Effect of Temperature on Electrochemical Corrosion Behavior of X90 Pipeline Steel and Its Weld

The microstructure and electrochemical corrosion behavior of X90 pipeline steel and its weld in near neutral simulated soil solution were investigated by optical microscopy (OM) and electrochemical testing at different temperatures. The effects of temperature on electrochemical corrosion behavior were analyzed. The results show that the microstructure of the base metal of X90 pipeline steel consisted of granular bainite and a small amount of polygonal ferrite, the microstructure of the weld consisted of acicular ferrite and a small amount of granular bainite. With the increase of temperature, the open circuit potentials of the base metal and weld shifted negatively, the thermodynamic stability decreased, and the corrosion tendency increased for the materials. The polarization curves of the metal base and weld displayed typical characteristic of anodic dissolution without remarkable passivation region. With the increase of temperature, the corrosion current densities of the base metal and weld increased, the polarization resistance decreased, and the corrosion resistance decreased. At the same temperature the corrosion rate of the weld was higher than that of the base metal, so the weld had worse corrosion resistance. The corrosion of X90 pipeline steel was controlled by cathodic diffusion process in the test environment.