Effects of Alternating Current Corrosion Behavior of X80 Pipeline Steel under Delaminated Coating Defects

In the present study, the effect of an alternating current (AC) on pipeline corrosion under delaminated coating defects has been studied by performing adhesion tests, immersion experiments and characterizations by electrochemical impedance spectroscopy (EIS). Results showed the adhesion of an epoxy coating significantly decreased after immersion for 7 d. The corrosion degree around the defects became more severe with an increase in the AC density. According to the CLSM images, the maximum depth and width of the defect increased continuously and the corrosion type around the defect shifted from uniform to localized. This was attributed to the anodic dissolution of the X80 steel, which was accelerated by the AC after the coating failure. The AC corrosion was quite severe, which was due to the localized environmental alkalization near the defect and the oscillation of the interface. Thus, the alkaline environment of the cathode region accelerated the coating cathodic delamination. The oscillation effect further promoted corrosion.