Must parts from every plating tank be tested, or can one be considered representative of all identical tanks?

A. Because I do not have a copy of QQ-N-290 handy, I had intended to refrain from commenting. But then I remembered that the objective of the 'letter of the law' is to secure the 'spirit of the law'. And, certainly, the spirit of such specifications is to try to insure that vital fasteners will not fail due to hydrogen embrittlement.

I don't see how the supplier could assure that the three tanks are so identical in their operating parameters that the untested ones can be guaranteed to not cause embrittlement; all manner of things could be tank-specific: rectifier ripple, contamination, stray currents, and temperature, to name a few. Monthly testing is infrequent enough that embrittlement could come and go in between tests anyway; to further extrapolate that one tank is fully representative of three seems unreasonable to me. Only a free opinion, for what it's worth, about 'the way things oughta be'.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

A. Three identical tanks are no longer identical as soon as one plating run has been done in each.

I have never heard of any buyer, and most certainly not Boeing, ever allowing pull tests to be done on only one tank. even if the test is done on the tanks on a rotating basis.

If you have a failure, what do you do, recall every part plated in all three tanks?

Penny wise and pound foolish.

A. Gary, The tests are designed primarily to evaluate the chemistry, unless the tanks have the same solution being pumped through them, EACH tank must be qualified or ONLY the tank qualified can be used for certification purposes.

I'm glad to hear that the comments I have been getting are exactly my own. I have always required suppliers to run notched bars in all of their tanks, but I continue to get objections from suppliers and others within the industry as to the necessity of the tests when it comes to multiple tanks. Their statement is that the hydrogen is picked up during the activation process, which is true, however they don't take into consideration the conditions within the plating tank itself. I don't want to get into a discussion on hydrogen embrittlement, which I have sufficient knowledge; I just wanted to get some support. I do know for a fact, that there are major companies that do take the philosophy that one tank is sufficient.

Thanks, for the backing.