The reliability and performance of any machine is determined by two factors. These are as follows:
The way the machine was designed, and
The way it is operated.
Model showing the definition of Inherent Capability Loss
(ICL).
Expected
Failures
Failure characteristics and economics are such that for some
failures, the defined maintenance strategy is “No Scheduled
Maintenance” (NSM)4. This may be because of the two scenarios
described below:
The failure is random, and the PF interval is too short to be
of any use, or
because the cost of prevention is more than the costs of the
failure.
This reality means that there will be a certain level of
unavailability inherent in the design and operating conditions.
Failure modes which have NSM strategies will inevitably become
breakdowns and result in capability loss. We call such failure
modes Expected Failures. This is because over the life of the
asset, it is expected that such failures will occur and result in
loss of production.
Planned Maintenance
While some failures or breakdowns will be accepted as being
inevitable, others will be prevented either through condition
monitoring or fixed time component replacement. Where these
preventive actions require that the plant is taken off line, then
the preventive maintenance is another loss that is inherent.
In addition, condition monitoring may detect the onset of failure.
The rectification action taken in such cases may require the plant
to be taken off line. All of these losses combine to form the
Inherent Capability Loss shown. The Inherent Performance Level is
therefore the total time less the Inherent Capability Loss.
NOTE - It is worth noting that if the
failure consequences are hazardous, a NSM strategy can not be made.
In such cases, a modification is required to reduce the risk of
failure to a tolerable level.
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