ASQ - Statistics Division

Probability of Detection Analysis for Fluorescent Penetrant Inspection Systems

Abstract: Fluorescent penetrant inspection (FPI) is a Nondestructive Testing (NDT) method commonly used for flight quality assurance of commercial, military, and rocket engine hardware. FPI is used to detect defects that are open to the surface. In the Aerospace industry, the detection of linear indications is often of primary interest when performing FPI on engine hardware. A linear indication may be indicative of a surface crack, which can occur during manufacturing or service life. The objective of FPI is to detect low cycle fatigue cracks before they grow to a critical length which could impact the structural integrity of the hardware. To determine the smallest size indication that an inspector can distinguish as linear with a specified level of reliability, a Probability of Detection (POD) demonstration test and analysis is performed. Each inspector is tested on each production FPI system they perform work on using a known specimen standard. The results are analyzed using established statistical regression methods, the outcome of which is used to determine an inspector's capability.

Keywords: binomial regression - logistic regression - logit - probit - hit/miss analysis - probability of detection - POD - fluorescent penetrant inspection - FPI

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