Corrosion Behavior of Austenitic and Duplex Stainless Steels in Thiosulfate- and Chloride-Containing Environments

The effect of thiosulfate concentration on the corrosion behavior of duplex stainless steels S32101 and S31803 was investigated in thiosulfate- and chloride-containing environments, of relevance to the paper machine environments and other chemical industrial processes. Electrochemical methods including cyclic potentiodynamic polarization and potentiostatic scratch test were used to study the localized corrosion behavior of these alloys. Corrosion behavior of tested duplex stainless steels was compared with austenitic stainless steels S30403 and S31603, which are typically used in relevant industrial equipment, like paper machines. Cyclic potentiodynamic polarization results indicated that the presence of thiosulfate ions considerably lowered the repassivation potential of all stainless steels tested. In presence of thiosulfate ions, different grades of duplex stainless steels behaved differently. S31803, with the highest molybdenum and chromium content, was the most resistant to pitting corrosion among the four grades of stainless steels tested. Preferential dissolution of the ferritic phase was observed in pits formed on S32101.