Material of construction for Nitric Acid Passivation Tanks

We've picked our passivation process. We will be performing Nitric Acid passivation. We have some spare tanks. One is a stainless steel and one is a lead lined mild steel. Plus a Deionized water rinse tank. Would we be best off inserting a plastic liner? My ancient chemistry tells me all nitrates are soluble therefore all metal tanks would have a finite life. Am I getting close? Lip extraction is already fitted. Is there anything really obvious I am missing.

Your old chemistry knowledge is correct as far as all nitrates being soluble in water, but that fact has absolutely nothing to do with the life expectancy of a tank containing nitric acid. You need to use stainless steel, but not all SS is created equal. If you do not know the exact grade and method of manufacture of your existing tank, I would not risk using it. Contact a reputable tank manufacturer and have a new one made. I think that they will tell you that the best choice is 316L (3/16" thick would be good). The tank should be welded inside and out (w/316L rod) and should be equipped with appropriate girth supports.

Jon Barrows, MSF, EHSSC Chemical Process Engineer Polyfab Plastics & Supply Springfield, Missouri

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Ed. note: We had an older thread on this subject, letter 051, which we've now merged into this one in lieu of maintaining seperately . . . (1995) I have been asked to provide the proper equipment for Passivating of 300 series Stainless Steel. The passivate solution is Nitric acid and run at 150 deg. F. We would like to bulk passivate and was wondering what material of construction you would recommend for the bulk processing of these parts. I thought there might be a possible problem having two dissimilar metals in the Passivate. Do you have any suggestions? Thanks.   N. Corriere (1995) Like they always say, coupon testing is the only way to know for sure, because there can always be some little idiosyncrasy you missed. But I'd be very surprised if 316SS didn't fill the bill perfectly in all regards, Nick Ted Mooney, P.E. finishing.com Brick, New Jersey (1995) We always used polypropylene for tanks and baskets. Thanks,      Ron Landrette plating equipment supplier - Bristol, Connecticut (1995) You could be right, Ron, but I don't think it's the best stuff for the tanks because the passivating solution is a very strong oxidizing agent; I'm still pretty sure that 316 stainless steel is best. A third opinion would be really welcome here! Ted Mooney, P.E. finishing.com Brick, New Jersey