| RCM provides a framework which enables users to respond to these challenges,
quickly and simply. It does so because it never loses sight of the fact
that maintenance is about physical assets. If these assets did not exist,
the maintenance function itself would not exist. So RCM starts with a comprehensive,
zero-based review of the maintenance requirements of each, asset in its
operating context. |
|
All too often, these requirements are taken for granted. This results in
the development of organization structures, the deployment of resources
and the implementation of systems on the basis of incomplete or incorrect
assumptions about the real needs of the assets. On the other hand, if these
requirements are defined correctly in the light of modem thinking, it is
possible to achieve quite remarkable step changes in maintenance efficiency
and effectiveness. |
|
The rest of this chapter introduces RCM in more detail. It begins by exploring
the meaning of 'maintenance' itself. It goes on to define RCM and to describe
the seven key steps involved in applying this process. |
| Maintenance and RCM |
|
From the engineering viewpoint, there are two elements to the management
of any physical asset. It must be maintained and from time to time it may
also need to be modified. |
|
The major dictionaries define maintain as cause to continue (Oxford) or
keep in an existing state (Webster). This suggests that maintenance means
preserving something. On the other hand, they agree that to modify something
means to change it in some way. This distinction between maintain and modify
has profound implications which are discussed at length in later chapters.
However, we focus on maintenance at this point. |
|
When we set out to maintain something, what is it that we wish to cause
to continue? What is the existing state that we wish to preserve? |
|
The answer to these questions can be found in the fact that every physical
asset is put into service because someone wants it to do something. In
other words, they expect it to fulfill a specific function or functions.
So it follows that when we maintain an asset, the state we wish to preserve
must be one in which it continues to do whatever its users want it to do. |
|
Maintenance: Ensuring that physical assets continue to do what their
users want them to do |
|
What the users want will depend on exactly where and how the asset is being
used (the operating context). This leads to the following formal definition
of Reliability-centered Maintenance: |
|
Reliability-centered Maintenance: a process used to determine the maintenance
requirements of any physical asset in its operating context |
|
In the light of the earlier definition of maintenance, a fuller definition
of RCM could be 'a process used to determine what must be done to ensure
that any physical asset continues to do whatever its users want it to do
in its present operating context |
| 1.3 RCM: The seven basic
questions |
|
The RCM process entails asking seven questions about the asset or system
under review, as follows: |
-
what are the functions and associated
performance standards of the asset in its present operating context?
|
-
in what ways does it fail to
fulfill its functions?
|
-
what causes each functional
failure?
|
-
what happens when each failure
occurs?
|
-
in what way does each failure
matter?
|
-
what can be done to predict
or prevent each failure?
|
-
what should be done if a suitable
proactive task cannot be found?
|
|
These questions are introduced briefly in the following paragraphs, and
then considered in detail in Chapters 2 to 10 of the book. |
| Functions and Performance
Standards |
|
Before it is possible to apply a process used to determine what must be
done to ensure that any physical asset continues to do whatever its users
want it to do in its present operating context, we need to do two things: |
-
determine what its users want
it to do.
|
-
ensure that it is capable of
doing what its users want to start with.
|
|
This is why the first step in the RCM process is to define the functions
of each asset in its operating context, together with the associated desired
standards of performance. What users expect assets to be able to do can
be split into two categories: |
-
primary functions, which
summarize why the asset was acquired in the first place. This category
of functions covers issues such as speed, out-put, carrying or storage
capacity, product quality and customer service.
|
-
secondary functions,
which recognize that every asset is expected to do more than simply fulfill
its primary functions. Users also have expectations in areas such as safety,
control, containment, comfort, structural integrity, economy, protection,
efficiency of operation, compliance with environmental regulations and
even the appearance of the asset,
|
|
The users of the assets are usually in the best position by far to know
exactly what contribution each asset makes to the physical and financial
well-being of the organization as a whole, so it is essential that they
are involved in the RCM process from the outset. |
|
Done properly, this step alone usually takes up about a third of the time
involved in an entire RCM analysis. It also usually causes the team doing
the analysis to learn a remarkable amount - often a frightening amount
- about how the equipment actually works. Functions are explored in more
detail in Chapter 2 of the book. |
| Functional Failures |
|
The objectives of maintenance are defined by the functions and associated
performance expectations of the asset under consideration. But how does
maintenance achieve these objectives? |
|
The only occurrence which is likely to stop any asset performing to the
standard required by its users is some kind of failure. This suggests that
maintenance achieves its objectives by adopting a suitable approach to
the management of failure. However, before we can apply a suitable blend
of failure management tools, we need to identify what failures can occur.
The RCM process does this at two levels: |
-
firstly, by identifying what
circumstances amount to a failed state then by asking what events can cause
the asset to get into a failed state.
|
-
in the world of RCM, failed
states are known as functional failures because they occur when an asset
is unable to fulfill a function to a standard of performance which is acceptable
to the user.
|
|
In addition to the total inability to function, this definition encompasses
partial failures, where the asset still functions but at an unacceptable
level of performance (including situations where the asset cannot sustain
acceptable levels of quality or accuracy). Clearly these can only be identified
after the functions and performance standards of the asset have been defined.
Functional failures are discussed at greater length in Chapter 3 of the
book. |
| Failure Modes |
|
As mentioned in the previous paragraph, once each functional failure has
been identified, the next step is to try to identify all the events which
are reasonably likely to cause each failed state. |
|
These events are known as failure modes. "Reasonably likely" failure modes
include those which have occurred on the same or similar equipment operating
in the same context, failures which are currently being prevented by existing
maintenance regimes, and failures which have not happened yet but which
are considered to be real possibilities in the context in question. |
|
Most traditional lists of failure modes incorporate failures caused by
deterioration or normal wear and tear. However, the list should include
failures caused by human errors (on the part of operators and maintainers)
and design flaws so that all reasonably likely causes of equipment failure
can be identified and dealt with appropriately. It is also important to
identify the cause of each failure in enough detail to ensure that time
and effort are not wasted trying to treat symptoms instead of causes. On
the other hand, it is equally important to ensure that time is not wasted
on the analysis itself by going into too much detail. |
| Failure Effects |
|
The fourth step in the RCM process entails listing failure effects, which
describe what happens when each failure mode occurs. These descriptions
should include all the information needed to support the evaluation of
the consequences of the failure, such as: |
-
what evidence (if any) that
the failure has occurred
|
-
in what ways (if any) it poses
a threat to safety or the environment
|
-
in what ways (if any) it affects
production or operations
|
-
what physical damage (if any)
is caused by the failure
|
-
what must be done to repair
the failure.
|
|
Failure modes and effects are discussed at greater length in Chapter 4
of the book. |
|
The process of identifying functions functional failures failure modes
and failure effects yields surprising and often very exciting opportunities
for improving performance and safety, and also for eliminating waste. |
| Failure Consequences |
|
A detailed analysis of an average industrial undertaking is likely to yield
between three and ten thousand possible failure modes. Each of these failures
affects the organization in some way, but in each case, the effects are
different. They may affect operations. They may also affect product quality,
customer service, safety or the environment. They will all take time and
cost money to repair. |
|
It is these consequences which most strongly influence the extent to which
we try to prevent each failure. In other words, if a failure has serious
consequences, we are likely to go to great lengths to try to avoid it.
On the other hand, if it has little or no effect, then we may decide to
do no routine maintenance beyond basic cleaning and lubrication. |
|
A great strength of RCM is that it recognizes that the consequences of
failures are far more important than their technical characteristics. In
fact, it recognizes that the only reason for doing any kind of proactive
maintenance is not to avoid failures per se, but to avoid or at least to
reduce the consequences of failure. The RCM process classifies these consequences
into four groups, as follows: |
-
Hidden failure consequences:
Hidden failures have no direct impact, but they expose the organization
to multiple failures with serious, often catastrophic, consequences. (Most
of these failures are associated with protective devices which are not
fail-safe.)
|
-
Safety and environmental consequences:
A failure has safety consequences if it could hurt or kill someone. It
has environmental consequences if it could lead to a breach of any corporate,
regional, national or international environmental standard.
|
-
Operational consequences: A
failure has operational consequences if it affects production (output,
product quality, customer service or operating costs in addition to the
direct cost of repair)
|
-
Non-operational consequences:
Evident failures which fall into this category affect neither safety nor
production, so they involve only the direct cost of repair.
|
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