Hastelloy C22 Compared C276 in Hydrochloric Acid

Q:  I have a maintenance shut-down and am looking into replacing the 2.4602 / Hastelloy C22 bolts and nuts in. To save time, I was thinking of using Hastelloy C276 / 2.4819 fasteners since I’m hoping to get stock parts. My medium is mainly hydrochloric acid approximately 20%. Would 2.4819 bolts work ?

A:  Hastelloy 2.4602 (C-22) alloy, UNS N06022, has better overall corrosion resistance in oxidizing corrosives than 2.4819 (C-276) due to the higher chromium content. More specifically, C22 bolts provide better protection when used in certain saturated wet chlorine environments. In addition, its high chromium content provides 2.4602 (C-22) fasteners much better resistance to oxidizing media that of 2.4819 (C276).

So the answer is “it depends”. For non-oxidizing acidic media like “pure” hydrochloric acid the corrosion rates are comparable and screws can likely be substituted. But if the acid contains oxidizing components (like e.g. nitric acid) the corrosion rates of  2.4819 (C-276) may be significantly higher than 2.4602 (C-22) and a substitution may not be suitable.

 

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