Electrochemical impedance spectroscopy study on the corrosion of the weld zone of 3Cr steel welded joints in CO₂ environments

The welded joints of 3Cr pipeline steel were fabricated with commercial welding wire using the gas tungsten arc welding (GTAW) technique. Potentiodynamic polarization curves, linear polarization resistance (LPR), electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), and energy-dispersive spectrometry (EDS) were used to investigate the corrosion resistance and the growth of a corrosion film on the weld zone (WZ). The changes in electrochemical characteristics of the film were obtained through fitting of the EIS data. The results showed that the average corrosion rate of the WZ in CO₂ environments first increased, then fluctuated, and finally decreased gradually. The formation of the film on the WZ was divided into three stages:dynamic adsorption, incomplete-coverage layer formation, and integral layer formation.