I am trying to select a material for a pressure vessel that will be in constant contact with highly concentrated carbonic acid and sulfuric acid at 100-150 degrees C. The concentration of the sulfuric acid is dilute and carbonic acid is up to 30%. Could you please suggest what grade of stainless steel (or any other) would be suitable for a very long life time?
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Brian Dalder Forum Moderator 169 Posts
Re: What's the best material for use with carbonic and sulfuric acid?7 June 2012 at 1:29pmIt wasn’t clear whether you have a mixture of dilute sulfuric acid and carbonic acid or will be handling these acids separately in the same equipment. In either case, a place to start is to look up compatibility data for the individual components. A quick check of Schweitzer’s Corrosion Resistance Tables rates 316L stainless steel as “good” with carbonic acid up to 175 degrees C. However, “good” is a corrosion rate of < 20 mpy which is enough corrosion that equipment would not likely last “for a long time”. Dilute sulfuric acid is very corrosive and 316L stainless steel is not recommended at all. On paper, a better choice for both carbonic acid and dilute sulfuric acid is Alloy 20, a nickel based alloy. If you are dealing with a mixture, it would be best to test potential alloy choices in the lab since mixtures can behave differently than their individual components. Impurities can also have an effect so use of representative samples for lab testing is important.