Probability of detection as a function of multiple influencing parameters

It is not always only the size of the flaw that determines the severity of the flaw for the structure. In such cases, it is important to express the capability of the non-destructive testing (NDT) system to detect a flaw with respect to exactly those parameters that determine flaw severity. The multi-parameter reliability model presented in this article shows a way of calculating and expressing the probability of detection (POD) as a function of different influencing parameters, using numerically simulated NDT system responses and experimentally measured responses. A successful application of the model is demonstrated on the data from a transmit-receive longitudinal (TRL) ultrasonic inspection of a cast iron component. The POD of the surfacebreaking semi-elliptical crack-like flaw is expressed as a function of its depth and length. In a direct comparison with the conventional signal response analysis, where the POD is expressed as a function of only the flaw size, the method provides a more comprehensive estimation of the reliability of the NDT system.