Explain Reliability Centred
Maintenance (RCM) and its process of implementation.
Reliability-centred
maintenance (RCM) is a systematic process of preserving a system's
function
by selecting and applying effective Preventive Maintenance (PM) tasks.
However
it differs from most approaches to PM by focusing on function rather than
equipment.
RCM
governs the maintenance policy at the level of plant or equipment type. In
general the concept of RCM is applicable in large and complex systems such as
large passenger aircraft, chemical plant, oil refineries and power stations.
The RCM approach arose in
the late 1960s and early 1970s when the increasing complexity
of
systems and consequent increasing size of the preventive maintenance task
forced a rethink of maintenance policies among manufacturers and operators of
large passenger aircraft. Pioneering work on the subject was done by United
Airlines in the 1970s to support the development and licensing of the Boeing
747.
The principles which define and characterise RCM are:
- a focus on the preservation of system function;
- the identification of specific failure modes to define loss of function or functional failure;
- the prioritisation of the importance of the failure modes, because not all functions or functional failures are equal; and
- the identification of effective and applicable PM tasks for the appropriate failure modes. Applicable means that the task will prevent, mitigate, detect the onset of, or discover, the failure mode. Effective means that among competing candidates the selected PM task is the most cost-effective option.
- The objectives of maintenance with respect to any particular item/asset are defined by the functions of the asset and its associated desired performance standards.
- Functional failure (the inability of an item/asset to meet a desired standard of performance) is identified. This can only be identified after the functions and performance standards of the asset have been defined.
- Failure modes are identified, which are reasonably likely to cause loss of each function.
- Failure effects are documented, describing what will happen if any of the failure modes occur.
- Failure consequences are quantified to identify the criticality of failure. RCM not only recognises the importance of the failure consequences but also classifies these into four groups: Hidden failure; Safety and environmental; Operational and Non-operational.
- Functions, functional failures, failure modes and consequences are criticality analysed to identify opportunities for improving performance and/or safety.
These principles are implemented in a seven step
process:
Preventive tasks are established. These may be
one of three main types i) scheduled on-condition tasks which employ
condition-based or predictive maintenance; ii) scheduled restoration; and iii)
scheduled discard tasks.
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