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I'm building a 304 SS beer keg boiler, I'm having some SS ferrules and a drain fitting welded on. My question is, after I have it welded can I use a citric acid bath to passivate the stainless steel to prevent the welds from corroding? I read that a solution of 4% to 10% citric acid and water heated to 150 degrees F will remove any iron from the stainless steel surface and after rinsing with clean water it will promote a good chromium oxide layer to make the SS more corrosion resistant. Manufacturers of SS pots, cookware and other stainless steel products use a hot nitric acid bath to passivate the SS. I can get nitric acid but it's nasty stuff and it has to be used in a certain way or it can ruin your stainless, on the other hand citric acid is said to not attack the SS but only remove any iron from the surface and after rinsing and drying the SS is much more corrosion resistant.