullgear for such a compressor has over a threemonth lead time. Many dollars and much "image" would go down the drain if such a loss were suffered.

Figure 2 is the spectrum of a steam turbine's HP-IP bearing in which was

discovered a very large 600 Hz spike. All other similar machines had no such

indication, let alone one of such high magnitude. This was brought to the

attention of the plant personnel, who simply shrugged it off as being odd, but

nothing more. Thirty-two days later the turbine tore apart, with a subsequent

and very expensive loss. It was a classic case of not wanting or caring enough

to find out what the indication meant. It was later determined by metallurgical analysis that there was some cracking; the spike may have been an early

indication of such impending failure. In any case, the other machines had no

such indication.

ih5
Figure 1. Author taking data for vibration analysis

of a high speed centrifugal compressor

vi bration

.

Shock Pulse Analysis is a fine method of determining very high frequency

components of mechanical vibrations. It operates on the principle that certain

discrepant parts within a machine (such as pitted, spalled, or brinelled bearing

and gear elements) release abnormal amounts of frictional and/or kinetic

energy. In the frequency domain, frictional energy generates "white noise."

The kinetic event, for the most part, is lost in the noise and machine vibration.

It so happens, however, that above a certain frequency the amplitude of

kinetic energy release will be greater than that of the machine vibration. It is difficult, if not impossible to detect characteristic kinetic events using

conventional vibration analysis techniques, but with the use of envelope

detection, the natural resonance of certain types of accelero meters and

subsequent FFT spectrum analysis, these important characteristic kinetic

events can be "retrieved."

Figure 3 details the procedure for analysis of these kinetic events. It is interesting to note, that as with standard low-frequency vibration, the data can be used for either incipient fault detection and analysis or for machine

monitoring. The shock pulse train can be sent "to a spectrum analyzer or to a shock pulse monitor. In any case, a new vista of machinery health monitoring

has been allowed by the use of imaginative engineering and state-of-the-art

electronics.

lk6
Figure 2. Signature from a bearing of a steam

turbine; unit later failed.

Acoustic Emission Analysis is yet another advanced method for incipient fault

detection. Similar in some ways to both vibration and shock, it studies the

acoustic kinetic events produced by a material under stress. Acoustic

Emission (AE) measurements are specifically intended to reveal very small

(thus early stage) incipient faults. Unlike vibration, these AE measurements

relate directly to sound energy emitted in a material and not to the machine

component behavior. Even though most machines are quite noisy, this

operating noise tends to be in the same part of the frequency spectrum as machine component vibrations. AE analysis studies that portion of the

spectrum in which defect-originated energy extends itself; even higher than

that of shock pulse frequencies. By definition, acoustic emission is a transient

elastic wave that has been generated within a material by the very rapid

release of energy. AE is quite sensitive and can detect quick displacements of
-12

as little as 10 inch. Many AE sensors have a natural resonance in the 300

kHz to 500 kHz range, and sensor response and types can be selected to fit the

particular problem at hand.

AE techniques have been found to be very useful for incipient fault detection

in areas where other techniques are weak in comparison. Typical applications are the location of underground leaks in gas transmission lines, fault detection

and of monitoring of pressure vessels, and the testing of composite material

integrity. Many industries are finding a useful tool in AE analysis including

utilities, chemical plants, aerospace, railways, mining and metal fabrication.

The basis for this technique is that materials undergoing deformation, for one

reason or another, normally emit acoustic energy. This energy is usually in the

form of short bursts or trains of fast impulses in the ultrasonic frequency

range. AE analysis can study these internal releases of energy by the use of

transducers to detect these transient elastic waves. These signals can then be

related to the physical integrity of the material or structure in which they

were generated. Monitoring of these events permits the detection and

location of flaws, as well as the prediction of impending failure. See Figure 4.

ACC E LE HOT Ttl

1) Kinetic and frlctlonel encrjy W Telexed by discrepant part

1) Kinetic and fTlctlonal encrfy decnys less rapidly thin vibrational enersy In the frequency domain. Thus at frequcnele

treatcr than ( L

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than vlhmtlonal energy. response amplifies kinetic and

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T *" ter th,n f E4) The bandpass filter eliwinntrj non- resonunt response of the accelercaeter, and the envelope detector follows the amplitude Modulation* of the ac ee le ro«e ter rcmnonco (shock pulses).

Figure 3. Shock pulse flow chart.

148
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Figure 4.

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Figure 5. Typical display on a RTA of a transfer

function. Resonance at 264 Hz.

lk9
An advance two-channel FFT spectrum analyzer allows the investigation of

some more esoteric vibration-related information. One such parameter is called "the transfer function." For any machine, the harmonic part of the

spectrum due to running speed is usually known in its frequency content. The

non-harmonic part, that is frequencies unrelated to running speed, are unknown (both in frequency and amplitude content). This non-harmonic data

has a wealth of information which is unrelated to running speed, though it may

be excited by it. In order to retrieve this data, Transfer Function Analysis is employed. Transfer Function Analysis is done by exciting an object by

external means, usually a shaker or calibrated force hammer. The recorded

response is a measure of the structural characteristics of the machine. The

response is actually the complex ratio of the cross spectrum to the input

power spectrum, which defines the gain and phase lag introduced by a transmission system excited by the known force and responding with a measured result.

Figure 5 is a typical recorded transfer function. One can see that the system

resonance is at 264 Hz by the peak at that frequency as well as the associated

phase shift. Many times a machine has caused major problems because of

unknown component resonance. This type of analysis allows the detection of

such problems. Taking a number of transfer functions allows us the ability to

do a Modal Analysis using an advanced two-channel spectrum analyzer with

modal analysis capability. We can express the vibration of any structure as a sum of its vibration modes and thus represent any vibration as a sum of much

simpler vibration modes. Modal Analysis can determine the shape and

magnitude of the structural deformation in each vibration mode; and once

these are known, it usually becomes apparent how to change the overall

vibration.

Conclusion ;

Predictive analysis is as important a part to a company's welfare as predictive

medicine is to one's health. Just as periodic checks of one's heart, lungs, and

other vital organs of one's body are made to prevent breakdowns and ensure

better health and longer life. ..the protection of the vital organs of a business,

the operating equipment and plant facilities, is also very essential.

To ensure against broken production schedules, maintenance stock shortages,

unnecessary deterioration of equipment, and to prolong the life of operating

machinery, regular inspection and service of equipment are major considerations of any business. Top performance of equipment for a healthy business is a direct result of creative and predictive analysis.

150
Bibliography

Board, David, Shock Pulse Analysis, SKF Industries, King of Prussia, PA.

Mehr, Robert I. and Bob A. Hedges, Risk Management: Concepts and

Applications, Richard D. Irwin, Inc., Homewood, IL, 1974.

Willett, Allan H., The Economic Theory of Risk and Insurance, University of

Pennsylvania Press, Philadelphia, 1951.

Williams, Jr., C. Arthur and Richard M. Heins, Risk Management and Insur- ance, McGraw-Hill Book Co., New York, 1976.

Williams, Jr., C. Arthur, George L. Head and G. William Glendenning,

Principles of Risk Management and Insurance, Vol. 1, American Institute for

Property and Liability Underwriters, Malvern, PA, 1978.

Vargas, Alfred, Acoustic Emission, Acoustic Emission Technology, Sacramento, California.

151
RECENT EXPERIENCES WITH STEAM TURBINE

DISC CRACKING

Gerald A. Lamping

Southwest Research Institute

San Antonio, Texas 78284

Abstract: Steam turbine disc cracking in large power generation turbines was essentially undetected until recently when utilities and

turbine manufacturers started performing extensive nondestructive

examination (NDE) programs. These were initiated in part due to the severe disc cracking problems experienced by British utilities during

the 1970' s. NDE being performed in the United States revealed significant disc bore and disc keyway cracking and erosion cutting previously undetected. Disc rim cracking in the blade attachment area

also was experienced in some cases. The paper describes some typical

areas where disc cracking has occurred and the NDE methods usually

used to inspect for these defects. Metallurgical analysis work

performed on several of the disc cracks shows intergranular stress

corrosion cracking as the mode of failure. Repair methods presently

employed to return the turbines to service and research programs

under way to study the problem are also discussed.

Key words: Low alloy steels; steam turbine component failure; stress

corrosion cracking; United States experiences; ultrasonic inspection.

1 .0 Introduction

The U.S. electric utilities have been experiencing a significant increase in the number of cracking incidents in forged, low

alloy steel discs used on low pressure steam turbine rotors. Since

mid 1979, over 25 cases of disc cracking have been reported. In most

of these cases, multiple disc cracks were found, indicating that the

extent of the problem is very severe.

The increase in the discovery of disc cracking is due partially

to the undertaking of extensive nondestructive examination (NDE)

programs by the utilities with the assistance of the turbine manufacturers. The NDE programs were developed to inspect for disc keyway

and disc bore cracks on U.S. turbines after the British electric

utilities found extensive cracking in 124 low pressure turbine discs

during the early 1970s 1

. In a few U.S. cases, NDE inspection found

cracks that were close to the calculated critical crack size, and

thus catastrophic disc bursts were prevented. However, in one unit

which was uninspectable due to disc geometry access limitations, a disc burst did occur that resulted in extensive damage to the

turbine.

152
In all cases where a failure analysis was performed, the cause

of disc cracking was stress corrosion cracking (SCC). However, not

all disc cracks have been submitted for metallurgical analysis since

some ultrasonic (UT) indications were judged to be small enough to

allow the turbine to be returned to service. In these cases, a reinspection is planned for the near future.

Because of the serious nature of the stress-corrosion caused

disc problems, the electric utilities have continued their UT inspection programs and have initiated a massive research effort for the

development of preventive measures through their research organization, the Electric Power Research Institute (EPRI). The utilities'

goals are to prevent serious damage to their plants and harm to their

personnel, while at the same time, to achieve the maximum productivity from equipment. For example, a unit outage day for inspection

can cost up to $500,000, while a unit outage for repair from a disc

failure can result in equipment replacement costs from two to six

million dollars, in addition to removing the plant from service for

up to one year. Techniques for disc cracking detection, diagnosis,

and prognosis (DD&P) have been introduced and applied to prevent

mechanical failures, but improvements in all three areas are desired

to optimize inspection costs and to validate run/retire decisions.

In addition to the utilities' activities, the turbine manufacturers, the equipment insurance companies, and the Nuclear Regulatory

Commission (NRC) have initiated their own fact gathering and data

analysis programs. One result of this intense effort to determine

the scope of the disc cracking problem is that a considerable amount

of information has been generated from the crack analyses and

research programs conducted so far. While all of this information is

not presently available for public disclosure, the remainder of this

paper will present information which is available and inform the

reader from where future information will be coming.

2 . 0 Background

A steam turbine disc is a rotor component which connects the

torque-producing blades to the torque-transmitting shaft. This disc

is sometimes referred to as a wheel. A cross section of a low pressure steam turbine is shown in Figure 1. The typical locations where

disc cracking has occurred for shrunk on designs, as shown in the

figure, are disc rim/blade attachments, the disc external web and hub

surfaces, and the disc internal bore and keyway surfaces. In integral rotor designs, where bore and keyways are not present, cracking

has occurred on the disc rim, web, and hub surfaces. There are from

ten to sixteen discs per rotor and one to three rotors per unit. A

large 800 MW unit might have up to 48 individual discs. While cracking has been found on all disc surfaces, keyway and bore cracks have

predominated and are more serious, since they are harder to detect

before reaching critical size.

153
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For built-up rotor designs with shrunk-on discs, the materials

presently used for discs are 3.5 percent NiCrMoV alloys produced in

accordance with a manufacturer's proprietary specifications which are similar to ASTM A471. The materials presently used for integral

rotor designs are also 3.5 percent NiCrMoV alloys similar to ASTM

A470. Figures 2 and 3 show that the specified mechanical properties

and the material chemical composition for a Class 6 A471 disc steel

and a Class 5 A470 rotor steel. Chemical composition of either steel

is essentially the same. The A471 steel is generally produced at a higher strength level. Other steels sometimes used previously for

these components include 2.5 percent NiCrMoV, 3 percent CrMoV and 3

percent Ni, although the last steel has not been used in the U.S.

Figure 4 shows the areas of a disc where cracking has occurred.

The keyway and bore cracks have been radial-axial in extent and orientation as shown in Figure 5. The disc hub and web cracks have been

both radial-axial and radial-circumferential. For disc rim/blade

attachment cracks, orientation depends very much on the blade root

configuration. Figure 6 shows the typical cracks found in each of

the root designs used by U.S. manufacturers. The axial entry fir

tree-type root has experienced both axial-circumferential Type 1 cracks and axial-radial Type II cracks. The Type I cracks are

MECHANICAL PROPERTIES

ASTM A 470 CLASS 5 STEEL ASTM A 471 CLASS 6 STEEL

PROPERTY

UTS (KSI)

YS (KSI)

% EL. (2 IN.)

% RA

SPECIFIED

90 MIN.

70 (0.02%) MIN.

75 (0.2%) MIN.

18 MIN.

50 MIN.

SPECIFIED

140 MIN.

125 TO 145 (0.02%)

130 TO ±%0 (0.2%)

15 MIN.

43 MIN.

FIGURE 2. MECHANICAL PROPERTIES FOR TURBINE DISC AND ROTOR STEELS

155
CHEMICAL COMPOSITION

ASTM A470 — CLASS 5 VACUUM-TREATED CARBON AND

ALLOY STEEL FORGINGS FOR

TURBINE ROTORS AND SHAFTS

ASTM A471 — CLASS 6

VACUUM-TREATED CARBON

AND ALLOY STEEL FORGINGS

FOR TURBINE ROTOR DISCS

AND WHEELS

ELEMENT SPECIFIED SPECIFIED

C

Mn

p

ssi

Ni

cr

Mo

V

0.28 MAX

0.20-0.60

0.015 MAX

0.018 MAX

0.15-0.30*

3.25-4.00

1.25-2.00

0.25-0.60

0.05-0.15

0.40 MAX

0.70 MAX

0.015 MAX

0.015 MAX

0.15-0.35*

2.00-4.00

0.75-2.00

0.20-0.70

0.05 MIN

* 0.10 MAX IF VACUUM-DEOXIDIZED.

FIGURE 3. CHEMICAL COMPOSITION OF TURBINE DISC AND ROTOR STEELS

confined to the serrations or steeples and propagate in the tangential direction relative to the disc rim. Type II cracks propagate

from the innermost serration in the radial direction.

For notch entry, dovetail-type and T-slot type blade attachment

designs, the cracks propagate axially and circumferentially

.

Figure 7 shows the type of magnetic particle indication produced on a fir tree-type disc rim. The axial-circumferential type

cracks have resulted in blade lifting and blade loss from fracture

around the disc rim. Radial-axial cracks have resulted in complete

fracture and disc burst as shown in Figure 8.

Another disc degradation problem has been found on non-reheat,

shrunk-on discs of one design. In these cases one or two grooves

have been found in the disc hub and keyway in the axial-radial direction. The cause of the grooves has been attributed to water cutting.

No metallurgical analyses have been performed since the affected

discs are still in service, but the grooving mechanism is thought to

be corrosion-erosion and not sLress corrosion.

156
157
FIGURE 5. MAGNETIC PARTICLE INDICATIONS OF

DISK KEYWAY CRACK

A few cases of shaft cracking have been experienced also in

which corrosion fatigue cracks initiated on the shaft surface between

the shrunk-on discs.

3.0 British Experience

The disc cracking problems in the U.S. were properly forecast

by those in the industry who were following the British disc inspection and repair program in the early 1970s. After a catastrophic

failure of a low pressure steam turbine disc at Hinkley Point A in

1969^, the British initiated a program to prevent any further disc

burst incidents-*. The Hinkley Point A failure was determined to be

caused by stress corrosion cracks in a keyway. The Central Electric

Generating Board (CEGB) and the South of Scotland Electricity Board

undertook the inspection of 810 discs from 102 turbine rotors to find

cracks in these discs, and to determine the cause of the cracking.

A total of 124 discs on 50 rotors were found to have stress

corrosion cracks in their keyways and/or bores. Table 1 presents a summary of the British experience-'- . The different type rotors represent a system where the British catalogued the rotors by blade design

and keyway shape.

The British disc rehabilitation program was supported by a laboratory research program and both efforts were documented^ and

revealed significant findings. Several of these findings correlate

well to the recent U.S. experience.

158
159
FIGURE 7. DISC RIM MAGNETIC PARTICLE CRACK INDICATIONS

FOR FIR TREE ROOT

TABLE 1. BRITISH SUMMARY OF DISC CRACKING EXPERIENCES (REF 1)

(1) (2) (3) (4) (5)

Type of No. of No. of Rotors No. of No. of

Rotor Rotors Containing Discs Discs

Examined Cracked Discs Examined Cracked

(% of 2) (% of 4)

Type 1 33 15 (45%) 136 31 (23%)

Type 2 9 1 (11%) 108 1 ( 1%)

Type 3 49 34 (69%) 460 92 (20%)

Type 4 11 0 106 0

Totals 102 50 (49%) 810 124 (15%)

160
l6i
The British found that the cracking was concentrated on those

discs that carried turbine stages where the steam expansion crossed

the condensation line. This would allow moist conditions to occur in

the disc keyway and bore when the metal temperatures are below the

saturation temperatures. Indeed, the disc-cracking experience statistics are more severe if only discs operating in this condition are considered.

The British found disc cracking in discs which had semicircular

keyways (Rotor Types 1 and 3, Table 1) with high stresses and small

clearance fits between the keys and keyways. Discs with rectangular

keyways (Rotor Types 2 and 4) had higher stress concentration factors, but had either lower bore tangential stresses or larger key/

keyway clearances. No keyway cracks were reported, and only one bore

crack was found in these types of designs.

For both discs and laboratory specimens, the crack sites were

associated with either nonmetallic inclusions, corrosion pits, machining defects, heavily worked surface layers, or blisters of oxide.

The cracks were intergranular , heavily branched, and filled with dark

oxide corrosion products. Some cracks began in a transgranular mode,

but changed to an intergranular mode within the distance of one or two grains.

No correlation was found, nor evident, between the incidence of

disc cracking and the presence of or lack of any aggressive chemical

contaminant in the steam. Although some differences in cracking

experiences exist between different plants operating similar units,

operating practices could not be used to justify these differences.

Laboratory tests conducted with disc and rotor steels showed

that stress-corrosion cracks could be produced in "pure" wet steam at

high loads near or beyond yield stress, and with tight crevice conditions or stagnant conditions which promoted pitting.

For the most part the British discs were made from 3 percent

CrMo steel, but some 3.5 percent NiCrMoV and 3.5 percent Ni low alloy

steel were also used. The 3 percent CrMo and 3.5 percent NiCrMoV

steels were found to be equally susceptible to SCC. No cracks were

found on the 3.5 percent Ni steel, but this steel is not suitable for

most disc applications.

The British did experience disc-rim cracking on one of their

units, and they warn of the possibility of more extensive cracking in

this area due to the high stress and crevice conditions present in

this location. One British report^ states that "the work suggests

that highly stressed, tight crevices operating in wet, pure steam are required for pitting and eventual cracking of the typical turbine

material used throughout the world."

162
4.0 United States Experiences

In the U.S., the incidences of disc cracking have been more extensive with cracks not only in the keyway and bore, but also on the disc hub, web and rim in both nuclear and fossil fuel power

plants. The total number of disc- cracking cases will probably never

be determined since many repairs are completed without reports being

published. However, sufficient data is available from public reports

to determine the extent and nature of the problem^

In addition to the 25 earlier mentioned disc-cracking cases for

which detailed information is available, since 1969 approximately

another 25 units have experienced disc cracks about which little

information is publicly available. Table 2 presents a summary of the

reported U.S. disc cracking experiences. At least three disc bursts

have occurred and more have been prevented by correct operator action

and utility precautions. One unit was shut down prior to a disc

burst when the cracked disc caused high vibrations from mass unbalance and blade rubbing. Other units have been shut down specifically

for disc inspections and found to have significant disc cracks.

Several correlations between the British and the U.S. experiences can be made. The cracking has occurred at the dry-to-wet steam

transition zone, sometimes called the Wilson line. Only discs with

semicircular keyways have experienced stress-corrosion cracks in the

keyways and bores-'-. The cracks are predominately intergranular , heavily branched, and filled with dark oxide corrosion products^. A significant amount of an aggressive chemical corrodent is not always

found. Although pitting has been evident and associated with some of

the cracks, it has not been entirely correlated with all of the

cracks as was the British experience.

5 . 0 Nondestructive Examination Methods For Crack Detection

Magnetic particle and dye penetrant NDE methods have been used

to inspect for cracking of accessible disc surfaces; however, most of

the cracking has occurred in crevice locations inaccessible to direct

visual observation. The application of ultrasonic (NDE) methods has

been necessary and successful to examine discs for keyway and bore

cracks. UT systems used so far have been developed by the turbine

manufacturers. Much of the detailed information about these systems

is classified as proprietary by the vendors but enough information

has been publicly reported to present the general approach used^.

Figures 9a and 9b show the search unit arrangements used for scanning

the disc hub and webs.

The transducers are fitted to plexiglass shoes which have been

constructed to match the compound curvature of the disc surface while

directing the sound beam at the correct orientation at the bore. A

pulse-echo technique is used primarily, but for some disc shapes a pitch-catch method is necessary to inspect the region of the bore and

163
TABLE 2. SUMMARY OF STRESS CORROSION DISC

CRACKING EXPERIENCES IN U.S.

Location of Crack in Disc Number of Reported Disc Cracks Experienced*

Nuclear Fossil

Rim/Blade Attachment 25 25

Face, Hub and Web 4 34

Keyway 32 2

Bore 4 0

Complete Disc Burst 3 2

*Some discs contained cracks in more than one location.

keyway not accessible when using a single, pulse-echo transducer. In

this pitch-catch method a pair of shear wave transducers are placed

on opposite sides of the disc web and are aimed tangent to the bore

and keyway. Proper coordination of the inward and outward radial

movement of the transducer is controlled by automated manipulator

arms. Precise locations and angles have been calculated by a dedicated minicomputer which controls the manipulators. In one inspection system, two pulse-echo techniques are used: one for detecting

crack indications while the other is used for verifying and measuring

crack depth. In the initial technique, a 2.25 MHz transducer is

mounted on a contoured plexiglass block so that the ultrasonic waves

are directed tangentially toward the keyway. Any cracks above the

keyway area will be perpendicular to the sound and will reflect it.

Echoes are also received from the keyway and a time difference can be

determined and analyzed. By circumf erentially scanning in both clockwise and counterclockwise directions, enough sonic information is

compiled to compare with a mathematical model of the disc. An analysis of the time differences between signals is made to determine if

they are caused by true flaws or spurious and false indications.

Time measurement in ys/division on the oscilloscope is multiplied by

0.113 in/ys for shear wave travel to convert to inches.

161*


Once a crack indication is located, a 5 MHz shear wave transducer is aimed perpendicular to the keyway and in line with the

crack. An assumption is made that the crack is intergranular and is

branching and spreading as it grows. Since this part of the crack is

reflecting ultrasound back to the transducer, the time difference

between the keyway echo and the flaw echo can be measured and con- verted to an estimated crack length. The assumption that the crack

is intergranular and heavily branched has been proven to be correct

by both U.S. and English experiences. However, an uncertainty factor

of 0.060 inch is added to the UT-determined crack length to account

for the crack tip beyond the branching extension and measurement

errors

.

Because of the complex disc geometry, additional signal sources

often make interpretation very tedious and time consuming. Use of

different transducer frequencies and computerized signal processing

greatly increases the speed and accuracy of distinguishing between

nonrelevant signals and true defects. It has been found that score marks produced on the bore during assembly operations generated large

nonlinear indication amplitudes at a 2.25 MHz transducer frequency.

A lower frequency transducer, which produces a more linear response

to these small defects, is used to reexamine the disc for defect con- firmation. Signals were also coming from mode conversions at keyways

which could be mistaken for a defect. These signals have to be carefully examined to see if they are coming from a location which varies

with the position of the transducer or if they are originating at a fixed position, as would be expected for a defect. A computerized

signal processing correlation technique is used to enhance defect

signals and suppress nonrelevant indications.

6.0 Metallurgical Analysis and Diagnosis

Metallographic and f ractographic examinations of cracked-disc

sections have been performed for both British and U.S. cases. Many

U.S. metallurgical investigations are still in progress; therefore,

not much failure analysis information has been published and publicly

disclosed.

From the reports released the analyses have shown that the

alloy microstructures have been normal and the chemical compositions

have been within specifications. The cracking has been wholly intergranular in nature in 3.5 percent NiCr MoV steel, although transgranular cracking has been found in some discs made of other types of

steel. Typical examples of metallographic sections and fractographs

are shown in Figures 10 and 11, respectively. The cracks contain

dark oxide corrosion products in varying amounts. Pitting damage has

been found on the disc rims in most blade-attachment cracking incidents. Also, pitting corrosion has been seen in some of the disc

keyway/bore cracking incidents, but insufficient information has been

published to say that pitting has been present in all keyway/bore

167
168
FIGURE 11. FRACTOGRAPH OF A DISC CRACK 300X

cracks. Unlike the British experience, a correlation between pitting

and cracking cannot be inferred in the U.S., as yet. Cracking has

been found in surfaces that were adjacent to pitted surfaces, but the

cracks usually did not originate at the pits.

As stated earlier, the British disc-cracking failure analyses

and laboratory testing programs revealed that the cracks were intergranular. In a few cases the initial growth was transgranular , but

switched to intergranular at one to two grains deep. Crack initiation was associated with surface irregularities caused by either

nonmetallic inclusions, corrosion pits, machining defects, or heavily

cold worked layers. Laboratory-cracked specimens showed crack initiation was enhanced by stagnant conditions which promoted pitting.

Tests in wet steam produced blisters of oxide on the specimen sur- faces or in small, gapped crevices. Crevice tests were performed

with pure steam passing through gaps between bent beams of disc steel

and disc key materials. Of the four gap sizes employed [(1) 0.05 mm,

(2) 0.05 mm, (3) 0.25 mm and (4) 1 mm] , cracks were found only in the

gaps of .05 mm or less. This correlated to the finding of "high

spots" on disc bores that contained cracks and produced crevices

between the bore and the shaft^.

169
Manufacturing processes that changed the residual surface

stresses have been shown to change the potential threat of SCC by

affecting initiation. Residual compression stresses were shown to be

beneficial in resisting crack initiation. Test specimens that were prepared by surface grinding and then thermally stress relieved had a reduced time-to-failure compared to specimens that were not stress

relieved^. Other work performed by CEGB showed that residual

stresses produced by machining could modify both the rate of corrosion pit initiation and the depth of pit required to initiate a stress corrosion crack**.

Disc cracking is being experienced on discs that operate within

the steam expansion region near the saturation line where condensate

may be present on the disc surfaces. In the British turbine designs

and the U.S. nuclear turbine designs, this region is toward the L.P.

turbine inlet. In most fossil turbine designs, this region is toward

the turbine exhaust due to higher superheated steam conditions at the

turbine inlet. Changes in turbine loading by varying the steam pressure or temperature will shift the location of the moisture forming

region.

In this region, trace impurities in the steam tend to precipitate out and be deposited on the metal surfaces. Concentrating

mechanisms can then produce significant corrosive solutions on the

disc surfaces. Some of these trace impurities have been identified

as species which are known or suspected to cause SCC in turbine

steels. Contaminants such as sodium, copper, hydroxides, chlorides,

sulfates, sulfides, and organic acids can be introduced into the

steam cycle by feedwater treatment system malfunction or from cycle

in/leakage from cooling water systems. Oxygen levels may also be

significant during operating periods when system leaks are occurring.

Variations in the concentration of impurities within the LP turbine

environment are difficult to monitor and control.

While it is recognized that the concentration of corrosive

contaminants can promote SCC, further improvements in steam/water

chemistry practices might prove to be impractical as a solution to

the problem since research results indicate that solubilities of some contaminants in steam may be too low to detect with available

analytical equipment and procedures.

Since the early 1960's, the yield strengths of the turbine

steels have been increased to allow greater electrical ratings and

power conversion while limiting equipment physical size. The yield

strengths now range from 90 to 160 ksi. Extensive material testing

programs are currently in progress to determine the effect of yield

strength levels of steels used in the U.S. for susceptibility to SCC

in turbine environments. Preliminary results indicate crack propagation rates increase with yield strength, but crack initiation is

essentially independent of yield strength.

170
While high yield strength steels may be a factor, lowering the

yield strength may not be possible on discs presently in service,

since the discs' stress levels are determined by the physical space

constraints within the overall turbine casing.

Other material properties and manufacturing procedures such as trace elements and their segregation at grain boundaries, embrittlement , and heat treatment methods, are being studied to determine

their effects on the disc cracking potential.

As mentioned earlier, locations on the disc where tight crevices are formed seem more susceptible to cracking. Elimination or redesign of the crevices was performed by the British turbine manufacturers and operators and is now being considered in the United

States

7 .0 Risk Assessment and Prognosis

As mentioned in the Introduction, the utilities want to prevent

serious damage to their plants and harm to their employees while

achieving high productivity from equipment. Each utility has to make

a risk assessment as to its NDE inspection program and to its actions

after an NDE indication has been found in a disc. An important factor in any prognosis is the crack growth behavior of a defect under

actual operating conditions. Unfortunately, the SCC growth behavior

of 3.5 percent NiCrMoV turbine steel has been difficult to assess due

to some variations in disc steel material and mechanical properties

and to large variations in disc environmental conditions, including

temperature and chemical contamination. Available data on SCC growth

rate, as determined on fracture mechanic-type specimens, is limited

and variable and is summarized in Figure 12.

Noting the trend for increased crack growth rates with higher

temperatures and higher yield strengths, empirical crack growth rate curves have been prepared from the British and U.S. experiences with

certain assumptions about crack initiation and chemical contamination. An example of the type of curves used to predict crack sizes

and calculate remaining life is shown in Figure 13. These curves

take into account the two main parameters of yield strength and

disc-operating temperature.

The assumptions made in determining the remaining life are:

(1) Crack growth occurs only in discs where moisture conditions could be present during operation. Discs that

operate ahead of the moisture-forming zone are not con- sidered to be susceptible to SCC. The moisture-forming

zone can vary considerably, depending on steam superheat

temperature at the turbine inlet.

171
120°C!248°FJ

1 90°C(194°F)

1 70°C(158°F)

I

3-3-1/2 NiCrMoV

# 35% NaOH; FATT = + 32° C; CEGB

O 35% NaOH; FATT « -50°C; CEGB

35% NaOH; 2 NiCrMoV; SECV

V 35% NaOH; CERL/GEC

X ® IN-PLANT STEAM; CEGB

2.4 2.5 2.6 2.7 2.8 2.9

FIGURE 12. SUMMARY OF STAGE 11 CRACK GROWTH DATA FOR

3-1/2 NiCrMoV TURBINE STEELS

172
FIGURE 13. ESTIMATED CRACK GROWTH RATES IN 3.5%

NiCrMoV DISC MATERIAL AT DIFFERENT

STRENGTH LEVELS

173
(2) Crack growth begins at initial operation. Very little

data is available concerning crack initiation time. The

exact operating conditions for crack incubation are not

adequately understood nor monitored so that any lifetime

prediction analyses assuming anything other than zero initiation time are not possible.

(3) A factor for environmental conditions is considered for some plants where problems have existed in maintaining

low steam purity limits, and corrosive contamination is

known or suspected.

(4) Crack propagation is continuous and at a constant rate.

An example of the calculations used for prognosis is shown in

Table 3. A critical crack size, Ac , is calculated based on a crack

shape factor, fracture toughness, (Kjq), and operating stress. A

postulated crack size is determined from the crack growth rate curves

and the time period from initial operation to the planned inspection.

In the table, two examples of medium strength discs are shown at

different disc metal operating temperatures. From the crack growth

curves, the rate for each example is determined and multiplied by the

total operational period from start-up to time of inspection. The

postulated crack size, a, is the product of the two. Critical crack

sizes for the bore, A^g and the keyway, A^ are calculated with a fracture mechanics method. The postulated crack size is compared to

the calculated critical crack size to determine a degree-of-criticality ratio, a/Ac

.

The British found that they were able to predict crack size

fairly accurately with fracture mechanics methods and were able to

delay the replacement of some rotors, which were made of 3.5 percent

NiCrMoV steel and had higher toughness than 3 percent CrMo steel

discs. Their disc examination program revealed cracks in the keyways

as big as the calculated critical size; however, these had not

failed. They attribute this to conservative calculations in that an intergranular stress-corrosion crack branches significantly when it

grows longer than about one millimeter-'- . It was also demonstrated

from laboratory specimens with such branched cracks that their failure load was about 50 percent higher than identical specimens containing fatigue cracks of the same projected length. The English determined that the effective stress intensity for a branched stresscorrosion keyway crack was less than predicted by conventional analysis, i.e., the effective crack-tip stress intensity is lowered due to

crack branching. To validate their prognostic technique the British

recorded the maximum crack depths from 28 rotors following destructive examinations. The crack growth rate data for even the deepest

cracks found were in close agreement with data obtained from laboratory tests showing that initiation times are short in comparison with

crack growth periods.

llh
The Midlands Region of CEGB used a "probability of survival" of

a rotor risk assessment method in which they developed an empirical

three stage model of disc failure 10 . Probabilities were ascribed to

crack initiation, to crack growth in pure wet steam, and to brittle

fracture when the crack grew to its critical depth. From these

TABLE 3. EXAMPLE OF PROGNOSTIC TECHNIQUE

(3a) Postulated Crack Size From Initial Operation

DISC

A

B

DISC METAL DISC

TEMPERATURE YIELD

°F STRENGTH

330

210

MED

MED

CRACK MONTHS

GROWTH TO

RATE, IN. /MO. INSPECTION

0.030

0.004

30

30

POSTULATED

CRACK SIZE,

A, IN.

0.90

0.120

(3b) Critical Crack Size and Ratio

K 1C

DISC (KSI /IN.)

TANGENTIAL CRITICAL

BORE STRESS, CRACK SIZE

AT BORE,

a T (KSI) Acb (IN.)

A 200 75 2.52

B 230 70 3.83

Acb = (Q/1.2lTr)(Kic /aT ) 2 Where Q

=

CRITICAL

CRACK SIZE

AT KEYWAY,

Ac k (IN ->

2.15

3.45

CRACK RATIO

AT INSPECTION

a / Ack

0.42

0.03

SHAPE FACTOR FOR ASPECT

RATIO AND STRESS TO YIELD

STRENGTH RATIO, Q = 1.35

FOR EXAMPLE

L ck = Acb KEYWAY RADIUS

175
failure probabilities, a survival probability of each disc was calculated and the probability of survival of a rotor was determined as the product of its individual disc probabilities of survival.

Disc cracking statistics were obtained for each type of rotor,

composition of disc, and the disc position on the rotor to generate

probabilities for crack initiation. Growth rate probability was deduced from confidence limits superimposed on a plot of apparent

velocity of the deepest cracks in keyways versus the operating temperature. Brittle-fracture probability was estimated from confidence limits superimposed on a plot of the fracture toughness versus

disc operating temperature minus the 50 percent Charpy FATT

.

Survival probabilities were calculated for the failed Hinkley

Point A rotor and other rotors with known cracks. The Hinkley Point

A rotor had a probability of survival of 0.38 while another type of

rotor had a probability of survival of 0.85. One rotor of this type

had not failed in service but was found to contain cracks as big as the calculated critical crack size. All other rotor types studied

had a probability of survival of at least 0.9969.

Using probability of survival data, the Midlands Region was able to assign priorities in their rotor inspection and rehabilitation program which minimized the risk of rotor failure and had

minimum effect on system operation.

In the U.S., a main concern is the possibility that a disc fail

ure in a nuclear turbine would generate a missile that would penetrate the turbine casing and have enough energy remaining to strike

and damage a plant component critical to the safety of the nuclear

steam supply system. A missile generated by a fractured disc could

weigh over 3100 pounds, have an exit velocity over 400 ft/sec, and a calculated injection energy over 10 million ft-lbs.

The NRC has an interest in this and the probability (P4) of the

occurrence of damage to safety-related components is calculated as the product of the probability (P]^) that a turbine failure will

result in the ejection of a missile, the probability (P2) that the

missile will strike a barrier which houses a critical plant component, and the probability (P3) that a missile will penetrate a barrier and thus damage a critical plant component. P4 valves of

lO- -^ per year have been calculated for design overspeed accident

conditions

.

The probability (Pi) of a turbine failure resulting in the

ejection of a missile has been reevaluated to consider the SCC

problem experienced and the nondestructive testing program being

performed. Even with the reassessment, the probability of turbine

missile-caused damage to a safety-related component is extremely

small but is dependent on the inspection interval.

176
8 . 0 Industry Response

As a result of the recent turbine disc-cracking experiences in

the U.S., a multi-task response by electric utilities has been undertaken. Working with the turbine vendors, the detection programs have

been accelerated on a priority basis for the more susceptible type

rotors. Repairs and modifications to component configurations have

been performed as expeditiously as possible.

Failure diagnoses have been performed and prognosis-based fracture mechanics evaluations have been completed which allowed some units to return to service with small NDE indications. In other

cases, the discs have been mechanically removed and replaced by tempo

rary pressure reducing plates to allow the unit to be returned to ser vice at a reduced electrical generation output. Spare rotors have

been used when available and additional spare equipment has been

ordered by the utilities for future use.

The utilities, through their research organization, EPRI, have

initiated a series of research programs to develop a thorough understanding of the causes of disc cracking, to identify techniques to

eliminate or minimize disc cracking in the future, and to further

develop the probabilistic methodology for risk assessment of turbine

missile- induced damage to nuclear power plant structures and

components

.

A major program being conducted under EPRI sponsorship is

Research Project (RP) 1398, "Stress Corrosion Cracking of Low-Pressure Turbine Discs." The objectives of RP 1398 are:

(1) to determine and rank the contributions of environmental,

material and structural variables with regard to SCC

crack initiation and growth in shrunk-on discs,

(2) to establish the costs versus detection probability of

state-of-the-art NDE methods,

(3) to provide utilities with a basis for determining the

most cost-effective maintenance plan for their turbines,

and

(4) to evaluate methods for preventing or reducing the

frequency of cracking incidents.

Other existing EPRI projects are concerned with turbine steam

chemistry and environment, material properties effects, missile

impact tests, and analysis techniques of missile risks. Table 4 is a listing of current EPRI projects in the turbine disc-cracking area.

ITT
TABLE 4. EXISTING EPRI PROJECTS

RELATED TO TURBINE DISC CRACKING

PROJECT

RP399

RP559

RP700-4

RP700-5

RP969

RP1068-1

RP1124

RP1166-1

RP1398-1

RP1398-2

RP1398-4

RP1398-5

RP1549

TITLE

MISSILE IMPACT TESTING AND ANALYSIS

ELIMINATION OF IMPURITY-INDUCED EMBRITTLEMENT IN

STEELS

TURBINE-RELATED FAILURE ANALYSIS

STRUCTURAL AND MECHANICAL ANALYSIS METHODS

TRANSPORT OF CORROSIVE SALTS FROM STEAM

DEPOSITION OF SALTS FROM STEAM

TURBINE CHEMICAL MONITORING

CORROSION AND CORROSION CRACKING OF MATERIALS FOR

WATER COOLED REACTORS

A METALLURGICAL INVESTIGATION OF RIM CRACKING IN A

LP STEAM TURBINE DISC

STRESS CORROSION CHARACTERISTICS OF TURBINE ROTOR

MATERIALS

TURBINE ROTOR & DISC METALLURGICAL CHARACTERISTICS

RELATED TO STRESS CORROSION CRACKING BEHAVIOR

CRACKING OF STEAM TURBINE DISCS

PROBABILISTIC ANALYSIS OF TURBINE MISSILE RISKS

178
The major turbine vendors, the utility insurance companies, and

the NRC have been involved and have responded with their investigations and analyses of the turbine disc-cracking problem.

Hopefully, the combined efforts of all interested and active

organizations will result in the elimination of future disc-cracking

problems by providing the necessary detection equipment, diagnostic

evaluations, and prognostic techniques. Through these efforts the

electric utilities will be able to continue to provide for our electrical energy needs.

9 .0 Acknowledgement

This paper presents information that was obtained from several

published sources and from individuals who have worked extensively in

trying to resolve the disc cracking problem. I wish to thank the

following for their contributions: Dr. G. R. Leverant, Dr. C. M.

Teller, Mr. F. F. Lyle, Jr., and Mr. H. C. Burghard, Jr. I want to

acknowledge the Electric Power Research Institute for encouraging the

presentation of this information and for their support of the research

programs for improved DD&P techniques. Special recognition is also

given to the British utilities, turbine manufacturers, universities,

and authors for their efforts in publishing their turbine disc

cracking experiences so that all could benefit from their results.

179
REFERENCES

1. Hodge, J.M., and Mogford, I.L., "UK Experiences of Stress

Corrosion Cracking In Steam Turbine Discs," 1979 Proceedings of

the Institution of Mechanical Engineers, Steam Plant Group,

Vol. 193, No. 11, 1979, 93-109.

2. Kalderon, D., "Steam Turbine Failure at Hinkley Point 'A',"

1972 Proceedings of the Institution of Mechanical Engineers,

Steam Plant Group, Vol. 186, No. 31, 1972, 341-377.

3. Gray, J.L. , "Investigation Into the Consequences of the Failure

of a Turbine-Generator at Hinkley Point 'A' Power Station,"

1972 Proceedings of the Institution of Mechanical Engineers,

Steam Plant Group, Vol. 186, No. 32, 1972, 379-390.

4. Roberts, B.W., and Greenfield, P., "Stress Corrosion of Steam

Turbine Disc and Rotor Steels," Corrosion , Vol. 35, No. 9,

September, 1979, 402-409.

5. Roberts, B.W. , and Greenfield, P., "Stress Corrosion of Steam

Turbine Disc and Rotor Steels," Corrosion , Vol. 35, No. 9,

Stepmber, 1979, 408.

6. Lyle, Jr., F.F., Bursle, A.J., Burghard, Jr., H.C. and

Leverant, G.R. , "Stress Corrosion Cracking of Steels in

Low-Pressure Turbine Environments," National Association of

Corrosion Engineers, Corrosion-80 Conference, Paper No. 233,

Chicago, Illinois, March 3-6, 1980.

7. Kolar, M.J., Seminar Leader, "Seminar on Low Pressure Turbine

Disc Cracking, Electric Power Research Institute," Palo Alto,

California, April 10-11, 1980.

8. Flewitt, P.E.J. , and Gravesend, P. Dorg, "Discussion on J.M.

Hodge and I.L. Mogford, U K Experience of Stress Corrosion

Cracking in Steam Turbine Discs," Vol. 193, No. 11, 1979,

93-109.

9. Wigmore, G., "Discussion on J. M. Hodge and I. L. Mogford, UK

Experience of Stress Corrosion Cracking in Steam Turbine

Discs," Vol. 193, No. 11, 1979, 93-109.

10. Sparks, G. M. and Williams, H. D. , "Discussion on J. M. Hodge

and I. L. Mogford, UK Experience of Stress Corrosion Cracking

in Steam Turbine Discs," Vol. 193, No. 11, 1979, 93-109.

180
A DOPPLER TECHNIQUE FOR DETECTING AND LOCATING EXCESSIVELY

VIBRATING BLADES IN A RUNNING TURBINE

R. L. Leon

Principal Engineer

Franklin Research Center

A Division of The Franklin Institute

Philadelphia, Pennsylvania 19103

ABSTRACT

A method is presented for pinpointing those blades of a running

turbine that might be vibrating excessively in resonance with either

running speed, nozzle passing frequency, or one of their harmonics.

Only one stationary sensor per stage is required, along with a onceper-rev phase reference signal. The method utilizes specific signal

manipulations in both the time and frequency domains to uncover the

telltale Doppler signature, which normally would be masked in the raw

signal. It is shown in step-by-step fashion how each part of this

manipulation process combines to achieve the desired goal. The technique appears to be well suited for eventual use in an on-line, microprocessor based, blade vibration monitoring system. However, since an experimental procedure to prove the technique has not yet been undertaken, it must still be considered as conceptual.

INTRODUCTION

The Need

Data collected by the Edison Electric Institute from 1967 to 1976

shows that turbine blade failures are a major cause of forced outages

for U.S. utilities (1). The Electric Power Research Institute, EPRI,

considers blade failures their highest priority problem item in the

turbine-generator area (2).

The prime suspected cause of blade cracking is high cycle fatigue,

or more likely, stress corrosion combined with fatigue. In either case,

fatigue plays a major role. Therefore, some means for detecting ex- cessively vibrating blades might be useful in helping to avoid catastrophic blade failures, and with prompt reaction, even the cracks

themselves might be prevented.

To date, there are no good techniques for spotting either vibrating blades or cracked blades in service. The technique described in

this paper, however, appears to hold some promise for finding excessively vibrating blades in a running turbine, and for detecting when a significant crack results from that vibration.

181
Resonant Blade Vibrations

High amplitude, resonant, blade vibration results when one of the

many forcing frequencies that act on the blade coincides with one of

its many natural frequencies.

The forcing frequencies consist of all the multiples of nozzle

passing frequency, and all the multiples of running speed. The former

arise from the series of kicks each blade receives in passing the

nozzle wakes, while the latter are due to flow non-uniformities arising

from the horizontal split of the nozzle diaphragms and casing, from

internal struts, inlet or exhaust openings, nozzle plates or the like.

In each case, the multiples, or harmonics of the fundamental frequency

are caused by the non-sinusoidal nature of the force waveform. Obviously, for a constant speed turbine, the values of all these forcing

frequencies are precisely known for each stage.

This is not the case, however, for the natural frequencies. Here,

uncertainties in the degree of fixity between fastener and wheel or tenon and shroud, and empirical estimations as to the effects of cen- trifugal loading, all lead to uncertainties in the predicted values of

the natural frequencies. Also, normal manufacturing and assembly tol- erances lead to variations from one blade to the next. Since the most

predictable modes are the lower frequency modes, and since they are also the most likely to be subjected to high amplitude excitation,

they are the ones that manufacturers concentrate on in attempting to

avoid resonant matches.

Actual vibration amplitudes in a resonant match depend on the level

of the input at the forcing frequency, on the mode shape and amplification factor of the affected mode, and on the degree of match between

the natural frequency and the forcing frequency. Where the two frequencies differ, the vibration occurs at the forcing frequency, not the

natural frequency. For some steam turbine blade modes, amplification

factors as high as 400 are not uncommon. In addition to indicating

the level of increase in amplitude for an exact resonant match, the

amplification factor indicates how the vibration amplitude varies with

the degree of match. For example, for just a 1% difference between

the forcing frequency and the natural frequency, the vibration amplitude drops to 25% of its full resonant value for an amplification

factor of 200, and to 12% of its full resonant value for an amplification factor of 400. Therefore, though the high amplification factor

modes are potentially more damaging, they require a more perfect frequency match to excite them at their most damaging levels.

Coupling this with the previously mentioned variation in the natural frequencies blade to blade, one can see that even in a problem

situation, only a few of the blades or blade groups in a given row might undergo excessive, high amplitude vibration.

182
The extreme sensitivity to the degree of match between the forcing

and natural frequencies for high amplification factor modes, has still

another potential benefit. If a resonantly vibrating blade develops a fatigue crack, it is likely that this will shift the affected natural

frequency by 1% or more. The accompanying reduction in amplitude

should be significant, and can be used as an indicator of the appearance of a crack. Thus, a monitoring system designed to measure res- onant blade vibrations, might also be able to indicate crack inception

and growth.

The Basic Measurement Problem

The problem is how to find resonant blades before fatigue cracking

actually occurs.

Stationary measurements. If one could measure all the natural

frequencies of each blade or blade group of an exposed non-running

rotor, then it seems that one ought to be able to spot those blades

having an exact resonant match, and replace them even before the unit

is ever run. Actually, measuring the natural frequencies of the non- running blades is easy. The problem is that these frequencies will be

altered by centrifugal loading, and thus the natural frequencies in the

running turbine will be different. For most modes, this difference is

great enough, and uncertain enough, to make this procedure unworkable.

Rotating measurements . One obvious technique would be to install

a strain gage or two on each and every rotating blade, and look for ex- cessive outputs during operation. In addition to requiring telemetry,

the sheer impractical ity of this approach appears to be overwhelming.

Another possible approach centers around the fact that a resonantly

vibrating rotor blade will result in some corresponding rotor vibration.

This rotor vibration will occur at the blade vibration frequency when

viewed from the rotor's own coordinate system. However, when sensed by

a stationary sensor at one of the bearing caps, it will appear displaced

from this frequency, both above and below, by the running speed of the

rotor (3). Thus, one must look for these frequencies, not the actual

vibration frequency. Still, one might have difficulty discerning the

existence of any excessively vibrating rotor blades. The major problem

here is that the signal will likely be very low level and may be small

when compared to the corresponding harmonics of running speed which are also likely to be present. If this is true, no averaging, either in

the time domain or in the frequency domain, can improve the situation.

Nonetheless, assuming one were able to determine the existence of an excessively vibrating rotor blade with this technique, finding its location from this data would be virtually impossible.

THE PROPOSED TECHNIQUE

183
Moving Source Doppler

The vibrating turbine blade. Any rotating turbine blade that is

vibrating excessively will radiate acoustic energy into the surrounding

steam at the frequency of its vibration.

If this energy is to be detected by some fixed sensor, and if the

radiating blade is moving such that it has a velocity component along

a line joining the moving blade and the fixed sensor, then the frequency seen by the sensor will be altered.

This is known as moving source Doppler, and the new frequency is

given by the following relationship (4),

f = f (V + w) (1)

(V + w - v)

where f is the frequency of the source f is the frequency seen by the sensor

v is the instantaneous velocity of the source

toward the fixed sensor along a line joining

the source and the sensor

w is the average velocity of the steam toward

the fixed sensor along a line joining the source and the sensor

V is the velocity of sound in the steam.

Figures 1 and 2 show a typical turbine stage, arbitrarily assumed

to have 64 nozzles and 67 rotating blades. A single dynamic pressure

transducer is mounted in the casing just downstream of the rotating

blades. The turbine is assumed to rotate at 3,000 rpm. Thus, the

rotating blades with an effective radius of 30 in. (.762 m), are moving

with a circumferential velocity of 9,425 in/s (239.4 m/s). The radius

at the sensor is 33 in. (.838 m). The velocity of sound in the steam

is assumed to be 15, 000. in/s (381 m/s), and since the absolute velocity

of the steam leaving the blades is mostly axial, it serves to increase

the effective sound velocity only when the source is near the sensor.

For simplicity, this is neglected in the ensuing discussion.

Assume now that a single blade is vibrating excessively at nozzle

passing frequency 3,200 Hz.

Figure 3 shows how this vibration would appear to a strain gage

mounted directly on the vibrating blade. Note the 64 constant amplitude cycles in the single revolution record. The blade is presumed

to be at position B of Figure 2 at the start of the record.

Figure 4 shows how a simultaneous record from the dynamic pressure

sensor might look. This characteristic Doppler waveform was generated

here in the following way.

181*
First the waveform of Figure 3 was sampled at 512 equispaced points,

each point obviously corresponding to both an instantaneous vibration

value, and to a blade position in the rotational cycle. For each

blade position, the distance from the blade to the sensor was calculated. Next, the propagation times were calculated by simply dividing

these distances by the speed of sound. Then, assuming the amplitude

at the sensor to be inversely proportional to the propagation distance,

each instantaneous amplitude was first divided by this distance, then

transformed to Figure 4, displaced to the right by its propagation

time. Those points at the end of the record that fell outside the

initial time span were folded around to fill in the missing points at

the beginning of the record.

Though no use was made of Equation 1 in deriving the waveform in

Figure 4, it can be helpful along with Figure 2 in obtaining a better

physical understanding. With the vibrating blade in position A, the sensor sees the lowest amplitude, and the actual frequency. At B,

with the blade closer to the sensor, and with a significant velocity

component toward it, both the amplitude and frequency are substantially increased. At C, the blade is closer yet, and at the position

of the maximum velocity component toward the sensor. Thus, the sensor

sees still higher amplitude, and maximum frequency. At D, the blade

is closest to the sensor, and so this is the position of maximum amplitude. However, the frequency returns to actual since there is no velocity component in the direction of the sensor. At E, the position

of the maximum velocity component away from the sensor, the amplitude

is the same as at C, but the frequency is at its minimum. At F, the

amplitude is the same as at B, but the still negative velocity com- ponent keeps the frequency below actual.

Since the propagation times vary through the rotational cycle,

the 512 points that make up Figure 4 are not equispaced, as they would

be had an actual signal been sampled by an actual A to D converter.

To put the signal in this proper form, Figure 4 is acted upon by an interpolation algorithm, and the result is displayed as Figure 5. Now

the signal can be input to an analyzer (as if it had been obtained by

the analyzer) and the corresponding frequency spectrum determined,

shown here as Figure 6. As expected, the spectrum is broadbanded and

extends essentially from 1965 Hz to 8,610 Hz, the lower and upper frequencies as predicted by Equation 1 for this case. Also, since it

takes the same amount of time for the frequency to traverse 5,410 Hz on the upper end, as it does to traverse 1,235 Hz on the lower end, the

higher sweep rate in frequency-per-unit-time on the upper end, com- paratively attenuates this region of the spectrum.

Since the waveforms of Figure 4 and 5 start at a known rotor position, the time till the telltale frequency drop indicates the reverse

rotational angular distance from the sensor to the radiating blade at

this known rotor position. Thus, the characteristic Doppler waveform

185
detects the vibrating blade, indicates its relative vibration level,

and pinpoints its location.

It should be noted here that the known start time allows for the

determination of the phase of the spectrum as well as the magnitude.

This makes it possible to go back and forth between the frequency and

time domains, a facility which will be put to good use in the section

on signal manipulations.

Multiple blade vibrations . It is of course possible that more

than one blade or blade group in the row will be vibrating in res- onance. Because of the variations between blades, and the precise

frequency match required for high amplitude, resonant vibration, a practical upper limit for the number of blades vibrating in resonance

might be three.

In addition to the vibrating blade of the previous example, which

was located 90 deg behind the sensor at the start of the time record,

two additional vibrating blades are assumed in the present example.

One is located 8 blades behind the origi nal in the reverse rotational

direction, and the other is located 9 blades behind that. Recall that

there are 67 rotating blades in this example.

All three vibrating blades are assumed to vibrate with the same

ampl i tude.

Figure 7 shows the resulting time waveform, and Figure 8 the

spectrum. The spectrum, though somewhat different than before, still

spans the same frequency range. The time waveform shows three distinct

Doppler signatures located as they should be. In the section on signal

manipulations, a method will be presented for greatly improving the

pinpointing capability of the technique.

In any event, use of the basic Doppler waveform appears to show

promise, even for multiple vibrating blades.

Important Signal Manipulations

Until now, some knotty, real-world problems have been ignored, but

they must be dealt with if this is to be a viable blade monitoring technique. Fortunately, there appear to be some straightforward signal manipulations capable of circumventing these problems. Both the problems,

and their solutions are discussed in this section.

The first major problem is that of steam flow noise. The rush of

steam around the sensor and the adjacent area is bound to result in a significant, broadband, random signal which could easily be an order

of magnitude greater than the anticipated Doppler waveform.

The second major problem is that of other order related signals.

186
The most significant of these will probably be blade passing frequency,

since the sensor will see a large impulse with the passing of each blade.

If this series of impulses is not perfectly sinusoidal, harmonics of

blade passing frequency will also be present. In addition, components

at running speed and low orders of running speed are also likely to

exist. The blade passing component could be more than an order of magnitude greater than the Doppler waveform, while the orders of running

speed will likely be somewhat lower.

Time domain averaging. The steam flow noise can be substantially

reduced through a procedure known as time domain averaging.

A once-per-rev phase reference signal is needed, and this can be

obtained by using a fixed fiberoptic probe to sense the passing of a small reflective tape segment, located on the rotor shaft. A pulse is

generated each time the tape segment passes beneath the probe, each

pulse corresponding to that same, known, rotor position.

The pulse is used to start a sampling process of the dynamic pres- sure transducer signal. The sampling interval is adjusted so that when

multiplied by the total number of samples in the window, 512 for instance, it equals the time for one shaft revolution. Also, the signal

must be low pass filtered at a little less than half the sample rate,

prior to being sampled to prevent aliasing. After the first sampling

process is complete, the averager waits for the next pulse then starts

sampling again. It keeps repeating this process, adding corresponding

sampled points and dividing by the total number of averages. The result

is that anything that is not repetitive in the rotational cycle will

eventually average to zero. Obviously, the steam flow noise falls in

this category and can be substantially reduced. The Doppler waveform

and the other order related components will remain undiminished.

A feel for how fast the steam flow noise could be reduced by time

averaging can be gained from Figures 9 through 11. In Figure 9 is

shown an un-averaged broadband random signal. Figure 10 shows the same

signal after 100 averages. Figure 11 after 10,000 averages. Figure 12

shows the corresponding spectra. It should be noted that for the case

of a turbine running at 3,000 rpm, 10,000 averages could be completed

in less than 7 minutes, even taking into account the nearly full rev- olution rest between each block of samples.

Frequency domain blanking . It will be seen that even though time

domain averaging is very powerful in reducing the noise, it is still

not enough. Figure 13 shows how a real, single revolution waveform

might look after significant time averaging. Figure 14 shows the cor- responding spectrum. Recall that even though only the magnitude is

shown here, this is a spectrum with both magnitude and phase and therefore it is possible to inverse transform this spectrum back into time

domain. This capability will be made use of shortly.

187
Though Figure 14 shows the characteristic Doppler spectrum, the

waveform of Figure 13 gives no hint of how many blades are involved,

or where they might be. In fact, it shows no evidence of Doppler at

all. The problem, of course, relates to the presence of a few large

discrete components, clearly visible in the spectrum. The largest

component at 3,350 Hz is the blade passing component, and it clearly

dominates the scene. In fact, anyone so inclined will be able to

count the 67 peaks in the single revolution waveform. Also included

are large components at running speed, and the 2nd and 3rd harmonics

of running speed, 50 Hz, 100 Hz and 150 Hz. These are evidenced in

the general up and down movement of the waveform.

All of these components are order related and therefore not re- movable through time averaging. But they can be removed, or blanked,

directly from the spectrum. Then this modified spectrum can be inverse

transformed back into the time domain, and the Doppler waveform should

then be apparent. These components can be either completely blanked

(replaced with zeroes), or the real and imaginary values of the affected

spectral points can be replaced with interpolated values. It is this

latter technique that was used here to modify the spectrum of Figure 14.

Figure 15 shows the modified spectrum, and Figure 16 the new time

waveform obtained by inverse transforming the modified spectrum. The

Doppler that was buried in the original waveform was that of the three

blade case previously cited. Note the similarity between the waveform

of Figure 16 and that of Figure 7. The three Doppler signatures are

still readily apparent, and just as important, no shifting in the time

domain occurs as a result of this procedure. Thus, the locating capability remains unimpaired.

The essence of the technique should now be clear. The Doppler

mechanism transforms the single frequency of the vibrating blade into

a broadband mul ti -frequency function which contains information as to

its location. Like the original frequency, all the new frequencies

are order related since the waveform retains its. rotational ly repetitive nature in the time domain. Thus, it is at once possible to use time domain averaging to remove the non-rotational masking effects,

and to use discrete frequency blanking to remove the order related

masking effects, the latter process hardly distorting the desired

signal since the information in the Doppler is spread so broadly in the

frequency domain.

Envelope detection. A key feature of this technique is its ability

to locate the vibrating blades. This paragraph will describe a process

for simplifying and improving this aspect of the Doppler technique.

The object is to know exactly when the vibrating blade is directly

beneath the sensor. This does not coincide with the maximum frequency

point or with the minimum frequency point, each of which is difficult

to ascertain from the waveform anyway. Rather, it coincides with the

188
maximum of the amplitude envelope of the waveform, corrected by the time

it takes for sound to travel to the sensor from a blade directly beneath

it. For the example cited in this paper, this time is 3 in. (.0762 m)

divided by 15,000 in/s (381 m/s), or 0.20 ms.

The amplitude envelope can be developed in the following manner.

First, using the Doppler waveform of Figure 7 as an example, all the

negative going peaks are made positive as in Figure 17. This has the

dual effect of shifting the frequency of the original Doppler band

upward, and adding in a new low frequency band as shown in the cor- responding spectrum, Figure 18. Next, all the components above 1965 Hz,

the original Doppler minimum frequency, are blanked to zero, leaving

just the low frequency portion of the spectrum. Reconstructing this

low frequency portion then yields a new waveform, proportional to and

synchronized with the envelope of the original Doppler waveform (see

Figure 19).

The three time markers at 5.20 ms, 7.59 ms, and 10.27 ms (with

0.20 ms added for the travel time correction) correspond to the times

that the three blades pass beneath the sensor. Recall that the resolution from one blade to the next is 0.30 ms in this example. Clearly,

when comparing Fig. 19 with Fig. 7, a great improvement in the ease and

accuracy of determining exactly which blades are vibrating has been

made.

SUMMARY

A technique has been presented for detecting and locating turbine

blades vibrating excessively in resonance with either running speed,

nozzle passing frequency, or one of their harmonics.

Only a single dynamic pressure transducer per stage is required,

along with a once-per-rev phase reference signal. The pressure sensor

sees the radiated energy from the vibrating blade as a rotationally

repetitive Doppler waveform.

The nature of the Doppler signal allows it to be greatly enhanced

through the use of specific signal manipulations such as time domain

averaging, frequency domain blanking, and envelope detection. These

enhancement procedures are essential to the technique since they help uncover the Doppler signal itself and the information it bears. Consequently, the technique has been dubbed Enhanced Doppler at FRC.

A mathematically developed Doppler signal has been utilized in this

paper, and with it, the techniques described appear to work well in

being able to detect and locate three vibrating blades in a hypothetical

exampl e.

189
The next step would be to conduct tests on a test stand, utilizing

an actual turbine stage. With the rotor blades strain gaged and their

outputs telemetered sequentially, the speed could be adjusted till one

or more of the blades is vibrating in resonance. The corresponding

pressure transducer signal could then be manipulated as described in

this paper to see if the vibrating blades can be successfully detected.

Means of dealing with problems such as multiple transmission paths, or echoes, may also have to be developed.

Assuming positive results here, the next step would be to develop

a prototype monitoring system to be put in service on an actual turbine.

As indicated in the paper, this system might also be able to detect the

appearance of a crack in a blade that has been vibrating excessively.

ACKNOWLEDGEMENTS

The author would like to acknowledge the very valuable assistance

of his colleagues Dale Righter and Mark Altschuler of FRC, and the

early encouragement of Dr. Simon Braun of Technion Israel Institute

of Technology.

This paper was initially presented at the ASME 1980 International

Conference on Reliability, Stress Analysis and Failure Prevention,

August, 1980, and published in the conference proceedings.

REFERENCES

1 "Equipment Availability Component Cause Code Summary Report for

the Ten-Year Period 1967-1976", Edison Electric Institute, EEI

Publication No. 76-64.

2 "EPRI's Fossil Plant Performance and Reliability Program and

Turbine Generator Subprogram", pp. 40-45, Turboniachinery International,

April 1979".

3 Benko, G. B., "Notes on the Measurement of Vibrations on Rotating Systems", Vibrations in Hydraulic Pumps and Turbines , The

Institution of Mechanical Engineers, Proceedings 1966-67 Vol. 181,

Part 3A, pp. 50-54.

4 Lindsay, R. B., Mechanical Radiation, 1st Ed., McGraw-Hill,

New York, 1960, pp. 311-313.

190
REAL

-4.8888 .

0.0 SEC 28.888

Fig. 3. Blade vibration as seen by a strain gage sounted on it

4.08

REAL

-4.88

8.0 SEC 28.388

Fig. 4. The blade vibration as seen by che pressure sensor

191
4. 3000 _

REAL

-4. 3000 JHj

1 1 , L

100. 30

3. 0 Fig. 5. Waveform or rig.

3ampling

10. 300

1965 Hz 3610 Hz

se: 2a- 300 " 0. 0 HZ 12. 300 K

., but with equispaced ?lg . 6 . ne frequency spectrum of Fig. 5

100. 30

4. 3000

REAL

-4. 3000

3. 3

-i—i—i—,—i

LGMAG

1965 Hz 3610 Hz

y

\

SEC 20. 333 3.3 hZ 12. 000 K Fig. 7. The Doppler waveform with three vibracing Fig. 3. The frequency spectrum of Fig. 7 blades

43. 300

REAL

-43. 300

40. 300

REAL

40. 303

0.3 SEC 22.000 * 3. 3 SEC 20. 300 7i Fig. 9. Unaveraged random signal Indicative of steam Fig. 10. Signal of Fig. 9 after 100 tiae averages noise

192
40. 300

REAL

-40. 000

100. 00

0.0 SEC

LGMAG J

10.300

Unaveraged

100 Averages

10,000 Averages

20.000 0.0 HZ 12. 300 K Fig. 11. Signal of Fig. 9 after 10,000 time averages Fig. 12. The frequency spectra of Figs. 9, 10 and 11

3.0 SEC 20.000 m a. a HZ 12.000 K

Fig. 13. Hypothetical wvtfon after significant ?1 8- !* Th* frequency spectrum of Fig. 13 time averaging

193
4.0000 _

REAL

-4.0000 _

0.0 SEC

Fig. 17. The waveform of Fig. 7 with negative

going peaks made positive

100.00

LGMAG _

10.000

M 0.0 HZ 12.000 K Fig. 18. The frequency spectrum of Fig. 17

0.0 SEC 20.000 m Fig. 19. Reconstructed low frequency portion of

Fig. 18

19^
IMACS COST SAVINGS ESTIMATOR

A TRADE-OFF ANALYSIS FOR A BUILT-IN MONITORING SYSTEM

F. E. Bishop

Pall International Corporation

Glen Cove, New York 115^2

Abstract: Using aircraft as an example, the author presents the tradeoff "benefits achievable with a built-in, on-board monitoring system

that instantaneously alerts users to malfunctions in their fluid system.

The system, also applicable to naval vessels and military combat ve- hicles, is called IMACS (instantaneous Maintenance and Analysis Checkout System)

.

Continuous in-system active sensors monitor fluid system flight-critical

components for limit parameters such as temperature, leakage, flow,

pressure, fluid level, presence of air, differential pressure, etc.

The paper analyzes problems that can and do occur in aircraft hydraulic

systems causing primary and secondary failures. An economic analysis

is presented contrasting an aircraft with and without IMACS experiencing these problems. The effect of the problem is indicated and the

necessary corrective action spelled out in terms of maintenance, manhours, material and downtime.

Additional benefits derived from IMACS, such as reduced energy consumption, reduced logistic support, improved maintenance forecasting,

reduced turnaround, improved scheduling and improved capability of

personnel' skill levels, are also discussed.

Key words: Aircraft hydraulic systems; cost reduction; energy savings;

failure detection; failure prevention; flight safety; fluid system

components; maintenance effectiveness; on-board monitoring system.

INTRODUCTION

Early detection and identification of system component malfunction is

the key to reducing ever rising maintenance costs and the cost of own- ership of today's sophisticated vehicles. Fluid system components are subject to a number of adverse conditions during operation for a variety

of reasons, some of which are controllable and some of which are not

controllable. These conditions can result in malfunction or a primary

failure of a single system component which, if not detected, can cause additional component failures and added cost of repair, or even affect

safety

.

An additional factor that often contributes to maintenance costs is the

inability of the maintenance system to detect and identify which com195
ponent in the system is in an early state of failure. Maximizing this

factor can achieve major cost savings.

Another factor contributing to maintenance costs is the skill level of

personnel and equipment available to perform maintenance on today's and

tomorrow's ever increasingly more sophisticated vehicle systems. Some

maintenance systems "benefit from a stable, experienced, well equipped

system, but many lack the necessary combination of ingredients to adequately, from a minimum operating cost point of view, deal with today's

complex systems.

Therefore, monitoring of critical fluid system component operation has

been recognized as an increasingly important contributor to cost control

in the maintenance and operational areas.

One of the most neglected fluid systems to benefit from cost effective

monitoring is the hydraulic system. Maintenance of this system has

tried to cope with increasing system compexity with too few maintenance

tools, relying mostly on experience of personnel. Real cost savings

can be gained by a serious close look at what a reliable built-in mon- itoring system can provide and what it has to deal with.

COST SIGNIFICANCE OF SYSTEM COMPONENT FAILURES

As previously discussed, early diagnosis of an imminent system component

primary failure can be very cost effective, especially in preventing

secondary system failures. Examples of common hydraulic system com- ponent primary failures are shown in figure A. Let us analyze some of

these failures in an aircraft to really see what the consequences can be.

One common hydraulic system component failure is caused by internal wear

in a pump, resulting in excessive case drain leakage. If this condition

continues unnoticed, increased temperature will result, with the possibilities of a series of secondary failures such as fluid breakdown,

filters becoming contaminated and overheated, loss of pump seal and loss

of system.

Another more difficult problem to diagnose is free air in a nonvented

system reservoir. If this problem goes undetected, it can cause pump

cavitation or loss of pump prime and possible broken lines with the

resultant loss of the system. Safety obviously can be affected by this

problem.

Contaminated or plugged filters can cause a variety of system failures

which depend on whether the filter assembly incorporates an internal

relief valve. Filters are usually located throughout the system and

often require panel removal for maintenance checking. This is time

consuming and dependent on dedication of maintenance personnel whether

all filters are serviced.

196
If a filter element becomes contaminated and is not changed and causes

the filter bypass to open, the system fluid contamination level will

increase. This can cause a number of possible secondary failures such

as pump overheat due to internal wear, high fluid temperature, pump

seal failure caused by wear or high temperature and loss of system

fluid and system due to pump seal failure, and possible servovalve malfunction caused by contamination and wear.

On the other hand, if a system filter element becomes contaminated and

the filter assembly has no bypass, the differential pressure across the

filter element will continue to increase. This will cause the flow to

become restricted, and the fluid temperature can rise which, in turn,

can cause an external pump seal to fail and breakdown of the hydraulic

fluid.

Excessive system relief valve leakage, if allowed to continue, will

cause a fluid over-temperature condition. This condition can be ex- tremely detrimental since it can affect the integrity and safety of

critical system components such as the pump, filters and reservoir.

If the system over-temperature condition is severe, replacement of the

identified components may be required.

Loss of minimum accumulator precharge and/or improper position of the

internal piston can result in inadequate discharge and system malfunctions. It is common practice to check accumulators for precharge

only.

Moisture and loss of charge in pneumatic bottles can cause a failure to

discharge or an insufficient discharge resulting in a system malfunction. Pneumatic bottles are commonly checked for charge only.

Still another common system component is excessive internal servoactuator leakage. This condition is usually caused by wear of the metering

edge and spool and sleeve surfaces. Because of the relatively large

number of servoactuators used in today's vehicle hydraulic systems,

determining which servoactuator must be replaced is not easily or quickly accomplished. The diagnosis of excessive internal leakage

ranges from involved experienced maintenance techniques to trial and

error by replacement.

Excessive aircraft main gear internal leakage is another component

problem requiring extensive maintenance action which is usually accom- plished at a main overhaul facility with scheduling.

Moisture in reservoir pressurization lines puts unwanted water into the

hydraulic system, which causes corrosion and erosion of system components and can further cause decreased lubricity, oxidation, and acid

formation in the system fluid.

197
Low reservoir fluid level is a very common hydraulic system problem

that can cause a variety of secondary failures with the possible loss

of the system.

The examples discussed are the more common component failures experienced but are not all the problems that occur. However, they serve to

illustrate that an undetected primary component failure can lead to far more extensive and serious secondary failures which always involve increased cost.

OBJECTIVES OF MONITORING SYSTEM

It would seem reasonable, based on our review of today's maintenance

capabilities and the significance of penalties to operation, that we

can define the objectives of a built-in monitoring system that can reduce cost and demonstrate it. With this in mind, the following are listed:

• Provide early warning of system component malfunction and/or

failure

.

• Monitor critical and vital component parameters on a real-time

opportunistic basis.

• Be able to detect and identify faulty components anywhere in

the system.

• Display readout conveniently centrally located requiring no interpretation thus reducing maintenance skill required.

• Utilize available flight tested hardware which will not interfere with system operation, even if it fails to operate.

• Provide signal to ground maintenance and let the signal be the

basis for maintenance action.

• Monitoring system must be self contained requiring no auxiliary

equipment to operate.

• Operation of monitoring system must minimize energy consumption

• Provide a system which is ret rofittable to today's operating

systems and newly designed systems.

• Provide a system which is cost effective.

IMACS IS AN ALTERNATE TO HIGH MAINTENANCE AND OPERATING COSTS

As shown in figure B, IMACS is a built-in system that provides Instantaneous Maintenance Analysis and Checkout of critical system com198
ponents acceptable limit parameters. It provides small, lightweight

sensors permanently installed at each monitored component that signal

"by activating a red light on a centrally located panel that a particular

component has reached the limit for the parameters being monitored. It

detects and identifies the component and indicates which parameter limit

has been reached. This simply indicates that a maintenance action is

required. The system performs this important maintenence function on demand, reliably, and requiring no interpretation or auxiliary equipment. All that is needed is that the system being monitored is operating. Instant diagnosis is provided indicating a maintenance action to

be performed on the identified component. A simultaneous local visual

signal is also provided for some components. This signal must be can- celled at the component after the component has been replaced. This

feature provides a quality assurance check that the proper maintenance

has been performed. A vehicle fluid system utilizing IMACS can be operated on condition basis thus providing the opportunity for planned

maintenance and additional cost savings.

FAILURE ANALYSIS AND COST

Now let us analyze one of the most frequently occurring hydraulic system

component failures to see what cost factors are involved.

The more obvious factors to be accounted for in our analysis will be

hardware, labor, and loss due to unscheduled non-availability. An

accounting of the effect on safety of the component failure also seems appropriate. For our analysis, we will use the schedule of estimated

costs shown in figure C. These costs will have to be updated from time

to time and altered to suit individual maintenance and supply systems.

Referring to figure D, we have chosen the problem of excessive pump

case drain leakage in an aircraft hydraulic system to illustrate our analysis of the maintenance actions required.

The maintenance action steps involved are:

• Diagnosing the problem,

• Performing the actual corrective labor,

• Performing the system integrity check after corrective action

has been taken,

• Accounting for materials used,

• Accounting for loss due to unscheduled non-availability.

The possible effect on flight safety is also listed in general, non- monetary terms.

199
Our analysis will be performed on the basis of a system monitored by

IMACS and one without IMACS.

As shown in figure D, if excessive pump case drain leakage is permitted

to continue, it results in increasing fluid temperature. Over-temperature can lead to fluid breakdown, filter contamination and overheating

and eventually the loss of the pump seal and the entire system. This

failure can occur in flight and affect safety.

The costs attributed to diagnosing the excessive pump case drain leakage, labor to replace the pump, perform the system integrity check,

account for the pump replacement, account for the aircraft unscheduled

downtime are shown in figure D using the cost values listed in figure C Although no monitoring value is ascribed to flight safety, it is listed

as an important factor in our analysis. The costs associated with the

primary failure are listed in figure C for the aircraft not monitored

by IMACS.

If the aircraft was monitored by the IMACS system, more certainly the

excessive case drain pump leakage would be detected in the post-flight

checkout by ground maintenance. Replacing the pump before further system damage occurs eliminates secondary maintenance actions and any

effect on flight safety.

The costs are listed for one of the secondary failures requiring filter

elements change due to high fluid temperature. The IMACS system avoids

this secondary failure and the associated cost.

Listed in the same fashion is another possible secondary maintenance

action — that of decontamination of the system brought about by the

fluid breakdown. Again, this secondary failure would have been avoided

with the use of IMACS.

The summary of cost trade-offs clearly indicates the substantial savings that the IMACS system can accomplish with just one of the common failures associated with this system. This cost can quickly escalate

with multiple failures and the size of the fleet. Break-even costs for

IMACS applied to a particular system can easily be determined using

this analysis.

Military applications concerned with operational readiness can analyze

additional flying hours available using this analysis due to anticipated improvements in maintenance or convert this improvement to fewer

aircraft required.

Individual analysis sheets are included in this paper for ten other

common hydraulic system failures. No cost values have been listed and

the reader is invited to apply the described analysis to failures of

his concern using his own cost values.

200
There are additional cost factors that can be considered to extend the

present analysis.

ADDITIONAL COST FACTORS

As shown in figure E, fuel savings may also he considered, taking into

account the cost of fuel consumption attributed to internal hydraulic

leakage. As internal surfaces wear in pumps and servoactuators , clearances increase and internal leakage results in wasted horsepower. A

reported United Airlines study estimates that a reduction of internal

leakage of one GPM could reduce engine fuel consumption by 2000 gallons

per year based on eight (8) hours a day utilization.

Additional fuel savings may be considered where main engines and/or

auxiliary power such as APU and ground carts are used for hydraulic

system troubleshooting.

Improvement of logistic support can also be considered as reduced cost

of ownership.

A long term benefit of IMACS is reduced inventory management of hydraulic system component spare parts. Another factor is improved scheduling and utilization of people and auxiliary equipment. Removal of worn

components at convenient, opportune times can also be considered. Also

improved logistic energy conservation can be estimated.

Still other cost factors affecting depot and main base maintenance that

can benefit from utilization of IMACS include improved maintenence

forecasting and scheduling, reduced turn-around and improved capability

of personnel skill levels with maintenence requirements.

Life cycle costs of vehicles with and without IMACS can be shown to con tribute significantly to reducing cost of ownership by improving maintenance .

ADVANTAGES OF IMACS

There are many advantages of IMACS that can improve maintenance such as

• Reduces preflight hydraulic system checkout time of flight crit

ical components.

• Display panel identifies malfunctioning components throughout

the vehicle.

• Reduces skill level required for routine maintenence.

1. Reported in the minutes of the SAE A- 6 Committee Meeting, October,

1978

201
• Allows for component removal on "as required" basis between

major overhauls as scheduled, thus reducing logistic support

and costs.

• Maintains in-flight check of all critical components.

• Identifies faulty components on post-flight check.

• Requires no ground support equipment for check out.

• Increases maintenance efficiency and operational utility.

• Utilizes proven and available hardware.

• Is simple, reliable, practical and essentially maintenance free.

• Can be tailored to incorporate additional design and maintenance

requirements

.

Shown in figure F is the installation of IMACS in a U. S. Navy A6E

aircraft. The flight test is in progress and is proceeding with no reported problems. A full report will be issued at the conclusion of

the program.

IMACS has broad applications in the field of diagnostics and monitoring

and is worth serious investigation.

202
COMMON HYDRAULIC SYSTEM COMPONENT PRIMARY FAILURES

• EXCESSIVE PUMP CASE DRAIN LEAKAGE

• AIR IN A NON-VENTED RESERVOIR

• FILTER ELEMENTS CONTAMINATED

t EXCESSIVE SYSTEM RELIEF VALVE LEAKAGE

• LOSS OF MINIMUM ACCUMULATOR PRECHARGE AND/OR IMPROPER PISTON POSITION

• LOSS OF CHARGE AND/OR PRESENCE OF MOISTURE IN

PNEUMATIC BOTTLE

• EXCESSIVE LEAKAGE IN SERVOACTUATOR

• EXCESSIVE LEAKAGE IN MAIN GEAR ACTUATORS

• MOISTURE IN RESERVOIR PRESSURIZATI ON LINE

• LOW RESERVOIR FLUID LEVEL

FIGURE A

203

Schedule

of estimated costs

• MAINTENANCE MAN HOURS: Military/ Commercial $30/Hr

• UNSCHEDULED DOWNTIME Commercial $7500/Hr LOSS OF OPERATIONAL

READINESS:

• HYDRAULIC FLUID Phosphate Ester $T7/Gal MIL-H-5606 $3/Gal MIL-H-83282 $1 0/Gal

• PUMP New $3500

Overhaul $2000

• SERVOVALVE New $800

Overhaul $400

• RELIEF VALVE (SYSTEM) New $200

Overhaul $100

• ACCUMULATOR New $400

Overhaul $100

• ACTUATOR New $8-15,000

Overhaul $4-7,000

• FILTER ELEMENTS: PRES,

RET, C D $100 Ea. FILTER MANIFOLDS Overhaul $1000 Ea

• DESICCANT REPLACEMENT $70-150

• JET FUEL ' GAL $ 1 /Gal (RESERVOIR NEW) $4-8000

(RESERVOIR SEALS REPLACE) $2-4000

ACTUATOR New $3-7000

Overhaul $1-2000

• NEW HYDRAULIC LINES $500

Figure C

205
EXAMPLE (SUMMARY)

COMPONENT: Pump

PROBLEM: Excessive Case Drain Leakage —High Temperature

EFFECT: Filters Contaminated and Overheated, Pump Seal Lost, Pump Lost, and

System Lost. Fuel Loss (1 GPM Internal Leakage = 2000 Gal. Fuel/Year)

Maintenance

Man Hour

Requirements

CORRECTIVE ACTION PRIMARY

Replace

Pump

SECONDARY

Change Filter Elements

SECONDARY

Decontaminate

System

WITHfll vv m nuuITi THE IMACS " SYSTEMWITH vv 1 1 n THF inc

IMACS

SYSTEM

WITHOUT vv 1 1 n kj\j i THE IMACS

SYSTEM

WITH vv 1 1 n THF i n c IMACS

SYSTEM

WITHOI vv 1 1 nuuITI THE IMACS

SYSTEM

WITH Vvl in THF 1 PIC IMACS

SYSTEM

Diagnose

Problem .05 HRS 08 HRS — — — —

Maintenance

Labor A/C

1 HR 1 HR 1 HR AVOIDED 6 HRS AVOIDED

System

Integrity

Check

1 HR 1 HR — AVOIDED — AVOIDED

Component

Effected NEW

PUMP

OH.

PUMP

N/A AVOIDED N/A AVOIDED

Total Man Hours

2.5 HRS 2.1 HRS 1 HR 6 HRS

Aircraft Downtime 8 HRS 2 HRS AVOIDED AVOIDED

Flight

Safety YES NO YES NO YES NO

Costs: Man Hours

Material

Downtime

$75 $63 $30 AVOIDED $180 AVOIDED

$3500 $2000 $100 . AVOIDED $340 AVOIDED

$60,000 $15,000 AVOIDED AVOIDED

Total Costs $63,575 $17,063 $130 0 $520 0

TRADE OFF COSTS

Cost without the IMACS System $64,225 Cost with the IMACS System $17,063 Net Savings $47, 1 62

Figure D

206
ADDITIONAL COST FACTORS

FUEL COSTS DUE TO INTERNAL SYSTEM LEAKAGE

FUEL COSTS ATTRIBUTED TO SYSTEM TROUBLE SHOOTING

LOGISTIC MAINTENANCE SUPPORT

INVENTORY MANAGEMENT OF SPARE PARTS

SCHEDULING AND UTILIZATION OF PEOPLE AND AUXILIARY EQUIPMENT

OPPORTUNISTIC AND CONVENIENCE RENEWAL OF WORN COMPONENTS

LOGISTIC ENERGY CONSERVATION

MAINTENANCE FORECASTING AND SCHEDULING

REDUCED TURN-AROUND

FIGURE E

207
208
ESTIMATE OF COST EFFECTIVENESS PER

INDIVIDUAL SYSTEM

CORRECTIVE ACTION

Maintenance

Man Hour

Requirements

PRIMARY

Cycle & Bleed System

SECONDARY

Replace

Pump

SECONDARY

Replace

Lines

SECONDARY

Decontaminate

System

SECONDARY

Replace

Fluid WITHOUT

THE IMACS " SYSTEM

WITH

THE IMACS SYSTEM

WITHOUT

THE IMACS SYSTEM

WITH

THE IMACS SYSTEM

WITHOUT

THE IMACS SYSTEM

WITH

THE IMACS SYSTEM

WITHOUT

THE IMACS SYSTEM

WITH

THE IMACS SYSTEM

WITHOUT

THE IMACS SYSTEM

WITH

THE IMACS SYSTEM

Diagnose Problem NO

PROVISION 08 HRS 0.5 HRS — 0 5 HRS - 1 HR — 08 HRS —

Maintenance

Labor A/C

1 HR 1 HR 1 HR AVOIDED 2 HRS AVOIDED 6 HRS AVOIDED 0.5 HRS AVOIDED

jyb LCI11 Integrity Check

.08 HRS 1 HR AVOIDED 1 HR AVOIDED AVOIDED AVOIDED

Component

Effected

N/A N/A NEW

PUMP

AVOIDED

INSTAI I NEW

LINES AVOIDED N/A AVOIDED ADD

ELUID AVOIDED

Total Man Hours

1 HR 1 HR 2 5 HRS AVOIDED 3.5 HRS AVOIDED 7 HRS AVOIDED 0.5 HRS AVOIDED

Aircraft Downtime

5 HRS 1 HR AVOIDED AVOIDED AVOIDED AVOIDED

Flight

Safety

YES NO YES NO YES NO YES NO YES NO

Costs: Man Hours

Material Downtime

AVOIDED AVOIDED AVOIDED AVOIDED

AVOIDED AVOIDED AVOIDED AVOIDED

AVOIDED AVOIDED AVOIDED AVOIDED

Total Costs 0 0 0

Cost without the IMACS System Cost with the IMACS System Net Savings

209
ESTIMATE OF COST EFFECTIVENESS PER

INDIVIDUAL SYSTEM

CORRECTIVE ACTION

Maintenance

Man Hour

Requirements

PRIMARY

Replace

Pump

SECONDARY

Change Filter Elements

SECONDARY

Decontaminate

System

SECONDARY

Replace

Fluid WITHOUT

THE IMACS"

SYSTEM

WITH

THE IMACS

SYSTEM

WITHOUT

THE IMACS

SYSTEM

WITH

THE IMACS

SYSTEM

WITHOUT

THE IMACS

SYSTEM

WITH

THE IMACS

SYSTEM

WITHOUT

THE IMACS

SYSTEM

WITH

THE IMACS

SYSTEM

PiL/iayi i an niujc ns.e* Problem

.05 HRS .08 HRS N/A .08 HRS

Maintenance

Labor A/C

1 HR 1 HR 1 HR AVOIDED 6 HRS AVOIDED 0.5 HRS AVOIDED

System

Integrity

Check

1 HR 1 HR AVOIDED AVOIDED AVOIDED

Component

Effected NEW

PUMP

O.H. PUMPNEW

ELEMENTS AVOIDED N/A AVOIDED ADD

FLUID AVOIDED

Total Man Hours 2.5 HRS 2.1 HRS 1 HR 6 HRS 0.5 HRS

Aircraft Downtime 8 HRS 2 HRS AVOIDED AVOIDED AVOIDED

Flight

Safety YES NO YES NO YES NO YES NO

Costs: Man Hours

Material Downtime

AVOIDED AVOIDED AVOIDED

AVOIDED AVOIDED AVOIDED

AVOIDED AVOIDED AVOIDED

Total Costs

0 0 0

Cost without the IMACS System Cost with the IMACS System Net Savings

210
ESTIMATE OF COST EFFECTIVENESS PER

INDIVIDUAL SYSTEM

CORRECTIVE ACTION

Maintenance

Man Hour

Ron r\ trl_| 1U1 i

1 rpmontc 1 CM 1 1 CI 1

PRIMARY

Replace Filter Elements

SECONDARY

Replace

Pumps

SECONDARY

Decontaminate

System

SECONDARY

Replace

Fluid WITHOUT

THE IMACS " SYSTEM

WITH

THE IMACS

SYSTEM

WITHOUT

THE IMACS

SYSTEM

WITH

THE IMACS

SYSTEM

WITHOUT

THE IMACS

SYSTEM

WITH

THE IMACS

SYSTEM

WITHOUT

ti i r

II H t IMACS

SYSTEM

WITH

THE IMACS

SYSTEM

Diagnose

Problem .08 HRS .08 HRS 0.5 HRS AVOIDED 1 HR .08 HRS .08 HRS AVOIDED

Maintenance

Labor A/C

1 HR 1 HR 1 HR AVOIDED 6 HRS AVOIDED 0.5 HRS AVOIDED

System

Integrity

Check

08 HRS 1 HR AVOIDED AVOIDED AVOIDED

Component

Effected NEWELEMENTS NEW

ELEMENTS

NEW

PUMP OR

OVERHAUL

AVOIDED N/A AVOIDED ADD

FLUID AVOIDED

Total Man Hours

1 HR 1 HR 2.5 HRS AVOIDED 7 HRS .08 HRS 0.5 HRS AVOIDED

Aircraft Downtime 8 HRS 1 HR AVOIDED AVOIDED AVOIDED

Flight

Safety

NO NO YES NO ' YES NO YES NO

Costs: Man Hours

Material Downtime

AVOIDED

AVOIDED

AVOIDED

Total Costs

Cost without the IMACS System Cost with the IMACS System Net Savings

211
ESTIMATE OF COST EFFECTIVENESS PER

INDIVIDUAL SYSTEM

CORRECTIVE ACTION

Maintenance

Man Hour

Requirements

PRIMARY

Replace

Filter

SECONDARY

Replace Servo- Valve & Actuator

SECONDARY

Replace

Pump

SECONDARY

Decontaminate

System

SECONDARY

Refill System

WITHOUT

THE IMACS"

ji j| C TVl

WITH

THE IMACS QVCTCM jT jI cm

WITHOUT

THE IMACS

CVCTCPL/I

WITH

THE IMACS

c5T3ltM vcTcim

WITHOUT

THE IMACS SYSTEM

WITH

THE IMACS SYSTEM

WITHOUT

THE IMACS SYSTEM

WITH

THE IMACS SYSTEM

WITHOUT

THE IMACS SYSTEM

WITH

THE IMACS SYSTEM

Diagnose

Problem

08 HRS 08HRS 2 HRS 0 5 HRS 08 HRS 1 HR .08 HRS

Maintenance

Labor A/C

1 HR 1 HR 8 HRS AVOIDED 1 HR AVOIDED 6 HRS AVOIDED 0.5 HRS AVOIDED

System

Integrity

Check

08HRS 1 HR AVOIDED 1 HR AVOIDED AVOIDED AVOIDED

Component

Effected NEW

ELEMENT NEWELEMENT

0 H SERVO- ACTUATOR

AVOIDED NEW

PUMP AVOIDED N/A AVOIDED AVOIDED

Total Man Hours

1 HR 1 HR 1 1 HRS 2 5 HRS 0 8 HRS 7 HRS 0.5 HRS

Aircraft Downtime

8HRS 1 HR AVOIDED AVOIDED AVOIDED AVOIDED

Flight

Safety

YES NO YES NO YES NO YES NO YES NO

Costs: Man Hours

Material Downtime

AVOIDED AVOIDED AVOIDED AVOIDED

AVOIDED AVOIDED AVOIDED AVOIDED

AVOIDED AVOIDED AVOIDED AVOIDED

Total Costs

0 0 0 0

Cost without the IMACS System Cost with the IMACS System Net Savings

212
ESTIMATE OF COST EFFECTIVENESS PER

INDIVIDUAL SYSTEM

CORRECTIVE ACTION

Maintenance

Man Hour

DiMfAMIquircFTicnis PA Anh

PRIMARY

Replace System

Relief Valve

SECONDARY

Replace

Pump

SECONDARY

Replace Seal in Reservoir

SECONDARY

Overhaul Filter Manifold

WITHOUT

1 Pit IMACS TM SYSTEM

WITH

TUt 1 Mb

IMACS

SYSTEM

WITHOUT

TUC 1 nt IMACS

SYSTEM

WITH

I lit IMACS

SYSTEM

WITHOUT

1 nt IMACS

SYSTEM

WITH

TU C 1 nt IMACS

SYSTEM

WITHOUT

I nt IMACS

SYSTEM

WITH

TUC I nt IMACS

SYSTEM

Diagnose

Problem

1 HR .08 HRS 0.5 HRS 08 HRS 1 HR AVOIDED 1 HR AVOIDED

Maintenance

Labor A/C

2 HRS 2 HRS 1 HR AVOIDED 4 HRS AVOIDED 1 HR AVOIDED

System

Integrity

Check

1 HR .08 HRS 1 HR AVOIDED 1 HR AVOIDED 1 HR AVOIDED

Component

Effected NEW

R/V

NEW

R/V

O.H. PUMP

AVOIDED

O.H. RESER- VOIR AVOIDED OVERHAUL

MANIEOLD AVOIDED

Total Man Hours 4 HRS 2 HRS 2.5 HRS .08 HRS 6 HRS AVOIDED 3 HRS AVOIDED

Aircraft Downtime 8 HRS 2 HRS AVOIDED AVOIDED AVOIDED

Flight

Safety YES NO YES NO YES NO YES NO

Costs: Man Hours

Material Downtime

AVOIDED AVOIDED AVOIDED

AVOIDED AVOIDED AVOIDED

AVOIDED AVOIDED AVOIDED

Total Costs

0 0

Cost without the IMACS System Cost with the IMACS System Net Savings

213
ESTIMATE OF COST EFFECTIVENESS PER

INDIVIDUAL SYSTEM

CORRECTIVE ACTION

Maintenance

Man Hour

Requirements

PRIMARY

Replace

Accumulator

SECONDARY

Replace

Pump

SECONDARY

Replace

Lines

SECONDARY

Cycle & Bleed System

SECONDARY

Decontaminate

System

WITHOUT

THE IMACS"

SYSTEM

WITH

THE IMACS SYSTEM

WITHOUT

THE IMACS SYSTEM

WITH

THE IMACS SYSTEM

WITHOUT

THE IMACS SYSTEM

WITH

THE IMACS SYSTEM

WITHOUT

THE IMACS SYSTEM

WITH

THE IMACS SYSTEM

WITHOUT

THE IMACS SYSTEM

WITH

THE IMACS SYSTEM

Diagnose

Problem 1 HR .08 HRS 0.5 HRS 0 5 HRS

NO

PROVISION

1 HR

Maintenance

Labor A/C 2 HRS 2 HRS 1 HR AVOIDED 2 HRS AVOIDED 1 HR AVOIDED 6 HRS AVOIDED

System

Integrity

Check

1 HR .08 HRS 1 HR AVOIDED 1 HR AVOIDED AVOIDED AVOIDED

Component

Effected 0 H ACCUMULATOR NEW

PUMP AVOIDED

INSTALL NEW

LINES AVOIDED N/A AVOIDED N/A AVOIDED

Total Man Hours 4 HRS 2 HRS 2 5 HRS AVOIDED 3 5 HRS AVOIDED 1 HR AVOIDED 7 HRS AVOIDED

Aircraft Downtime 5 HRS SCHED

MAINT

AVOIDED AVOIDED AVOIDED AVOIDED

Flight

Safety YES NO YES NO YES NO YES NO YES NO

Costs: Man Hours

Material Downtime

AVOIDED AVOIDED AVOIDED AVOIDED

AVOIDED AVOIDED AVOIDED AVOIDED

AVOIDED AVOIDED AVOIDED AVOIDED

Total Costs

0 0 0 0

Cost without the IMACS System Cost with the IMACS System Net Savings

21k
ESTIMATE OF COST EFFECTIVENESS PER

INDIVIDUAL SYSTEM

CORRECTIVE ACTION

Maintenance

Man Hour

Requirements

PRIMARY

Check

Charge

PRIMARY

Check for Moisture

SECONDARY

Recharge

Bottle

SECONDARY

Purge System

of Moisture

WITHOUT

THE

ill A f C " IMALi

SYSTEM

WITH

THE IMACS

SYSTEM

WITHOUT

THE

lrvlAl_"> SYSTEM

WITH

THE

IRA A /~C IMALi

SYSTEM

WITHOUT

THE

IIViALd SYSTEM

WITH

THE

IM ATC SYSTEM

WITHOUT

THE IMATC JfVI AC 3 SYSTEM

WITH

THE

IMIrVl ALb ACC SYSTEM

Diagnose

Problem

C\0 L-i DC Uo MKb no u d c

Utt tiro NO

rKUVISION

HQ UDC

Maintenance

Labor A/C AVOIDED AVOIDED 1 HR 1 HR 4 HRS 4 HRS

System

Integrity

Check

N/A N/A

NO

PROVISION AVOIDED

24 HR DELAY

REQ'D

LESS THAN 24 HR DELAY

NO

PROVI- SION

.08 HRS

Component

Effected N/A N/A N/A AVOIDED N/A N/A

LINES, VALVES, BOTTLES

LINES, VALVES, BOTTLES

Total Man Hours AVOIDED 1 HR 1 HR 4 HRS 4 HRS

Aircraft Downtime* 4HRS 4 HRS N/A

Flight

Safety YES YES YES YES YES YES YES YES

Costs: Man Hours

Material

Downtime

NO

PROVISION AVOIDED

NO

PROVISION AVOIDED

NO

PROVISION AVOIDED

Total Costs

NO

PROVISION0

Cost without the IMACS System Cost with the IMACS System Net Savings

215
ESTIMATE OF COST EFFECTIVENESS PER

INDIVIDUAL SYSTEM

CORRECTIVE ACTION

Maintenance

Man Hour

Requirements

PRIMARY

Replace

Pump

SECONDARY

Change Filter Elements

SECONDARY

Decontaminate

System

SECONDARY

Replace

Fluid WITHOUT

THE IMACS"

SYSTEM

WITH

THE IMACS

SYSTEM

WITHOUT

THE IMACS

SYSTEM

WITH

THE IMACS

SYSTEM

WITHOUT

THE IMACS

SYSTEM

WITH

THE IMACS

SYSTEM

WITHOUT

THE IMACS

SYSTEM

WITH

THE IMACS

SYSTEM

Diagnose Problem

0.5 HRS .08 HRS 1 HR .08 HR AVOIDED

Maintenance

Labor A/C

1 HR 1 HR 1 HR AVOIDED 6 HRS AVOIDED 0.5 HRS AVOIDED

System

Integrity

Check

1 HR 1 HR AVOIDED AVOIDED AVOIDED

Component

Effected NEW

PUMP

OH

PUMP

NEW

ELEMENT

AVOIDED N/A AVOIDED ADD

FLUID AVOIDED

Total Man Hours 2 5 HRS 1 HR 1 HR AVOIDED 7 HRS 0 5 HRS AVOIDED

Aircraft Downtime 8 HRS AVOIDED SCHED

MAINT

AVOIDED AVOIDED AVOIDED

Flight Safety YES NO YES NO YES NO YES NO

Costs: Man Hours

Material Downtime

AVOIDED AVOIDED AVOIDED

AVOIDED AVOIDED AVOIDED

AVOIDED AVOIDED AVOIDED

Total Costs

0 0 0

Cost without the IMACS System Cost with the IMACS System Net Savings

216
ESTIMATE OF COST EFFECTIVENESS PER

INDIVIDUAL SYSTEM

CORRECTIVE ACTION

Maintenance

Man Hour

Dnc^uirciTicnis Am ii ramantc

PRIMARY

Replace

Leaking Actuator

PRIMARY

Re-rig the

Control Surface WITHOUT

THEIMACS " SYSTEM

WITH THE IMACS

SYSTEM

WITHOUT

THEIMACS

J T j 1 C IVU

WITH THE IMACS

cJ y<;tfm 1 J 1 C 1VB Diagnose

Problem

2 HRS* .08 HRS N/A 08 HRS

Maintenance

Labor A/C 8 HRS 8 HRS 4 HRS 4 HRS

System

Integrity

Check

2 HRS .08 HRS 1 HR 08 HRS

Component

1 Effected OVERHAUL

SERVOACTUATOR N/A N/A

Total Man Hours 12 HRS 8 HRS 5 HRS 4 HRS

Aircraft Downtime 4 HRS. SCHED. MAINT

SCHED. MAINT

Flight Safety YES YES YES YES

Costs: Man Hours

Material Downtime

Total Costs

'Assume at least two servoactuators have to be removed and tested to find

Cost without the IMACS System Cost with the IMACS System Net Savings

217
ESTIMATE OF COST EFFECTIVENESS PER

INDIVIDUAL SYSTEM

CORRECTIVE ACTION

Maintenance

Man Hour

Requirements

PRIMARY

Replace

Leaking Actuator

PRIMARY

Jack A/C and

Swing Main Gear WITHOUT

THE IMACS"

SYSTEM

WITH

THE IMACS

SYSTEM

WITHOUT

THE IMACS

SYSTEM

WITH

THE IMACS

SYSTEM

Diagnose

2 HRS 08 HRS 2 HRS 08 HRS

Maintenance

Labor A/C

4HRS 4 HRS 8 HRS 8 HRS

System

Integrity

Check

1 HR 08 HRS 1 HRS 08 HRS

Component

Effected

REPLACE ACTUATORREPLACE ACTUATOR N/A N/A

Total Man Hours

7 HRS 4 HRS 9 HRS 8 HRS

Aircraft Downtime 4 HRS SCHED

MAINT.

8 HRS SCHED MAINT

Flight

Safety YES YES YES YES

Costs: Man Hours

Material Downtime

Total Costs

Cost without the IMACS System Cost with the IMACS System Net Savings

218
ESTIMATE OF COST EFFECTIVENESS PER

INDIVIDUAL SYSTEM

CORRECTIVE ACTION

Maintenance

Man Hour

Requirements

PRIMARY

Replace

Desiccant

SECONDARY

Remove & Test Servoactuators

SECONDARY

Replace

Pump

SECONDARY

Decontaminate

System

WITHOUT

THE IMACS"

SYSTEM

WITH

THE IMACS

SYSTEM

WITHOUT

THE IMACS

SYSTEM

WITH

THE IMACS

SYSTEM

WITHOUT

THE IMACS

SYSTEM

WITH

THE IMACS

SYSTEM

WITHOUT

THE IMACS

SYSTEM

WITH

THE IMACS

SYSTEM

Diagnose

Problem

0 5 HRS .08 HRS 1 HR 0 5 HRS 1 HR

Maintenance

Labor A/C 2 HRS 2 HRS 4 HRS AVOIDED 1 HR AVOIDED 6 HRS AVOIDED

System

Integrity

Check

1 HR .08 HRS 1 HR AVOIDED 1 HR AVOIDED AVOIDED

Component

Effected NEW

DESICCANT NEWDESICCANT

REPLACE ACTUATOR AVOIDED

REPLACE PUMP AVOIDED N/A N/A

Total Man Hours

3.5 HRS 2 HRS 6 HRS 2.5 HRS 7 HRS

Aircraft Downtime 10 HRS 1 HR AVOIDED AVOIDED AVOIDED

Flight

Safety NO NO YES NO YES NO NO NO

Costs: Man Hours AVOIDED AVOIDED AVOIDED

Material AVOIDED AVOIDED AVOIDED Downtime AVOIDED AVOIDED AVOIDED

Total Costs

0 0 0

Cost without the IMACS System Cost with the IMACS System Net Savings

219
OPERATING EXPERIENCE WITH ADVANCED COMPUTER

BASED SURVEILLANCE SYSTEM

S. Paul Mohan

Exxon Chemical Company

Central Engineering Division

Florham Park, NJ 07932

Abstract

For a large grass roots ethylene plant, a computer system was developed

and commissioned to provide continuous surveillance to its critical

unspared as well as general purpose machinery. This system was justified on the "basis of minimizing unplanned shutdowns and overall improvements in equipment availability factors. Based on utilization of

the system during the plant start-up and normal operation over the past

year, the computer system is earning its anticipated credits. The data

gathered by the computer system has been critical to (a) pinpointing

the cause of events affecting machinery and (b) providing a basis for

soundly engineered solutions. The following functional capabilities

have been useful:

Dynamic storage of process and vibration data at once per

second scan rate. When the train trips, this scanning is

suspended to provide data before and after a trip for postmortem analysis. This data helps to diagnose the cause of

trips and minimize "downtime."

Monitor critical machinery parameters like vibrations, temperatures, hot alignment, horsepower, etc., provide integrated

alarm annunciation to operators via CRT's in the Control Center.

Current operating data are displayed and updated via user built

profiles and schematics.

Alarm initiated data logging capability to capture data before

and after an alarm. These data are used to analyze the cause

of selected alarms.

On-line signature analysis of machinery vibrations with routine

comparison of current frequency spectra with the user defined

alarm and base line signatures. Vibrations with frequencies up

to 100 kHz can be analyzed.

On-line monitoring of the performance of the compressors and

steam turbines to evaluate performance deterioration and

schedule washing as appropriate.

220
Monitor the high frequency signals (80 to 120 kHz) from pumps

to detect incipient failures in anti-friction bearings and

mechanical seals.

Predict alarms "based on trends in data for incipient detection

of slow deterioration. Provide alarms based on calculated

variables

Over 1500 instrument points are being monitored via three (3) satellites

and four (k) multiplexers located throughout the plant. The satellites

do all the input processing including limit checking for alarms. The

historical data storage, data manipulation and man/machine interface

requirements are handled by the host computer located in the Control

Center.

221
MECHANICAL AND AEROTHERMAL DIAGNOSTICS OF TURBOMACHINERY

M. P. Boyce and P. J. Norris

Boyce Engineering International, Inc.

Houston, Texas 77099

ABSTRACT

To fully diagnose turbomachinery problems, both the mechanical and

aerothermal parameters must be considered, since there is always a close

interaction between them. The technique outlined in this paper deals with the

complex aerothermal and mechanical problems in turbomachinery, and the

interrelation of these parameters. Historically, the aerospace industry has

been concerned with performance, while the petrochemical industry with

reliability. Each of these industries looked at the two parameters exclusive of

their interrelated relationships. The current trend is to use both mechanical and

aerothermal parameters for monitoring and diagnostics.

This paper outlines techniques which can be used both for online

diagnostics or offline problem solving. To determine deterioration in performance of a unit, it is necessary to first, determine whether the changes in

performance are due to changes in ambient or process conditions, or whether

these changes are due to an actual physical deterioration of the unit. Once it has been determined that the deterioration is due to physical deterioration of

the system, the analysis must indicate the cause. This is done by examination

of the various parameters and noting which of these parameters have caused the

decay. Various groups of parameter changes indicate specific problems and

these are correlated to diagnose problems.

1.0 INTRODUCTION

This paper describes the requirements and techniques for instrumentation,

analysis and diagnostics for application on turbomachinery equipment.

To achieve effective monitoring and diagnostics of turbomachinery it is necessary to gather and analyze both the mechanical and aerothermal operating

data from the machines. The instrumentation and diagnostics must also be

custom tailored to suit the individual machines in the system, and also to meet

the requirements of the end users. The reasons for this being that, there can

be significant differences in machines of the same type or manufacturer,

because of differences in installation and operation.

222
2.0 REQUIREMENTS FOR AN EFFECTIVE DIAGNOSTIC SYSTEM

The following is a list of requirements for a diagnostic system:

A. The system must produce diagnostic and failure prediction information in a timely manner before serious problems occur on the

machines monitored.

B. When equipment shutdown becomes necessary, diagnostics must be

precise enough to accomplish problem identification and rectification

with minimal downtime.

C. The system should be useable and understood sufficiently by production personnel so that an engineer is not always necessary when

urgent decisions need to be made.

D. The system should be simple and reliable and cause negligible

downtime for repairs, routine calibration and checks.

E. The system must be cost effective, namely it should cost less to

operate and maintain than the expenses resulting from loss of

production and machinery repairs that would have resulted if the

machinery was not under monitoring and predictive surveillance.

F. System flexibility to incorporate improvements in the state of the art

is desirable.

G. System expansion capabilities to accept projected increases in

installed machinery or increases in number of channels must be

considered.

H. The use of excess capacity in a computer system available at the

plant can result in considerable savings equipment costs. System

components that mate with the existing computer system may,

therefore, be a necessary prerequisite.

3.0 DIAGNOSTIC SYSTEM COMPONENTS & FUNCTIONS

A. Instrumentation and Instrumentation Mountings

B. Signal Conditioning and Amplifiers for Instrumentation

C. Data Transmission System: Cables, Telephone Linkup, or Microwave.

D. Data Integrity Checking, Data Selection, Data Normalization and

Storage.

E. Baseline Generation and Comparison.

223
F. Problem Detection

G. Diagnostics Generation.

H. Prognosis Generation.

I. Onsite Display.

J. Systems for Curve Plotting, Documentation and Reporting

Figures 1A and IB are schematic representations of typical systems.

4.0 DATA INPUTS

Obtaining good data inputs is a fundamental requirement, since any

analysis system is only as good as the inputs to the system. A full audit of the

various trains to be monitored must be made in order to obtain optimum

instrumentation selection.

The factors that need to be considered are the instrument type, its

measurement range, accuracy requirements and the operational environmental

conditions. These factors must be carefully evaluated to select instruments of

optimum function and cost to match the total requirements of the system. For

instance, the frequency range of the vibration sensor should be adequate for

monitoring and diagnostics and should match with the frequency range of

analysis equipment. Sensors should be selected to operate reliably and

accurately within the environmental conditions that prevail, for example, when

used on high temperature turbine casings. Resistance temperature sensors with

their higher accuracy and reliability as compared to thermocouples may be

necessary for analysis accuracy and reliability.

Calibration of instrumentation should be conducted on a schedule established after reliability factors have been analyzed.

All data should be checked for validity and as to whether they are within

reasonable limits. Data that is beyond predetermined limits should be discarded

and flagged for investigation. An unreasonable result or analysis should set up

a routine for identification of possible discrepant input data.

5.0 MONITORING/DIAGNOSTIC SYSTEM

It is essential that the instrumentation requirements be tailored to the

requirements of the machine being monitored. However, the following

instrumentation requirements should exist to cover the requirements for both

vibration and aerothermal monitoring.

Any existing instrumentation should be used if found to be adequate. While

there are advantages in the use of non-contacting sensors built into the machine

for measurement of journal displacements, this instrumentation is often

22k
225
226
impossible to install in existing machinery. Suitably selected and located

accelerometers can adequately cover the vibration monitoring requirements of

machinery. Accelerometers are often an essential supplement to displacement

sensors to cover the higher frequencies generated by gear mesh, blade passing,

rubs and other conditions.

A. Instrumentation Typical -Minimum Requirements for Each Machine

Note: Locations and type of sensors would depend on the type of

machine under consideration.

1. Accelerometer

a. At machine inlet bearing case, vertical

b. At the machine discharge bearing case, vertical

c. At machine inlet bearing case, axial

2. Process Pressure

a. Pressure at machine inlet

b. Pressure at machine discharge

3. Process Temperature

a. Temperature at machine inlet

b. Temperature at machine discharge

4. Machine Speed

a. Machine speed of all shafts

5. Thrust Bearing Temperature

a. One thermocouple or resistance temperature element

embedded in forward and aft thrust bearing

B. Instrumentation-Desirable-Optional

1. Non-contacting eddy current vibration displacement probe adjacent to:

a. Inlet bearing, vertical

b. Inlet beariner. horizontal

c. Discharge bearing, vertical

d. Discharge bearing, horizontal

227
2. Non-contacting eddy current gap sensing probe adjacent to:

a. Forward face of thrust bearing collar

b. Aft face of thrust bearing collar

Note : The non-contacting sensor in its role of measure- ment of gap-D.C. voltage is sensitive to probe and driver

temperature variations. Careful evaluation must hence be

conducted of sensor type, its mounting and location, for

this measurement.

3. Process flow measurement at inlet or discharge of machine

4. Radial bearing temperature-thermocouple or resistance temperature element embedded in each bearing, or temperature at

lube oil discharge of each bearing.

5. Lube oil pressure and temperature

6. Dynamic pressure transducer at compressor discharge for

indication of flow instability

Figures 2A and 2B shows possible instrument locations for an industrial gas

turbine and centrifugal compressor.

6.0 CRITERIA FOR THE COLLECTION OF AEROTHERMAL DATA

Turbomachinery operating pressures, temperatures and speeds are very

important parameters. Obtaining accurate pressures and temperatures will

depend not only on the type and quality of the transducers selected, but also on

their location in the gas path of the machine. These factors should be carefully

evaluted. The accuracy of pressure and temperature measurements required will

depend on the analysis and diagnostics that need to be performed. Figure 3

presents some criteria for selection of aerothermal instrumentation of pressure

and temperature sensors for measurement of compressor efficiency. Note that

the percentage accuracy requirements are more critical for temperature sensors than pressure sensors. The requirements are also dependent on the compressor

pressure ratio.

7.0 VIBRATION INSTRUMENTATION SELECTION

The type of vibration instrumentation, its frequency ranges, its accuracy

and its location within, or on the machine, must be carefully analyzed with

respect to the diagnostics required to be achieved. Figure 4 presents guidelines on the selection of vibration sensors.

The displacement non-contacting eddy current sensor is most effective for

monitoring and measuring vibrations near rotational and subrotational speeds.

228
229
230
CRITERIA FOR SELECTION OF PRESSURE AND

TEMPERATURE SENSORS FOR COMPRESSOR EFFICIENCY MEASUREMENTS

COMPRESSOR

PRESSURE

RATIO

P9/P1

P 2 SENSITIVITY PERCENT

T2 SENSITIVITY PERCENT

6 .704 .218

7 .750 .231

8 .788 .240

9 .820 .250

10 .848 .260

11 .873 .265

12 .895 .270

13 .906 .277

14 .933 .282

15 .948 .287

16 .963 .290

Tabulation showing percent changes in P 2 and T2 needed to cause

one-half percent change in air compressor efficiency. Ideal gas equations are used.

Figure 3: Criteria for Selection of Pressure and Temperature Sensors for Compressor Efficiency Measurements

231
HI)

cu

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l.u

0.1

0.01

Velocity . 3 In/Sec Zero to Peak

/0.056G

^ 1

IK

\0.1 Mil \

L

10 Hz 100 Hz l KHz

VIBRATION FREQUENCY IN HERTZ

"T^KHz

lKHz

Range for Displacement Sensors

I Range for Velocity Sensors K^^^S^ 3KHz

10 KHz

Range for Accelerometer Sensors

FIGURE 4: GUIDELINES FOR VIBRATION TRANSDUCER SELECTION

100 KHz k )

232
While the displacement sensor is capable of measuring vibration frequencies well

above 2kHz, the amplitude of vibrational displacement levels that occur at

frequencies above lkH z are extremely small, and are usually lost or buried in the

noise level of the readout system. The acceleration sensor is best suited for

measurements at high frequencies, such as blade passing and gear meshing

frequencies; however, the signals at once rotational speed are usually at low

acceleration levels, and may be lost in the noise level of the measurement

system monitoring. Low pass filtering and additional amplification stages may,

therefore, be necessary to bring out the rotational speed signals when

measurements are made with accelerometers.

Velocity sensors, because of their limited operational frequency range of

usually from 10Hz to 2kH z, are not recommended for application in a diagnostic

system for high speed machinery. Velocity sensors have moving elements and

are subject to reliability problems at operational temperatures above 250°F.

Gas turbine engine casing temperatures are usually in the 500°F level or above,

hence sensor locations must be carefully examined for temperature levels.

Accelerometers for these higher temperatures are more easily available than

velocity sensors. At these elevated operational temperatures, high frequency

accelerometers (20 kHz and above) are available from only a few selected

manufacturers.

8.0 SELECTION OF SYSTEMS FOR ANALYSIS OF VIBRATION DATA

The overall vibration level on a machine is satisfactory for initial or rough

check. However, when a machine has a seemingly acceptable overall level of

vibration, there may be hidden under this level some small levels of vibrations

at discrete frequencies that are known to be dangerous. An example of this is subsynchronous instabilities in a rotor system.

In the analysis of vibration data, there is most often the need to transform

the data from the time domain to the frequency domain or, in other words, to

obtain a spectrum analysis of the vibration. The original and inexpensive system

to obtain this analysis is the tuneable swept filter analyzer. Because of inherent

limitations of this system, this process, despite the use of automated sweep, is time consuming when analyzing low frequencies. When the spectrum data needs

to be digitized for computer inputing, there are further limitations in capability

of tuneable filter analysis systems.

Real Time Spectrum Analyzers using "Time Compression" or the "Fast

Fourier Transform" (FFT) techniques, are extensively used for performing

vibration spectrum analysis in computerized diagnostic systems. The FFT

analyzers use digital signal processing, and hence are easier to integrate with

the modern digital computer. FFT analyzers are often hybrids using microprocessors and FFT dedicated circuitry.

The FFT can be implemented in a computer using the FFT algorithm for

obtaining a pure mathematical computation. While this computation is an error

free process, its implementation in a digital computer can introduce several

errors. To avoid these errors, it is essential to provide signal conditioning,

233
upstream of the computer. Such signal conditioning minimizes the errors such

as, aliasing and signal leakage introduced in sampling and digitizing the time

domain. Such signal conditioning system will introduce considerable expense and

complexity in effecting the mathematical FFT in a computer. The computerized

FFT is also slower than a dedicated FFT analyzer. It also has limitations in

frequency resolution. Hence, the use of a dedicated FFT analyzer is considered

to be the most reliable and cost effective means for performing frequency

spectrum analysis and plots in a computerized system for machinery diagnostics.

Careful analysis must be made of the type of spectrum analysis systems

and the computational techniques used in vibrational analysis. There are several

factors which must be considered, some of which are:

A. Frequency analysis ranges

B. Single or multi-channel analysis

C. Dynamic range

D. Accuracy of measurements necessary

E. Speed at which analysis are required to be made

F. System portability, especially if the analysis system is required for

both lab and field use

G. Fase of integration with the host computer system

9.0 BASELINE FOR MACHINERY

A. Mechanical Baseline

The vibration baseline for a machine can be defined as the normal or average operating condition of a machine. It can be represented on

a vibration spectrum plot showing vibration frequency on the X-axis

and vibration amplitude (peak-to-peak displacement, peak velocity, or peak acceleration) on the Y-axis. Since the vibration spectrum will

be different at different positions, the spectrum must be associated

with a specific measurement position or sensor location on the

machine. When portable vibration measurement equipment is used, it is essential to ensure that the sensor is relocated at exactly the same

point on the machine each time vibration readings are taken.

Changes of baseline with machine speed and process conditions should

be investigated and where necessary, baseline should be generated for

set ranges of speeds and process conditions. When the operating

vibration levels exceed the baseline levels beyond set values, an alert

signal should be activated for investigation of this condition.

B. Aerothermal Baseline

In addition to the vibration baseline spectrum, a machine also has an aerothermal performance baseline or its normal operating point on the aerothermal characteristic. Significant deviation of the

operating point beyond its base point should generate alert signals.

23k
When a compressor ooerates beyond its surge margin, a danger alert should be

activated. A typical compressor characteristic is presented in Figure 5. Some

of the other monitoring and operating outputs are loss in compressor flow, loss

in pressure ratio and increase in operating fuel cost due to, for instance,

operating at off design conditions or with a dirty compressor.

Since the aerothermal performance of compressors and turbines are very sensitive to inlet temperature and pressure variations, it is essential to normalize the aerothermal performance parameters such

as, flow, speed, horsepower, etc. to standard day conditions. When

these corrections to standard conditions are not applied, then a performance degradation may appear to occur when in fact it was a performance change resulting merely from ambient pressure and

temperature changes. Some of the equations for obtaining correction

to standard day conditions are given in Figure 6.

10.0 DATA TRENDING

The data received should first be corrected for sensing errors. This usually

consists of sensor calibration correction.

The trending technique essentially involves evaluating the slope of a curve

derived from the received data. The slope of the curve is calculated for both

a long-term trend, about 168 hours, and a short-term trend, based on the last

24 hours. If the short-term slope deviates from the long-term slope beyond a

set limit, it means that the rate of deterioration is changed and the maintenance

schedule will be affected. Thus, the program might take into account the

biasing of the long-term slope by the short-term slope. Figure 7 shows a schematic of this type of trending. Numerous statistical techniques are

available for trending.

Trended data is used to obtain predictions which would be helpful in the

scheduling of maintenance. Referring to Figure 8, for example, it is possible to

estimate when compressor cleaning will be necessary. This figure was prepared

by recording the compressor exit temperature and pressure each day. These

points are then joined and a dotted line is projected to predict when cleaning

will be required. In this case, two parameters were monitored, but since their

rates differed, the cleaning was based on the first parameter to reach the

critical point. However, using a trend of both temperature and pressure provides

a cross check on the validity of the diagnostics.

11.0 COMPRESSOR AEROTHERMAL CHARACTERISTICS & COMPRESSOR

SURGE

Figure 9 shows a typical performance map for a centrifugal compressor,

showing efficiency islands and constant aerodynamic speed lines. The total

pressure ratio can be seen to change with flow and speed. Usually compres - sors are operated on a working line-' separated by some safety margin

from the surge line.

235
AEROTHERMAL CONDITION MONITORING FOR COMPRESSORS

Compressor Mass Flow

DATA INPUT

Ambient Pressure

Compressor Inlet Pressure

Compressor Discharge Pressure

Compressor Inlet Temperature

Compressor Discharge Temperature

Compressor Speed

Compressor Inlet or Discharge Flow if Available

DIAGNOSTICS OUTPUTS Compressor Efficiency Lower than Design

Compressor Approaching Surge Conditions

Compressor Approaching CIIOKK CONDITIONS Dirty Compressor

CONDITION MONITORING OUT PUTS

Loss in Compressor Flow Through Put Loss in Compressor Pressure Ratio

Fuel Cost Penalty

Projected Increase in Fuel Cost After One Month Operation

Surge Point Deterioration Trend and Anticipated Outage Date

Figure 5

236
FACTORS FOR CORRECTION TO STANDARD DAY TEMPERATURE & PRESSURE

CONDITIONS

Assumed Standard Day Pressure 14.7 psia

Assumed Standard Day Temperature 60°F (520°R)

Conditions of Test

Inlet Temperature Tj °R

Inlet Pressure Pj psia

Corrected Temperature = (Observed Temperature) (520/T^)

Corrected Pressure = (Observed Pressure) (14.7/Pj)

Corrected Speed = (Observed Speed) x/520/Tj

Corrected Air Flow = (Observed Flow) (14.7/Pj) v/Tj/520

Corrected Horsepower = (Observed Power) (14.7/Pj) V^520/Tj

Figure 6: Gas Turbine Aerothermal Performance Equations for Correction

to Standard Day Conditions.

237
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Kfgure 8: DATA TRENDING TO PREDICT MAINTENANCE SCHEDULES

239
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Compressor surge is essentially a situation of unstable operation and

should, therefore, be avoided in both design and operation. Surge has been

traditionally defined as the lower limit of stable operation of a compressor

and involves the reversal of flow. This reversal of flow occurs because of

some kind of aerodynamic instability within the system. Usually it is a part

of the compressor that is the cause of the aerodynamic instability though it is possible that the system arrangement could be capable of magnifying this

instability.

Usually, surge is linked with excessive vibration and an audible sound;

yet, there have been cases in which surge problems which are not audible

have caused failures.

12.0 DIAGNOSTICS

Problem evaluation in turbomachinery is complex, but with the aid of

performance and mechanical signals, solutions can be found to diagnose various

types of failures. This is done by using several inputs and a matrix. A sample

of some of the problems are given in the next few sections.

A. Compressor Analysis

Compressor analysis is done by monitoring the inlet and exit

pressures and temperatures, the ambient pressure, vibration at each

bearing, and the pressure and temperature of the lubrication system.

Table I shows the effect various parameters have on some of the

major problems encountered in a compressor. Monitoring these

parameters allows the detection of the following problems:

1. Clogged air filter- A clogged air filter may be detected by

noting an increase in the pressure drop through the filter

2. Compressor surging-Surge may be detected by noting a rapid

increase in shaft vibration, along with a discharge pressure

instability. If more than one stage is present, the probes

located within the bleed air chambers are useful in locating the

problem stage by checking for pressure fluctuations

3. Compressor Fouling-This is indicated by a decrease in pressure

ratio and flow accompanied by an increase of exit temperature

with time. The change in the temperature and pressure ratio

tend to show a decrease in efficiency. If a change in vibration

has occurred, the fouling is critical, since it indicates excessive

build up of deposits on the rotor

4. Bearing failure-Symptoms of bearing trouble include a loss of

lubrication pressure, an increase in the temperature difference

across the bearing, and an increase in vibration. If oil whirl or other bearing instabilities are present, there will be a vibration

at subsynchronous frequency

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Chamber

Pressure

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Highly

Fluctuating 1

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Pressure 1

A

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1

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Highly

Fluctuating

Compressor

Fluid Mass

Flow — •

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1

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1 1

1

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Variable 1

1 1

Clogged

Filter Surge

Fouling

Damaged

Blade

Bearing Failure

2h2
B. Combustor Analysis

In the combustor, the only two parameters which can be measured

are fuel pressure and evenness of combustion noise. Turbine inlet

temperatures are not usually meassured, due to very high temperatures and limited probe life. Table II shows the effect of various

parameters on important functions of the combustor.

1. Plugged Nozzle-This is indicated by an increase in fuel pressure

in conjuction with increased combustion uneveness. This is a common problem when residual fuels are used

2. Cracked or Detached Liner-This is indicated by an increase in an acoustic meter reading and a large spread in exhaust

temperature

3. Combustor Inspection or Overhaul-This is based on equivalent

engine hours which are based on number of starts, fuel and

temperature. Figure 10 shows the effect of these parameters

on the life of the unit. Note the strong effect that fuel and

number of starts has on the life.

C. Turbine Analysis

To analyze a turbine, it is necessary to measure pressures and

temperatures across the turbine, shaft vibration, and the temperature

and pressure of the lubrication system. Table III shows the effect

various parameters have on important functions of the turbines.

Analysis of these parameters will aid in the prediction of the

following:

1. Turbine Fouling-This is indicated by an increase in turbine

exhaust temperature. Change in vibration amplitude will occur when fouling is excessive and causes rotor imbalance.

2. Damaged Turbine Blades-This results in a large vibration

increase accompanied by an increase in the exhaust temperature.

3. Bowed Nozzle-The exhaust temperature will increase, and there

may be an increase in turbine vibration.

4. Bearing Failure-The symptoms of bearing problems for a turbine are the same as for a compressor

5. Cooling Air Failure-Problems associated with the blade cooling

system may be detected by an increase in the pressure drop in

the cooling line.

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6. Turbine Maintenance-This should be based on "Equivalent Engine

Time" which is the function of temperature, fuel used, and

number of starts and fuel is substantial. Figure 11 shows the

correction that can be applied to running hours for intermittent

duty units with high start/stop operation.

D. Turbine Efficiency

1. With the current high costs of fuel, very significant savings can be

achieved by monitoring equipment operating efficiencies and corr- ecting for operational inefficiencies. Some of these operational

inefficiencies may be very simple to correct such as wash or clean

of the compressor on a gas turbine unit. In other cases, it may be

necessary to develop a load distribution program that achieves

maximum overall efficiency of the plant equipment for a given load

demand.

2. Figure 12 shows the significant dollar cost penalties that occur when

operating a turbine at a very small percentage efficiency degr adation.

3. Figure 13 shows a load distribution program for a 87.5 MW powerstation comprising of steam turbines and gas turbines. The selection

of equipment and their loading for the most efficient operation can

be programmed when the efficiency of individual units are monitored.

The program selects the units which should be operated to provide

the power load demand at the maximum overall efficiency of the

combination of units.

13.0 MECHANICAL PROBLEM DIAGNOSTICS

The advent of new, more reliable and sensitive vibration instrumentation

such as, the eddy current sensor and the accelerometer coupled with modern

technology analysis equipment such as the real time vibration spectrum analyzer

and low cost computers gives the mechanical engineer very powerful aids in

achieving machinery diagnostics.

A chart for vibration diagnosis is presented in Figure 14. While this is a general criteria or rough guideline for diagnosis of mechanical problems, it can

be developed into a very powerful diagnostic system when specific problems and

their associated frequency domain vibration spectrums are logged and correlated

in a computerized system. With the extensive memory capability of the

computer system, case histories can be recalled and efficient diagnostics

achieved.

14.0 DATA RETRIEVAL

In addition to being valuable as a diagnostic and analysis tool, a Data

Retrieval program would also provide an extremely flexible method of data

2^8
600K |_

120K

Fuel Cost $2.7/Million BTU approximately $l/gal. Based on a unit consuming 280 x 10^ Btu/hr.

For a 1500MW Gas Turbine Unit

1500 3500 5500 7500

Figure 12:

OPERATING HOURS

Savings Vs. Efficiency

2k9
DESCRIPTION OF UTILITY PLANTS UNITS

UNIT# DESIGN MW

TURBINE

TYPE

EFFICIENCY AT

DESIGN OUTPUT

POINT

1

23

4

56

78

9

10

2.5 2.5

5.0

5.0

5.0

7.5 1515

15

15

Steam

Steam

Steam Steam

Steam

Steam

Steam

Steam

Gas Gas

22

22

2424

24

25

3023

21

21

COMBINATION OF UNITS TO YIELD EFFICIENT

POWER LOAD DISTRIBUTION FOR DIFFERENT DEMAND LOADS

UNITS NOT WORKING IN ASCENDING ORDER

1,4,9 EFFICIENT POWER LOAD DISTRIBUTION PROGRAM

TOTAL DEM AND= 30.00 MW

TOTAL OUTPUT SUPPLIED^ 30.00 MW

TOTAL DEMAND^ 50.00 MW

TOTAL OUTPUT SUPPLIED 50.00 MW

Units Not Workings 14 9 0 Units Not Workings 14 0 0 Unit 1 = 0.00 0.00 Unit 1 = 0.00 0.00 Unit 2= 0.00 0.00 Unit 2 2.50 22.01 Unit 3

= 2.50 21.00 Unit 3= 5.00 24.50 Unit 4= 0.00 0.00 Unit 4= 0.00 0.00 Unit 5 = 5.00 24.50 Unit 5= 5.00 24.50 Unit 6 = 7.50 25.19 Unit 6= 7.50 25.19 Unit 7= 15.00 29.91 Unit 7= 15.00 29.81 Unit 8= 0.00 0. 00 Unit 8 0.00 0.00 Unit 9= 0.00 0.00 Unit 9= 0.00 0.00 Unit 10 = 0.00 0.00 Unit 10= 15.00 21.00 MAXIMUM OVERALL EFFIC1ENCY=27.04 MAXIMUM OVERALL EFFICIENCY=25.02

Power Demands MW(Max.Demand=87.5)

Figure 13: Load Sharing Program

250
Usual Predominant Frequency Cause of Vibration

0-40% Running Frequency

40-50% Running Frequency

Loose assembly of bearing liner,

bearing casing, or casing and

Support

Loose rotor shrink fits

Friction Induced Whirl

Thrust Bearing Damage

Bearing Support Excitation

Loose Assembly of Bearing Liner,

Bearing Case, or Casing and

Support

Oil Whirl

Resonant Whirl

Clearance Induced Vibration

Running Frequency

Odd Frequency

Initial Unbalance

Rotor Bow

Lost Rotor Parts

Casing Distortion

Foundation Distortion

Misalignment

Piping Forces

Journal & Bearing Eccentricity

Bearing Damage

Rotor Bearing System Critical

Coupling Critical

Structural Resonance

Thrust Bearing Damage

Loose Casing and Support

Pressure Pulsations

Vibration Transmission

Very High Frequency Gear Inaccuracy

Valve Vibration

Dry Whirl

Blade Passage

Occurs in most cases predominantly at this frequency, harmonics may or may not agree.

Figure 14: Vibration Diagnosis

251
storage and recovery. By careful design of a health monitoring system, an

engineer or technician could compare the present operation of this unit with the

operation of the same machine, or of another machine, under similar conditions

in the past. This could be done by selecting one, or several limiting parameters

and defining the other parameters which are to be displayed when the limiting

parameters are met. This would eliminate the necessity of sifting through large

amounts of data. A few examples of how this system would be used are:

A. Retrieval by Time-In this mode, the computer would retrieve data

taken during a specified time period, thus enabling the user to

evaluate the period of interest

B. Retrieval by Ambient Temperature-The failure of the gas turbine

may occur during an unusually hot or cold period, and the operator

may wish to determine how his unit has functioned at this

temperature in the past

C. Retrieval by Turbine Exhaust Temperature-The exhaust temperature

can be an important parameter in failure investigations. An analysis

of this parameter can verify the existence of a problem with either

the combustor or turbine

D. Retrieval by Vibration Levels-Inspection of data provided by this

mode can be useful in determining compressor fouling, compressor or turbine blade failure, nozzle bowing, uneven combustion and bearing

problems.

E. Retrieval by Output Power-In this mode, the user should input the

output power range of interest and would thus obtain only data

applying to that particular power setting. In this manner, he would

only have to consider the pertinent data to pinpoint the problem

areas.

F. Retrieval by Two or More Limiting Parameters-By retrieving data

with limits on several parameters, the data can be evaluated and will

be even further reduced. Diagnostic criteria can then be developed.

15.0 CONCLUSIONS

A. The monitoring of mechanical characteristics of turbomachinery,

such as vibrations, has been extensively applied this past decade. The advent of

the accelerometer and the real time vibration spectrum analyzer has required a computer to match and utilize the extensive analysis and diagnostic capability

of these instruments.

B. The high cost for machinery replacements and downtime makes

machinery operational reliability very important, however with the currently

prevailing and projected futher increases in fuel costs, aerothermal monitoring

has become very important. Aerothermal monitoring can provide not merely

252
increased operational efficiency for turbomachinery, but when combined with

mechanical monitoring, provides an overall, more effective system than one that

monitors only the mechanical functions or aerothermal functions.

C. While there had been concern on the reliability of computer systems,

they are currently receiving wide acceptance and are fast replacing analog

systems.

D. The systematized application of modern technology instrumentation,

both mechanical and aerothermal, low cost computers and turbomachinery

engineering experience will result in the development and application of cost

effective systems.

253

SESSION V

OPPORTUNITIES FOR DETECTION,

DIAGNOSIS, AND PROGNOSIS

IN THE ENERGY FIELD

Chairmen: R. Hohenberg, Mechanical Technology, Inc.

J. L. Frarey, Shaker Research Corporation

DATA ACQUISITION AND ANALYSIS IN THE DOE/NASA

WIND ENERGY PROGRAM

Dr. Harold E. Neustadter

Wind Energy Project Office

NASA-Lewis Research Center

Cleveland, OH 44135, (216)433-4000

Abstract: The Lewis Research Center of NASA manages for the

Department of Energy, the technology and engineering development of

all large horizontal axis wind turbines. In support of this

activity each wind turbine has various data systems used to acauire,

process and analyze data. This report will identify four categories

of data systems, each responding to a distinct information need.

The categories are: Control, Technology, Engineering and

Performance.

The focus of this report is on the Technology data system which

consists of the following elements: (1) sensors which measure

critical parameters such as wind speed and direction, output power,

blade loads and strains, and tower vibrations; (2) remote

multiplexing units (RMUs) mounted on each wind turbine which

frequency modulate, multiplex and transmit sensor outputs; (3) the

instrumentation available to record, process and display these

signals; and (4) centralized computer analysis of data at the

NASA-Lewis Research Center in Cleveland, Ohio.

RMU characteristics and multiplexing techniaues are presented. Data

processing is illustrated by following a typical signal through

instruments such as the analog tape recorder, analog-to-digital

converter, data compressor, digital tape recorder, video (CRT)

display, and strip chart recorder. Sample output data from the 200

kW Mod-OA wind turbine at Clayton, New Mexico, are presented.

Key words: Wind energy; wind turbine generators; wind turbine

performance; horizontal axis wind turbines; wind turbine data

systems.

I. Introduction

The U.S. Government has established a Wind Energy Program within the

Department of Energy (DOE) to encourage the development and promote

commercialization of wind energy systems. One phase of this program

is being managed by the NASA Lewis Research Center (LeRC). An

agreement with DOE stipulates that LeRC shall manage both the

257
Technology and Engineering Development for all large ( > 100 kW)

horizontal axis wind turbines. 1 Four wind turbine projects,

designated the Mod-02

, Mod-OA^, Mod-1^, and Mod-25

, are part

of the current development program. In addition to these projects,

efforts aimed at achieving lower machine costs have been initiated

These include an advanced 1,000 kW-class wind turbine project

(Mod-5) and an advanced 200 to 500 kW wind turbine project (Mod-6).

The four existing models are shown in -figure 1 and the major features

of all these machines are summarized in Table 1.

With regard to all these machines, LeRC maintains the continuing

capability to monitor, analyze, understand and report on their

performance. Despite the diversity in Wind Turbine Generator

characteristics amongst the machines listed in Table I, we can nonetheless identify four distinct information/user categories that

are common to all wind turbines. Namely: operations/ the wind

turbine itself; technology/field operations personnel;

engineering/system and component designers; performance/utility or program manager. The requirements for each category are sufficiently uniaue that we have developed a separate data system to

meet each need. At one extreme, with the highest sampling rates, are the computer based control systems which govern the routine

operation of each wind turbine generator. The data portion of the

control system provides information regarding adequacy of the wind,

status of all critical systems, machine alignment with the wind,

etc., and often monitors over 100 sensors. In the case of critical

controls it must be capable of responding within milliseconds. This

system is considered to be an integral part of the wind turbine and

varies significantly from one design to the next. At the other

extreme, with the lowest sampling rate, would be a Performance Data

System to provide data for evaluation of wind turbines in terms of

availability, reliability and energy production. These data

requirements are generally limited to meteorological and electrical

parameters with time scales from an hour to the lifetime of the

machine. The two remaining information systems, namely Technology

and Engineering are discussed in greater detail in the remainder of

this report. The next two sections deal with the signal

conditioning acquisition and data display. The fourth section

discusses the subsequent statistical analysis.

II. Technology Information Systems

The Technology Data Acquisition/Display System has three

functionally (and spatially) distinct components. As one follows

the data signals from the sensors through the system, these are:

signal conditioning, acquisition/display, and post processing for

statistical analysis. Physically these functions occur: on the

258
wind turbine, at or near the base of the wind turbine tower and at

LeRC, respectively. As mentioned earlier in connection with Table

I, the wind turbines display considerable variability as to source,

location, blade composition and design. Despite, and to some extent

because of this variability, it was decided that all data system

implementations of must have the same (or functionally equivalent)

hardware and software.

Signal Conditioning

Signal conditioning is performed by a Remote Multiplexing Unit

(RMU). As input, an RMU can accept up to 32 low-level or high-level

data signals from a variety of transducers. Each RMU contains

reference junctions for thermocouples as well as the necessary

electronics for excitation and bridge completion of strain gauges.

As a specific example, Table II contains a list of all the

transducers monitored by the Technology Information System during

the initial start-up of the Mod-1 at Boone, North Carolina. Each

wind turbine has one RMU located in the hub, another in the nacelle

and (with the exception of Mod-2) a third unit at the base of the

tower in the controls room.

After a signal is received at the RMU it is conditioned (scale

and/or offset; amplification or attenuation) to a common range and

frequency multiplexed for output. Each RMU can generate two

multiplex groups. Each multiplex group consists of up to 16 FM

subcarriers (+_ 125 Hz centered at 500 Hz intervals from 1000 Hz thru

8500 Hz) plus a precise reference tone at 9500 Hz. Other

significant features of the RMU include a 4-pole active Butterworth

low pass filter and an end-to-end system calibration capability

(upon command from an external source).

Acquisition/Display

LeRC has two nearly identical Technology Acquisition/Display

Facilities. One is installed at the LeRC Plum Brook station in

Sandusky, Ohio and is used by the LeRC engineering staff to conduct

the Supporting Research and Technology program based on the Mod-0

machine. The other is installed in a large van. 6 This latter

relocatable system is used to support field engineers thru assembly,

check-out and initial operation of the first units of each new wind

turbine design.

A schematic representation of the electronic data processing

capability of this facility is shown in figure 2. All RMU generated

FM multiplexes entering this facility are, with the addition of a

259
time code, recorded in direct analog form. This recording can be

performed independent of any other eauipment or processing activity

within the facility. Simultaneously, the data can also be routed

thru a set of 6 banks of 16 discriminators which de-multiplex the

signals and generate analog ( +5V) signals. Any or all of these 96

analog signals can be digitized and routed thru the mini-computer.

From there it can be processed for real-time digital display on a CRT and/or for transmittal on digital tape to the LeRC main-frame

computers for further analysis. In addition, any 24 of the 96

analog signals may be selected for display on strip charts and any

single analog signal may be routed to a spectrum analyzer for

frequency content evaluation. All the components shown with a gray

stipling in figure 2, can be set up and run under computer control

at the discretion of the facility operator via the operator's

console. The facility in the van has sufficient capacity to

simultaneously support up to three wind turbines at a single site.

STATISTICAL ANALYSIS

Large volumes of data are of little value in their raw form. Even

after processing, they may well be of negligible value if the end

product is overwhelmingly voluminous, inadequately disseminated, or excessively delayed. To preclude these occurrences we routinely

perform statistical analyses of both the technology and the

engineering data. Condensed summaries are provided in a timely

fashion in both graphic and tabular form, using microfiche as the

distribution medium.

Pre-Processing

Digital magnetic tapes are generated at one of the Technology

Acquisition/ Display facilities. The digital data consist of 11

readings per parameter per (nominal) revolution and are stored as a tightly packed, randomly sequenced record. Each datum is

accompanied by an identifying tag. Time markers (to nearest

millisecond) are merged with the data.

As the first step, these data tapes are transferred to disk for

short term (i.e. days) storage on the LeRC main frame system.

During the transfer process, the internal representation is

transformed (in software) from ASCII to EBCDIC. The next step in

the processing compacts this initially large dataset (~ 5x10^ data

values + 5x10° tags + 1x10^ time markers) into a more manageable

form, as follows: The rotor shaft position is used to mark the

start of each rotation. These markers are then combined with the

associated time markers and processed to give rotor speed (rpm) as a

260
function of time. Then, the data from approximately 30 sensors of

general interest are screened to yield maximum and minimum values

for each parameter for each revolution of the rotor. This smaller

data set (~5xlo5data values) is stored on disk and is the data

base for all further processing.

Standard Analysis

In the final step, this latter data set is processed onto a microfiche containing the time history and statistical summary of

each parameter of general interest. While the specific set of sensors and their associated scale factors will vary from machine to

machine, the same presentation format is, nevertheless, applied to

all data from all machines. This entire process is shown

schematically in Figure 3.

The data, which have been stored as maximum and minimum values for

each revolution, are combined to represent the midpoint and cyclic

values for each revolution. The transformation eauations are:

midpoint = (maximum + minimum) / 2

and

cyclic = (maximum - minimum) / 2) x (1 + f(rpm))

where,

f(rpm) = 2xl0-5 (rpm) 2 .

The correction function, f(rpm), is introduced to compensate for the

consistent underestimation of cyclic values resulting from the data

sampling rate of 11 per (nominal) revolution.

The results of the analysis of each sensor are displayed as two

frames, one graphical and one tabular on the microfiche card. The

first of the two frames (see fig. 4) for each sensor contains three

graphs. On each graph there are two plots, one of the midpoint

values with circles as symbols and the other of the cyclic values

with diamonds as symbols. The three graphs are:

1. Time history. This graph summarizes the information in the

continuous trace associated with a strip chart recorder. One

plot is of the average, over 30 second intervals, of the midpoint values. The other plot is of the corresponding cyclic

values.

2. Partitioned distributions. 7 The abscissa for this graph is

the wind speed midpoint value as measured at the nacelle. These

wind speed values are used as the basis for sorting

corresponding data values of the sensor of interest. The data

values for the sensor of interest are grouped into subsets such

261
that for each subset all the sensor data values were obtained at

approximately the same measured wind speed. Then the data

values within each subset are separately ranked in ascending

order. We find the 16th and 84th percentile for each such

sequenced subset and display these percentiles as horizontal

tabs at the end of a vertical bar. We also estimate the

confidence interval (at the 0.95 level) for significant

differences of the median7 and display it as an interval

(denoted by the occurrences of a circle or diamond) on the same vertical bar. This entire process is performed separately for

the midpoint (circle) and cyclic (diamond) data values.

3. Cumulative distribution. This graph corresponds to a normal

distribution , i.e. the abscissa is in units of normalized

standard deviations and is segmented with tick marks and

labelled by percentiles. Such a graph has the characteristic

that if the plotted data have a normal (i.e. gaussian)

distribution, the plot will appear linear. For this graph the

entire set of all midpoint values is sequenced and plotted by

percentile. This process is repeated, separately, for the

cyclic values.

The second frame (see fig. 5) for each sensor presents two tables

listing all the plotted data points from both distributional plots.

Some additional related but non-plotted, data are also tabulated.

Because some of these present extreme values (i.e. maxima and

minima), these tabulated values must be addressed with caution as they might represent spurious noise.

III. Engineering Acguisitional/Display System

After the initial check-out, LeRC retains the responsibility to

monitor, analyze, understand and report on all the wind turbines

under our supervision . Since the Technology Acauisition/Display

System described above is too elaborate and expensive for long term

monitoring at each site we have identified a subset which we call

the Engineering Acauisition/Display System. This system is

installed in the control area of each wind turbine. This latter

facility provides on-line analog display on strip chart (8 channels

per wind turbine) and continuously records 48 signals (as 3 FM

multiplexes) plus time on 4 tracks of analog magnetic tape. The

analog magnetic tape record operates in either of two modes,

depending on local conditions and requirements. At some sites they

record until the tape is full (32 hours) and then automatically

rewind (10 minutes) and restart, erasing old data as new data are recoraed. At other sites the recorders operate for 96 hours (by

making 3 passes thru the tape using a total of 12 tracks) and then

262
automatically turn off. They remain off until the tape is replaced

and the unit is manually restarted. These analog tapes can be

played back onto strip charts at the site, and they can also be sent

to one of the Technology Acauisition/ Display facilities for further

processing of the data.

ACKNOWLEDGEMENTS

The author wishes to especially acknowledge the understanding of FM

data systems obtained from many conversations with Robert Wolf, who

technically managed the procurement and operation of the first of

the Signal Conditioning and the Technology Data Acauisition/Display

Systems described in this report. I also wish to acknowledge the

insights into wind turbine data interpretation provided by numerous

colleagues with particular thanks for the patience shown by Timothy

Richards, Richard Shaltens and Dr. David Spera.

263
REFERENCES

1. "Wind Energy Systems Program Summary," Raytheon Service Company,

DOE/CS/20097-01, 1980.

2. "Design and Operating Experience on the U.S. DOE Experimental

Mod-0 100 kW Wind Turbine," 3. C. Glasgow and A. G. Birchenough,

NASA TM-78915, 1978.

3. "Utility Operational Experience on the NASA/DOE Mod-OA 200 kW

Wind Turbine," J. C. Glasgow and W. H. Robbins, NASA TM-79084,

1979.

A. R. L. Puthoff, J. L. Collins and R. A. Wolf, "Installation and

Checkout of the DOE/NASA Mod-1 2000 kW Wind Turbine Generator,

NASA TM-81444, 1980.

5. "Mod-2 Wind Turbine System; Concept and Preliminary Design

Report," Boeing Engineering and Construction, NASA CR-159609,

1979.

6. "DOE/NASA Wind Turbine Data Acquisition System (Part 1:

Equipment)," EMR Data Systems, NASA CR-159779.

7. R. McGill, J. W. Tukey and W. A. Larsen, "Variations of Box

Plots," The American Statisticism, Vol. 32, No. 1, P. 12-16,

1978.

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TABLE II - INSTRUMENTATION LIST MOD-1 BOONE, NC AS OF 5 AUGUST 1980

*********************************************************

PARAMETER ****** SIGNAL ************ ENGINEERING ************

UNITS LOWER UPPER *UNITS LOWER UPPER **********************************************************************

ROTOR BNG IN RACE *MV +0.391 +5.28] * DEG F +50 +250

PITCH CHANGE BNG *MV -0.674 +3.967'* DEG F 0 +200

SPAN STRAIN 469 *MV -20 +20 *FT-LBS -4. 728 E5 4. 728 E5

SPAN STRAIN 390 *MV -10 + 10 * PSI -2. 8409E4 2. 8409E4

CB 907.5 *MV -10 + 10 *FT-LBS

CHORD STRAIN 390 *MV - 5 + 5 * PSI -5. 6818E4 5. 6818E4

DIAG STRAIN 469 *MV - 5 + 5 * PSI -5. 6818E4 5. 6818E4

FB 907.5 *MV -50 +50 *FT-LBS

SPAN STRAIN 482 *MV -20 +20 * PSI -1. 1364E5 1. 1364E5

CB 469 *MV -20 +20 *FT-LBS -2. 1561E6 2. 1561E6

HUB OUTSIDE BRL *MV -20 +20 * PSI -1. 1364E5 1. 1364E5

HUB INSIDE BRL *MV -20 +20 * PSI -1. 1364E5 1. 1364E5

HUB TAIL X BEND *MV -20 +20 *FT-LBS

HUB TAIL Y BEND *MV1*1 V -20 +20 *FT-LBS

PITCH T X 1 01 l ROD 1 \UU #1(T/C) 7* 1 \ I/O/ *MVl"l V -20 +20 *IN/IN All/ ±n -2. 5 E4 2. 5 E4

NOT USED * * FR 117 *MVl T

l V -50 0 + 50 0 *FT-LBS 1 1 1—UJ -1. 3967E7 1. 3967E7

CB 117 *MVl T

l V -20 +20 *FT-LBS -6. 4008E6 6. 4008E6

FR 469 *MVII V -50 + 50 * 1PSIji -1. 1364E5 1. 1364E5

FRr D Zl£9 HO/ rl V +sn *fTT_| DC 1 1 1 LJ _) -2. 7444E6 2. 7444E6

SPAN STRAIN 482 *MV - 5 + 5 * PSI -2. 8409E4 2. 8409E4

FB 117 *MV *FT-LBS

FB 907.5 *MV -50 +50 *FT-LBS -5. 4356E6 5. 4356E6

SPAN STRAIN 46 *MV -10 +10 * PSI -5. 6818E4 5. 6818E4

CB 907.5 *MV -10 + 10 *FT-LBS -2. 2338E6 2. 2338E6

SPAN STRAIN 299 *MV -10 +10 * PSI -1. 1364E5 1. 1364E5

CB 117 *MV -20 +20 *FT-LBS

CB 469 *MV -20 +20 * PSI -2. 8409E4 2. 8409E4

HUB INSIDE BRL *MV -20 +20 * PSI -1. 1364E5 1. 1364E5

HUB OUTSIDE TAIL *MV -20 +20 * PSI -1. 1364E5 1. 1364E5

SHAFT TORSION *MV -20 +20 *IN/IN -1. 0 E3 1. 0 E3

PITCH ROD #2(T/C) *MV - 5 + 5 *IN/IN -2. 5 E4 2. 5 E4

INLET OIL TEMP *MV -.674 +5. 283 * DEG F 0 + 250

SERVO OUT (TP 1) * v 0 +10 * RTR BNG OUT RACE *MV -3.91 +5.28] * DEG F +50 +250.5

TRANS LUBE TEMP *MV -.674 +5.281 * DEG F 0 + 250

266
INLET OIL TEMP *MV .391

GEARBOX FLANGE *MV -20

AIR TEMP (OUT) *MV -1.667

PITCH ROD DEC P * V 0

GEN BNG SHAFT END * V 0

GEN WINDING TEMP * V 0

AFT HORIZONTAL *MV -20

GEN SHAFT SPEED * V 0

PITCH ROD INC P * V 0

RTR BED VIB (Z) *MA -3.325

RTR BED VIB (Y) *MA -3.325

RTR BED VIB (X) *MA -3.325

BLADE PITCH ANGLE * V +6.54

RTR BED VIB (Z) *MA -3.325

FWD BED VIB (Y) *MA -3.325

SERVO OUT (TP 4) * V 0

YAW TORQUE CCW * V 0

YAW ERROR * V 0

BLADE PITCH ANGLE * V 0

WIND SPEED (NAC) * V +0.25

COVER FLANGE *MV -20

GEARBOX WEB *MV -20

RTR SHAFT POS * V 0

AFT 45° *MV -20

YAW TORQUE CW * V 0

AFT VERTICAL *MV -20

YAW POSITION * V 0

SERVO CURRENT * V 0

SOUND (5/27/80) * V -2.0

SOUND (5/27/80) * V -2.0

SOUND (5/27/80) * V -2.0

UTILITY VOLT EXP * V +7.2

GEN CURRENT A * V 0

GEN CURRENT B * V 0

GEN CURRENT C * V 0

TOW VIB SITE#1(X) *MA -3.325

TOW VIB SITE#2(X) *MA -3.325

EXCITER FLD CURR * V 0

NOT USED * —

NOT USED * —

UTILITY VOLT * V 0

NOT USED * —

NOT USED * —

NOT USED * TOW VIB SITE#1(Y) *MA -3.325

GEN PWR KVARS * V -10

GEN PWR WATTS * V -2.38

+5.281* DEG F 50 + 250

+20 *IN/IN -9.9E-4 +9.9E-4

+3.967* DEG F -50 +2001

+ 5 * PSI 0 +4000

+10 * DEG F -30 +300

+10 * DEG F -30 +300

+20 *IN/IN -9.9E-4 +9.9E-4

+10 * RPM 0 39.5

+ 5 * PSI 0 +4000

+3.325* G -2.5 +2.5

+3.325* G -2.5 +2.5

+3.325* G -2.5 +2.5

+9.11 * DEG +24.0 -4.2

+3.325* G -2.5 +2.5

+3.325* G -2.5 +2.5

+ 10 *

+ 5 * PSI 0 +4000

+10.0 * DEG -270 +270

10 * DEG +96.0 -14.0

+10.0 * MPH 2.5 100

+20 *IN/IN -9.9E-4 +9.9E-4

+20 *IN/IN -9.9E-4 +9.9E-4

+10 * DEG F 0 +360

+20 *IN/IN -9.9E-4 +9.9E-4

+ 5 * PSI 0 +4000

+20 *IN/IN -9.9E-4 +9.9E-4

+10 * DEG 0 + 360

+1.5 * +2.0 * PSF/db

+2.0 * PSF/db

+2.0 * PSF/db

+8.8 * KVOLT 3.78 4.62

+10.0 * AMPS 0 600

+10.0 * AMPS 0 600

+10.0 * AMPS 0 600

+3.325* G -2.5 +2.5

+3.325* G -2.5 +2.5

2.5 * AMPS 0 10

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* +10.0 * KVOLT 0 5.25

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* +3.325* G -2.5 +2.5

+10 * KVARS -4200 4200

+10 * KW -1050 4200

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267
TOW VIB SITE #1(Z) *MA -3.325 +3.325* G -2.5 +2.5

WIND SPEED 250' * V 0 5

* MPH 0 100

TOW VIB SITE #2(Z) *MA -3.325 +3.325* G -2.5 +2.5

ROTOR SHAFT SPEED * V -10 +10 * RPM 20.0 40.0

NOT USED "X"

k mT i #— i— i—

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WIND DIRECT 250' * V 0 5 * DEG 0 360

WIND DIRECT 150' * V 0 5 * DEG 0 360

WIND SPEED 60 * V 0 5 * MPH 0 100

TOW VIB SITE #2(,Y) *MA "7 ~7 o cr -3.325 +3.325* G -2.5 +2.5

WIND DIRECT 60 * V 0 5 * DEG 0 360

WIND SPEED 150' * V 0 5 * MPH 0 100

GEN PWR WATTS * V -10 + 10 * KW -3600 +3600

STRAIN 669

pTr|A TKI /"SI. STRAIN 664 *

Wfl ITTI— Ol— hi MHT n

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cr r~i -5.0 +5.0 * V -5.0 +5.0

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DIAG STRAIN 390 *MV - 5 + 5 * PS I -2.8409E4 2.8409E4

SPAN STRAIN 299 *MV -10 +10 * PSI -5.6818E4 5.6818E4

FWD BED VIB (X) *MA -3.325 +3.325* G -2.5 +2.5 *************************************************

268
Figure 1.

269
R. M. U. ^

WIND TURBINE 2 MULTIPLEXES

OF 16 CHANNELS

PER R.M. U.

UP TO 3 PER WIND

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6 SETS OF 16 DISCRIMINATORS

14 TRACK

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DATA VAN 32 K; DISK

ACQUISITION/DISPLAY

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1i

I

I (calibrate)

OVERALL ERROR

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LEWIS RESEARCH CENTER

Figure 2. - Schematic representation of the electronic data processing in the Technology Acquisition/Display Facility. Every device shown with graystipling can be controlled by the operator vis the computer console.

270
Figure 3. - Schematic representation of the data processing at the LeRC

main computer facility.

271
CLAYTON. NEW MEXICO MACHINE: MOD OA1 1980

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PERIODIC VIBRATION MONITORING AT THE

SYNTHANE COAL-GASIFICATION PILOT PLANT

J.T. McCabe

Manager, Fossil Energy Projects

Mechanical Technology Incorporated

968 Albany-Shaker Road

Latham, New York 12110

Abstract : Periodic vibration monitoring of mechanical equipment has

proven to be an effective early-detection method for identifying and

scheduling preventive maintenance. As a means of demonstrating this approach to the emerging U.S. synthetic fuel production industry, vibration monitoring was performed at the SYNTHANE pilot plant, one of several

coal-gasification facilities sponsored by the U.S. Department of Energy

(DOE). The procedures used in obtaining, analyzing and interpreting vibration data are described in this paper and, to provide a cost basis,

the level of effort required to obtain, process, and report the data is

given. The utility of the data as an aid to maintenance management in

the pilot plant is evaluated and extrapolated to predict the general use- fulness of periodic vibration monitoring as a data source for the management and operation of future, large, coal -conversion plants.

Key Words : Vibration monitoring; mechanical components; coal conversion;

SYNTHANE pilot plant.

Introduction : In order to assess the feasibility of various coal-conversion process technologies, several pilot plants have been developed under

U.S. DOE sponsorship. This paper discusses the data obtained by monitoring the vibrations of the mechanical equipment in one of these facilities, the SYNTHANE pilot plant. The transition from bench-scale apparatus to a virtually complete pilot plant has been made for the SYNTHANE

process; and, even though the pilot plant has been placed on mothball

status since January 1979, many of the initial complex uncertainties that

existed during the design of the plant in 1972 have been resolved and

recorded.

In early 1978, a DOE-sponsored program was undertaken to provide mechanical data for future large plants by evaluating the equipment used in the

SYNTHANE pilot plant. As part of this program, vibration measurements

were made on all major rotating and reciprocating equipment. The general

program coupled the analysis of vibration data with an analysis of maintenance history and a systems analysis of the entire plant [1]*.

*Numbers in brackets designate references at the end of this paper.

27k
This recorded information now constitutes a valuable part of the data

base that is available from the U.S. Coal Conversion Program. The coal

program is important to the U.S. because it deals with a domestic re- source that is critical to meeting national energy needs. The coal program is also important to the Mechanical Failures Prevention Group for

two reasons: 1) implementation of the proposed Federal Synthetic Fuels

Program will require large numbers of mechanical components in many commercial plants that are still to be built, and 2) the failure rate of

mechanical components operated in the predecessor pilot plant program

was alarmingly high.

Pilot Plant Background : SYNTHANE (Synthetic Methane ) is a high-Btu,

high-pressure, coal -gasification pilot plant, owned by the U.S. Government and located in South Park Township, Allegheny County, Pennsylvania.

SYNTHANE 's unique feature is its potential to gasify caking coals found

in the eastern section of the U.S. The heart of the process is the pretreater-gasifier , operating at about 1000 psia. The gasifier is an oxygen-blown, single-stage, fluidized-bed reactor which is preceded by a high-pressure, in-line, oxygen-fed, fluidized-bed pretreater.

The SYNTHANE process was developed by bench-scale experiments conducted

at the Pittsburgh Energy Research Center in 1965. The preliminary design for the 72-tons-of-coal -per-day pilot plant was made by M.W. Kellogg

Company in 1970, and the bid package was subsequently prepared by the

C-E Lummus Company. Rust Engineering Company constructed the plant,

which was turned over to C-E Lummus in August 1974 for start-up and

operation.

Operation of the SYNTHANE gasification pilot plant was officially inaugurated by Test Directive No. 1, issued from ERDA (now DOE) on June 9, 1976.

Figure 1 shows a schematic of the overall SYNTHANE process. Figure 2 shows the test periods, the equipment operating time per month and the

period during which vibration monitoring was performed.

An explosion occurred in the high-pressure boiler on September 21, 1978,

and, in January 1979, DOE directed the operating contractor to place the

plant in mothball status. As a consequence, equipment in functional

blocks downstream of the gas scrubbing and cooling section were never operated in the integrated mode.

Monitoring Objectives : SYNTHANE was the first U.S. coal -conversion plant

to investigate the plantwide use of vibration monitoring as a potential

data source for managing plant operations. The principal objective was

to demonstrate if vibration monitoring produced useful data in a costeffective manner, while contending with the uncertain schedule of the

pilot-plant test program. Specific objectives of the monitoring program

were to:

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t Establish initial tolerance tables relating vibration amplitudes to machine conditions.

• Demonstrate that an analysis of sequence of periodic vibration readings, referenced to the tolerance tables, provides

an accurate estimate of the present and future condition of

the equipment.

t Demonstrate that acquiring useful vibration data does not

necessitate access to the machine internals, but is possible from sensors mounted on the housing.

The Monitoring Procedure : Selection of the equipment to be monitored

was based on critical ity to the process, size, and frequency of use. Table 1 lists the 16 equipment trains selected for vibration monitoring

and provides an overall assessment of their repair history.

Metal discs for mounting sensors were cemented to the machine housing

and adjacent piping; vertical, horizontal and axial locations were chosen

near key elements, such as bearings, couplings and seals, and depending

upon accessibility and need. Vibration signals from both low-frequency

and high-frequency portable transducers were recorded on magnetic tape

for later analysis. The low-frequency transducers were the seismic type

where the voltage output was linearly proportional to frequency in the

range 15 to 1700 Hz. The high-frequency transducers were the piezoelectric type where the voltage output was linearly proportional to frequency

in the range 1 to 10 kHz. In addition to these transducers, a large number of unusual problems with the two carbon dioxide compressors prompted

plans to install the special diagnostic equipment, as listed on Table 2.

However, because the plant was unexpectedly shut down, this instrumentation was not installed.

A two-man team conducted surveys at monthly intervals while the equipment

was operating under normal load. The base-line signatures were recorded

in two days with subsequent data recorded at the rate of 30 to 40 data

points per hour. Each survey collected a total of 138 data points, and was executed by the team in less than one day.

Data Analysis : Two types of analysis were performed on the collected

data. The first was a severity analysis that provided the basic frequency/amplitude data to assess the present condition of the equipment

The second was a trend analysis that focused on changes in vibration

levels, as compared with the initial base-line measurements and subsequent readings.

Based on past experience with similar equipment, maintenance data

and the base-line signatures, tolerance tables for each machine were

formulated. Tables 3A, 3B and 3C represent a sample tolerance table

for a specific machine. Table 3A lists the conditions that must be

2?8
TABLE 1

LIST OF EQUIPMENT SELECTED FOR VIBRATION MONITORING

Assessment of Repair History

Secti on Descri ption

Item

Number

Major

Repair

Frequent

Repair

Normal

Maintenance

Coal Handling Drying Air Blower

Drying Fan

GB-101

GB-102

X

X

Char System Wilson - Snyder

Pump

GA-401S X

Filter Feed Pump

Filter Feed Puitid Spare

GA-406

GA-406S

X

X

X

X Vacuum Pump

Vacuum Pump Spare

GB-401X

GB-401XS

X

X

Gas Scrubbing

and Cooling

Venturi Scrubber

Recycle Pump

GA-207 X X

Venturi Scrubber

Recycle Pump

Spare

GA-207S X X

Scrubber Tower

Recycle Pump

GA-201 X X

Utilities Air Compressor

Air Compressor

Spare

GB-304

GB-304S

X

X

BFW High-Pressure

Pump

GA-303 X X

BFW High-Pressure

Pump Spare

GA-303S X

CO2 Compressor GB-301 X X CO2 Compressor

Spare

GB-301S X X

279
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TABLE 3A

SAMPLE TOLERANCE TABLE

Conditions To Be Satisfied Before Oata Table Is Printed

1 . All IX & 2X Synchronous Oata Code

• frequency equals shaft speed 2

2. Maximum Ampl i tudes

• Amplitude is ^ lowest severity desired 8

• Acceleration > lowest desired 16

3. Trends

• New ampl i tude/BL "Amp 1 i tude > 0.5 and 3L amplitude > 0.0785 in. /sec 32

• New amplitude/BL amplitude > 3.0 and 8L amplitude > 0.0196 in. /sec 64

• New amplitude/previous amplitude > 0.7 and previpus amplitude > 0.0785 in. /sec 128

• New amplitude/previous amplitude i, 2.0 and previous

ampl itude >, 0.0196 in. /sec 256

LOWEST SEVERITY DESIRED = 0.0392 in. /sec LOWEST ACCELERATION 0ESIRED = 1 g

Printed Oata

• Sensor position • Mils, peak-to-peak t Transducer type

• Frequency • Velpcity, in. /sec • Trigger code

t Shaft speed • Acceleration, g's • Oate of last observation

*8L = 9ase Hne; first readings of all sensors used as refsrence level for measuring changes and rate of change.

TABLE 33

SAMPLE TOLERANCE TABLE

Relationship Between Velocity Transducer Reading and Running Condition of Machine

Maximum Velocity

Index Lass than, in. /sec Running Condition

1 0.0049 Extremely smootn

2 0.0098 Very smooth

3 0.0196 Smooth

4 0.0392 Very good

5 0.0785 Good

6 0.1570 Fair

7 0.3H0 Slightly rough

8 0.6280 Rough

9 1 .2560 Very rough

10 > 1.2560 Extremely rough

TABLE 3C

SAMPLE TOLERANCE TABLE

Relationship Between Accelerometer Transducer Reading

and Running Condition of Machine

Maximum Acceleration

Index Running Condition

4 <0.6 Very good

5 >0.6 Good

6 >3.0 Fair

7 >6.5 Slightly rough

8 >10.0 Rough

9 >25.0 Very rough

10 >40.0 Extremely rough

281
satisfied before a data table is generated. Table 3B presents the relationship between the reduced velocity transducer signal and the machine

condition; Table 3C shows that same relationship for acceleration. A

computer code was used to search the data tape for amplitudes exceeding

the preset limits of the tolerance table. This code, together with

equipment drawings and repair records, was used to analyze present problems and to predict future conditions. Table 4 illustrates a generally

accepted correlation [3] between frequency ranges and vibration phenomena

the correlation is often used as a guide in this type of cause-and effect

analysis. Although vibration data acquisition and processing are key

elements, the real value of the results is heavily dependent upon the

skill and experience of the data analyst.

Reporting : After the field data were analyzed and recommendations were formulated, the following reporting steps were taken:

1. If the analysis indicated there was a reasonable probability that any machine was close to a catastrophic failure, the plant manager was notified by telephone and a confirmation telegram was transmitted.

2. A monthly report was issued containing:

• A one-page executive summary of problem machinery,

status, and recommended corrective action.

• Tables of severity and trend data for all machines

satisfying similar conditions to those given in

Table 3A.

• Computer-generated multicolor pen plots of selected

machines showing time-spaced trends in amplitude

versus frequency.

Results : During the initial plant survey in July 1978, sensor mounting

pads were installed and preliminary vibration measurements were made to assess the initial status of the equipment. Taped vibration data for

analysis were taken in August. In September, one week before plant operations were terminated by DOE, a second set of data was recorded.

Vibration monitoring results are presented in three forms: charts for

quick status assessment, specific recommendations for maintenance ac- tions, and reduced measured data giving quantitative status and trends.

Based on vibration data taken on September 13, 1978, Figure 3 shows the

relative need for maintenance by dividing the equipment into three

categories

• Components that are running satisfactorily

• Components that show a trend toward failure and are expected to need maintenance soon

282
TABLE 4

CORRELATION OF FREQUENCY RANGES WITH VIBRATION PHENOMENA

Frequency Cause Ampl i tude

Less than 1 x running

speed

Flexible critical speed

Oil whirl

Structural rp^onanrp^

from impact loading

Often severe

Often severe

D"F1"Pn Ul LcM cpwprp jcvci

Running speed Unbalance

Rotor-stator rubs under

some conditions

Proportional to

unbalance

Proportional to

unbal ance

2 x running speed Mechanical looseness

Bent shaft

Misaligned coupling

Nonlinearities

Drive belts

Often severe Often severe Often severe

Smal 1 May be 3 to 4 x run- ning speed

60, 120, 250, 360 Hz Electrical Generally small

High multiples of

running speed

Gear tooth passing

frequency

Blade pass frequency

Generally small

Often severe

2,000 to 10,000 Hz

random noise

Gas or liquid

turbul ence Aerodynamic noise dueto high Reynolds No.

2,000 to 50,000 Hz

discrete frequencies,

often amplitude

modulated

Rubs, damaged rollingelement bearings

Often severe

283

• Components that show a critical problem and need maintenance now.

In Figure 3, the components are designated by the item numbers given in

Table 1. Machines that are running satisfactorily are at the base of

the pyramid, while the machine with the highest maintenance priority is

in the block at the top of the pyramid. The pyramid format is used to

permit quick review by plant management. Thus, components that reappear

at the top of these monthly charts would be highlighted as troublesome

items so as to alert management of the need to seek corrective action.

Of the 17 components surveyed, Figure 3 shows that 9 components, or 53%, were running satisfactorily, 6 components, or 35%, were in need of scheduled maintenance and 2 components, or 12%, were in need of immediate

attention.

In addition to qualitative data for plant management, analysis of the

vibration data (given in detail in Reference [2]) produced recommendations for specific maintenance actions. These recommendations are re- peated here because they are believed to be representative of the type

of guidance that can be expected from periodic vibration monitoring.

1 . Components Believed to Warrant Immediate Corrective Action :

• Boiler feedwater pump GA-303 near catastrophic failure; recommend immediate shutdown. Mass unbalance

of high-speed rotors, bearing damage and seal deterioration suspected.*

• Coal drying system fan GB-102 has excessive unbalance;

recommend balancing as soon as possible. Replacement

of drive belts and realignment of sheaves recommended.**

2. Components Believed to Warrant Scheduled Maintenance

• Boiler feedwater pump GA-303S motor rotor out of balance; recommend cleaning and balancing.

• Hammer mill PA-102 motor either misaligned with mill

sheave or mounting bolts loose; recommend inspection

of belt/sheave alignment and check mounting bolt

torque.

3. Components Believed to Have Developing Problems; However,

Corrective Action Is not Currently Recommended

• Venturi Scrubber Water Recycle Pump GA-207 believed to

have unbalanced impeller. Some degradation of pump

bearing and misalignment of motor to pump suspected.

inspection showed broken gear tooth and bearing damage.

**Inspection showed fan blades bent from water accumulation in fan

housing.

285
• Venturi Scrubber Water Recycle Pump GA-207S and

Scrubber Tower Water Recycle Pump GA-201 believed

to have unbalanced impellers.

The above results imply that the role of vibration monitoring in a pilot

plant clearly can be a significant benefit in maintaining mechanical

equipment. As a decision-making tool for management, vibration monitoring is a simple and cost-effective source of quantitative data on the

condition of machines.

Vibration Monitoring for the Future Synthetic Fuels Program : The development of new processes in the petrochemical industry often proceeds

through trials that address a succession of key technical and economic

issues. The scope of these trials might include bench-scale tests,

followed by small pilot-plant tests, and, in turn, large pilot-plant

tests. At this point, if test data meet preset goals, a pioneer plant

is built that completes the economic forecast and demonstrates any re- maining question of scale-up. The equivalent DOE program steps generally

include bench-scale testing, pilot-plant testing and demonstration-plant

testing. At the end of this sequence, DOE, through various economic

incentives, expects to entice industry to commercialize the technology.

During all phases of plant testing, effort should be focused on the

mechanical equipment so as to produce the data needed to formulate a detailed mechanical failure prevention plan for the commercial plant.

The SYNTHANE process was evaluated through bench-scale and pilot-plant

tests. Sufficient data were collected to permit DOE to conclude that

the SYNTHANE process was not as promising as other process options;

consequently, DOE currently does not plan to scale-up this process.

However, the magnitude of managing future equipment problems can be

sensed from other processes that are in advanced development stages.

One of these, the Solvent Refined Coal Process (SRC II) demo project,

is directed at converting coal to liquid; it is one of five different

coal -conversion technology demonstration plants being funded simultaneously by DOE. The 6000-ton-per-day (TPD) SCR II demo plant is expected

to cost $1.4 billion when full operation is reached in late 1984. The

current SCR II project will demonstrate one full-size train of a planned commercial plant that will consist of five identical trains. The

five-train commercial SCR II plant is designed to process 30,000 TPD of

coal and produce 100,000 barrels of oil equivalent per day (B0E/D).

Since the current National Energy Plan calls for producing about 2 million B0E/D from coal by 1990, the equivalent of 20 SRC II commercial

plants will be required if this goal is to be met. Placing this goal

in a machinery perspective, consider the following preliminary estimate

of the compressor needed for a single SCR II train:

286
COMPRESSORS FOR ONE TRAIN OF SCR II PLANT

Fl ow

(scfm)

Suction

Pressure

Discharge

Pressure

Gas (psia) (Psia) Horsepower

Air 220,000

Hydrogen 80,000

Hydrogen Recycle 180,000

Oxygen 40,000

Nitrogen 20,000

15

1,100

2,300

15

5

110

2,500

2,500

1,500

300

44,000

8,500

1 ,200

22,000

7,000

In addition to the fact that all of these compressors will be large and

costly, the oxygen compressor presents a unique problem because there is

a lack of commercial experience at these high-pressure and high-flow

rates.

In some respects, the magnitude of the equipment requirements for an SRC II commercial plant is similar to the SASOL 2 coal -conversion plant

in South Africa, which cost $3 billion to design and construct. This

plant, which occupies an area 2.5 km by 3.5 km, consumes coal at the rate

of 40,000 TPD and produces 58,000 bbl/D of transportation fuels. In con- structing this plant, 186,000 tons of steel were erected, 120 km of

underground pipe were laid, 66,000 valves were fitted and 6100 items of

equipment were installed [4]. As an example of the size of some of the

machinery, the 15,000-TPD, 500-psia oxygen plant uses six 200-ton axialcentrifugal air compressors; each is driven by a 73-ton synchronous motor

rated at 35,500 kW. Oxygen from the air separation plant is compressed

to the delivery pressure by six 27-ton centrifugal compressors; each is

driven by a 21 -ton induction motor rated at 13,700 kW. As one measure of

similarity between SASOL 2 and the proposed U.S. SRC II commercial plant,

both plants require 192-MW electrical input to drive the air compressors

for their oxygen plants.

SASOL I, the first coal -conversion plant built in South Africa, has

accumulated more than 20 years of commercial operating experience. During the five-year period following construction of this plant, the process was refined and many pieces of equipment were modified. Operating

and maintenance procedures were established and SASOL I became the pio- neer plant for SASOL 2 and SASOL 3. The U.S. is about to embark on a similar venture, probably using several different conversion technologies, some of which may be at high pressure compared to SASOL. If the U.S.

Synthetic Fuels Program plant proceeds on schedule, plant availability

assurance is certain to be a priority topic. As a part of this topic,

vibration monitoring can help to provide a controlling handle on the

complex problem of dealing with large numbers of components. This emerging field offers the Mechanical Failures Prevention Group a unique opportunity to contribute toward organizing and executing the plans that will

be necessary to make this undertaking successful.

287
' Summary : The analysis of vibration data can often clarify the present

conditions of a dynamic component. Each piece of equipment has unique

signature frequencies; changes in amplitude and slight shifts in frequencies can frequently be correlated with the onset of specific, identifiable problems. Early trouble signs can often be detected by periodic

measurements made by transducers mounted on the machine housing; because

the majority of mechanical problems develop slowly, adequate time is

usually available to plan corrections. Electronic hardware and computer

codes for analyzing the cause of trouble signs are readily available,

and the scope of their capabilities is increasing steadily. The cost of

vibration monitoring and data analysis is low, and this procedure is an effective means of acquiring quantitative data to manage the maintenance

of dynamic equipment.

The vibration monitoring performed on the equipment used in the SYNTHANE

plant produced useful and important information that otherwise would not

have been available to plant personnel. Analysis of the data produced a concise list of machine problems, weighted according to relative urgency

and accompanied by specific recommendations for corrective action.

The U.S. Synthetic Fuels Program will involve plants that are large in

comparison to the SYNTHANE pilot plant, and these plants will require

effective maintenance if a reasonable overall plant availability goal is

to be met. An attractive attribute of the vibration monitoring program

demonstrated in the SYNTHANE pilot plant is that this approach can be

scaled-up to meet the demands of the Synthetic Fuels Program without

significant loss in simplicity or utility. While most components can be

monitored satisfactorily on a periodic basis, some equipment may require

dedicated diagnostic systems until sufficient data can be gathered to

determine how to make these special components more serviceable. In any

case, the monitoring results demonstrated at SYNTHANE indicate that the

burden of operating the new generation of coal-conversion plants in a cost-effective manner will be greatly enhanced by incorporating a vibration monitoring program in the initial operating plan for these facilities .

References:

1. McCabe, J.T.; Kramberger, F.E.; Hao, B.R.; Dubis, D. ; Carson, S.E.;

"An Assessment of SYNTHANE Mechanical Equipment," MTI Report No.

79TR5, for the U.S. DOE, Contract DE-AT21-77MC02615, Task 6, May 1980.

2. Rickert, B., "Periodic Vibration Monitoring of Mechanical Equipment

at the SYNTHANE Pilot Plant," MTI Interim Report 2615-6-1, Contract

EF-77-C-01-2615, September 1978.

3. Machinery Vibration Seminar Course Notes by Mechanical Technology

Incorporated, June 1980.

4. "Synthetic Fuel the SASOL Way," Engineering and Mining Journal,

December 1979, pp. 54-60.

288
DESCRIPTION OF "LA RANCE" TIDAL POWER PLANT

. USE OF THE PLANT

. ANTICIPATION, DETECTION AND IDENTIFICATION

OF ELECTROMECHANICAL EQUIPMENT FAULTS

Jean RABAUD

Electromechanical Division

Water Power Production Department

Electricite de France

3, rue de Messine

75008 PARIS - FRANCE

1. - DESCRIPTION OF PLANT

1.1 - Introduction to the plant

Before showing you a film in English on the Ranee plant, and

especially its design features, I must point out that it has

become very difficult to say anything really original on the

subject. People have been writing about tidal machinery since

the year 1737 (a French Army engineer called BELIDOR), about

tidal electricity production since 1918 (MAYNARD) and about the

La Ranee site in particular since 1944 (GIBRAT). Also, La Ranee

is still the only tidal power plant in the world, at least for

the time being.

For additional general design details, therefore. I will refer

to an extensive bibliography, part of which is in English. For

particularly interesting technical features, I will quote from

articles by or conversations with Mr. ROUX, Mr.JULLIARD and other

successive managers of the plant, Mr. LEFRANCOIS and Mr .HILLAIRET,

chief power production executives for Brittany, and Mr. ANDRE,

Mr. COTILLON and Mr. BANAL and technicians of equipment manufacturers and E.D.F. who have been most active in circulating full

information on the technology tried out at La Ranee in English.

289
1.2 - Other bulb units

The bulb units at La Ranee are derived from similar units which

have been operating satisfactorily elsewhere, both before and

since La Ranee. Table 1 shows some statistics for these units.

I also thought you might be interested in seeing a descriptive

film on the technology and installation of the turbines at one

of these plants (Pierre Benite on the river Rhone) at a later

session

.

2 - USE OF "LA RANCE" PLANT

2.1 - Principles

A) The two following major principles should be borne in mind :

a) Electricity cannot be stored permanently . Producers have to

adapt the use of their production facilities to consumer's

requirements

.

b) Tides are not governed by the solar cycle on which most human

activities depend, but follow the lunar cycle . In France, two

tides at approximately 12 l/'Z hour intervals are observed.

The peak equinoctial spring tide amplitude at La Ranee is

13.5 m

.

B) The basic principle of harnessing tidal energy consists in

aamming-o77" one or more areas from the sea to form storage ponds

and thus obtain a difference in water levels across a barrage

containing the power plant.

The diagrams in Table 2 illustrate the one-way and two-way

cycles - with and without pumping - to which tidal power plant

operates. La Ranee, which has a single storage basin, is designed for use of all cycles.

C) The next consideration is to match the available facilities

as closely as possible to power system requirements (cost per

marginal kW) and tidal potential.

For this, a computer program is prepared from tide table data,

the energy cost histogram and both operating conditions and

limitations (environment, plant and equipment, power system).

It operates by dynamic programming on a CII 9040 computer,

optimizing the power unit and gate-operating conditions in

10-minute steps, and of course, over several tides (usually a week's tides).

290
The results are fed into an automatic plant-operating unit

(PDP 8) which applies all marginal corrections according to the

actual tide, or if limitations or requirements vary. The operator in charge takes over manually if such variations become

excessive. In this connection, you may be interested to know

that the simulations show pumping to be a more attractive proposition than two-way operation.

A further point to note is that, assuming constant cost, total

availability of plant and equipment and no pumping limitations,

tidal output may vary in proportions of 1 to 18, for a neap tide

on*J an equinoctial spring tide respectively, which is within

conventional hydrology dispersion limits.

D) Just as a reminder , the plant is equipped with twenty-four

10 MW bulb units each capable of discharging 250 M /s, with

5.35 m-diameter runners at 93.75 r.p.m. Peak natural flow is

16,000 M

3/s.

2.2 - Operating results

A) Water-power plant operation can be organized to maximalize one

of the following :

a) Production

b) Scope for emergency compensating action for power system

failures

c) Income (a function of varying production cost), by determining the maximum value for :

. Q . H . p . dt

where : n = number of units in service

= efficiency (see efficiency curves) : f (Q,H)

Q = rate of flow through each unit : f (H)

H = level difference

p = cost of energy at time t : f (t)

291
It was decided to run La Ranee for maximum profit, which explains

why -as we are frequently asked- the plant has been generally

operating at below its full production capacity (the estimated

deficit is rou ghly 60 GWh).

I will now illustrate the operating results with a few tables.

B) Gross and net production (Table 3)

The difference is accounted for by the pumping operation I mentioned earlier on, which was suspended to avoid premature ageing

of the generators (see para. 3.2) and gradually resumed in step

with preventive maintenance.

C) Availabili ty of uni ts (Table 4)

Note the excellent, gradually increasing availability rate before preventive renovation of the equipment. A rate of 95 %

corresponds to ave rage annual availability of twenty-three of

the twenty-four units. Since 1976, this average rate has been

reduced to twenty units out of the twenty-four ( three units

under renovation plus one under maintenance).

D) Number of boats through the lock (Table 5)

This is not an operating result, but together with the amount

of automobile traffic over the bridge, it provides a convincing

illustration of how well the plant fits in with its environment.

A marina opened in 1976 temporarily slowed-down the upward trend

of boat transits.

Incidentally, half the annual transits take place in July and

August

.

E) Costs (Table 6)

These figures are accountancy data corrected by application of

the gross internal product index.

Note the increase in operating costs since preventive maintenance

and its low value (23 %) in relation to the total cost, a major

proportion of which is accounted for by financial costs.

292
3. - ANTICIPATION, DETECTION AND

IDENTIFICATION OF FAULTS

3.1 - General remarks

We now come to a brief description of a few problems experienced

at La Ranee, with some examples of our Service's electrical and

mechanical equipment maintenance policy.

The La Ranee plant is one of four hundred and forty-nine waterpower plants run by E.D.F. Though certainly one of the most

famous of these, it is only the sixteenth in order of out put.

Its total output is 1,800 MW, with an annual productivity of

roughly 58,000 GWh . My purpose in stating this is not so much

to emphasize that we are the biggest water-power company in the

world (of which we are of course very proud !), but rather to demonstrate the degree of interaction of the system .

Whenever a major problem arises or is solved at one of the 448

other power plants, someone starts thinking about how it might

apply to La Ranee, that is to say in the form of a risk, an improvement, or possible profit for example. Whenever there is a major

problem at La Ranee, or one is solved, the information is transmitted in the reverse direction. No single power plant maintenance

system can be considered independently of trie others .

As a second preliminary comment, we have developed a planned inspection and maintenance procedure (MECEP) which is based on the

philosophy that overall preventive inspection aimed at anticipating the probable behaviour of plant and equipment so as to be

able to prepare for maintenance at an acceptable time is wiser

than having to deal with unexpected trouble. In other words, we

would rather pay for preventive medicine for water-power plant

equipment and structures than for remedial surgery. In this, I believe we differ considerably from our colleagues in this country.

My third and final remark before the examples is that dismantling

conditions at La Ranee (and for submerged horizontal units in

general) differ appreciably from those for conventional low-head

vertical units. While the major turbine components - e.g. blades,

faired nose-cap - are more conveniently accessible (in roughly

one-third of the time) on bulb units and subject to a few precautions, all medium-size components can be removed through the

access shaft. The generator stator on the other hand is much more

difficult to get at and takes five times as long to dismantle.

293
To fully appreciate the importance of this remark, one must have

witnessed a scheduled inspection and seen how plant operators react

if a single drop of seawater has found its way inside a unit : very

much like a competent mechanic seeing a drop of oil leaking from

a powerful motor he has just reassembled.

3.2 - Special study of problems experienced with the electromecha - nical equipment at La Ranee

A) Before going any further, I think we should bear in mind that

the equipment at La Ranee has behaved very satisfactorily on

the whole, as shown by the operating results quoted in para.

2.2. Standing before this 'assembled court' of technicians,

however, I feel that an objective description of some of the

problems we have had to deal with on various items of equipment can hardly be out of place.

B) Marine corrosion

Considering that we are just by the ocean I do not think

I need waste words in explaining our misgivings as regards

corrosive seawater action on the plant equipment.

In our efforts to reduce this to a minimum, we relied on careful

design, a suitable choice of materials, effective coatings and

linings and provision of an applied-current cathodic protection

system. Here, I will simply say that the latter was remarkably

designed and has been eminently successful in operation.

Here are a few figures :

Each unit is protected by 36 anodes, each gate by 4 anodes and

the lock by 6 anodes. Tantalum anodes are provided throughout,

with a 50 m m platinum surface coating (for a consumption rate

of lOjum in 30 years). Potential is maintained2at roughly 300

to 1,200 mV, for a current density of 170 mA/m of protected

surface area. The overall annua^energy requirement for the

system is 130,000 kWh and a 1 cm anode area protects an unpointed metal surface area of 1.5 m2.

C) Gates

With paint as their only protection, the gates initially suffered a certain amount of corrosion, especially as the paintwork

was vulnerable to damage by flotsam. Installation of the cathodic protection system was completed in 1972, since then all we can say about the gates is "nothing to report".

29k
D) Turbines

D.l Guide-vanes

Overtightness of the self-lubricated plastic bearing shells

on initial assembly caused a few problems, but these were very

soon put right.

D.2 Resistance to cavitation

No significant indications of cavitation were observed on the

throat ring and blades after 100,000 hours under water, including 80,000 hours in operation.

The absence of blade damage can no doubt be attributed to the

use of cupro-aluminium and 17/4 (17 % Cr, 4 % Ni) stainlesssteel for these components.

D.3 Runner blade leakage

Serious runner blade problems were experienced, with water penetrating through the seals and mixing with the turbine oil after

a certain amount of seal wear. The trouble was remedied by increasing the internal turbine oil pressure and fitting annular

or herringbone-pattern seals of a carefully-selected material.

D.4 Labyrinths

The labyrinths, wetted with seawater from which all sediment

has been settled out, are in excellent condition, which is quite

surprising after fourteen years of service. They do not show

any signs of abrasion, cavitation damage or corrosion ; the only

signs of service are a few tiny mussels clinging fast at the

bottom of cavities, which probably helps to reduce leakage. A

good thing for production !

D.5 Shaft seals

Some trouble was experienced initially with the shaft seals, in

the form of abnormal wear of the fourth sealing ring (a carbon

ring like two of the others ; the last ring is of high-resistance polyethylene). Decisive modifications consisted in improving lubrification and increasing the seal bearing pressure

against the wearing component. Thirty-two different schemes were

tried out.

From 1976 onwards, signs of severe corrosion damage were observed on operating components inadequately covered by the cathodic system. We are trying to solve the problem by improving the

cathodic system layout.

29'5
D.6 Couplings

These will be discussed in para. 3.3. later on as they come under

the general category of high-capacity bolted assemblies which

have been the subject of very detailed study by our Service.

E) Generators

E.l Iron circuit

On January 1st 1975, a serious incident caused the stator of a unit to foul the rotor. Subsequent inspection of the unit and a thorough 'post-mortem' showed a design fault to have been responsible, a minor component having been insufficiently dimensioned

for the winding stresses and repeated loads on the iron circuit

caused by 500 startups and 7500 asynchronous couplings. To prevent further similar trouble, the most severe cycles were eliminated and a preventive renovation schedule was put into effect,

covering three machines yearly. It was intended to apply this

procedure from 1975 to 1983, but thanks to satisfactory services

from certain manufacturers, we will now be able to end it by the

beginning of 1982. There was also some trouble with the iron circuit clamping and securing arrangements.

E.2 Stator

Insulation measurements at regular intervals occasionally produced comparatively low values after several days at a standstill. This was attributed to the fact that the only access to

the turbine runner is through the generator. Appropriate shielding has now been installed to protect the insulation from

'micro-damage', but for our new designs, we will try to provide

direct access to the runner from the downstream end.

E.3 Damping bars

The first case of rotor damping-bar damage, in the form of severe

electro-erosion, was observed at one of our other power stations.

Inspection of the units at La Ranee showed several poles to have

been affected. This trouble was remedied by modifying the bar

distribution, reducing tolerances, and by argon-welding and caulking the bars secure in position.

E.4 Brushgear

Slipring and brush performance was unsatisfactory at the start,

with wear as high as 10 mm per 1000 hours in some cases. Many

different types and makes of brush were tried, but the drastic

296
improvement was obtained by enclosing the sliprings in a separate

compartment accessible for inspection and under depression to

eliminate dust. The brushes which were finally adopted are char*-

ged with silver.

The units at La Ranee unfortunately could not be provided with

static excitation as this type of system did not come into use in

France until three years after the plant was commissioned.

E.5 Pressurization system

Pressurization at 2 bars absolute assists the heat-exchange processes taking place in the unit (heat-exchange being proportional

to the specific mass of air). An output of 10 MW is obtained,

whereas it would be limited to 7 MW in atmospheric air. No problems have been experienced with this equipment.

F)Preliminary conclusions

The so-called 'series effect 1 does not apply to water-power equipment. La Ranee must be one of the very few examples in the world

of a plant equipped with more than ten similar units. Successful

results obtained from one unit can therefore be generalized for

twenty-three units, but unfortunately, the same also applies to

unfortunate incidents on a single unit.

3.3 - Examples of anticipation, detection and identification expe - rience for mechanical equipment at EPF water-power plants

A) As Table 7 shows, most of the effects observed at La Ranee can be

generalized to apply to the 220 bulb units we are operating. Many

of these effects can also be extrapolated to the 1,500 units of

all types operating at EDF water-power stations. However, reverting to your particular subject of interest, I will now explain

our maintenance policies for a few examples of unitary, similar

and strictly repetitive equipment.

B) Strictly repetitive equipment

B.l Circuit-breakers

Many circuit-breakers operate in power plant which is frequently

put into and out of service in order to follow the system load

curve, but are only required to deal with low current. Thus, although the breaker chamber is operating well within design limits, the operating mechanism and mechanical components in general

have to withstand very severe conditions.

297
The policy of EDF, therefore, has been to define a preventive

accelerated-ageing test which, of course, includes critical breaking conditions, but also a series of 10,000 breaker operations.

Each new breaker design has to pass this test before it can be

accepted for use in the EDF power system.

B. 2 Hydraulic operating controls

These are mainly used for gate and turbine blading operation.

Here again, and in addition to strict dimensioning rules, we specify preventive approval tests. Solenoid valves for example are

tested especially for their ability to operate after prolonged

service and without voltage. For safety operations, systematic

use is made of electric distributors with wi thout-voltage operated pilot valves.

C) Similar equipment

Potentially-destructive prototype tests cannot be envisaged for

this type of equipment.

C. l Generator iron circuits

From our unfortunate iron circuit trouble experience and with the

assistance of our usual suppliers of equipment, we have established a few rules which we consider to be essential. They apply to

design (monolithic character, clamping and securing arrangements),

and in addition, to manufacture (cutting-out and deburring of laminations, insulation) and to assembly and installation (intermediate stack-compression, acceptance tests).

C.2 Pelton turbines

Pelton buckets are subjected to superimposed vibration and impact

stresses, which can only be determined by telemeasurements on the

actual unit. Knowing these stresses and the maximum safe number

of impacts without trouble from fatigue or fatigue failure, and

since tests in air have been found to be representative, the

following action was possible in each case :

a) Preventive maintenance on runners in service

b) Correct dimensioning of new runners.

Specially-designed, closely-adjusted vibration detectors are provided to give warning of abnormal operation.

298
D) Unitary equipment

Such items of equipment all differ from each other. Experience can yield no more than design principles, to which one can also add

general supervision methods.

D.l Couplings

This brings us back to a problem experienced at La Ranee and with

bulb units in general.

Heavy rotating components overhung on a horizontal shaft require

assembling by means of studs and nuts 70 mm to 100 m in diameter

and of short length compared to their diameter. The studs are

subjected to severe cyclic stresses during rotation. Correct stud

tightness is achieved by the following :

a) Machining the nut bearing surfaces, ensuring they are truly

perpendicular to the stud centerlines.

b) selecting more elastic steel for the stud than for the nut.

c) Tapered extruded threads radiused at the bottom.

d) Maximum possible shank length between threaded portions,

thinner than the latter with a transition radius to the

thread diameter.

e) Tightening by controlled elongation of the stud under heat

or using a jack.

A very rigourous method as been made up with help of makers.

Here again, the vibration pickups give warning of abnormal conditions.

D.2 Transformers

The transformers are monitored during operation by periodic cinematography of dissolved gas in the oil. Faults are identifiable by

the type of gas they produce. By this preventive measure the consequences of transformer faults at French water-power stations were

reduced to roughly one-fifth in eight years. Single major faults

are located by a system using ultrasonic waves emitted by partial

discharges.

£99
E) Preli minary conclusions

I hope I have not bored you with this long enumeration, but as any specialist will agree, there are many more items that

I could have mentioned, such as dielectric strength measurements

on generators for example.

In giving you these examples, I wanted to show you our general

policy for the generally heterogeneous equipment that we operate

day in, day out for 24 hours on end (or 25 hours if possible !)

for 365 days of the year (sometimes 366 or 367 days).

Instead of 'detection, identification, anticipation 1 , we prefer

a policy in the following order :

1) Anticipation or prevention based on experience gradually

acquired with closely-related, similar or identical machines,

relating to design, acceptance tests, and checks required in

service

2) Detection with the aid of carefully adjusted overall protection systems checked at regular intervals and each designed

to respond to a variety of causes.

3) Identification (and repairs), also based on experience acquired by plant operators and in repair shops.

3.4 - Final conclusions

A) Regarding La Ranee and tidal plant in general, we consider that,

with present experience, it should be possible to avoid the hazards normally associated with new forms of energy, but that one

should also be careful not to expect too much from tidal energy at

the present stage.

There is a limit to the amount of power that can be produced from

tides, the structures at a tidal power site are of a size which

will require very substantial capital investment, and their geographical extension is such that their effect on the environment will

concern far more people than is the case for other forms of power

plant.

Even though it is by no means certain that present technological

progress is sufficient to ensure immediate cost-effectiveness of

tidal energy in France, it seems highly probable that it will

compare favorably with other forms of modulable energy in the fu300
ture. The cost price for assumed implementation in 1980 o^ a project by methods applied in 1960 would amount to 1.45 x 10 French

Finally, from our own experience , we would unhesitatingly opt for

bulb units (as we do for river plant) for a potential new French

power plant for which we are presently engaged in effective preliminary development studies.

In particular, one should compare the cost of the additional

complication of a two-way unit also operating as a pump with the

additional return obtainable from this type of operation. If the

comparison showed a one-way unit to be preferable, one would no doubt be well advised to set the unit at a higher elevation.

B) As I have already mentioned, we prefer, 1 anticipation, detection, identification' to 'detection, diagnosis prevention'.

However, I also said that our system is based on an exchange of

experience and information. To conclude, therefore, I would like

to add that this system includes the following :

a) A 'non-availability' card-index system compiled by local

plant operators, the data of which is processed at a central

station, the results being used for information, locating

similar cases and later on, compiling statistics.

b) Generalized personal contacts and meetings to discuss and

analyze points of individual concern and problems, thus

providing information from which a few specialists can establish a 'doctrine' of instructions and principles.

The main effects of this are as follows :

. Repetitive equipment : Systematization of preliminary

and representative prototype tests.

. Unitary equipment : Availability of a list of attempted

solutions. Practically systematic location of similar or

closely-related cases.

301
Orientation of technical or technological action and justi

fication for investment : Subsequent application of statis

tics based on operating results from a large number of

power stations.

302
TABLE 1

STATISTICAL DATA FOR BULB UNITS

OPERATING IN FRANCE

1. 'Micro' bulb units (up

Number in operation

Individual output

Average output

Head

Rated discharge

Runner diameter

When commissioned

2. Other bulb units (over

Number in operation

Individual output

Average output

Head

Rated discharge

Runner diameter

When commissioned

Note for reference :

Rock Island bulb units

output

diameter

head

to 1.5 MW)

: about 120

: 38 kW to 1,400 kW

: 490 kW

: 1.5 m to 17.4 m

: 1.9 m

3/s to 39 m

3/s

: 630 mm to 3,000 mm

: between 1954 and 1979

2 MW)

about 100

5 MW to 40 MW

21 MW

3.4 m to 16.5 m 38 m

3/s to 410 m3/s

2,500 mm to 6,900 mm between 1957 and 1979

54 MW

7.4 m 12.1 m

303
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308
TABLE 7

GENERALIZATION OF PROBLEMS EXPERIENCED WITH

ELECTRICAL AND MECHANICAL EQUIPMENT AT LA RANCE

Problem Problem

Affected Problem specific specific generally

enui Dme n t to to V-a O O U -L. \J U — ^—

La Ranee bulb units with

water-power

equipment

Corrosion X

i

(none)

Gq te s

i X (none) vA AY

Turbines : Guide vanes X (initially) X X Cavitation vA , none

)

X X

Blade leaks X .initially) X X

Labyrinths X . none) X X

Shaft seals X >yes) X X

Cou pli ng s X ^initially) X X

Generators : Iron circuits X 1 Jyes) X

Stator X ( initially) X X

Damping bars X ( ^initially) X

Brushgear X (

( yes) X X

Pressurization x ( none) X system

Other equipment not mentioned above : no major problems.

309
DETECTION, DIAGNOSIS AND PROGNOSIS IN

GEOTHERMAL WELL TECHNOLOGY

A. F. Veneruso and Hsi-Tien Chang

Geothermal Technology Division 4742

Sandia National Laboratories

Albuquerque, NM 87185

Abstract: For successful and safe operation of a geothermal

well, the condition of the casing and cement must be accurately determined. Measurements on casing wall thickness,

corrosion damage, holes, cracks, splits, etc., are needed to

assess casing integrity. Cement bond logs are needed to detect channels or water pockets in cement behind pipe and to

determine the state of the cement bond to the pipe and formation. Instrumentation for making such measurements is

limited by the temperature capabilities (<175°C) of existing

logging equipment developed for the oil and gas industry.

This paper reviews the instruments that are needed for geothermal casing and cementing inspection, identifies the

principal deficiencies in their high temperature use, and

describes Sandia's upgrade research program on multi-arm

caliper and acoustic cement bond logging tool. The key electronic section in a multi-arm caliper will consist of 275°C

circuits designed by Sandia. In an acoustic cement bond logging tool, a simple circuit with possibilities of using commercially available components for high temperature operation is being developed. These new tools will be field

tested for operation at a minimum temperature of 275°C and

pressure of 7000 psi for up to 1000 hours.

Key words: Casing inspection; cement bond logging tool;

geothermal technology.

Introduction: Downhole conditions very often cause casing

and cementing problems in geothermal wells as illustrated in

Figure 1. Proper engineering development and production of

a geothermal field requires periodic inspection and evaluation of the wellbore's casing and cementation. According to

a recent study by Knutson and Boardman (1978) , the most common tools for assessing casing integrity are spinner surveys,

radioactive tracer surveys, electromagnetic surveys, and

calipers. The logs commonly used to evaluate cement bond

are temperature logs, nuclear cement logs, noise, and acoustic cement bond logs (CBL)

.

310
CROSSFLOW, CEMENT WASHED OUT OR DISSOLVED BY WATER FLOW

LOST CIRCULATION ZONE , POOR MUD DISPLACEMENT BY CEMENT

INTERNAL PITTING BY HOT BRINE w/ACID GASES

SCALE FORMATION AT DIAMETER

CHANGE

SCALE FORMATION AT WATER

FLASH POINT

Figure 1 Casing

Well

and Cementing Problems in a Geothermal

A spinner-type flowmeter responds to and locates fluid flow

through holes in the casing. Fluid leakage sometimes also

causes temperature anomalies, A differential temperature

log describes the slope of the absolute temperature curve

and is capable of pinpointing these anomalies even though

they may be minute. Sandia National Laboratories has developed prototypes of the flow tool and the temperature tool

for operation up to 275°C. (Veneruso, 1979). All the component parts for these tools will soon become commercially

avai lable

.

Radioactive tracer surveys are useful in locating casing

leaks by logging the movement of injected tracers. These

surveys are very useful in detecting low flow rate leaks.

Commercially available downhole electromagnetic surveys utilize a coil for generating a magnetic field. The phase

changes detected by the receiving coil are related to the

casing wall thickness. If the inner diameter is known (this

can be measured by a caliper) , then the electromagnetic surveys will reveal the outer diameter's condition and thereby

indicate the extent of pipe wear and corrosion.

311
Caliper tools have multiple expanding arms that make contact

with the casing walls. The diamter recorded is that of a circle described by the tips of the arms. The caliper log

is useful in analyzing corrosion damage, scale buildup, collapsed and parted casing, and casing breaks.

In oil and gas wells, a temperature log is also used to detect the cement top when the hydrating cement undergoes an

exothermic reaction that provides a temperature anomaly.

Unfortunately, temperature anomalies are common in geothermal wells, and therefore, the interpretation of cement tops

is ambiguous. Also, this log must be run while the cement

is reacting because afterward thermal equalibrium is

achieved and no information can be obtained about the position of cured cement behind the pipe.

The nuclear cement log functions as a modified density log.

If there is a density contrast between the cement and the

mud or fluid being displaced by the cement, the log provides

an estimate of the amount of cement fill at any position in

the well by indicating the material density.

The noise log is a display of high frequency sound being produced at any vertical location in the wellbore. An evaluation of this log can pinpoint areas in a well where fluid

flow channels occur behind the pipe.

The acoustic CB1 tool determines the quality and extent of

the physical bond between the casing pipe and the surrounding cement sheath, and between the cement and formation.

This log measures the amplitude of the acoustic signals from

the casing pipe and the amplitude of a later arrival which

reflects the cement bound to the formation.

There are currently no commercially available high temperature cement bond and casing integrity logging systems for

geothermal wells with maximum temperatures in excess of

275°C. Most commercial logging tools become unreliable

above 175°C in actual field tests. As a consequence, operators must cool the well in order to run surveys. The thermal shock in cooling could cause well damage. Also, loss in

production time is expensive. Therefore, high temperature

logging capabilities are needed for rapid development of geothermal energy.

Sandia's R§D objective is to develop and commercialize high

temperature tools for operation up to 275°C. The technology

must be adaptable to the industry to stimulate the development of a large enough market such that commercial suppliers

and logging companies can provide the required hardware ser312
vices on a routine basis. Although the tools described

above all provide information on casing and cementing conditions, the multi-arm caliper and acoustic CBL tool are the

most versatile and widely used tools in the field. For this

reason, we select them as our first set of tools for upgrading.

Table 1 summarizes casing and cementing inspection tools,

their limitations in geothermal applications , and the recommended upgrading procedures. The following section will describe the upgrade procedures on a multi-arm caliper and an

acoustic CBL tool in more detail.

Sandia's Upgrade Research Program: 1. Multi-arm Caliper - The casing caliper utilizes a single conductor cable plus

ground for all power and data transmission. This is accomplished through a multiplexer built into the tool's electronics. The tool uses potentiometers that convert the motion of mechanical arms into electronic signals that are

proportional to the casing pipe's inside dimensions. In

general, commercially available calipers are specified for

operation up to 175°C, because of the temperature limitations

of their electronic circuits, DC motors and dynamic seals.

Therefore, we propose to use high - temperature - rated linear

or rotary displacement transducers (LTDs or RDTsJ , if high

temperature potentiometers cannot be found. As shown in

Figure 2, the tool's electronics will consist of a high temperature vol tage- to- frequency converter, pulse stretcher,

line driver, voltage regulator and a multiplexer. These

275°C circuits were designed by Sandia and will be manufactured by Teledyne and General Electric-Houston. Additional

R§D may be necessary to develop the high temperature DC

motor that is used to retract the caliper's mechanical arms.

In addition, high temperature elastomeric seals or metal

bellows may be required to prevent brine from entering the

tool's electronic and motor housing compartment.

2. Acoustic CBL Tool - Figure 3 illustrates the cement bond

sonde and the related signals. Casing suspended freely,

i.e., uncemented, in a well transmits sound energy with relatively little weakening of the vibrations between the transmitter and receiver. However, when hardened cement is behind the casing and when this cement is properly bonded to

the pipe and formation, the vibrations sent out from the

tool to the casing will impart similar motion in the cement

but at a lower velocity. From the strength and the time of

the vibrations received, one can determine the degree of

cement bonding. A recording of the free pipe is presented

on each log as a reference for evaluating the other signals

(Figure 4). In the variable density log, strong casing signal and weak formation signal is an indication of free pipe.

313
TABLE 1 TOOLS COMMONLY USED FOR CASING INSPECTION AND

CEMENT BOND EVALUATION

Tools Geothermal Limitations Upgrade Recommendations

Casing Inspection

None - Technology is

availab le

None - only field test verif i cat i on Spinner Survey

Radioactive

Tracer

Operating Temperature

<175°C

Possible Environmental

T TTin 3 c t

Design high temperature

c i rcui t

Electromagnetic

Tool

Operating Temperature

<175°C

Redesign circuits using. high

temperature electronics

Cal ipe r Operating Temperature

<175°C

Use high temperature electronics

Select high temperature dynamic

seals

Develop high temperature motor

Or use mechanical design to

eliminate motor and thus the

need of dynamic seals

Cement Bond

Evaluation

Temperature Tool None - Technology is

avai lable

Mainly for locating

cement top and

major void

Extend into a differential

temperature logging tool

for casing inspection

Nuclear CBL Tool Operating Temperature

<175°C

Possible Environmental

Impact

Develop high temperature

op amp and detector

Noise Tool Subject to Operator's

Interpretat ion

Operating Temperature

not crucial (not

being used in

production wells)

Acoustic CBL Tool Electronics limited to <175°C

Develop high temperature SCR

Replace circuit with high

temperature electronics

31k
UPHOLE ELECTRONICS

DOWNHOLE ELECTRONICS

UPHOLE

POWER PROCESSING

LINE DRIVER

MUTI PLEXER

RELAY CIRCUIT

MOTOR

LIMIT SW. T

FEELER' ARM

VOLT/

REGU1

^GE .ATOR

POWER CIRCUIT

PULSE STRETCHER HVOLTAGE TO FREQUENCY CONVERTER

-H TRANSDUCER

< C^^IH

CASING

Figure 2. Block Diagram for a Caliper

TRANSMITTER

RECEIVERA

' ^—CASING

CEMENT

SHEATH

-SIGNAL

PATH

^j- FORMATION

|CASING|FORMATION| TIME IN MICROSECONDS PER FOOT

0 50 100 150 200

CASING SIGNAL HAS HIGH AMPLITUDE

IN UNCEMENTED SECTION. FORMATION

SIGNAL IS VERY LOW.

LOW AMPLITUDE CASING SIGNAL AND FORMATION SIGNAL SHOWS POOR BOND

CASING SIGNAL IS LOW SHOWING GOOD BOND TO CEMENT. FORMATION SIGNAL

HAS HIGH AMPLITUDE SHOWING GOOD

BOND BETWEEN CEMENT AND FORMATION. Figure 3. Cement Bond Sonde and Acoustic Signal

315
A well bonded casing with good cement-to-formation bond. will

show strong formation signal and weak casing signal.

Some of the commercial CBL tools contain very complex electronic circuits. These systems use many sensors and require

complex circuitry in order to provide precise clocking time

and signal transmission under a wide variety of conditions

in oil and gas wells. However, it is extremely difficult to

upgrade a sophisticated circuit for high temperature operation since most commercial electronics are specified for

operation only up to 175°C. Therefore, a simplified CBL circuit is essential before any upgrading can take place. In

an acoustic CBL tool for operation in geothermal fluid, a single transmitter and a single receiver with adequate spatial separation should provide sufficient information about

cement bond conditions in the well. Also, in order to minimize the downhole electronics, signal processing and data

reduction will be done uphole.

Figure 5 is an example of a straightforward circuit that is

capable of generating a short high voltage, high current

pulse for an acoustic transmitter at room temperature.

Here , C\ is used to supply energy to the SCR switch and the

acoustic transmitter when the line driver cuts off input

power. Lx is used to boost the voltage at C]_ . When the SCR

conducts, Li, L2 , and C2 prevent the ripples from feeding

back to the input. To provide a reference for the returned

signal, the input line detects the transmitting time through

C4 . Ri , R2 , and C5 limit the imposed voltage on the unijunction transistor which will not be triggered until the

capacitor C3 is sufficiently charged. Thus, the R3 C3 time

constant will determine the firing frequency of the SCR.

Transformer T sharpens and boosts the amplitude of the trigger pulse to the SCR. On Figure 5 we have not specified

component values because their values would be different

for different acoustic transducers and temperature ranges.

We are currently working to develop a high temperature version of this circuit.

Commercial SCRs (Semiconductor Controlled Rectifiers) rated

at 175°C or lower place a limitation on a tool's operating

temperature. We have initiated a project to upgrade the SCR

for operation at 275°C. It is expected that the theory and

optimal f abricat ional approach will be determined by September 1981 and a "GaP" or "GaAs" SCR will be ready in prototype

by October 1982. We are also exploring the possibility of

combining a thermoelectric cooler with an SCR in order to

run the unit in an ambient of 275°C while the temperature of

the SCR chip is only 175°C. Commercial vacuum tubes, such

as sprytrons and thyratrons , are other possibilities that

316
0% AMPLITUDE 100%

100* BOND 0% VARIABLE DENSITY LOG TIME, ys —

LOW AMPLITUDE

CASING SIGNAL

(POOR BOND)

STRONG CASING SIGNAL

(ALMOST FREE PIPE)-

STRONG FORMATION

SIGNAL

WEAK CASING SIGNAL

(WELL BONDED CASING

WITH GOOD CEMENTTO- FORMAT I ON BOND)

(!) 1

mm!! M

I! m

Figure 4

mm

Acoustic Cement Bond Log

INPUT

LINE C,

UNIJUNCTION

TRANSISTOR

'

r

SCR ACOUSTIC TRANSDUCER

1

Figure 5. Cement Bond Transmitter Schematic

317
might be used as a substitute for an SCR. In these options,

the shortcoming is in the limited number of shots that can

be guaranteed; we are investigating the possibility of modifying a tube's design for longer life time.

Return signals at the receiver must be amplified so that

they can be detectable uphole. Specially selected commercial junction field effect transistors (JFETs) can withstand

high temperature and will be considered. Another possibility is the electronic tubes. Although, an electronic tube

amplifier may operate stably only up to 250°C as reported by

Cannon (1979), development of integrated thermionic circuits

has resulted in a much higher operating temperature (McCormick and Wilde, 1980). In addition, Harris Semiconductor

Corp. is working under contract with Sandia to develop a high- temper ature operational amplifier (Ohr, 1980). Other

commercial products that may be used to upgrade a tool for

geothermal application are summarized in Table 2. For a step-by-step 275°C fabrication technology, one may refer to

a report by Bonn and Palmer (1980).

Summary: In this report, we describe a project to upgrade a multi-arm caliper and an acoustic cement bond logging tool

for operation at a minimum temperatue of 275°C and pressure

of 7000 psi for up to 1000 hours. The commercially available materials and devices, and the electronic components

developed by Sandia National Laboratories for high temperature operation will be fabricated and field tested in partnership with industry. The final stage of this project is

to commercialize the design and transfer the technology to

industry

.

318
TABLE 2 MAXIMUM OPERATING TEMPERATURE FOR SOME

COMMERCIAL PRODUCTS

Company

Caddock Electronics

Cermal loy

Philips (MEPCO)

Custom Electronics

Sprague

Cermal loy

General Magnetics

Permalust re

Hy-Temp Transducers

Cermalloy

DuPont

Abies t i ck

I tern

Maximum

Temperature

Res is tors

Thick Film Chips

Thick Film Inks

Capacitors

Solid Aluminum Electrolytic

High Voltage

Thin Film Si02

Thick Film Inks

Trans formers

Transformers

Conductors

Anodized Aluminum Wire

Ceramic Coated Copper Wire

Conductor Inks

Solder

High Temperature Paste

Epoxy

Conductor or Dielectric

500°C

500°C

300°C

300°C

300°C

500°C

500°C

500°C

500°C

300°C

300°C

300°C

Motorola

DuPont

Tekform

3M

Transistors

JTET

P. C. Board

Poly imide

Packages

Metal Packages

Ceramic Packages

300 °C

300°C

350°C

350°C

319
REFERENCES

Bonn, P. A. and Palmer, D. W. , "275°C Thick Film Hybrid

Microcircuit ry Fabrication Technology," Sandia National

Laboratories, SAND80-0078, 1980, available through NTIS,

U.S. Department of Commerce, 5285 Port Royal Road,

Springfield, VA 22161.

Cannon, W. L. , "Ultra High Temperature Instrumentation

Amplifier," System Development Corporation, Santa Monica,

California. TM- (L) - 6158/006/00 , 1980.

Knutson, C. K. and Boardman, C. R. , "An Assessment of

Non - Des t rue t i ve Testing of Well Casing, Cement and

Cement Bond in High Temperature Wells," GeoEnergy Corporation, Las Vegas, Nevada, 1978.

McCormick, J. B. and Wilde, D. , "Development of Integrated Thermionic Circuits for High-Temperature Applications," High Temperature Electronics and Instrumentation

Seminar Proceedings, Sandia National Laboratories,

SAND80-0834C, p. 73-75, 1980. Available from NTIS, U.S.

Department of Commerce, 5285 Port Royal Road, Springfield, VA 22161.

Ohr, S., Analog Circuit Editor, "Dielectrically Isolated

Op Amps and Comparators Take High Temperatures," Electronic Design 9, p. 38-40, 1980.

Veneruso, A. F., "High Temperature Electronics for Geothermal Energy," IEEE Circuits and Systems Magazine , Vol. 1, No. 3, p. 11-17, 1979.

320
APPENDIX

MECHANICAL FAILURES PREVENTION GROUP

DETECTION, DIAGNOSIS AND PROGNOSIS:

CONTRIBUTION TO THE ENERGY CHALLENGE

32nd MEETING

October 7-9, 1980

ATTENDANCE LIST

R. W. Adams on Andy Callahan

California Polytechnic Endevco

Mechanical Engineering Dept. 2^172 McCoy

San Luis Ooispo, CA 93^07 El Toro, CA 92630

John J. Aloi

Power Authority of the State of

New York

P.O. Box 5309 Woolsey Station

Long Island City, NY 11105

John Anderson

Spectral Dynamics

P.O. Box 152

Parsippany, NJ 0705^

F. E. Bishop

Pall International Corporation

30 Sea Cliff Avenue

Glen Cove, NY 115^2

David B. Board

SKF Industries, Inc.

1100 First Avenue

King of Prussia, PA 19^06

Thomas J. Bullock

Colt Industries Operating Corp.

701 Lawton Avenue

Beloit, WI 535H

Harry C. Burnett

Metallurgy Division

National Bureau of Standards

Washington, DC 2023^

Ron Canada

Technology for Energy Corporation

10770 Dutchtown Road

Knoxville, TN 37922

Tom Carlson

Exxon Company, USA

3^00 East 2nd Street

Benecia, CA 9^510

Edward G. Carpenter

Jet Propulsion Laboratory

4800 Oak Grove Drive

Pasadena, CA 917^5

Michael E. Cohill

ManTech International Corporation

23^1 S. Jefferson Davis Highway

Arlington, VA 22202

Raymond A. Coulomhe

Naval Ship Engineering Center

National Center h, Code 6l468

Washington, DC 20362

Martin J. Devine

General Technology

2560 Prescott Road

Havertown, PA 19083

323
Francois Envent

ManTech International Corporation

23^1 S. Jefferson Davis Highway

Arlington, VA 22202

Daniel Fairchild

FRAM Corporation of Bendix

105 Pawtucket Avenue

East Providence, RI 029l6

Jack L. Frarey

Shaker Research Corporation

Northway 10, Executive Park

Ballston Lake, NY 12019

Alfred Genot

S.E.M.T.-Pielstick

2, Quai de Seine

93202 Saint-Denis, France

John A. George

Parks College of St. Louis

University

Cahokia, IL 62206

Steve Goldman

Nicolet Scientific Corporation

2^5 Livingston Street

Northvalt, NJ O76U7

G. E. Gulbrandsen

Philadelphia Manufacturers Mutual

Insurance Company

8 Executive Mall - Box Q2h

Valley Forge, PA 19^82

Henry R. Hegner

ManTech International Corporation

23^1 S. Jefferson Davis Highway

Arlington, VA 22202

Wsewolod Hnatczuk

Department of the Army, TARACOM

DRDTA-RGD

Warren, MI U8090

Rudy Hohenberg

Mechanical Technology, Inc.

968 Albany /Shaker Road

Latham, NY 12110

Robert R. Holden

Hughes Aircraft Company

P.O. Box 90515, Bldg. 117, MS 1

Los Angeles, CA 90009

Tom Houlihan

Propulsion Dynamics

2200 Somerville Road

Annapolis, MD 2lU6l

Paul Howard

Energy & Minerals Research Company

96U E. Swedesford Road, P.O. Box 389

Exton, PA 193U1

Gordon Jones

FRAM Corporation of Bendix

105 Pawtucket Avenue

East Providence, RI 029l6

Gerald A. Lamping

Southwest Research Institute

6220 Culebra Road

San Antonio, TX 7828I+

Richard Lee

U.S. Army, JOAP-TSC

Building 780

Pensacola NAS , FL 32508

Robert Leon

Franklin Research Center

20th and Parkway

Philadelphia, PA 19103

J. T. 'McCabe

Mechanical Technology, Inc.

968 Albany/Shaker Road

Latham, NY 12110

R. M. McCord

United Technologies Corporation

P.O. Box 2691

West Palm Beach, FL 33^02

W. R. McWhirter

David Taylor Naval Ship R&D

Center

Code 2731

Annapolis, MD 21^02

32l+
Raymond F. Misialek

Department of the Navy

Philadelphia, PA 19112

S. Paul Mohan

Exxon Chemical, Olefines Plant

P.O. Box 100

Baytown, TX 77520

Angelo Muzi

RCA Corporation

P.O. Box 588, MS 20-1

Burlington, MA 01803

Alan Napier

SKF Industries

1100 First Avenue

King of Prussia, PA 19I+06

Harold E. Neustadter

NASA-Lewis Research Center

Wind Energy Project Office

Cleveland, OH UU135

Patrick Norris

Boyce Engineering International

10555 Rockley

Houston, TX 77099

Paul Olivier

Garrett Corporation

P.O. Box 7217

Phoenix, AZ 85OIO

Hernan Otano

National Air and Space Museum

6th and Independence Avenue, NW

Washington, DC 20560

Marshall Peterson

Wear Sciences, Inc.

925 Mallard Circle

Arnold, MD 21012

James L. Pettigrew

United States Air Force

P.O.B. 33563, AMC Branch, ASD/YZE

Wright Patterson AFB, OH k^h33

Jerry Philips

David Taylor Naval Ship R&D

Center

Code 2832 DTNSRDC

Annapolis, MD 21^02

Kenneth R. Piety

Technology for Energy Corporati

10770 Dutchtown Road

Knoxville, TN 37922

Cecil Preston

Canadian Pacific, Ltd.

Windsor Station

Montreal, Quebec H3C 3EU

Jean Rabaud

Electricite de France

3 Rue de Messine 75008

Paris, France

Neil P. Ruzic

Island for Science, Inc.

P.O. Box 527

Beverly Shores, IN U6301

Henry M. Salisbury

Sperry Vickers AMD Division

5353 Highland Drive

Jackson, MS 39206

Richard Salter

Rand Corporation

1700 Main Street

Santa Monica, CA 90^06

Don Schover

GARD Incorporated

7^9 Natchez Avenue

Niles, IL 606U8

Cyrus M. Smith

Oak Ridge National Laboratory

P.O. Box X

Oak Ridge, TN 37830

Kempton Smith

General Electric Company

1 River Road (Bldg. h, Rm. 210)

Schenectady, NY 123^5

325
Ross K. Smith

Hughes Aircraft Company

Box 90515, Bldg. Ill, M/S 12

Los Angeles, CA 90009

Ernest F. Spano

U. S. Army Aviation Center

Attn: ATZQ-DI-S/S (Oil Analysis

Section

Fort Rucker, AL 36362

Leo L # Stavinoha

Southwest Research Institute

6220 Culebra, P.O. Drawer 285IO

San Antonio, TX 78281+

F. J. Sweeny

Oak Ridge National Laboratory

P.O. Box X, Bldg. 3500

Oak Ridge, TN 37830

Thomas Tauter

Technical Development Company

2k East Glenolden Avenue

Glenolden, PA 19036

Tony Veneruso

Sandia Laboratories

Division klk2, P.O. Box 58OO

Alberquerque, NM 87185

Harry P. Wertheimer

Bendix Autolite Corporation

1600 N. Union Street, P.O. Box 880

Fostoria, OH U83O

Al Whittaker

Honeywell, Inc., MS-MN 173657

2600 Ridgeway Parkway

Minneapolis, MN 55^13

Robert M. Whittier

Endevco Corporation

Rancho Viejo Road

San Juan Capistrano, CA 92675

James P. Wright

ManTech International Corporation

5336 West Rose crans Avenue

Lawndale, CA 90260

326
MFPG PUBLICATIONS

Both printed and microfiche copies of the following MFPG publications

(1-12) whose catalog numbers start with "AD" or "COM" may "be obtained

from the NTIS.

National Technical Information Service

5285 Port Royal Road

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1. Glossary of Terms AD 721 35 1*

2. Proceedings of Meeting Nos. 1-9 (set of 5) AD 721 359

Meeting Nos. 1-5 Papers and discussion on failure

analysis and control.

"Detection, Diagnosis and Prognosis,"

December 6, 1968.

"Failure Mechanisms as Identified

with Helicopter Transmissions,"

March 27, 1969.

"Critical Failure Problem Areas in

the Aircraft Gas Turbine Engine,"

June 25-26, 1969.

"Potential for Reduction of Mechanical

Failure through Design Methodology,"

November 5-6, 1969.

3. Proceedings of Meeting No. 10 AD 721 912

"Vibration Analysis Systems"

January 21-22, 1970

k. Proceedings of Meeting No. 11 AD 72^ ^75

"Failure Mechanisms: Fatigue"

April 7-8, 1970

5. Proceedings of Meeting No. 12 AD 721 913

"Identification and Prevention of Mechanical

Failures in Internal Combustion Engines"

July 8-9, 1970

Meeting No. 6

Meeting No. 7

Meeting No. 8

Meeting No. 9

327
6. Proceedings of Meeting No. 13 AD 12k 637

"Standards as a Design Tool in Surface

Specification for Mechanical Components

and Structures"

October 19-20, 1970

7. Proceedings of Meeting No. ik AD 721 355

"Advances in Decision-Making Processes

in Detection, Diagnosis and Prognosis"

January 25-26, 1971

8. Proceedings of Meeting No. 15 AD 725 200

"Failure Mechanisms: Corrosion"

April lk-15, 1971

9. Proceedings of Meeting No. l6 AD 738 855

"Mechanical Failure Prevention through

Lubri eating Oil Analysis"

November 2-h , 1971

10. Proceedings of Meeting No. 17 AD 750 kll

"Effects of Environment upon Mechanical

Failures, Mechanisms and Detection"

April 25-27, 1972

11. Proceedings of Meeting No. 18 AD 772 082

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November 8-10, 1972

12. Proceedings of Meeting No. 19 (NBS SP 39*0 C0M-7 i+-50523

"The Role of Cavitation in Mechanical

Failures"

October 31 - November 2, 1973

Printed copies of the following MFPG publications (catalog numbers

starting with SN) may be obtained from the U. S. Government Printing

Office.

Superintendent of Documents

U. S. Government Printing Office

Washington, DC 20^02

13. Proceedings of Meeting No. 20 (NBS SP k23) . . . SN003-003-01U51-6

"Mechanical Failure - Definition of

the Problem"

May 8-10, 19lh

Cost: $6.10

328
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"Success by Design: Progress through

Failure Analysis"

November 7-8, 197^

Cost: $3-50

15. Proceedings of Meeting No. 22 (NBS SP ^36) . . . SN003-003-01556-3

"Detection, Diagnosis and Prognosis"

April 23-25, 1975

Coat: $U , 25

16. Proceedings of Meeting No. 23 (NBS SP ^52) . . . SN003-003-0166U-1

"The Role of Coatings in the Prevention

of Mechanical Failures"

October 29-31, 1975

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17. Proceedings of Meeting No. 2h (NBS SP 1+68) . . . SN003-003-01760-1+

"Prevention of Failures in Coal

Conversion Systems"

April 21-21+ , 1976

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22. Proceedings of Meeting No. 29 (NBS SP 563) . . . SN003-003-02120-2

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May 23-25, 1979

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329
23. Proceedings of Meeting No. 30 (NBS SP 58U

)

"Joint Conference on Measurements and

Standards for Recycled Oil/Systems

Performance and Durability"

October 23-26, 1979

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2k. Proceedings of Meeting No. 31

"Failure Prevention in Ground Transportation

Systems"

April 22-21+ , 1980

In Press

330

ir US. GOVERNMENT PRINTING OFFICE : 1981 O—340-997 (1821)
NBS-114A (REV. 2-8C) U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET (See instructions)

l^PUBLICATION OR

"'REPORT NO. NBS SP 622

2. Performing Organ. Report No 3. Publication Date

October 1981

4. TITLE AND SUBTITLE

Detection, Diagnosis and Prognosis: Contribution to the Energy Challenge

Proceedings of the 32nd Meeting of the Mechanical Failures Prevention Group,

Held at the Inn at Santa Monica, Santa Monica, CA, October 7-9, 1980

5. AUTHOR(S)

T. Robert Shives and William A. Willard, Editors

6. PERFORMING ORGANIZATION (If joint or other than NBS. see instructions) 7. Contract/Grant No. NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE 8. Type of Report & Period Covered

WASHINGTON, D.C. 20234 Final

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City, State, ZIP)

NBS; Office of Naval Research, Dept. of the Navy, Arlington, VA 22217;

Naval Air Systems Command, Washington, DC 20360; National Aeronautics & Space

Admin., Goddard Space Flight Center, Greenbelt, MD 20771

10. SUPPLEMENTARY NOTES

Library of Congress Catalog Card Number: 81-600125

2] Document describes a computer program; SF-185, FlPS Software Summary, is attached. H. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here)

These proceedings consist of a group of 21 submitted entries (19 papers and

2 abstracts) from the 32nd meeting of the Mechanical Failures Prevention Group

which was held at the Inn at Santa Monica, Santa Monica, CA, October 7-9, 1980.

The subject of the symposium was the contribution of failure detection, diagnosis

and prognosis to the energy challenge. Areas of special emphasis included

energy management, techniques for failure detection in energy related systems,

improved prognostic techniques for energy related systems, and opportunities for

detection, diagnosis and prognosis in the energy field.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolon s) Energy; energy conservation; failure detection; failure diagnosis;

failure prevention; monitoring techniques; prognosis; sensors; wear; wear analysis.

13. AVAILABILITY

r^~J Unlimited

P~1 For Official Distribution. Do Not Release to NTIS

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14. NO. OF

PRINTED PAGES

329

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NBS Interagency Reports (NBSIR)—A special series of interim or

final reports on work performed by NBS for outside sponsors

(both government and non-government). In general, initial dis- tribution is handled by the sponsor; public distribution is by the National Technical Information Services, Springfield, VA 22161,

in paper copy or microfiche form.
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