Probability of detection (POD) demonstration tests are required by the National Aeronautics and Space Administration (NASA) for programs under fracture control. To be qualified to perform fluorescent liquid penetrant testing (PT) on production hardware that is classified as fracture-critical, an inspector must be able to demonstrate the ability to reliably detect crack-like discontinuities equal to or greater than the critical initial discontinuity size. To determine the smallest size indication that an inspector can distinguish as linear with a specified level of reliability, our company periodically conducts POD demonstration exams of both in-house inspectors and approved external vendors' inspectors. Each inspector is tested on each production fluorescent PT system they perform work on, using a known specimen standard. The results are analyzed using established statistical techniques, the outcome of which is used to determine an inspector's capability. However, the validity of the statistical analysis and the associated uncertainty is highly dependent on the design of the specimen standard. The guidelines stated in MIL-HDBK-1823 (1999) provide only minimum guidelines for designing a specimen standard for POD demonstration tests on a fluorescent PT system. This paper provides a practical and statistical review of the guidelines stated in M/L-HDBK-2823 regarding the number of discontinuities, the distribution of discontinuity sizes and how the sizes are distributed across the specimen standard (note that M/L-HDBK-1823 uses the term 'flaw' for 'discontinuity'). A general overview of the accepted POD analysis technique for fluorescent PT systems and interpretation of results will also be given, since the results of the statistical analysis can be subject to misinterpretation even with a well-designed specimen standard.
Applying MIL-HDBK-1823 for POD demonstration on a fluorescent penetrant system
Anwendung von MIL-HDBK-1823 zur POD-Darstellung von Fluoreszenz-Eindringprüfsystemen
ME - Materials Evaluation ; 67 , 3 ; 293-301
2009
9 Seiten, 3 Bilder, 8 Quellen
Article (Journal)
English
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