SCC of X-52 and X-60 weldements in diluted NaHCO{sub}3 solutions with chloride and sulfate ions

摘要

Stress corrosion cracking tests were performed in both X-52 and X-60 weldments in sodium bicarbonate (NaHCO{sub}3) solutions at 50 ℃ using the Slow Strain Rate Testing (SSRT) technique. Solution concentrations varied between 0.1 to 0.0001 M, and to simulate the NS-4 solution, chloride (Cl{sup}-) and/or sulfate ((SO{sub}4){sup}(2-) ) ions were added to the 0.01 M solution. Tests were complemented with hydrogen permeation measurements and polarization curves. It was found that the corrosion rate, taken as the corrosion current, I{sub}(corr), was maximum in 0.01 M NaHCO{sub}3 and with additions of (SO{sub}4){sup}(2-) ions. Higher or lower solution concentrations or additions of Cl{sup}- alone decreased the corrosion rate of the weldment. The SSC susceptibility, measured as the percentage reduction in area, was maximum in 0.01M NaHCO{sub}3. Higher or lower solution concentrations of additions of Cl{sup}- or (SO{sub}4){sup}(2-) decreased the SCC susceptibility of the weldment. The amount of hydrogen uptake for the weldment was also highest in 0.01 M NaHCO{sub}3 solution, but it was minimum with the addition of Cl{sup}- or (SO{sub}4){sup}(2-) ions. Thus, the most likely mechanism for the cracking susceptibility of X-52 and X-60 weldments in diluted NaHCO{sub}3 solutions seems to be hydrogen-assisted anodic dissolution.