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Reliability Centered Maintenance (RCM)

RCM is generally used to achieve improvements in fields such as the establishment of safe minimum levels of maintenance, changes to operating procedures and strategies and the establishment of capital maintenance regimes and plans. Successful implementation of RCM will lead to increase in cost effectiveness, improved asset availability and reliability (machine uptime), and will help provides a greater insight to the level of risk that the organisation is managing.

It is defined by the technical standard SAE JA1011 [3], Evaluation Criteria for RCM Processes, which sets out the minimum criteria that any process should meet before it can be called RCM. This starts with the 7 questions below, worked through in the order that they are listed:

1. What is the item supposed to do and its associated performance standards?
2. In what ways can it fail to provide the required functions?
3. What are the events that cause each failure?
4. What happens when each failure occurs?
5. In what way does each failure matter?
6. What systematic task can be performed proactively to prevent, or to diminish to a satisfactory degree, the consequences of the failure?
7. What must be done if a suitable preventive task cannot be found?

Reliability centered maintenance is an engineering framework which defines a complete maintenance regime. It regards maintenance as the means to maintain the functions stakeholders may require of their plant machinery in a defined operating context. As a discipline it enables stakeholders to monitor, assess, predict and generally understand the working of their physical assets.

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 (FMECA) of the machinery based on its operating context.

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 maintenance tasks are rationalised. It is important not to dismiss the applicability of maintenance in this phase.

The RCM process is kept live throughout the "in-service" life of the machinery, where the effectiveness of the maintenance is kept under constant review and adjusted in light of the experience gained.

RCM 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 can be identified; their dominant failure modes and causes determined; and the consequences of failure can be 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 acceptable). When the risk of such failure is very high, an RCM program encourages, and sometimes mandates the user to consider changing something which will reduce the risk to an acceptable level.

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

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

The RCM process emphasises three principal threats from equipment failures:

- Safety & environment,
- Operations,
- Maintenance budget.

RCM offers five principal options among the risk management strategies:

- Predictive maintenance tasks,
- Preventive Restoration or Preventive Replacement maintenance tasks,
- Detective maintenance tasks,
- Run-to-Failure, 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 an acceptable level?).

Identification of Safety Critical Elements (SCE) and maintaining associated pre-defined performance standards is the foundation of asset integrity management (AIM).
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Scenic Acoustic & Vibration Engineering Ltd, 41 Clarence Road, Barrow-in-Furness, Cumbria, England, UK. LA14 9RT
Tel: 01229 871171 Mobile 07855 253 458
info@scenicacoustic.co.uk

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