Risk-Based Inspection of Relief Valves

Historical methodologies for routine inspections of relief valves involve removing relief valves from service, inspecting, testing and repairing them as needed at some interval that was the same for most or all relief valves. Intuitively, it did not seem right to take this approach. Not all relief valves experience the same severity of service (probability of failure) and not all relief valves are in equally critical service where a failure of the relief valve to perform as intended would have the same effect (consequence of failure). However, until a methodology was developed to provide a logical and consistent approach, it was the best practice available. This paper will discuss a risk based inspection methodology developed for relief valves installed in industrial facilities and its application to two plants. Several benefits have resulted from the application of the risk based inspection program. Inspection resources are now more focused on relief valves that have a higher probability of failure or that are in a more critical service. Inspection intervals for these relief valves, on average, have been reduced so that they will be inspected on a more frequent basis. For the entire population of relief valves, however, the average inspection interval has increased which means that additional inspection resources will now be available to be focused on other critical areas of the plant. Thus producing a safer work environment and a decreased likelihood of a release to the atmosphere.