Producing a POD curve with emulated signal response data

Ultrasonic testing is an important tool for assessing the structural integrity of pressurised components in nuclear power plants during in-service inspection. Consequently, the reliability of inspection is of high significance. In particular, it is important to determine the largest crack that could conceivably be missed during in-service inspection. This information is utilised in order to choose the most effective method for different situations. Probability of detection (POD) curves are used to quantify the effectiveness of the inspection. However, these POD curves require a lot of data points in order to provide reliable estimates of the lower limit performance. Traditionally, obtaining these curves has been relatively expensive and this is why different simulation tools have been used to reduce costs and the number of physical test-pieces needed. In the current study, a novel method based on limited test-pieces is explored to produce a POD curve from the measured data. The present data contains just three artificial cracks made with thermal fatigue. This is insufficient to produce a POD curve. However, the data was sufficient to evaluate the novel approach and to gain preliminary estimates of the expected POD and the most important influential parameters. In this study, the idea is to emulate the amplitude response from the measured crack in a way that represents an amplitude response from a certain crack size. This amplitude data is converted to a B-scan image from which the inspector will evaluate whether there is a
crack or not. Then, a POD curve is generated from the achieved hit/miss data.