Cracking characteristics of alloy 690 in thiosulfate containing chloride solution

The cracking characteristics of Alloy 690 in deaerated lwt% NaCl solution with different Na₂S₂O₃ concentrations, namely 0.01, 0.1, 0.2 and 0.5 M, at controlled anodic potentials was investigated by using slow strain rate testing (SSRT) with a strain rate of 1 × 10^-6 s^-1. The results showed that the ultimate tensile strength and the ductility increased with increasing the concentration of Na₂S₂O₃ at the same anodic potential, but decreased with increasing potential at a fixed concentration of Na₂S₂O₃ Pitting corrosion could occur on Alloy 690 in lwt% NaCl solution with the concentration of Na₂S₂O₃ ≦ 0.1M, depending on the potential. The susceptibilities of Alloy 690 to pitting corrosion and environmentally-assisted cracking in lwt% NaCl solution were inhibited with the concentration of Na₂S₂O₃ ≧ 0.2M, regardless of the potential.