Reader Response: Penetrant Sensitivity – LCF crack POD panels

Words from the Wise

We often remind our readers that the content of this newsletter is largely driven by our readers and the interaction that we have with them. We are pleased to relate the following comments on penetrant system sensitivity that we received from Terry Kessler, which reflect the experience of a person who has spent his working life in the use of penetrants on aircraft engine
parts.

“Professor, I don’t often get to comment on anything you publish in The Penetrant Professor as I seem to agree on everything
that is there. I do feel I can add one additional comment on the subject of“Penetrant Sensitivity” from the Feb 2013 publication. While the sensitivity is of course equivalent across the methods, this sensitivity is determined on flat orsimple grooved LCF crack POD panels that lend themselves to optimum processing. That is there are no deep cavities and wells to retain fluids
as there are in most critical rotating life limited parts in jet engines these days. Even experienced inspectors cannot control the contact time for the removers whether they are water or hydrophilic removers. Over washing is thought to be a greater risk due to the difficulty in removing the water from the inside of the tire shaped rotor parts on water washable penetrant and lower
risk of over washing from the surface active remover used in Method D.

So the bottom line is the part geometry complexity raises the concern for over washing as the biggest variable in the choice of Method in the FPI selection process. Also entering the process is the possibility that the higher sensitivity penetrants in the water washable methods were not as available historically (1960’s and 1970’s) as the PEP Level 4 penetrants and OEM’s got used to using only PEP for higher sensitivity
inspections.”

We are grateful to Terry for this explanation and hope that it is of use to othersin this field.