ENIQ Technical Report - Link Between Risk-Informed In-Service Inspection and Inspection Qualification

摘要

There is a growing need for a quantitative measure of inspection effectiveness as an input to quantitative risk-informed in-service inspection (RI-ISI). A Probability of Detection (POD) curve could provide a suitable metric. However there can be significant problems associated with generating realistic POD curves by practical trials. The ENIQ inspection qualification methodology can provide high assurance that an inspection system will achieve its objectives, but is not designed to provide a quantitative measure of the type that can be used in RI-ISI analysis.A project, led by Doosan Babcock, was therefore set up with main objectives to investigate approaches to quantifying the confidence associated with inspection qualification and to produce guidelines on how to relate inspection qualification results, risk reduction and inspection interval.This report discusses how a simplified POD curve, such as a step curve, could be used as the target for inspection qualification, or as an output from it. Work to investigate the sensitivity of relative risk reduction to the details of the POD curve is described from which it is concluded that use of a simplified POD curve could be justified.Two methods for quantifying the outcome from inspection qualification are described. The first method is a relatively simple process based on direct expert judgement. The second method is based on a more rigorous structured process employing Bayesian statistics, in which the subjective degree of belief in inspection capability derived from a Technical Justification (TJ) is expressed in probabilistic terms, and combined with data from practical trials results. Two pilot studies are described which involved a qualification body applying the quantification methods in practice. Recommendations for further work to make the approaches developed more robust are provided.