Please compare and contrast the isocorrosion curve for 316/316L in unaerated H2SO4 Vs aerated H2SO4 (93-98%). Under ambient conditions in Beaumont, Texas, am I better off allowing moist air to enter the tank, risking local corrosion from moisture absorption and dilution at the gas-liquid interface? Does the mode of corrosion change (i.e., general to pitting) depending on aeration?
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Brian Dalder Forum Moderator 175 Posts
Re: Can you provide information on corrosion of austenitic stainless steels?15 February 2012 at 1:29pmSulfuric acid is tricky to deal with because its corrosive properties change dramatically with velocity, concentration, impurities, and temperature. Interestingly, 98% sulfuric acid is less corrosive than 93% and both are less corrosive than intermediate sulfuric acid concentrations. Due to velocity effects and other considerations, the proper MOCs for sulfuric acid might be different depending on the equipment (e.g., storage tank, piping, pumps, valves, etc.). You can find a lot of information on corrosion of austenitic stainless steels, including isocorrosion charts, in a publication entitled "The Corrosion Resistance of Nickel-Containing Alloys in Sulfuric Acid and Related Compounds," published by the old International Nickel Company (Inco). This is available free of charge at the Nickel Institute website (http://www.nickelinstitute.org). The isocorrosion charts from this publication suggest that aerated sulfuric acid is generally less corrosive than sulfuric acid purged with nitrogen. Because of the potential evolution of hydrogen from corrosion in sulfuric acid storage tanks, vent design is very important and ingress of moisture should be minimized. The reasons for this and other design details are covered in NACE standard SP0294 "Design, Fabrication, and Inspection of Storage Tank Systems for Concentrated Fresh and Process Sulfuric Acid and Oleum at Ambient Temperatures". It would be a good idea to get copies of both of these publications to gain additional insight not possible in this simple question/answer format.