A CRITICAL ANALYSIS OF ULTRASONIC ECHOES COMING FROM NATURAL AND ARTIFICIAL FLAWS AND ITS IMPLICATIONS IN THE DERIVATION OF “PROBABILITY OF DETECTION” CURVES

Structural integrity of safety components during service is strictly related to different factors such as: 1) the performance of the adopted non-destructive method; 2) the crack growth behavior of the material; 3) the load history during service. The present research is focused on ultrasonic non-destructive testing effectiveness which, during both the manufacturing stage and the in-service inspections, is essentially based on the adoption of suitable sample blocks for sensitivity calibration and the reliable knowledge of the Probability of Detection curve of the adopted non-destructive testing method. Firstly, the comparison between the ultrasonic responses coming from artificial flaws and natural fatigue cracks is carried out proposing a novel approach for their interpretation and coming to some interesting conclusions regarding the effective design of sample blocks for sensitivity calibration. Eventually, in order to improve their flexibility and the possible extrapolation to similar cases, also Probability of Detection curves were derived based on the proposed approach showing interesting advantages with respect to the traditional one.