Corrosion and Repassivation Behavior of Stainless steels in Chloride and Thiosulfate Containing Environments

In this study, the combined effect of chloride and thiosulfate ions and the effect of the ratio of the two ions on passivation in 304L, 316L, and the duplex stainless steels 2101 and 2205 are investigated using potentiostatic scratch tests. Cyclic polarization and the scratch tests were used to understand the role of anions on localized corrosion in these systems. It was found that the thiosulfate pitting began at a lower potential for 2101 than 304L in 0.6 M NaCl + 0.03 M Na₂S₂O₃ solution. The pit morphologies for 304L, 316L, and 2101 in an 0.6 M NaCl + 0.03 M Na₂S₂O₃ solution were very different from each other. The results indicate that the pitting switches from predominately thiosulfate pitting to chloride pitting at approximately 0.1 V.