Probability of Flaw Detection for Use in Fracture Control Plans.

Abstract : Failure prediction techniques using fracture mechanics requires the knowledge of the presence and size and location of potential defects within the component under stress. The design techniques uses the fact that a satifactory NDT inspection will screen out all flaws whose size would lead to premature failure within the component. The paper presents the results of a statistical study designed to determine the ability of several NDT methods to detect and identify small crack like defects. Three inspection procedures and materials were evaluated in a production inspection program, titanium penetrant, aluminum penetrant and steel magnetic particle inspection. The results were presented in terms of cumulative probability of detection; detection of flaws of a given size or larger, and range probability of detection, detection of flaws within a given size interval. The range detection results show that all three inspection procedures were capable of high sensitivity in detection of flaws whose size was greater than .080 inches in length. For flaws in the range 0.060 to 0.080 only the high resolution penetrants were able to find flaws to 95% at 90, 95 and 99% confidence levels. The relative ranking of the three inspection procedures are (1) titanium penetrant (2) aluminum penetrant and (3) magnetic particle on high strength steel. (Author)