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Maintenance Planning
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Maintenance
Planning
Methods and
mathematics
P. Lyonnet
Lecturer in Mechanical Engineering
University Institute of Technology
St Denis, France
English translation by
Jack Bowlett
I~nl
SPRINGER-SCIENCE+BUSINESS MEDIA, B.Y.
Original French language edition,
La maintenance: mathCmatiques et methodes
© 1991 Springer Science+Business Media Dordrecht
Originally published by Chapman & Hall in 1991
Softcover reprint of the hardcover 1s t edition 1991
Typeset in 10/12 Times on Lasercomp by
Thomson Press (India) Ltd., New Delhi
All rights reserved. No part of this publication may be reproduced or
transmitted, in any form or by any means, electronic, mechanical,
photocopying, recording or otherwise, or stored in any retrieval system of
any nature, without the written permission of the copyright holder and the
publisher, application for which shall be made to the publisher.
British Library Cataloguing in Publication Data
Lyonnet, P.
Maintenance Planning.
1. Engineering equipment. Planned maintenance
I. Title
620.0046
ISBN 978-94-010-5384-6 ISBN 978-94-011-3138-4 (eBook)
DOI 10.1007/978-94-011-3138-4
Library of Congress Cataloging-in-Publication Data
Lyonnet, P. (Patrick)
[Maintenance. English]
Maintenance planning:methods and mathematics / P. Lyonnet;
English translation by Jack Howlett.-English ed.
p. cm.
Translation 0[: La maintenance.
Inc1udes index.
I. Plant maintenance-Planning. 2. In dust rial equipment-
Maintenance and repair-Planning. r. Title.
TS192.L8613 1991 90-26663
658.2-dc20 CIP
Contents
Foreword vii
Introduction IX
1 Maintenance policies t
1.1 Preventive maintenance 2
1.2 Tools to aid maintenance 8
2 Organization of maintenance operations 28
2.1. 'ABC' analysis 28
2.2 Investigation of failures 31
2.3 Investigation of causes of failures: statistical techniques 33
2.4 Improvement of reliability by introducing redundancy 43
2.5 Markov chains, availability 48
2.6 Maintenance ratios 54
2.7 The 'total productive maintenance' (TPM) concept 61
3 Behaviour of physical equipment in service 63
3.1 Lifetime of physical equipment 63
3.2 Functions expressing failure rates and reliability 66
3.3 Reliability models 69
3.4 Tests of goodness of fit 89
3.5 Data banks for reliability and maintenance 94
3.6 Planning the preventive maintenance schedule 106
4 Management of maintenance operations 122
4.1 Management of replacements 122
4.2 Optimum replacement of equipment 133
4.3 Compute based maintenance (CBM) 143
5 Mathematics for maintenance: basic concepts and tools 149
5.1 Probability theory 149
5.2 Probability laws 151
5.3 The Laplace transform 165
Vl Contents
6 Applications: case studies 168
6.1 Case 1: Maintenance of a robot paint sprayer 168
6.2 Case 2: A food-products plant 172
Exercises 176
Annexe 191
Maintenance software suppliers 219
Index 223
Foreword
As the developments in engineering production techniques have resulted in
an increasing dependence on automation, the increasing complexity of these
systems has made the reliability of the machines a matter of great importance.
An unexpected breakdown can be a very expensive experience for the
company. Further, in the aerospace industry, problems of reliability,
maintainability and availability are critical.
For a long time industrial research and training centres have been
interested primarily in the problems of design, manufacture and production;
recently, however, there has been a growing interest in the study of
maintenance and reliability. The concept of maintainability, for example,
first appeared in 1954 in the US army. Since then a variety of techniques
and methodologies have been developed and implemented to meet the
challenge of the new needs.
The aim of this book is to present these methods and investigate their
effectiveness, and in so doing to help practising engineers gain a better
understanding of the problems. The many examples and applications given
here should make it a valuable teaching aid to students taking courses in
engineering maintenance. This second edition has been revised and enlarged
to take account of the most recent developments and illustrate their
application to the solution of problems. It should also help to orient the
reader to the modern concept of computer-aided maintenance.
Introduction
A maintenance service exists to keep equipment in running order and also
to reduce the number of breakdowns. Breakdowns can be expensive, giving
rise to costs for a number of reasons:
• the need for intervention in manufacturing or other processes;
• investigation and repair;
• lowered quality of the product;
• indirect costs such as:
- failure to meet fixed costs;
- variable costs not otherwise allowed for;
- extra costs incurred in compensating for loss of production;
- reduced profit margin.
Thus there is every reason to try to avoid breakdowns and to act quickly
to recover from any that occur, all with the aim of increasing the availability
of the plant or other equipment; these are the objectives behind the methods
described in this book.
In Chapter 1 the different maintenance policies are described, in particular,
that of corrective maintenance; he re the importance of the various methods
of failure analysis is explained in connection with:
• bringing to light the critical points;
• improving the technology;
• predicting the stocks of replacements to be held; and
• providing aids for the diagnosis of failures, e.g. failure trees, cause-effect
trees.
Methods of corrective maintenance are developed furt her in Chapter 2,
leading to a summary of the different ways of arriving at asound diagnosis.
Means for improving reliability by providing redundancies are discussed, as
is the evaluation of the availability of a system with the aim of predicting
the demands it will make in the future.
Chapter 3 deals with problems of costs, partly from the point of view of
predicting the economic stock levels, partly from that of deciding on a
replacement policy. Finally, there is a discussion of computer-assisted
maintenance (CAM), in which the power of the tools previously developed
is displa yed.
x Introduction
Chapters 4, 5. In order to model the lifetime of any of the devices in question
certain probability laws must be studied: these are introduced in Chapter 1
where the main laws, both discrete and continuous, are presented with their
underlying hypotheses and main features. The treatment is concise but
thorough. The laws are applied in the succeeding chapters.
The behaviour of materials and equipment in service is studied, using data
gathered on site; models are developed for the lifetimes of different types of
equipment - mechanical, electronic - and checklists are given to guide the
activities of preventive maintenance.
Much prominence is given to the Weibull model, which has extensive
applications in preventive maintenance. The use of goodness-of-fit tests to
establish the validity of a chosen model is explained.
The necessary mathematical tools are developed in Chapter 6, and case
studies concerning maintenance problems are described. There is a set of
problems for the reader to solve, for which answers are given.
1
Maintenance Policies
The objective of maintenance is to bring whatever is being maintained
towards astate of failure-free operation. This, however, is not to be
understood as implying 'at whatever cost'. Rather, the aim is to find an
optimum situation, taking into account the increasing costs of increasingly
sophisticated maintenance, as weH as costs resulting from increasingly high
failure rates. This is illustrated in Fig. 1.1.
To be able to achieve this, the maintenance expert must have asound
knowledge of the different types of maintenance, and must make an
appropriate selection of these to deal with each situation.
Before going into detail concerning the maintenance policies that can be
adopted, we must define the different types.
Preventive maintenance aims to reduce the probability of failure; this breaks
into two sub-types:
• systematic or scheduled maintenance, in wh ich specified components are
replaced (usuaHy at regular intervals) when they are becoming worn;
• condition-based maintenance, in whih the decision to replace or not to
replace is made according to the outcome of a diagnostic study.
Maintenance costs
Cost
Failure costs
Maintenance level
Fig 1.1 Maintenance and failure costs.
