20 | MOBLEY.FM Page i Wednesday, March 3, 1999 2:29 PM ROOT CAUSE FAILURE ANALYSIS 20 | MOBLEY.FM Page ii Wednesday, March 3, 1999 2:29 PM 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 A member of the Reed Elsevier group All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, with- out the prior written permission of the publisher. Recognizing the importance of preserving what has been written, Butterworth–Heinemann 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 British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library. The publisher offers special discounts on bulk orders of this book. For information, please contact: Manager of Special Sales Butterworth–Heinemann 225 Wildwood Avenue Woburn, MA 01801–2041 Tel: 781-904-2500 Fax: 781-904-2620 For information on all Newnes publications available, contact our World Wide Web home page at: http://www.newnespress.com 10 9 8 7 6 5 4 3 2 1 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