Why RCM is Different - A Case Study

 

The purpose of maintenance is to prevent or mitigate the consequences of failure. Reliability Centred Maintenance (RCM) is a method that allows to achieve this goal in an effective way. This definition leads to different maintenance being applicable to essentially the same equipment, as can be shown by the following example.

A company purchases three cooling water pumps: Pump A, Pump B and Pump C.

These pumps are the same make, model & type and have been manufactured from the same batch of material. In other words these pumps are identical and presumably, vendors maintenance recommendations would also be identical. However, consider what effect this would have if the pumps were configured as shown below.

Train 1

Pump A - Single Pump (continuous running)

Train 2

Pump B - Duty Pump (continuous running)

Pump C - Standby Pump (not normally running)

Letís say that the pumps are employed to supply cooling water to two parallel production trains. Loss of cooling water to either train results in losses of $200,000/day. The cooling water requirement is 95 litres/minute for each train and each pump is capable of delivering 100 litres/minute.

What will happen to the supply of cooling water to the production train 1 if Pump A develops a leak of 10 litres/minute? The pump will be unable to fulfil its function and production from train 1 will stop at a cost of $200,000/day. To prevent this, some form of preventive maintenance e.g. a periodic overhaul, may be an appropriate strategy for Pump A.

What will happen to the supply of cooling water to the production train 2 if Pump B develops a leak of 10 litres/minute given that Pump C will come on stream? The system will continue to fulfil its function and there will be no loss of production from train 2. Given that there is no impact on production from Pump B leakage then an on failure maintenance strategy would be appropriate for Pump B. As Pump C is not normally running, most failures are hidden. However it is required to start on demand so a periodic function test would be an appropriate maintenance strategy for Pump C.

Note that the maintenance would again change if similar dedicated duty and duty/standby configurations arose but nitric acid was the pumped fluid and leakage was the failure mode under consideration. Leakage would be a safety hazard and could not be allowed to happen. Now, some form of on-condition maintenance strategy would be appropriate.

RCM is a technique used to define the maintenance requirements of a system in the current operating context. The above example demonstrates that identical equipment can have completely different maintenance strategies depending on the operating context.

Our 4 day RCM seminar fully covers operating context selection, supplemented by an intensive and comprehensive case study.


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