AN INTRODUCTION TO PREDICTIVE MAINTENANCE Second Edition AN INTRODUCTION TO PREDICTIVE MAINTENANCE Second Edition R. Keith Mobley Amsterdam London New York Oxford Paris Tokyo Boston San Diego San Francisco Singapore Sydney Butterworth-Heinemann is an imprint of Elsevier Science. Copyright © 2002, Elsevier Science (USA). 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, without the prior written permission of the publisher. Recognizing the importance of preserving what has been written, Elsevier-Science prints its books on acid-free paper whenever possible. Library of Congress Cataloging-in-Publication Data Mobley, R. Keith, 1943–. An introduction to predictive maintenance / R. Keith Mobley.—2nd ed. p. cm. Includes index. ISBN 0-7506-7531-4 (alk. paper) 1. Plant maintenance—Management. I. Title. 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For information, please contact: Manager of Special Sales Elsevier Science 225 Wildwood Avenue Woburn, MA 01801-2041 Tel: 781-904-2500 Fax: 781-904-2620 For information on all Butterworth-Heinemann publications available, contact our World Wide Web home page at: http://www.bh.com 10987654321 Printed in the United States of America 1 Impact of Maintenance 1 1.1 Maintenance management methods 2 1.2 Optimizing predictive maintenance 10 2 Financial Implications and Cost Justification 23 2.1 Assessing the need for condition monitoring 24 2.2 Cost justification 25 2.3 Justifying predictive maintenance 29 2.4 Economics of preventive maintenance 32 3 Role of Maintenance Organization 43 3.1 Maintenance mission 43 3.2 Evaluation of the maintenance organization 44 3.3 Designing a predictive maintenance program 50 4 Benefits of Predictive Maintenance 60 4.1 Primary uses of predictive maintenance 61 5 Machine-Train Monitoring Parameters 74 5.1 Drivers 75 5.2 Intermediate drives 78 5.3 Driven components 86 6 Predictive Maintenance Techniques 99 6.1 Vibration monitoring 99 6.2 Themography 105 6.3 Tribology 108 6.4 Visual inspections 111 6.5 Ultrasonics 111 6.6 Other techniques 112 7 Vibration Monitoring and Analysis 114 7.1 Vibration analysis applications 114 7.2 Vibration analysis overview 117 7.3 Vibration sources 122 7.4 Vibration theory 125 7.5 Machine dynamics 132 7.6 Vibration data types and formats 146 7.7 Data acquisition 152 7.8 Vibration analyses techniques 161 Appendix 7.1 Abbreviations 165 Appendix 7.2 Glossary 166 Appendix 7.3 References 171 8 Thermography 172 8.1 Infrared basics 172 8.2 Types of infrared instruments 174 8.3 Training 175 8.4 Basic infrared theory 176 8.5 Infrared equipment 178 8.6 Infrared thermography safety 179 8.7 Infrared thermography procedures 179 8.8 Types of infrared problems 179 Appendix 8.1 Abbreviations 183 Appendix 8.2 Glossary 183 Appendix 8.3 Electrical terminology 187 Appendix 8.4 Materials list 193 9 Tribology 202 9.1 Lubricating oil analysis 203 9.2 Setting up an effective program 208 10 Process Parameters 217 10.1 Pumps 218 10.2 Fans, blowers, and fluidizers 225 10.3 Conveyors 229 10.4 Compressors 229 10.5 Mixers and agitators 240 10.6 Dust collectors 240 10.7 Process rolls 241 10.8 Gearboxes/reducers 242 10.9 Steam traps 249 10.10 Inverters 249 10.11 Control valves 249 10.12 Seals and packing 251 11 Ultrasonics 256 11.1 Ultrasonic applications 256 11.2 Types of ultrasonic systems 257 11.3 Limitations 258 12 Visual Inspection 259 12.1 Visual inspection methods 260 12.2 Thresholds 263 13 Operating Dynamics Analysis 267 13.1 It’s not predictive maintenance 267 14 Failure-Mode Analysis 285 14.1 Common general failure modes 286 14.2 Failure modes by machine-train component 301 15 Establishing A Predictive Maintenance Program 325 15.1 Goals, objectives, and benefits 325 15.2 Functional requirements 326 15.3 Selling predictive maintenance programs 330 15.4 Selecting a predictive maintenance system 334 15.5 Database development 343 15.6 Getting started 348 16 A Total-Plant Predictive Maintenance Program 352 16.1 The optimum predictive maintenance program 353 16.2 Predictive is not enough 356 17 Maintaining the Program 389 17.1 Trending techniques 389 17.2 Analysis techniques 390 17.4 Additional training 392 17.5 Technical support 393 17.6 Contract predictive maintenance programs 393 18 World-Class Maintenance 394 18.1 What is world-class maintenance? 394 18.2 Five fundamentals of world-class performance 395 18.3 Competitive advantage 396 18.4 Focus on quality 397 18.5 Focus on maintenance 398 18.6 Overall equimpment effectiveness 402 18.7 Elements of effective maintenance 406 18.8 Responsibilities 412 18.9 Three types of maintenance 413 18.10 Supervision 419 18.11 Standard procedures 424 18.12 Workforce development 426 Index 435 inventory cost, high overtime labor costs, high machine downtime, and low produc- tion availability. Because no attempt is made to anticipate maintenance requirements, a plant that uses true run-to-failure management must be able to react to all possible failures within the plant. This reactive method of management forces the maintenance department to maintain extensive spare parts inventories that include spare machines or at least all major components for all critical equipment in the plant. The alternative is to rely on equipment vendors that can provide immediate delivery of all required spare parts. Even if the latter option is possible, premiums for expedited delivery substantially increase the costs of repair parts and downtime required to correct machine failures. To minimize the impact on production created by unexpected machine failures, main- tenance personnel must also be able to react immediately to all machine failures. The net result of this reactive type of maintenance management is higher maintenance cost and lower availability of process machinery. Analysis of maintenance costs indicates that a repair performed in the reactive or run-to-failure mode will average about three times higher than the same repair made within a scheduled or preventive mode. Sched- uling the repair minimizes the repair time and associated labor costs. It also reduces the negative impact of expedited shipments and lost production. 1.1.2 Preventive Maintenance There are many definitions of preventive maintenance, but all preventive maintenance management programs are time-driven. In other words, maintenance tasks are based on elapsed time or hours of operation. Figure 1–1 illustrates an example of the sta- tistical life of a machine-train. The mean-time-to-failure (MTTF) or bathtub curve indicates that a new machine has a high probability of failure because of installation problems during the first few weeks of operation. After this initial period, the proba- bility of failure is relatively low for an extended period. After this normal machine life period, the probability of failure increases sharply with elapsed time. In preven- tive maintenance management, machine repairs or rebuilds are scheduled based on the MTTF statistic. The actual implementation of preventive maintenance varies greatly. Some programs are extremely limited and consist of only lubrication and minor adjustments. Comprehensive preventive maintenance programs schedule repairs, lubrication, adjustments, and machine rebuilds for all critical plant machinery. The common denominator for all of these preventive maintenance programs is the scheduling guideline—time. All preventive maintenance management programs assume that machines will degrade within a time frame typical of their particular classification. For example, a single- stage, horizontal split-case centrifugal pump will normally run 18 months before it must be rebuilt. Using preventive management techniques, the pump would be removed from service and rebuilt after 17 months of operation. The problem with this Impact of Maintenance 3 [...]... provide a predictive maintenance program that will virtually eliminate catastrophic failures and the need for corrective maintenance These methods will also extend the useful life and minimize the life cycle cost of critical production systems 16 An Introduction to Predictive Maintenance Predictive Maintenance Is More Than Maintenance Traditionally, predictive maintenance is used solely as a maintenance. .. that repairs made in a reactive (i.e., after failure) mode are normally three times greater than the same repairs made on a scheduled basis 1. 1.3 Predictive Maintenance Like preventive maintenance, predictive maintenance has many definitions To some workers, predictive maintenance is monitoring the vibration of rotating machinery in an attempt to detect incipient problems and to prevent catastrophic failure... of Maintenance 17 The Difference Other than the mission or intent of how predictive maintenance is used in your plant, the real difference between the limited benefits of a traditional predictive maintenance program and the maximum benefits that these technologies could provide is the diagnostic logic used In traditional predictive maintenance applications, analysts typically receive between 5 and 15 ... your program 1. 1.4 Other Maintenance Improvement Methods Over the past 10 years, a variety of management methods, such as total productive maintenance (TPM) and reliability-centered maintenance (RCM), have been developed and touted as the panacea for ineffective maintenance Many domestic plants have partially adopted one of these quick-fix methods in an attempt to compensate for perceived maintenance. .. plants Predictive maintenance is not vibration monitoring or thermal imaging or lubricating oil analysis or any of the other nondestructive testing techniques that are being marketed as predictive maintenance tools Predictive maintenance is a philosophy or attitude that, simply stated, uses the actual operating condition of plant equipment and systems to optimize total plant operation A comprehensive predictive. .. consequences—that is, they learned how to Impact of Maintenance 11 problems The remaining 83 percent are totally outside of the traditional maintenance function’s responsibility Inappropriate operating practices, poor design, nonspecification parts, and a myriad of other nonmaintenance reasons are the primary contributors to production and product-quality problems, not maintenance Predictive technologies should be used... and greatly reduces the cost of maintenance It also improves the product quality, productivity, and profitability of manufacturing and production plants Predictive maintenance is a condition-driven preventive maintenance program Instead of relying on industrial or in-plant average-life statistics (i.e., mean-time-to-failure) to schedule maintenance activities, predictive maintenance uses direct monitoring... is important, predictive maintenance can provide substantially more benefits by expanding the scope or mission of the program As a maintenance management tool, predictive maintenance can and should be used as a maintenance optimization tool The program’s focus should be on eliminating unnecessary downtime, both scheduled and unscheduled; eliminating unnecessary preventive and corrective maintenance tasks;... and the personal experience of the maintenance manager The addition of a comprehensive predictive maintenance program can and will provide factual data on the actual mechanical condition of each machine-train and the operating efficiency of each process system This data provides the maintenance manager with actual data for scheduling maintenance activities A predictive maintenance program can minimize...4 An Introduction to Predictive Maintenance Figure 1 1 Typical bathtub curve approach is that the mode of operation and system or plant-specific variables directly affect the normal operating life of machinery The mean-time-between-failures (MTBF) is not the same for a pump that handles water and one that handles abrasive slurries The normal result of using MTBF statistics to schedule maintenance . packing 2 51 11 Ultrasonics 256 11 .1 Ultrasonic applications 256 11 .2 Types of ultrasonic systems 257 11 .3 Limitations 258 12 Visual Inspection 259 12 .1 Visual inspection methods 260 12 .2 Thresholds. 229 10 .5 Mixers and agitators 240 10 .6 Dust collectors 240 10 .7 Process rolls 2 41 10 .8 Gearboxes/reducers 242 10 .9 Steam traps 249 10 .10 Inverters 249 10 .11 Control valves 249 10 .12 Seals. 86 6 Predictive Maintenance Techniques 99 6 .1 Vibration monitoring 99 6.2 Themography 10 5 6.3 Tribology 10 8 6.4 Visual inspections 11 1 6.5 Ultrasonics 11 1 6.6 Other techniques 11 2 7 Vibration