(149c) Quantitative Risk Based Methodology for Pressure Relief Valve (PRV) Inspection Optimization

Traditional API 581 risk calculation approach can have mixed results for establishing PRVs inspection interval. The problem here is twofold – Probability of Failure (PoF) is low for most cases therefore Consequence of Failure (CoF) drives risk, leading to impractical inspection frequencies at extreme ends of the spectrum. This coerces the engineering teams to evaluate other more realistic inspection intervals for cost/safety reasons either based on experience or industry data rather than asset information.

An alternative adaptive methodology is discussed in this presentation where PoF and CoF are based on user defined Risk Reduction Targets and Safety Integrity Levels, rather than financial risk basis. This methodology captures how using actual in-service testing results rather than default values in a Weibull distribution can deliver a more representative Probability of Failure on Demand (POFOD) and how it ultimately can be reliably used to deliver an optimum test frequency based on quantitative assessment of failure modes.