Effects of dissolved calcium and magnesium ions on lead-induced stress corrosion cracking susceptibility of nuclear steam generator tubing alloy in high temperature crevice solutions

The effects of Ca2+ and Mg2+ ions on the stress corrosion cracking (SCC) susceptibility of UNS N08800 are investigated using constant extension rate tensile (CERT) tests at 300 °C in simulated crevice chemistries. The presence of lead contamination in the crevice chemistries increases significantly the SCC susceptibility of the alloy. The lead-assisted SCC (PbSCC) susceptibility is reduced markedly by the addition of Ca2+ and Mg2+ ions into the solution and this mitigating effect is enhanced by increasing the total concentration of Ca2+ + Mg2+. The CERT test results are consistent with the types of fracture surfaces shown by Scanning Electron Microscopy (SEM). There is a reasonable correlation between the SCC susceptibility and the donor densities in the anodic films in accord with the role of lead-induced passivity degradation in PbSCC.