Determination of sample size to support diagnostic inspection of components

A complex engineering system like a nuclear power reactor consists of a large variety and number of engineering components. As a part of a component aging management program, the diagnostic inspections of various component populations are performed to detect the onset of any unanticipated degradation. A prudent selection of the inspection sample size is necessary to optimise inspection cost. Sample size selection is typically based on the traditional statistical hypothesis test, which tends to result in a fairly large sample size. This paper presents an alternate approach to the sample size determination (SSD) problem based on the concept of the value of information (VoI). The paper provides a comparative analysis of the VoI and hypothesis-testing approaches through illustrative examples. The VoI approach is shown to provide a more meaningful way to minimise the cost of inspection as a function of component-replacement cost and losses arising from a failure. The characteristics and advantages of the VoI approach are analysed.