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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 air-frame structures, Type 1 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: formulate and derive mathematically the resulting POD c urve for multiple inspection systems; investigate quantitatively the benefit and advantage of multiple inspection procedures; establish the direction in which the NDE capability should be improved under certain mission requirements; establish the strategy and sequence for multiple inspection procedures to reduce either Type 1 or Type 2 errors or both; determine the POD curve for a disk from the POD curve of an NDE system; determine the inspection reliability of engine disks; and evaluate the benefit of multiple inspections for engine disks.
Improving NDE (Non-destructive evaluation) capability through multiple inspection with application to gas turbine engine disks
Additional title:
Verbesserung der NDE (zerstoerungsfreie Pruefung) und ihrer Tauglichkeit durch Mehrfachinspektionen in der Anwendung zur Pruefung von Schaufelraedern in Gasturbinen