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Improving NDE Capability Through Multiple Inspection With Application to Gas Turbine Engine Disks

Report Number: AFWAL TR 82-4111
Author(s): Jann N. Yang; Robert C. Donath
Corporate Author: Materials Laboratory
Date of Publication: 1983-06-01
Pages: 85
AD Number: ADA131762

Techniques are not capable of repeatedly producing correct indications when applied to flaws of the same length. As a result, the probability of detection (POD) for all cracks of a given length has been used to define the capability of a particular NDE system in a given environment. Thus the NDE reliability consists of two types of errors. For safety-critical components in airframe structures, Type I error is of major concern. According to the damage tolerant requirement, the inspection limit or the reset crack size should be the crack length associated with a 90% detection probability and 95% confidence level. On the other hand the main criterion used for analysis of the retirement-for-cause of gas turbine engine components is the minimization of the life cycle cost. The objectives of this report are to: (1) formulate and derive mathematically the resulting POD curve for multiple inspection systems; (2) investigate quantitatively the benefit and advantage of multiple inspection procedures; (3) establish the direction in which the NDE capability should be improved under certain mission requirements; (4) establish the strategy and sequence for multiple inspection procedures to reduce either Type I or Type II errors or both; (5) determine the POD curve for a disk from the POD curve of an NDE system; (6)determine the inspection reliability of engine disks; and (7) evaluate the benefit of multiple inspections for engine disks.

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