Predictive maintenance is not vibration monitoring or thermal imaging or lubri-cating oil analysis or any of the other nondestructive testing techniques that are beingmarketed as predict
Trang 1AN INTRODUCTION TO
PREDICTIVE MAINTENANCE
Second Edition
Trang 4Butterworth-Heinemann is an imprint of Elsevier Science.
Copyright © 2002, Elsevier Science (USA) All rights reserved.
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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.
TS192 M624 2002
658.2¢02—dc21
2001056670
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Trang 51 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
Trang 66.3 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
Trang 7Appendix 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
Trang 813 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
Trang 918 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
Trang 10inventory cost, high overtime labor costs, high machine downtime, and low tion availability.
produc-Because no attempt is made to anticipate maintenance requirements, a plant that usestrue run-to-failure management must be able to react to all possible failures within theplant This reactive method of management forces the maintenance department tomaintain extensive spare parts inventories that include spare machines or at least allmajor components for all critical equipment in the plant The alternative is to rely onequipment vendors that can provide immediate delivery of all required spare parts.Even if the latter option is possible, premiums for expedited delivery substantiallyincrease the costs of repair parts and downtime required to correct machine failures
To minimize the impact on production created by unexpected machine failures, tenance personnel must also be able to react immediately to all machine failures Thenet result of this reactive type of maintenance management is higher maintenance costand lower availability of process machinery Analysis of maintenance costs indicatesthat a repair performed in the reactive or run-to-failure mode will average about threetimes 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 reducesthe negative impact of expedited shipments and lost production
sta-The actual implementation of preventive maintenance varies greatly Some programsare 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 commondenominator for all of these preventive maintenance programs is the scheduling guideline—time
All preventive maintenance management programs assume that machines will degradewithin a time frame typical of their particular classification For example, a single-stage, horizontal split-case centrifugal pump will normally run 18 months before itmust be rebuilt Using preventive management techniques, the pump would beremoved from service and rebuilt after 17 months of operation The problem with this
Impact of Maintenance 3
Trang 11approach is that the mode of operation and system or plant-specific variables directlyaffect 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 abrasiveslurries.
The normal result of using MTBF statistics to schedule maintenance is either essary repairs or catastrophic failure In the example, the pump may not need to berebuilt after 17 months Therefore, the labor and material used to make the repair waswasted The second option using preventive maintenance is even more costly If thepump fails before 17 months, it must be repaired using run-to-failure techniques.Analysis of maintenance costs has shown that repairs made in a reactive (i.e., afterfailure) mode are normally three times greater than the same repairs made on a scheduled basis
unnec-1.1.3 Predictive Maintenance
Like preventive maintenance, predictive maintenance has many definitions To someworkers, predictive maintenance is monitoring the vibration of rotating machinery in
an attempt to detect incipient problems and to prevent catastrophic failure To others,
it is monitoring the infrared image of electrical switchgear, motors, and other cal equipment to detect developing problems The common premise of predictivemaintenance is that regular monitoring of the actual mechanical condition, operatingefficiency, and other indicators of the operating condition of machine-trains andprocess systems will provide the data required to ensure the maximum intervalbetween repairs and minimize the number and cost of unscheduled outages created bymachine-train failures
electri-4 An Introduction to Predictive Maintenance
Figure 1–1 Typical bathtub curve.
Trang 12Predictive maintenance is much more, however It is the means of improving ductivity, product quality, and overall effectiveness of manufacturing and productionplants Predictive maintenance is not vibration monitoring or thermal imaging or lubri-cating oil analysis or any of the other nondestructive testing techniques that are beingmarketed as predictive maintenance tools.
pro-Predictive maintenance is a philosophy or attitude that, simply stated, uses the actualoperating condition of plant equipment and systems to optimize total plant operation
A comprehensive predictive maintenance management program uses the most effective tools (e.g., vibration monitoring, thermography, tribology) to obtain theactual operating condition of critical plant systems and based on this actual data schedules all maintenance activities on an as-needed basis Including predictive main-tenance in a comprehensive maintenance management program optimizes the avail-ability of process machinery and greatly reduces the cost of maintenance It alsoimproves the product quality, productivity, and profitability of manufacturing and production plants
cost-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) toschedule maintenance activities, predictive maintenance uses direct monitoring of themechanical condition, system efficiency, and other indicators to determine the actualmean-time-to-failure or loss of efficiency for each machine-train and system in theplant At best, traditional time-driven methods provide a guideline to “normal”machine-train life spans The final decision in preventive or run-to-failure programs
on repair or rebuild schedules must be made on the basis of intuition and the personalexperience of the maintenance manager
The addition of a comprehensive predictive maintenance program can and will providefactual data on the actual mechanical condition of each machine-train and the oper-ating efficiency of each process system This data provides the maintenance managerwith actual data for scheduling maintenance activities A predictive maintenanceprogram can minimize unscheduled breakdowns of all mechanical equipment in theplant and ensure that repaired equipment is in acceptable mechanical condition Theprogram can also identify machine-train problems before they become serious Mostmechanical problems can be minimized if they are detected and repaired early Normalmechanical failure modes degrade at a speed directly proportional to their severity Ifthe problem is detected early, major repairs can usually be prevented
Predictive maintenance using vibration signature analysis is predicated on two basicfacts: (1) all common failure modes have distinct vibration frequency components that can be isolated and identified, and (2) the amplitude of each distinct vibrationcomponent will remain constant unless the operating dynamics of the machine-train change These facts, their impact on machinery, and methods that will identifyand quantify the root cause of failure modes are developed in more detail in later chapters
Impact of Maintenance 5
Trang 13Predictive maintenance using process efficiency, heat loss, or other nondestructivetechniques can quantify the operating efficiency of nonmechanical plant equipment orsystems These techniques used in conjunction with vibration analysis can providemaintenance managers and plant engineers with information that will enable them toachieve optimum reliability and availability from their plants.
Five nondestructive techniques are normally used for predictive maintenance management: vibration monitoring, process parameter monitoring, thermography, tribology, and visual inspection Each technique has a unique data set that assists themaintenance manager in determining the actual need for maintenance
How do you determine which technique or techniques are required in your plant? How
do you determine the best method to implement each of the technologies? How doyou separate the good from the bad? Most comprehensive predictive maintenance pro-grams use vibration analysis as the primary tool Because most normal plant equip-ment is mechanical, vibration monitoring provides the best tool for routine monitoringand identification of incipient problems; however, vibration analysis does not providethe data required on electrical equipment, areas of heat loss, condition of lubricatingoil, or other parameters that should be included in your program
1.1.4 Other Maintenance Improvement Methods
Over the past 10 years, a variety of management methods, such as total productivemaintenance (TPM) and reliability-centered maintenance (RCM), have been devel-oped and touted as the panacea for ineffective maintenance Many domestic plantshave partially adopted one of these quick-fix methods in an attempt to compensate forperceived maintenance shortcomings
Total Productive Maintenance
Touted as the Japanese approach to effective maintenance management, the TPMconcept was developed by Deming in the late 1950s His concepts, as adapted by theJapanese, stress absolute adherence to the basics, such as lubrication, visual inspec-tions, and universal use of best practices in all aspects of maintenance
TPM is not a maintenance management program Most of the activities associatedwith the Japanese management approach are directed at the production function andassume that maintenance will provide the basic tasks required to maintain critical pro-duction assets All of the quantifiable benefits of TPM are couched in terms of capac-ity, product quality, and total production cost Unfortunately, domestic advocates ofTPM have tried to implement its concepts as maintenance-only activities As a result,few of these attempts have been successful
At the core of TPM is a new partnership among the manufacturing or productionpeople, maintenance, engineering, and technical services to improve what is called
overall equipment effectiveness (OEE) It is a program of zero breakdowns and zero
6 An Introduction to Predictive Maintenance
Trang 14defects aimed at improving or eliminating the following six crippling shop-floorlosses:
• Equipment breakdowns
• Setup and adjustment slowdowns
• Idling and short-term stoppages
Five Pillars of TPM Total productive maintenance stresses the basics of good
busi-ness practices as they relate to the maintenance function The five fundamentals ofthis approach include the following:
1 Improving equipment effectiveness In other words, looking for the six
big losses, finding out what causes your equipment to be ineffective, andmaking improvements
2 Involving operators in daily maintenance This does not necessarily mean
actually performing maintenance In many successful TPM programs, ators do not have to actively perform maintenance They are involved inthe maintenance activity—in the plan, in the program, and in the partner-ship—but not necessarily in the physical act of maintaining equipment
oper-3 Improving maintenance efficiency and effectiveness In most TPM plans,
though, the operator is directly involved in some level of maintenance Thiseffort involves better planning and scheduling better preventive mainte-nance, predictive maintenance, reliability-centered maintenance, spareparts equipment stores, and tool locations—the collective domain of themaintenance department and the maintenance technologies
4 Educating and training personnel This task is perhaps the most important
in the TPM approach It involves everyone in the company: Operators aretaught how to operate their machines properly and maintenance personnel
to maintain them properly Because operators will be performing some ofthe inspections, routine machine adjustments, and other preventive tasks,training involves teaching operators how to do those inspections and how
to work with maintenance in a partnership Also involved is training visors on how to supervise in a TPM-type team environment
super-5 Designing and managing equipment for maintenance prevention
Equip-ment is costly and should be viewed as a productive asset for its entire life.Designing equipment that is easier to operate and maintain than previousdesigns is a fundamental part of TPM Suggestions from operators andmaintenance technicians help engineers design, specify, and procure moreeffective equipment By evaluating the costs of operating and maintaining
Impact of Maintenance 7