SCC of X‐52 and X‐60 weldements in diluted NaHCO3 solutions with chloride and sulfate ions

Abstract

AbstractStress corrosion cracking tests were performed in both X‐52 and X‐60 weldments in sodium bicarbonate (NaHCO3) 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, Icorr, was maximum in 0.01 M NaHCO3 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 NaHCO3. 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 NaHCO3 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 NaHCO3 solutions seems to be hydrogen‐assisted anodic dissolution.