The Emergence of Extended Field Technology in the Air Force
The wide-field eddy-current probe was developed to fulfill the inspection requirement of the broach slots in Pratt & Whitney F100-PW-220 Stage-1 and Stage-3 Compressor Disks. The flaw-detection requirement is to inspect an area 0.07 in. from the inner radius of the slot and 0.10 in. from the top and bottom edges for determining the presence of 0.006-and 0.010-in.-deep axially oriented flaws (Figure 1). While the slot is relatively small, the time required for inspection using the previous method is considerable. With this method a D20 (0.029-in.-diameter) split “D” coil is scanned in a “sew-stitch” fashion in the axial direction of the slot. After each scan the probe is indexed one quarter of the coil diameter. A total of 88 scans per slot is required for complete coverage, the time per slot being 20 min; with 40 slots the total inspection time per part is 14 hr when gain-calibration time is taken into account.
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