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ROOT CAUSE FAILURE
ANALYSIS
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P
LANT
E
NGINEERING
M
AINTENANCE
S
ERIES
Vibration Fundamentals
R. Keith Mobley
Root Cause Failure Analysis
R. Keith Mobley
Maintenance Fundamentals
R. Keith Mobley
20 | MOBLEY.FM Page iii Wednesday, March 3, 1999 2:29 PM
ROOT CAUSE FAILURE
ANALYSIS
R. Keith Mobley
Boston Oxford Auckland Johannesburg Melbourne New Delhi
20 | MOBLEY.FM Page iv Wednesday, March 3, 1999 2:29 PM
Newnes is an imprint of Butterworth–Heinemann.
Copyright © 1999 by Butterworth–Heinemann
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prints its books on acid-free paper whenever possible.
Library of Congress Cataloging-in-Publication Data
Mobley, R. Keith, 1943-
Root cause failure analysis / by R. Keith Mobley.
p. cm. — (Plant engineering maintenance series)
Includes index.
ISBN 0-7506-7158-0 (alk. paper)
1. Plant maintenance. 2. System failures (Engineering)
I. Title. II. Series.
TS192.M625 1999
658.2’02—dc21 98-32097
CIP
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Printed in the United States of America
Part I THEORY: INTRODUCTION
TO VIBRATION ANALYSIS 1
Chapter 1 INTRODUCTION 2
Chapter 2 VIBRATION
Chapter 3 VIBRATION
Chapter 4 VIBRATION
Chapter 5 VIBRATION
Chapter 6 MACHINE
Chapter 7 VIBRATION DATA
Chapter 9 ANALYSIS
ANALYSIS APPLICATIONS 3
ANALYSIS OVERVIEW 6
SOURCES 13
THEORY 17
DYNAMICS 26
TYPES AND FORMATS 42
Chapter 8 DATA ACQUISITION 49
TECHNIQUES 60
Part II FREQUENCY-DOMAIN
VIBRATION ANALYSIS 65
Chapter 10 OVERVIEW 66
Chapter 11 MACHINE-TRAIN
Chapter 12 DATABASE
Chapter 13 VIBRATION DATA
Chapter 14 TRENDING
Chapter 15 FAILURE-MODE
MONITORING PARAMETERS 71
DEVELOPMENT 97
ACQUISITION 112
ANALYSIS 125
ANALYSIS 138
Chapter 16 SIGNATURE
ANALYSIS 181
Chapter 17 ROOT-CAUSE
ANALYSIS 189
Part III RESONANCE AND
CRITICAL SPEED ANALYSIS 200
Chapter 18 INTRODUCTION 201
Chapter 19 TYPES OF
Chapter 20 EXAMPLES OF
Chapter 21 TESTING FOR
RESONANCE 202
RESONANCE 208
RESONANCE 213
Chapter 22 MODE SHAPE 222
Part IV REAL-TIME ANALYSIS 224
Chapter 23 OVERVIEW 225
Chapter 25 DATA
Chapter 27 TRANSIENT
Chapter 28 SYNCHRONOUS
Chapter 30 TORSIONAL
Chapter 24 APPLICATIONS 230
ACQUISITION 235
Chapter 26 ANALYSIS SETUP 246
(WATERFALL) ANALYSIS 255
TIME AVERAGING 259
Chapter 29 ZOOM ANALYSIS 265
ANALYSIS 267
GLOSSARY 286
LIST OF ABBREVIATIONS 291
INDEX 293
01.Mobley.1-6 Page 1 Friday, February 5, 1999 9:44 AM
Part I
THEORY: INTRODUCTION TO
VIBRATION ANALYSIS
Part I is an introduction to vibration analysis that covers basic vibration theory. All
mechanical equipment in motion generates a vibration profile, or signature, that
reflects its operating condition. This is true regardless of speed or whether the mode
of operation is rotation, reciprocation, or linear motion. Vibration analysis is applica-
ble to all mechanical equipment, although a common—yet invalid—assumption is
that it is limited to simple rotating machinery with running speeds above 600 revolu-
tions per minute (rpm). Vibration profile analysis is a useful tool for predictive main-
tenance, diagnostics, and many other uses.
1
01.Mobley.1-6 Page 2 Friday, February 5, 1999 9:44 AM
Chapter 1
INTRODUCTION
Several predictive maintenance techniques are used to monitor and analyze critical
machines, equipment, and systems in a typical plant. These include vibration analysis,
ultrasonics, thermography, tribology, process monitoring, visual inspection, and other
nondestructive analysis techniques. Of these techniques, vibration analysis is the
dominant predictive maintenance technique used with maintenance management pro-
grams.
Predictive maintenance has become synonymous with monitoring vibration character-
istics of rotating machinery to detect budding problems and to head off catastrophic
failure. However, vibration analysis does not provide the data required to analyze
electrical equipment, areas of heat loss, the condition of lubricating oil, or other
parameters typically evaluated in a maintenance management program. Therefore, a
total plant predictive maintenance program must include several techniques, each
designed to provide specific information on plant equipment.
2
01.Mobley.1-6 Page 3 Friday, February 5, 1999 9:44 AM
Chapter 2
VIBRATION ANALYSIS APPLICATIONS
The use of vibration analysis is not restricted to predictive maintenance. This tech-
nique is useful for diagnostic applications as well. Vibration monitoring and analysis
are the primary diagnostic tools for most mechanical systems that are used to manu-
facture products. When used properly, vibration data provide the means to maintain
optimum operating conditions and efficiency of critical plant systems. Vibration anal-
ysis can be used to evaluate fluid flow through pipes or vessels, to detect leaks, and to
perform a variety of nondestructive testing functions that improve the reliability and
performance of critical plant systems.
Some of the applications that are discussed briefly in this chapter are predictive main-
tenance, acceptance testing, quality control, loose part detection, noise control, leak
detection, aircraft engine analyzers, and machine design and engineering. Table 2.1
lists rotating, or centrifugal, and nonrotating equipment, machine-trains, and continu-
ous processes typically monitored by vibration analysis.
Table 2.1 Equipment and Processes Typically Monitored by Vibration Analysis
Centrifugal Reciprocating Continuous Process
Pumps
Compressors
Blowers
Fans
Motor/generators
Ball mills
Chillers
Pumps
Compressors
Diesel engines
Gasoline engines
Cylinders
Other machines
Continuous casters
Hot and cold strip lines
Annealing lines
Plating lines
Paper machines
Can manufacturing lines
Pickle lines
continued
3
[...]... Systems, Inc PREDICTIVE MAINTENANCE The fact that vibration profiles can be obtained for all machinery that has rotating or moving elements allows vibration-based analysis techniques to be used for predic tive maintenance Vibration analysis is one of several predictive maintenance tech niques used to monitor and analyze critical machines, equipment, and systems in a typical plant However, as indicated... plant However, as indicated before, the use of vibration analysis to monitor rotating machinery to detect budding problems and to head off catastrophic failure is the dominant predictive maintenance technique used with maintenance management programs ACCEPTANCE TESTING Vibration analysis is a proven means of verifying the actual performance versus design parameters of new mechanical, process, and manufacturing... offers the same benefits to non-nuclear industries NOISE CONTROL Federal, state, and local regulations require serious attention be paid to noise levels within the plant Vibration analysis can be used to isolate the source of noise gener ated by plant equipment as well as background noises such as those generated by fluorescent lights and other less obvious sources The ability to isolate the source of abnormal... a mechanic to deter mine the source of the problem while continuous sensors alert the pilot to any devia tion from optimum operating condition MACHINE DESIGN AND ENGINEERING Vibration data have become a critical part of the design and engineering of new machines and process systems Data derived from similar or existing machinery can be extrapolated to form the basis of a preliminary design Prototype... 1 t ) + b sin ( ω 2 t ) Any periodic function can be represented as a series of sine functions having frequen cies of ω, 2ω, 3ω, etc.: 01.Mobley.1-6 Page 21 Friday, February 5, 1999 9:44 AM Vibration Theory 21 f ( t ) = A 0 + A 1 sin (ωt + φ 1 ) + A 2 sin (2ωt + φ 2 ) + A 3 sin (3ωt + φ 3 ) + … This equation is known as a Fourier series, which is a function of time or f(t) The amplitudes (Al, A2, etc.)... amplitude may be different 01.Mobley.1-6 Page 11 Friday, February 5, 1999 9:44 AM Vibration Analysis Overview 11 Interpretation of Vibration Data The key to using vibration signature analysis for predictive maintenance, diagnostic, and other applications is the ability to differentiate between normal and abnormal vibration profiles Many vibrations are normal for a piece of rotating or moving machinery Examples... However, specific problems with machinery generate abnormal, yet identifiable, vibrations Examples of these are loose bolts, misaligned shafts, worn bearings, leaks, and incipient metal fatigue Predictive maintenance utilizing vibration signature analysis is based on the following facts, which form the basis for the methods used to identify and quantify the root causes of failure: 1 All common machinery... routinely taken during the life of a machine, are directly comparable to historical data taken at exactly the same running speed and load How ever, this is not practical because of variations in day-to-day plant operations and changes in running speed This significantly affects the profile and makes it impossi ble to compare historical data Frequency Domain From a practical standpoint, simple harmonic vibration . Mobley. p. cm. — (Plant engineering maintenance series) Includes index. ISBN 0-7506-7158-0 (alk. paper) 1. Plant maintenance. 2. System failures (Engineering) I. Title. II. Series. TS192.M625. evaluated in a maintenance management program. Therefore, a total plant predictive maintenance program must include several techniques, each designed to provide specific information on plant equipment techniques, vibration analysis is the dominant predictive maintenance technique used with maintenance management pro- grams. Predictive maintenance has become synonymous with monitoring vibration
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