Analysis on properties of corrosion and hydrogen-permeation for weldment of SPV50Q steel

The difference in microstructures of the base metal (BM), weld metal (WM) and heat-affected zone (HAZ) of the weldment is one of the major causes for the failure of the welded equipments and pipelines serviced in corrosion environment, which would be essentially attributed to the non-homogeneous corrosion reaction occurred electrochemically on the weldment. Using potentiodynamic polarization measurement, electrochemical impedance spectroscopy (EIS) and hydrogen-permeation technique, the properties of corrosion and hydrogen-permeation for the weldment of SPV50Q steel used to fabricate LPG spherical tank were performed in H ₂S-containing solution. The results show that the difference in the various zones of weldment for SPV50Q steel affects the properties of corrosion and hydrogen-permeation in H ₂S-containing solution. BM has the best resistantomce compared wich HAZ and WM, and the resistance of WM is the poorest among them. As for the hydrogen-permeation properties, the diffusion efficient and rate for hydrogen increase in the order of BM, HAZ and WM.