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 [...]... February 5, 1999 9:44 AM 8 Vibration Fundamentals ACTUAL VIBRATION PROFILES The process of vibration analysis requires the gathering of complex machine data, which must then be deciphered As opposed to the simple theoretical vibration curves shown in Figures 3.1 and 3.2 above, the profile for a piece of equipment is extremely complex This is true because there are usually many sources of vibration Each source... essential for vibration analysis Free vibration refers to the vibration of a damped (as well as undamped) system of masses with motion entirely influenced by their potential energy Forced vibration occurs when motion is sustained or driven by an applied periodic force in either damped or undamped systems The following sections discuss free and forced vibration for both damped and undamped systems Free Vibration Undamped... 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... reciprocal is the frequency of the vibration, f, measured in cycles-per-second (cps) or Hertz (Hz) 17 01.Mobley.1-6 Page 18 Friday, February 5, 1999 9:44 AM 18 Vibration Fundamentals Figure 5.1 Illustration of vibration cycles 1 f = T Another measure of frequency is the circular frequency, ω, measured in radians per sec ond From Figure 5.1, it is clear that a full cycle of vibration (ωt) occurs after... Chapter 3 VIBRATION ANALYSIS OVERVIEW Vibration theory and vibration profile, or signature, analyses are complex subjects that are the topic of many textbooks The purpose of this chapter is to provide enough the ory to allow the concept of vibration profiles and their analyses to be understood before beginning the more in-depth discussions in the later sections of this module THEORETICAL VIBRATION PROFILES... VIBRATION PROFILES A vibration is a periodic motion or one that repeats itself after a certain interval of time This time interval is referred to as the period of the vibration, T A plot, or pro file, of a vibration is shown in Figure 3.1, which shows the period, T, and the maxi 1 mum displacement or amplitude, X0 The inverse of the period, - , is called the T frequency, f, of the vibration, which can... frequency-domain vibration signature is generally used for the analysis because it is comprised of discrete peaks, each representing a specific vibration source 3 There is a cause, referred to as a forcing function, for every frequency component in a machine-train’s vibration signature 4 When the signature of a machine is compared over time, it will repeat until some event changes the vibration pattern... amplitude variations be clearly understood VIBRATION MEASURING EQUIPMENT Vibration data are obtained by the following procedure: (1) Mount a transducer onto the machinery at various locations, typically machine housing and bearing caps, and (2) use a portable data-gathering device, referred to as a vibration monitor or analyzer, to connect to the transducer to obtain vibration readings Transducer The transducer... Chapter 4 VIBRATION SOURCES All machinery with moving parts generates mechanical forces during normal opera tion As the mechanical condition of the machine changes due to wear, changes in the operating environment, load variations, etc., so do these forces Understanding machinery dynamics and how forces create unique vibration frequency components is the key to understanding vibration sources Vibration. .. of these forces to occur In addition to imbalance generated by a rotating element, vibration may be caused by instability in the media flowing through the rotating machine 13 01.Mobley.1-6 Page 14 Friday, February 5, 1999 9:44 AM 14 Vibration Fundamentals Rotor Imbalance While mechanical imbalance generates a unique vibration profile, it is not the only form of imbalance that affects rotating elements . INTRODUCTION TO VIBRATION ANALYSIS 1 Chapter 1 INTRODUCTION 2 Chapter 2 VIBRATION Chapter 3 VIBRATION Chapter 4 VIBRATION Chapter 5 VIBRATION Chapter 6 MACHINE. bearing caps, and (2) use a portable data-gathering device, referred to as a vibration monitor or analyzer, to connect to the transducer to obtain vibration