Corrosion of an UNS S31803 distillation column for acetic acid recovery

• Failure of UNS S31803 rectifying column for acetic acid recovery was investigated.
• Corrosion damages were induced by sulphuric acid contamination of the process fluid.
• Addition of low amount of H2O2 was sufficient to stop metal degradation.
• Eventual replacement of UNS S31803 by UNS S32750 was evaluated.

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.