Reliability HotWire: eMagazine for the Reliability Professional
Reliability HotWire

Issue 72, February 2007

Reliability Basics

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:

  1. Prepare for the Analysis
  2. Select the Equipment to Be Analyzed
  3. Identify Functions
  4. Identify Functional Failures
  5. Identify and Evaluate (Categorize) the Effects of Failure
  6. Identify the Causes of Failure
  7. 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.

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