Page 623 - Marine Structural Design

Chapter 34 Risk Centered Maintenance 599

Scheduled overhaul can be applied to an item at or before a certain specified age limit. An
overhaul task may be applicable to an item when the following criteria are met:
There is an identifiable age af€er which the item's failure rate increases rapidly
Failure resistance of the item can be restored by overhaul
ScheduCed repfucement is a scheduled elimination of an item or its parts at or before a certain
age limit. A schedule replacement program can be applied under the following circumstances:
There exists an identifiable age afier which the item's failure rate increases rapidly
Failure resistance of the item can be restored by replacing the item or its parts
Schedukdfirnctwn test is a scheduled inspection of a hidden failure, which is normally an on-
demand failure. A SFT may be performed on an item under the following conditions:
A functional failure is not evident to the operating crew during the normal duty
No other type of preventive tasks are as cost-effective
Run tofiure is a deliberate decision allowing an item to run to failure. The main reason for
run to failure may be that no other preventive tasks are possible or as cost-eff'ective
The criteria given for using the preceding tasks serve only as guidelines for selecting a suitable
preventive task. An example of the RCM decision logic is illustrated in Figure 34.5. Note that
this is a simplified version of the decision logic. Such decision logic can not cover all
situations. For example, a hidden function with aging failures may be prevented by a
combination of scheduled replacements and function tests.

Can the failure be detected Yes Scheduled on-condition
by any technique?

Is the failure agerelated? 3
Is overhaul feasible?

Figure 34.5 RCM Decision Logic