EFFICIENCY OF INHIBITORS OF CHLORIDE-INDUCED CREVICE CORROSION OF A Ni-Cr-Mo ALLOY

Alloy 22 was considered as a candidate for the engineered barrier of the USA repository and it is still considered among the candidates in the scoping work for the Argentine repository system. Chloride ion is the only species present in groundwater that is able to promote crevice corrosion, if severe conditions such as high temperatures and a tight crevice are present. Other species present in groundwater have shown to be inhibitors or non-detrimental species. The objective of this work was to evaluate the efficiency of different species potentially found in groundwaters as possible inhibitors of crevice corrosion of alloy 22. A modification of the THE method (ASTM G 192) was used for determining the crevice corrosion repassivation potential of alloy 22 in chloride plus inhibitor solutions at 90ºC. The species tested as inhibitors were nitrate, sulfate, carbonate, bicarbonate, chromate and molybdate anions. The critical ratio for the complete inhibition ranged from 0.2 to 2. Nitrate was the most efficient among tested inhibitors. The carbonate was the only species of the carbonate/bicarbonate/carbonic acid equilibrium able to inhibit the chloride-induced crevice corrosion of alloy 22. Sulfate, chromate and molybdate were moderately good inhibitors.