Turbine Disk Retirement-for-Cause: Measurement of Inspection Uncertainty for Disk Eddy Current Inspections

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Rau, C
Hopkins, S
Eischen, J
Allison, D
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Review of Progress in Quantitative Nondestructive Evaluation
Center for Nondestructive Evaluation

Begun in 1973, the Review of Progress in Quantitative Nondestructive Evaluation (QNDE) is the premier international NDE meeting designed to provide an interface between research and early engineering through the presentation of current ideas and results focused on facilitating a rapid transfer to engineering development.

This site provides free, public access to papers presented at the annual QNDE conference between 1983 and 1999, and abstracts for papers presented at the conference since 2001.


Major cost savings are possible through life extension of high-cost jet engine components until damage develops. Retirement-for-cause (RFC) decisions will be based upon both non-destructive inspection (NDI) to detect and size defects, and engineering analysis to assess defect severity under future usage. Failure Analysis Associates is performing a three-year program for ARPA/AFML to define and verify an optimum RFC strategy for jet engine disks. In depth, quantitative characterization of NDI performance is a major part of this project. This presentation summarizes the quantitative evaluation of inspection (NDI) uncertainty for four independent inspections - two state-of-the-art eddy current inspections of disk bolt holes, one with conventional hardware but improved signal processing, and one higher resolution eddy current inspection system assembled for this project. Separate inspections of the same 490 bolt holes in 49, 3rd stage disks retired from service in TF33 engines were performed with each of the four NDI techniques. Inspection results were compared with each other and with the actual cracks measured by surface plastic replicas and selected destructive metallography. The variation of detection probability and sizing errors with flaw size and indication level is defined in a form suitable.for the probabilistic reliability analysis and RFC strategy formulation. Progress in the other project tasks, especially the stress and fracture mechanics analysis to define the conditional failure probability if a flaw of specified size were present will also be summarized.