Crevice corrosion behaviors of Alloy 690 and 405 stainless steel in chloride solutions with different concentrations of thiosulfate

•An electrochemical testing device for crevice corrosion was designed.•Reduction of S2O32− to H2S promoted pitting inside the crevice.•The increase of concentration ratio of Cl−/S2O32− promoted crevice corrosion.•Alloy 690 and 405 SS inside the crevice act as cathode and anode, respectively. The crevice corrosion behaviors of Alloy 690 and 405 stainless steel (SS) in chloride (Cl−) solutions with different concentrations of thiosulfate (S2O32−) were investigated using a self-designed electrochemical testing device for crevice corrosion. The increase of concentration ratio of Cl−/S2O32− promotes crevice corrosion of Alloy 690. When crevice corrosion occurs between Alloy 690 and 405 SS, Alloy 690 outside the crevice is used as the cathode for reduction reaction of O2, and Alloy 690 inside the crevice is also used as the cathode for hydrogen evolution reaction, both of which jointly promote the anodic dissolution of 405 SS inside the crevice. The crevice corrosion mechanisms of Alloy 690 and 405 SS are also discussed.