CREVICE CORROSION OF NICKEL-BASED ALLOYS IN NEUTRAL CHLORIDE AND THIOSULFATE SOLUTIONS

Electrochemical techniques were used for the study of crevice corrosion of two nickel-based alloys in aqueous solutions of 1 M NaCl and 1 M NaCl + 0.01 M Na2S2O3. Artificial metal/Teflon crevices were used and principal testing temperatures ranged from 20 to 80 C. The studies were supplemented by anodic polarization experiments. Inconel alloy 625 was resistant to crevice corrosion under all tests conditions, and its behavior is discussed in terms of the effect of the molybdenum-alloying element on the stability of passive films. Alloy 600 was more sensitive to crevice corrosion. The presence of thiosulfate, combined with chloride, decreased the crevice corrosion resistance. The deleterious effect of thiosulfate is discussed in terms of passivity breakdown and the formation reduced sulfur species within active crevices, with particular focus on the H2S(aq) species and its ability to increase the anodic dissolution of Ni.