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MAINTENANCE FUNDAMENTALS 2nd Edition Keith Mobley /Maintenance Fundamentals Final Proof 15.6.2004 4:42pm page i 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 Keith Mobley /Maintenance Fundamentals Final Proof 15.6.2004 4:42pm page ii MAINTENANCE FUNDAMENTALS 2nd Edition R. Keith Mobley AMSTERDAM • BOSTON • HEIDELBERG • LONDON • NEW YORK • OXFORD PARIS • SAN DIEGO • SAN FRANCISCO • SINGAPORE • SYDNEY • TOKYO Keith Mobley /Maintenance Fundamentals Final Proof 15.6.2004 4:42pm page iii Elsevier Butterworth–Heinemann 200 Wheeler Road, Burlington, MA 01803, USA Linacre House, Jordan Hill, Oxford OX2 8DP, UK Copyright # 2004, Elsevier Inc. 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. Permissions may be sought directly from Elsevier’s Science & Technology Rights Department in Oxford, UK: phone: (þ44) 1865 843830, fax: (þ44) 1865 853333, e-mail: permissions@elsevier.com.uk. You may also complete your request on-line via the Elsevier homepage (http://elsevier.com), by selecting ‘‘Customer Support’’ and then ‘‘Obtaining Permissions.’’ Recognizing the importance of preserving what has been written, Elsevier prints its books on acid-free paper whenever possible. Library of Congress Cataloging-in-Publication Data Application submitted British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library. ISBN: 0-7506-7798-8 For information on all Butterworth–Heinemann publications visit our Web site at www.bh.com 04 05 06 07 08 09 10 10 9 8 7 6 5 4 3 2 1 Printed in the United States of America Keith Mobley /Maintenance Fundamentals Final Proof 15.6.2004 4:42pm page iv CONTENTS Chapter 1 Impact of Maintenance 1 Chapter 2 Fundamental Requirements of Effective Preventive Maintenance 11 Chapter 3 Designing a Preventive Maintenance Program 25 Chapter 4 Planning and Scheduling 35 Chapter 5 Scheduled Preventive Maintenance 45 Chapter 6 Maintenance Engineering Roles and Responsibilities 55 Chapter 7 Shaft Alignment 71 Chapter 8 Rotor Balancing 112 Chapter 9 Bearings 125 Chapter 10 Couplings 171 Chapter 11 Gears and Gearboxes 201 Chapter 12 Compressors 231 Chapter 13 Control Valves 266 Chapter 14 Conveyors 287 Chapter 15 Fans, Blowers, and Fluidizers 299 Chapter 16 Dust Collectors 317 Chapter 17 Pumps 331 Chapter 18 Steam Traps 365 Chapter 19 Performance Measurement and Management 374 Glossary 390 Index 416 Keith Mobley /Maintenance Fundamentals Final Proof 15.6.2004 4:42pm page v v Keith Mobley /Maintenance Fundamentals Final Proof 15.6.2004 4:42pm page vi This page intentionally left blank 1 IMPACT OF MAINTENANCE Maintenance costs, as defined by normal plant accounting procedures, are normally a major portion of the total operating costs in most plants. Traditional maintenance costs (i.e., labor and material) in the United States have escalated at a tremendous rate over the past 10 years. In 1981, domestic plants spent more than $600 billion to maintain their critical plant systems. By 1991, the costs had increase to more than $800 billion, and they were projected to top $1.2 trillion by the year 2000. These evaluations indicate that on average, one third, or $250 billion, of all maintenance dollars are wasted through ineffective maintenance management methods. American industry cannot absorb the incredible level of inefficiency and hope to compete in the world market. Because of the exorbitant nature of maintenance costs, they represent the greatest potential short-term improvement. Delays, product rejects, scheduled maintenance downtime, and traditional maintenance costs—such as labor, overtime, and repair parts—are generally the major contributors to abnormal maintenance costs within a plant. The dominant reason for this ineffective management is the lack of factual data that quantify the actual need for repair or maintenance of plant machinery, equipment, and systems. Maintenance scheduling has been and in many in- stances still is predicated on statistical trend data or on the actual failure of plant equipment. Until recently, middle and corporate level management have ignored the impact of the maintenance operation on product quality, production costs, and more importantly on bottom-line profit. The general opinion has been ‘‘maintenance is Keith Mobley /Maintenance Fundamentals Final Proof 15.6.2004 4:44pm page 1 1 a necessary evil’’ or ‘‘nothing can be done to improve maintenance costs.’’ Perhaps these were true statements 10 or 20 years ago. However, the develop- ments of microprocessor or computer-based instrumentation that can be used to monitor the operating condition of plant equipment, machinery, and systems have provided the means to manage the maintenance operation. They have provided the means to reduce or eliminate unnecessary repairs, prevent cata- strophic machine failures, and reduce the negative impact of the maintenance operation on the profitability of manufacturing and production plants. M AINTENANCE P HILOSOPHIES Industrial and process plants typically utilize two types of maintenance manage- ment: (1) run-to-failure, or (2) preventive maintenance. Run-to-Failure Management The logic of run-to-failure management is simple and straightforward. When a machine breaks, fix it. This ‘‘if it ain’t broke, don’t fix it’’ method of maintaining plant machinery has been a major part of plant maintenance operations since the first manufacturing plant was built, and on the surface sounds reasonable. A plant using run-to-failure management does not spend any money on main- tenance until a machine or system fails to operate. Run-to-failure is a reactive management technique that waits for machine or equipment failure before any maintenance action is taken. It is in truth a no-maintenance approach of management. It is also the most expensive method of maintenance management. Few plants use a true run-to-failure management philosophy. In almost all instances, plants perform basic preventive tasks (i.e., lubrication, machine adjustments, and other adjustments) even in a run-to-failure environment. How- ever, in this type of management, machines and other plant equipment are not rebuilt nor are any major repairs made until the equipment fails to operate. The major expenses associated with this type of maintenance management are: (1) high spare parts inventory cost, (2) high overtime labor costs, (3) high machine downtime, and (4) low production availability. Since there is no attempt to anticipate maintenance requirements, a plant that uses true run-to-failure man- agement 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 compon- ents 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 is possible, premiums for expedited delivery substantially increase the costs Keith Mobley /Maintenance Fundamentals Final Proof 15.6.2004 4:44pm page 2 2 Maintenance Fundamentals of repair parts and downtime required for correcting machine failures. To minim- ize the impact on production created by unexpected machine failures, mainten- ance personnel must also be able to react immediately to all machine failures. The net result of this reactive type of maintenance management is higher main- tenance cost and lower availability of process machinery. Analysis of mainten- ance 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. Scheduling the repair provides the ability to minimize the repair time and associated labor costs. It also provides the means of reducing the negative impact of expedited shipments and lost production. Preventive Maintenance Management There are many definitions of preventive maintenance, but all preventive main- tenance 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 statistical 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 probability of failure is relatively low for an extended period of time. Following this normal machine life period, the probability of failure increases sharply with elapsed time. In preventive maintenance management, machine repairs or rebuilds are scheduled on the basis of the MTTF statistic. Break in or start up Number of failures Time Normal life Equipment worn out Figure 1.1 Bathtub curve. Keith Mobley /Maintenance Fundamentals Final Proof 15.6.2004 4:44pm page 3 Impact of Maintenance 3 [...]... plant systems, not waiting on something to break Three Types of Maintenance There are three main types of maintenance and three major divisions of preventive maintenance, as illustrated in Figure 1.2 Maintenance Improvement Picture these divisions as the five fingers on your hand Improvement maintenance efforts to reduce or eliminate the need for maintenance are like the thumb, the first and most valuable... Breakdowns Emergency Remedial Repairs Rebuilds Figure 1.2 Structure of maintenance Corrective Maintenance The little finger in our analogy to a human hand represents corrective maintenance (emergency, repair, remedial, unscheduled) At present, most maintenance is corrective Repairs will always be needed Better improvement maintenance and preventive maintenance, however, can reduce the need for emergency corrections... 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 operating efficiency of each process system These data provide the maintenance manager with actual data for scheduling maintenance activities A predictive maintenance program can minimize unscheduled... 30% 8 Maintenance Fundamentals of total production hours, reactive or breakdown response is the dominant management philosophy To be competitive in today’s market, delays caused by maintenance- related problems should represent less than 1% of the total production hours Another indicator of management effectiveness is the amount of maintenance overtime required to maintain the plant In a breakdown maintenance. .. Evaluate the percentage of maintenance labor as compared with total available labor hours that are expended on the actual repairs and maintenance prevention tasks In reactive maintenance management, the percentage will be less than 50% A well-managed maintenance organization should maintain consistent manpower utilization above 90% In other words, at least 90% of the available maintenance labor hours...4 Maintenance Fundamentals The actual implementation of preventive maintenance varies greatly Some programs are extremely limited and consist of lubrication and minor adjustments More comprehensive preventive maintenance programs schedule repairs, lubrication, adjustments, and machine rebuilds for all critical machinery in the plant The common denominator for all of these preventive maintenance. .. schedules all maintenance activities on an as-needed basis Including predictive maintenance in a comprehensive maintenance management program will provide the ability to optimize the availability of process machinery and greatly reduce the cost of maintenance It will also provide the means to improve product quality, productivity, and profitability of our manufacturing and production plants Predictive maintenance. .. monitoring, and fixed-interval preventive maintenance tasks Those techniques identify individual equipment as candidates for preventive maintenance Coordination with Production Equipment is not always available for preventive maintenance just when the maintenance schedulers would like it to be An overriding influence on Fundamental Requirements of Effective Preventive Maintenance 23 coordination should be... One means to quantify the maintenance philosophy in your plant is to analyze the maintenance tasks that have occurred over the past two to three years Attention should be given to the indices that define management philosophy One of the best indices of management attitude and the effectiveness of the maintenance function is the number of production interruptions caused by maintenance- related problems... repair made in a reactive mode (i.e., after failure) will normally be three times greater than the same repair made on a scheduled basis Predictive Maintenance Like preventive maintenance, predictive maintenance has many definitions To some, predictive maintenance is monitoring the vibration of rotating machinery in an attempt to detect incipient problems and to prevent catastrophic failure To others, . Structure of maintenance. Keith Mobley /Maintenance Fundamentals Final Proof 15.6.2004 4:44pm page 9 Impact of Maintenance 9 Reactive Maintenance Reactive maintenance. levels. The maintenance organization has the responsibility to Keith Mobley /Maintenance Fundamentals Final Proof 15.6.2004 4:44pm page 6 6 Maintenance Fundamentals