Reliability centered maintenance


Reliability centered maintenance

Reliability-Centered Maintenance, often known as "RCM", is an industrial improvement approach focused on identifying and establishing the operational, maintenance, and capital improvement policies that will manage the risks of equipment failure most effectively. It is defined by the technical standard SAE JA1011, Evaluation Criteria for RCM Processes.Reliability centered maintenance is an engineering framework that enables the definition of a complete maintenance regime. It regards maintenance as the means to maintain the functions a user may require of machinery in a defined operating context. As a discipline it enables machinery stakeholders to monitor, assess, predict and generally understand the working of their physical assets. This is embodied in the initial part of the RCM process which is to identify the operating context of the machinery, and write a Failure Mode Effects and Criticality Analysis, or FMECA. The second part of the analysis is to apply the "RCM logic", which helps determine the appropriate maintenance tasks for the identified failure modes in the FMECA. Once the logic is complete for all elements in the FMECA, the resulting list of maintenance is "packaged", so that the periodicities of the tasks are rationalised to be called up in work packages; it is important not to destroy the applicability of maintenance in this phase. Lastly, RCM is kept live throughout the "in-service" life of machinery, where the effectiveness of the maintenance is kept under constant review and adjusted in light of the experience gained.

Reliability Centered Maintenance can be used to create a cost-effective maintenance strategy to address dominant causes of equipment failure. It is a systematic approach to defining a routine maintenance program composed of cost-effective tasks that preserve important functions.

The important functions (of a piece of equipment) to preserve with routine maintenance are identified, their dominant failure modes and causes determined and the consequences of failure ascertained. Levels of criticality are assigned to the consequences of failure. Some functions are not critical and are left to "run to failure" while other functions must be preserved at all cost. Maintenance tasks are selected that address the dominant failure causes. This process directly addresses maintenance preventable failures. Failures caused by unlikely events, non-predictable acts of nature, etc. will usually receive no action provided their risk (combination of severity and frequency) is trivial (or at least tolerable). When the risk of such failures is very high, RCM encourages (and sometimes mandates) the user to consider changing something which will reduce the risk to a tolerable level.

The result is a maintenance program that focuses scarce economic resources on those items that would cause the most disruption if they were to fail.

RCM emphasizes the use of Predictive maintenance (PdM) techniques in addition to traditional preventive measures.

Historical Background

The term Reliability-Centered Maintenance (RCM) was first used in public papers authored by Tom Matteson, F. Stanley Nowlan, Howard Heap, and other senior executives and engineers at United Airlines to describe a process used to determine the optimum maintenance requirements for aircraft. The US Department of Defense (DOD) sponsored the authoring of both a textbook (by UAL) and an evaluation report (by Rand Corp.) on Reliability-Centered Maintenance, both published in 1978. They brought RCM concepts to the attention of a wider audience. The text book described efforts by commercial airlines and the US Navy in the 1960s and 70s to improve the reliability of their new jet.

The first generation of jet aircraft had a crash rate that would be considered highly alarming today, and both the Federal Aviation Administration (FAA) and the airlines' senior management felt strong pressure to improve matters. In the early 1960s, with FAA approval the airlines began to conduct a series of intensive engineering studies on in-service aircraft. The studies proved that the fundamental assumption of design engineers and maintenance planners -- that every airplane and every major component in the airplane (such as its engines) had a specific "lifetime" of reliable service, after which it had to be replaced (or overhauled) in order to prevent failures -- was wrong in nearly every specific example in a complex modern jet airliner.

This was one of many astounding discoveries that have revolutionized the managerial discipline of physical asset management and have been at the base of many developments since this seminal work was published. Among some of the paradigms shifts inspired by RCM were:
*an understanding that the vast majority of failures are not necessarily linked to the age of the asset
*changing from efforts to predict life expectancies to trying to manage the process of failure
*an understanding of the difference between the requirements of an assets from a user perspective, and the design reliability of the asset
*an understanding of the importance of managing assets on condition (often referred to as condition monitoring, condition based maintenance and predictive maintenance)
*an understanding of the four basic routine maintenance tasks
*linking levels of tolerable risk to maintenance strategy development

Today RCM is defined in the standard SAE JA1011, Evaluation Criteria for Reliability-Centered Maintenance (RCM) Processes. This sets out the minimum criteria for what is, and for what is not, able to be defined as RCM.

The standard is a watershed event in the ongoing evolution of the discipline of physical asset management. Prior to the development of the standard many processes were labeled as RCM even though they were not true to the intentions and the principles in the original report that defined the term publicly.

Today companies can use this standard to ensure that the processes, services and software they purchase and implement conforms with what is defined as RCM, ensuring the best possibility of achieving the many benefits attributable to rigorous application of RCM.

Basic Features

the RCM process described in the DOD/UAL report recognized three principal risks from equipment failures: threats
*to safety,
*to operations, and
*to the maintenance budget.

Modern RCM gives threats to the environment a separate classification, though most forms manage them in the same way as threats to safety.

RCM offers four principal options among the risk management strategies:
*on-condition maintenance tasks,
*scheduled restoration or discard maintenance tasks,
*failure-finding maintenance tasks, and
*one-time changes to the "system" (changes to hardware design, to operations, or to other things).

RCM also offers specific criteria to use when selecting a risk management strategy for a system that presents a specific risk when it fails. Some are technical in nature (can the proposed task detect the condition it needs to detect? does the equipment actually wear out, with use?). Others are goal-oriented (is it reasonably likely that the proposed task-and-task-frequency will reduce the risk to a tolerable level?). The criteria are often presented in the form of a decision-logic diagram, though this is not intrinsic to the nature of the process.

RCM In Use

After being created by the commercial aviation industry, RCM was adopted by the U.S. military (beginning in the mid-1970s) and by the U.S. commercial nuclear power industry (in the 1980s). It began to enter other commercial industries and fields in the early 1990s.

It is probably clear from the account of RCM's basic features that it is a highly complex analytic process. Starting in the late 1980s, a series of independent initiatives sprang up that were intended to reduce the process's complexity without reducing its benefits. A partial list of these initiatives would include:

*"RCM 2", [http://www.aladon.com/ Aladon]

*"Streamlined" RCM,

*"PM Optimisation," or PMO [http://en.wikipedia.org/wiki/PM_Optimisation] ,

* Naval Sea Systems Command "Classic RCM" and "Backfit RCM". Outlined in references below. Backfit RCM is used as a Continious Process Improvement process tool to evaluate existing maintenance tasks.

Since each initiative is sponsored by one or more consulting firms eager to help clients use it, there is still considerable disagreement about their relative merits (and dangers). Also there is a tendency for consulting firms to promote a software package as an alternative methodology.

However, the RCM standard ( [http://www.sae.org/technical/standards/JA1011_199908 SAE JA1011] , available from http://www.sae.org) provides the minimum criteria that processes must comply with if they are to be called RCM. Although a voluntary standard it provides a reference for companies looking to implement RCM to ensure they are getting a process, software package or service that is in line with the original report.

Nonetheless, everyone well-acquainted with RCM seems to agree that a thorough application of the RCM analytic process is still the most flexible and comprehensive tool available for identifying the actions that need to be taken to ensure that the risks of equipment failure are reduced to a tolerable level.

Further reading

[http://www.mt-online.com/current/06-99mm.html] "Standard To Define RCM," (Part 1), Dana Netherton, Maintenance Technology (1998) (Dead links)

[http://www.mt-online.com/current/08-99mm.html] "Standard To Define RCM," (Part 2), Dana Netherton, Maintenance Technology (1998)

References

Evaluation Criteria for Reliability-Centered Maintenance (RCM) Processes. Society of Automotive Engineers. Pittsburgh, PA. 1999. [http://www.sae.org SAE]

Guidelines for the Naval Aviation Reliability Centered Maintenance Process. Department of Defense. Washington, D.C. NAVAIR 00-25-403

Moubray, John. Reliability-Centered Maintenance. Industrial Press. New York, NY. 1997. ISBN 0-8311-3146-2

MSG-3. Maintenance Program Development Document. Air Transport Association, Washington, D.C. Revision 2, 1993.

Nowlan, F. Stanley, and Howard F. Heap. Reliability-Centered Maintenance. Department of Defense, Washington, D.C. 1978. Report Number AD-A066579.

Planned Maintenance System: Development of Maintenance Requirement Cards, Maintenance Index Pages, and Associated Documentation. Naval Sea Systems Command. Washington, D.C. Military Specification MIL-P-24534A(NAVY). 1985.

Reliability-Centered Maintenance Handbook. Naval Sea Systems Command. Washington, D.C. Handbook S9081-AB-GIB-010 (Revision 1). 18 April 2007.

Reliability-Centered Maintenance Requirements for Naval Aircraft, Weapons Systems and Support Equipment. Department of Defense. Washington, D.C. MIL-STD 2173(AS) (now cancelled)

ee also

*Maintenance, repair and operations


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