Corrosion of X80 steel welded joint under disbonded coating in an acidic soil solution

In this paper, the corrosion behaviors of a welded joint of X80 pipeline steel underneath disbonded coating in an acidic soil solution were studied through electrochemical measurements, SEM/EDS and 3D ultra-depth microscopy. The results showed that the corrosion rates of the heat affecting zone (HAZ) specimens were the largest during the experiment, while the smallest corrosion rates always appeared with the base metal (BM) specimens at the same position. The corrosion rate of all the specimens at the opening were always larger than those at the bottom of the disbanded coating during the whole experiment. General corrosion dominated the surface of all specimen at different position, with much nonuniform corrosion inlaying in it. The nonuniform corrosion sensitivity of the HAZ specimens was larger than that of the BM and welded zone (WZ) specimens, whether at the opening or at the bottom. Under the disbonded coating, the nonuniform corrosion sensitivity of the specimens firstly decreased with the distance from opening and increased at the bottom. The maximum corrosion fluctuation of the HAZ specimen was available at the opening.