Page 39 - RCM - A practical Guide_V1

RCM - A Practical Guide

If the criteria for OC maintenance are not met then the answer is, obviously, no and the analysis must
move on to the next available mitigation strategy.

Is a hard-time (HT) task applicable and effective?
Unlike OC maintenance, HT maintenance is dependent on the equipment type displaying wear out
characteristics consistent with patterns A, B and C (of the 6 patterns of failure)- or - to show an
increased conditional probability of failure (CpF) as it gets older.
Criteria
For HT maintenance to be selected certain criteria must be met:
• The asset type must show a definite age at which there is a rapid increase in the CpF
• Most items of that type must survive to that age

Yes

Types of hard time maintenance
There are two types of task of HT maintenance to be considered, both of which have their own
selection criteria and limitations. They are:
1. Scheduled Restoration
2. Scheduled Discard

Scheduled restoration
Maintenance’s old friend.
A restoration task involves acting at regular intervals to restore the asset to its inherent operational
capability and failure resistance. The asset must be maintained in order to prevent failure (or more
accurately, the consequences of failure).
Traditional (pre-RCM) thinking applied this strategy to most complex assets but, post-RCM, this
mitigation strategy is likely to be in the minority.
As is the RCM way, when considering a restoration task there are two options:
1. Full restoration - A general maintenance activity that is carried out on asset, in its totality
2. Partial restoration - A targeted maintenance activity at a specific, or dominant, failure
mode
To reiterate, a restoration task is only appropriate if the operation can restore the asset’s inherent
resistance to failure. If the asset type shows a definite age where the CpF rapidly increases but it is not
possible to restore its inherent resistance to failure, then a scheduled discard may be appropriate.
Scheduled discard
If it isn’t deemed possible to restore the inherent resistance to failure of the asset, it may be necessary
to consider replacing it on the assumption that by fitting a new item, the failure resistance, and hence
operational capability of the main equipment, will be restored.

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