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Introduction
to
Reliability-centered
Maintenance
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This is an excerpt of the first chapter of the book by John Moubray. You
may order Reliability-centered
Maintenance through this website. |
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| 1.1 The Changing World
of Maintenance |
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Over the past twenty years, maintenance has changed, perhaps more so than
any other management discipline. The changes are due to a huge increase
in the number and variety of physical assets (plant, equipment and buildings)
which must be maintained throughout the world, much more complex designs,
new maintenance techniques and changing views on maintenance organization
and responsibilities. |
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Maintenance is also responding to changing expectations. These include
a rapidly growing awareness of the extent to which equipment failure affects
safety and the environment, a growing awareness of the connection between
maintenance and product quality, and increasing pressure to achieve high
plant availability and to contain costs. |
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The changes are testing attitudes and skills in all branches of industry
to the limit. Maintenance people are having to adopt completely new ways
of thinking and acting, as engineers and as managers. At the same time
the limitations of maintenance systems are becoming increasingly apparent,
no matter how much they are computerized. |
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In the face of this avalanche of change, managers everywhere are looking
for a new approach to maintenance. They want to avoid the false starts
and dead ends which always accompany major upheavals. Instead they seek
a strategic framework which synthesizes the new developments into a coherent
pattern, so that they can evaluate them sensibly and apply those likely
to be of most value to them and their companies. |
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This book describes a philosophy which provides just such a frame-work.
It is called Reliability-centered Maintenance, or RCM. |
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If it is applied correctly, RCM transforms the relationships between the
undertakings which use it, their existing physical assets and the people
who operate and maintain those assets. It also enables new assets to be
put into effective service with great speed, confidence and precision. |
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This chapter provides a brief introduction to RCM, starting with a look
at how maintenance has evolved over the past fifty years. |
| 1.2 Reliability-centered
Maintenance |
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Since the 1930's, the evolution of maintenance can be traced through three
generations. RCM is rapidly becoming a cornerstone of the Third Generation,
but this generation can only be viewed in perspective in the light of the
First and Second Generations. |
| The First Generation |
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The First Generation covers the period up to World War II. In those days
industry was not very highly mechanized, so downtime did not matter much.
This meant that the prevention of equipment failure was not a very high
priority in the minds of most managers. At the same time, most equipment
was simple and much of it was over-designed. This made it reliable and
easy to repair. As a result, there was no need for systematic maintenance
of any sort beyond simple cleaning, servicing and lubrication routines.
The need for skills was also lower than it is today. |
| The Second Generation |
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Things changed dramatically during World War II. Wartime pressures increased
the demand for goods of all kinds while the supply of industrial manpower
dropped sharply. This led to increased mechanization. By the 1950's machines
of all types were more numerous and more complex. Industry was beginning
to depend on them. |
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As this dependence grew, downtime came into sharper focus. This led to
the idea that equipment failures could and should be prevented, which led
in turn to the concept of preventive maintenance. In the 1960's, this consisted
mainly of equipment overhauls done at fixed intervals. |
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The cost of maintenance also started to rise sharply relative to other
operating costs. This led to the growth of maintenance planning and control
systems. These have helped greatly to bring maintenance under control,
and are now an established part of the practice of maintenance. |
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Finally, the amount of capital tied up in fixed assets together with a
sharp increase in the cost of that capital led people to start seeking
ways in which they could maximize the life of the assets. |
| The Third Generation |
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Since the mid-seventies, the process of change in industry has gathered
even greater momentum. The changes can be classified under the headings
of new expectations, new research and new techniques. |
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Figure 1. 1 shows how expectations of maintenance have evolved. |
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Downtime has always affected the productive capability of physical assets
by reducing output, increasing operating costs and interfering with customer
service. By the 1960's and 1970's, this was already a major concern in
the mining, manufacturing and transport sectors. In manufacturing, the
effects of downtime are being aggravated by the worldwide move towards
just-in-time systems, where reduced stocks of work-in-progress mean that
quite small breakdowns are now much more likely to stop a whole plant.
In recent times, the growth of mechanization and automation has meant that
reliability and availability have now also become key issues in sectors
as diverse as health care, data processing, telecommunications and building
management. |
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Greater automation also means that more and more failures affect our ability
to sustain satisfactory quality standards. This applies as much to standards
of service as it does to product quality. For instance, equipment failures
can affect climate control in buildings and the punctuality of transport
networks as much as they can interfere with the consistent achievement
of specified tolerances in manufacturing. |
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More and more failures have serious safety or environmental consequences,
at a time when standards in these areas are rising rapidly. In some parts
of the world, the point is approaching where organizations either conform
to society's safety and environmental expectations, or they cease to operate.
This adds an order of magnitude to our dependence on the integrity of our
physical assets - one which goes beyond cost and which becomes a simple
matter of organizational survival. |
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At the same time as our dependence on physical assets is growing, so too
is their cost - to operate and to own. To secure the maximum return on
the investment which they represent, they must be kept working efficiently
for as long as we want them to. |
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Finally, the cost of maintenance itself is still rising, in absolute terms
and as a proportion of total expenditure. In some industries, it is now
the second highest or even the highest element of operating costs. As a
result, in only thirty years it has moved from almost nowhere to the top
of the league as a cost control priority. |
| New research |
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Quite apart from greater expectations, new research is changing many of
our most basic beliefs about age and failure. In particular, it is apparent
that there is less and less connection between the operating age of most
assets and how likely they are to fail. |
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Figure 1.2 shows how the earliest view of failure was simply that as things
got older, they were more likely to fail. A growing awareness of 'infant
mortality' led to widespread Second Generation belief in the "bathtub"
curve. |
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However, Third Generation research has revealed that not one or two but
six failure patterns actually occur in practice. This is discussed in detail
later, but it too is having a profound effect on maintenance. |
| New techniques |
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There has been explosive growth in new maintenance concepts and techniques.
Hundreds have been developed over the past fifteen years, and more are
emerging every week. |
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Figure 1.3 shows how the classical emphasis on overhauls and administrative
systems has grown to include many new developments in a number of different
fields. |
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| The new developments
include: |
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decision support tools, such
as hazard studies, failure modes and effects analyses and expert systems
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new maintenance techniques,
such as condition monitoring
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designing equipment with a much
greater emphasis on reliability and maintainability
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a major shift in organizational
thinking towards participation, team-working and flexibility.
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A major challenge facing maintenance people nowadays is not only to learn
what these techniques are, but to decide which are worthwhile and which
are not in their own organizations. If we make the right choices, it is
possible to improve asset performance and at the same time contain and
even reduce the cost of maintenance. If we make the wrong choices, new
problems are created while existing problems only get worse. |
| The challenges facing
maintenance |
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In a nutshell, the key challenges facing modem maintenance managers can
be summarized as follows: |
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to select the most appropriate
techniques to deal with each type of failure process in order to fulfill
all the expectations of the owners of the assets, the users of the assets
and of society as a whole
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in the most cost-effective and
enduring fashion
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with the active support and
co-operation of all the people involved.
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