The reliability of defect sentencing in manual ultrasonic inspection

A general model for NDE inspection techniques that predicts the probability of missing critical defects and misclassifying harmless defects has been developed. The model is exercised for the quantification of risks involved in v-butt weld measurement of defects, in relation to restricted access and the effect of human factors. The NDT technique modelled here is the 20 dB drop technique used in ultrasonic testing. The general methodology is based on quadrature summation, which allows all errors to be treated in an identical way. An explanation of the framework and methodology, as well as the data mining used to populate the model with human factors error probabilities, etc., are also presented here. The model is used in the first instance to quantify the possible consequences due to access limitations in v-butt weld inspections. Generalisation of the model to other techniques, such as manual eddy current inspection, is also discussed.