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Basic Steps of Applying Reliability
Centered Maintenance (RCM) Part I
The
previous
issue of
Reliability HotWire reflected on the philosophy and perspective that
Reliability Centered Maintenance (RCM) brings to the field of maintenance.
This article begins to present the system analysis process that is used to
implement an RCM program.
Although there is a great deal of variation
in the application of RCM, most procedures include some or all of the seven
steps shown below:
- Prepare for the Analysis
- Select the Equipment to Be Analyzed
- Identify Functions
- Identify Functional Failures
- Identify and Evaluate (Categorize) the
Effects of Failure
- Identify the Causes of Failure
- Select Maintenance Tasks
This article will discuss the first three
items, which are the preliminary steps that need to take place when
embarking on an RCM analysis project.
1- Prepare for the Analysis
Gathering the team
As with almost any project, some preliminary work and meticulous planning
will be required before beginning an RCM analysis. One of the first steps in
the analysis procedure is to assemble the proper team of knowledgeable
individuals to perform the analysis. The most efficient and effective
analysis teams are cross-functional, with different areas of expertise
represented. The size of the team should be adequate (typically 4 or 5
people) but not too large-- "too many cooks spoil the soup." At least one
person from maintenance should be part of the group. RCM is a multifaceted
process that requires a thorough understanding of the assets being
considered for RCM, the purpose of the assets and the impact of their
malfunction. The goal is to gather sufficient knowledge/expertise for an
effective analysis without wasting valuable resources and/or making meetings
unmanageable.
A facilitator is recommended to ensure that
the RCM analysis is carried out at the right level, that no important items
are overlooked and that the results of the analysis are properly recorded. A
facilitator also manages issues among the team members and helps in reaching
consensus in an orderly fashion as well as retaining the commitment of the
members and keeping them engaged.
Establishing ground rules and
discussing a plan
Identifying and documenting the ground rules and assumptions that will be
followed during the analysis can facilitate the analysis process by making
sure that all members of the analysis team understand and accept the
conditions of the analysis. Issues to be discussed when preparing for an RCM
project may include setting the goals of the RCM project, addressing project
management issues and resources required to carry out the project (such as
schedule and budget, meeting procedures, reports, how to make
recommendations, manpower, tools, consultants, software and meeting rooms)
and foreseeing, as much as possible but without getting swamped, the
obstacles that lie ahead of the project (company resistance and lack of
buy-in, lack of data, bureaucracy, lack of leadership and commitment, etc.).
Develop a plan with a viable vision for the future and run with it!
2- Select the Equipment to Be Analyzed
Scope of analysis
The RCM team has to reach a decision about the level of the asset at which
the analysis should be conducted
(e.g.
part, component, subsystem, system or plant)
and whether the entire plant/facility should
be considered for RCM. Consider starting your RCM analysis at the system
level, as it is a good, safe and manageable place to start then expand your
analysis upward and downward. Typically, systems are a logical starting
point for the analysis since they constitute the building blocks for
plants/facilities. Because RCM is focused on preserving the function of
equipment, performing the analysis at the system level, where functions are
usually derived, makes good sense. Focusing on levels below the system level
(e.g. components) limits visibility for the analysts and makes them
detached from the broad significance of failure, especially when components
support multiple functions. Also, comparing failure modes and prioritizing
resources become more useful and feasible if the analysis starts at the
system level rather than the component level, which might have only a few
failure modes. On the other hand, analyzing entire plants in one bite could
be overwhelming and might run the whole RCM program to a stall.
The suggestion of starting the analysis at
the system level may not work for everyone, of course. Depending on system
complexity, constraints and other factors that might be unique to your
application and asset, other levels might be more appropriate as a starting
point.
System boundaries
Selecting the equipment to be analyzed also involves defining system
boundaries. Defining system boundaries helps in specifying precisely what is
included and not included in the system so that an accurate and complete
list of components can be identified and no overlap with component lists of
other systems (especially adjacent systems or systems affected by components
in other systems) can happen. More importantly, the boundaries help in
determining the inputs, outputs and functions of the system.
System description
Once the equipment to be analyzed has been selected, it is time to describe
it. Identifying and documenting the essential details of the system is
necessary in order to perform the remaining steps in a thorough and
technically sound manner. Describing the system helps the analysts gather a
comprehensive understanding of the system. A well-documented system
description will help record an accurate baseline definition of the system
as it was at the time of the analysis (this is also useful because systems
can be upgraded or modified with time). A system description can also assure
that the analysts have identified critical design and operational parameters
that play a key role in delineating the degradation or loss of required
system functions.
System descriptions may include: Functional
block diagrams, component breakdowns and hierarchies, input/output
interfaces, electrical schematics, environmental conditions, design
specifications, equipment histories (especially information pertaining to
failures), the definitions of "failure" that will be followed during the
analysis, operation manuals, previous maintenance plans, specifications of
the operational environment for the equipment and any assumptions that may
affect the analysis.
Select the equipment
Once the level of analysis has been established, the candidate systems that
would benefit the most from a new maintenance program should be identified
and prioritized. Various criteria, such as safety, legal and economic
considerations, can be used in determining the benefit obtained from
maintenance.
Various equipment selection methods are
available.
One
approach would be to evaluate maintenance records (number of failures,
outages hours, loss of productions cost, safety problems, etc.) for a given
period (e.g. 1 year or 2 years).
The 80/20 rule states that most (80%)
of the problems in a plant or system can be attributed to a few (20%) vital
players, so it is useful to prioritize the issues in your plant before
deciding on a plan of attack.
Another approach would be to apply a pre-defined set of selection questions,
For example, the MSG-3 guideline (used in the aircraft industry) proposes
four questions:
- Could failure be undetectable or not
likely to be detected by the operating crew during normal duties?
- Could failure affect safety (on ground
or in flight), including safety/emergency systems or equipment?
- Could failure have significant
operational impact?
- Could failure have significant economic
impact?
Answering "yes" to at least one of the
above questions requires detailed analysis for the equipment.
Another method, called the Criticality
Factors method, consists of a set of factors designed to evaluate the
criticality of the equipment in terms of safety, maintenance, operations,
environmental impact, quality control and other factors. Each factor is
rated according to a pre-defined scale (e.g. 1 to 5 or 1 to 10) where
higher ratings indicate higher criticality. The combined criticality value
score can then be used as a ranking system for different types of equipment
or to be compared with a threshold in order to decide whether the equipment
will then be part of the RCM analysis.
Whichever method (or combination of
methods) is selected, the goal of this task is to provide a systematic
approach to focus the RCM analysis resources on the equipment that will
provide the maximum benefit and to ensure highest return on investment.
3- Identify Functions
Since the ultimate goal of an RCM project is "to preserve system function,"
it is therefore incumbent upon the team of RCM analysts to define a complete
list of system functions. The system functions would then drive the required
functions of the equipment supporting the system functions. (Tip: The
output of a system typically captures the function of the system; therefore,
every output interface could be translated into a function statement.) It is
desirable to start function statements with a verb (to pump water, to
provide alarm, etc). It is also recommended to specify the acceptable level
of performance desired by the user of the asset as opposed to the actual
performance that may reflect an operational or maintenance issue.
Keep in mind that function statements are
not about what types of equipment are within the system and therefore the
use of equipment names to describe system functions should be avoided.
Making a mistake about this leads to the common fallacy that the goal of
maintenance is protecting equipment.
For
example, "To maintain discharge flow of 500 gpm" would be a more useful
function statement than "To provide a centrifugal pump that delivers 500
gpm."
The function definition should be as
quantitative as possible. For example, a function should not be defined as
"To produce as many units as possible," but rather "To produce a target of
25 units with a minimum of 22 units in an 8 hour shift." It becomes
difficult to decide on maintenance strategies or to hold the people involved
in maintenance accountable for not meeting goals of maintenance when the
goals are not defined precisely. Qualitative definitions are, however,
needed in some circumstances. For example, aesthetic functions are hard to
define with exact terms and therefore words such as "should look acceptable"
or "to look attractive" can be used; however, there has to be a common
understanding and consensus about what such definitions mean.
Some function definitions are absolute (e.g.
"To contain liquid," where no leakage is acceptable) while others are
variable (e.g. "To remove unwanted particles of 100 microns from air
stream."). The RCM team should be careful about using absolute definitions
when a variable definition is more appropriate.
Conclusion
This article presented the first three basic steps of an RCM program, which
are the required steps to ensure that an RCM project is begun on the right
track. An article in next month's HotWire will discuss the remaining
steps.
References
ATA MSG-3 "Operator/Manufacturer Scheduled Maintenance Development," updated
in March 2003.
Moubray, John, Reliability-centered Maintenance, Industrial Press,
Inc., New York City, NY, 1997.
Nowlan, F. Stanley and Howard F. Heap, Reliability-Centered Maintenance.
Issued in December, 1978.
SAE JA1012 A Guide to the Reliability-Centered Maintenance (RCM) Standard,
issued in January 2002.
Smith, Anthony, Hinchcliffe, Glenn R., RCM - Gateway to World Class
Maintenance,
Elsevier Inc, Burlington, MA, 2004. | 
