We have been transitioning a lot of our NDI procedures to remove fasteners and inspect with bolt hole eddy current. A lot of them are through stacked structure, say 3 layers of aluminum that are not taken apart. We are getting a lot of what I'll call false positives, crack indications that cannot be detected using other methods and when the structure is disassembled so each layer can be inspected individually, the flaw can no longer be found by bolt hole eddy current either. So I think we're getting a lot of noise due to the surface interfaces, and possibly due to burs and shavings inside the hole since they typically were not deburred during manufacture. According to our NDI group they can't improve the inspection to make the problem go away.
Does anyone have any insight or experience on this matter? Thanks in advance.
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