SCC of X‐52 and X‐60 weldements in diluted NaHCO 3 solutions with chloride and sulfate ions

Stress corrosion cracking tests were performed in both X‐52 and X‐60 weldments in sodium bicarbonate (NaHCO 3 ) solutions at 50°C 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 − ) and/or sulfate ( $\rm SO_{4}^{2-}$ ) 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 corr , was maximum in 0.01 M NaHCO 3 and with additions of $\rm SO_{4}^{2-}$ ions. Higher or lower solution concentrations or additions of Cl − alone decreased the corrosion rate of the weldment. The SSC susceptibility, measured as the percentage reduction in area, was maximum in 0.01M NaHCO 3 . Higher or lower solution concentrations of additions of Cl − or $\rm SO_{4}^{2-}$ decreased the SCC susceptibility of the weldment. The amount of hydrogen uptake for the weldment was also highest in 0.01 M NaHCO 3 solution, but it was minimum with the addition of Cl − or $\rm SO_{4}^{2-}$ ions. Thus, the most likely mechanism for the cracking susceptibility of X‐52 and X‐60 weldments in diluted NaHCO 3 solutions seems to be hydrogen‐assisted anodic dissolution.