4. Discussion—comparison of RCM and the RRCM framework
Applying the RRCM framework may or may not result in different decisions compared with the RCM analysis methodology. For the flowline case, the RCM assessments (RCM logic) and the first parts of the RRCM framework led to scheduled PM for the steel lines and RTF for the valves. The importance of the factors identified may however change this, the conclusion being that the valves should be subject to predictive maintenance (condition monitoring) – maybe even continuous instead of scheduled – to prevent failure events.
Consider, for example, the hydraulic valves in the case presented (see Fig. 1): Valve B say, located about 20 km from the riser base. As condition monitoring (predictive maintenance) is unfeasible due to the long distance from the topside installation and the harsh seabed conditions, we are, by use of the RCM logic (see Fig. 2), led to answer the following question: is the failure rate of the valve increasing for the specific failure mode? Then we consider the second of the uncertainty factors; that we assume our data to be able to describe the ‘‘failure characteristics’’ of the valve. Having limited experience and no failures recorded in the data set, we may make the judgement that the probability of failure for this failure mode is low and we see no indication of increase in failure rate. However, corrosion and erosion wear on the valves could result in an increase in failure trend over time, for example for the failure modes ‘‘leakage in closed position’’ and ‘‘fail to close’’. The consequence is that the suitable PM task is to perform scheduled overhaul or replacement instead of RTF.