Crevice Corrosion of Alloy 600 in High Temperature Aqueous Environments

Small bore Inconel Alloy 600(1) tubing exhibits classical crevice behavior in an appropriate high temperature aqueous environment and is therefore useful for studying the crevice chemistry of this alloy in systems which are not readily amenable to crevice simulation by external electrochemical control. Experiments in high purity water at 288 C show that crevice corrosion generates mildly basic conditions in the occluded region, but thermodynamic arguments indicate that the mechanism for intergranular stress corrosion cracking (IGSCC) of Alloy 600 in high purity water should differ from that for conventional caustic cracking. The results also suggest that aqueous diffusion, rather than the kinetics of alloy dissolution, controls the rate of crevice corrosion, and that the film rupture theory of stress corrosion cracking (SCC) may not apply at high temperatures.