Pitting Corrosion of 316 Stainless Steel Alloy in Chloride/Thiosulfate Solutions

Abstract

In this study, the effect of the presence of thiosulfate ion on pitting corrosion of AISI (American iron and steel institute) 316 stainless steel alloy was investigated in four different concentrations of NaCl solutions (1, 0.1, 0.01, 0.001 M NaCl solutions). The experiments were conducted at 50 °C based on the potentiodynamic method. During the experiment, the effect of seven different thiosulfate/chloride concentration ratios were tested (zero, 0.01, 0.03, 0.075, 0.1, 0.2, and 0.3 S₂O₃^-2/Cl^-1 ratios). Pitting potential was recorded for each test. Results show that 316 stainless steel alloy has a passivity region in all tests performed. However, this passivity region was strongly affected by both the chloride concentration and the thiosulfate/chloride concentration ratio. The addition of little amount of thiosulfate to chloride solutions was found to decrease the pitting resistance of the 316 stainless steel alloy. The addition of S₂O₃^-2 to chloride solutions resulted in a lower pitting potential value at 0.03 thiosulfate/chloride concentration ratio compared to the other ratios.