Electrochemical Condition for SCC of Type 316L Stainless Steel in Chloride Solutions Containing Thiosulfate Ion

Abstract

Electrochemical conditions for stress corrosion cracking of Type 316L stainless steel have been investigated in the chloride solutions containing thiosulfate ion using polarization curves for Pt and Type 316L. And the following results were obtained; 1. At lower pH or at higher concentration of thiosulfate, chloride solution containing thiosulfate ion became turbid because of sulfur produced by disproportionation of thiosulfate ion. 2. In the region of potential at which stress corrosion cracking occurred, thiosulfate ion was reduced to sulfide in addition to main reduction reactions of dissolved oxygen and hydrogen ion. 3. Decrease in pH within pits and cracks of Type 316L leads to depassivation. Dissolved metal ion reacts with hydrogen sulfide to produce metal sulfide on the surface of pits and cracks. Therefore, this promotes local anodic dissolution.