Effects of microstructure and environment's chemical composition on oxidation and IGSCC of alloy 600 on the secondary side of PWRs

Abstract

The intergranular oxidation of Alloy 600 was investigated in model environments of steam generator (SG) flow restricted zones on the secondary side of PWRs. Various heat treatments were applied to the A600 plate to identify the effect of grain boundary carbide density and chromium depletion on intergranular oxidation. The effect of the conductivity was also investigated. For this purpose, oxidation tests were carried out in environments containing various amounts of chloride and sulfate ions. Results showed that oxide penetration depths increase with the conductivity of the environment for given pH and electrochemical potential. Yet, for environments with similar conductivities, some heat-treated samples showed an effect of the sulfate-to-chloride ratio on intergranular oxidation. Last, the presence of intergranular chromium depletion contributed to increase the oxide penetration depths.