Corrosion of an UNS S31803 distillation column for acetic acid recovery

Unusually extended corrosion phenomena were detected in a distillation column, made of UNS S31803 duplex stainless steel, of a plant for the production of cellulose acetate. The process fluid was an aqueous solution of 80% acetic acid to separate by simple rectification. Corrosion was in the form of uniform attack mainly on downcomers and plates corresponding to the feedstock line. The phenomenon was a consequence of incomplete neutralization of sulphuric acid in the process fluid, used as a catalyst for the hydrolysis of esters. Controlled addition of H2O2 was proposed to solve the problem.