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Procedure for when penetrant inspection gets rejected


Mar 22, 2019
I had a batch of 350 of these fairly simple knurled parts that went out for penetrant inspection per BAC 5423 and my supplier just got ahold of me saying all 350 parts had been rejected due to "Tears".

I've sent a bunch of parts out for penetrant inspection (including these same parts in the past) and never had anything rejected up until now. What's the standard procedure when this happens? Considering we've made these parts in the past a few times without rejection, I'm inclined to assume it's an issue in the raw material and not our machining process but I don't know how I'd prove that. Do I just take the hit and purchase more material so we can start over? Do I pass on the findings to my material supplier?
When you say “tears” as opposed to tears without a picture you can’t tell, it’s obviously round bar,, tearing can be the result of heavy machining with a tool problem, or lamellar tearing off the cold rolling as result of re rolling a skin lamination, usually there’s a trace of mould powder from casting in the defect.
Dye pen the stock bar to see if it’s already present, probably is.
Even if the bar is defective, you need to put eyes on the rejected feature to connect the dots. Get the parts that were inspected that resulted in the rejected lot so it is crystal clear what the problem is.
SWAG: any part knurled with a standard compression knurl will light up like a Xmas tree if you put dye penetrant on it and put it under the UV light.
Penetrant inspection can be surprisingly subjective. Different levels allow a certain size and quantity of indications per area. Some machined features will cause false indications, micro drilled holes, small internal threads, coarse surface textures etc. I have had mixed success with the same parts and different tech's.

Our main customer (teir one aerospace company) has an in house N.D.T. lab and has requested to referee any parts failing penetrant, they accept more than half of the parts submitted for referee. I think an inexperienced penetrant tech can interpret false positives from indications other than material flaws.
Remember many moons ago a part for Boeing made from 17-4 that needed mag particle inspection.
It failed,
so we removed a little material
failed again.
so we removed a little material
Failed again

At this point we were f'd. Thought we might have to start over again in 15-5

We talked to somebody at the Boeing materials lab about our conundrom , he said 'no surprise 17-4 can have ferrite stringers, that's what's showing up in the mag particle testing.'
He went onto say the mag particle tech should have known this about 17-4, and he was going to have a word with the Boeing design engineer who should also have known this, as a memo had been generated about using 15-5 instead of 17-4 for certain parts that req'd mag particle