Corrosion behavior of X80 pipeline steel in a simulated soil solution at different temperatures

For the X80 pipeline steel, electrochemical impedance spectroscopy and potentiodynamic polarization curves were employed to examine the electrochemical corrosion behaviors of its base metal and weld joint under varying test in NS4 simulated soil solution. The Arrhenius equation was further applied to evaluate how temperature impacts their corrosion behaviors. It was found that the weld joint of X80 pipeline steel possesses a microstructure rich in low-potential bainite, with grain sizes coarser than those of the base metal. Both the base metal and weld joint exhibited typical anodic dissolution features without apparent passivation. As the temperature increases, the corrosion current density (Icorr) of the base metal increased from 13.73 to 24.76 µA/cm2, while that of the weld joint rose from 14.42 to 29.52 µA/cm2. In parallel, the activation enthalpy (ΔHa0) of the base metal and weld joint decreased from 5.742 to 5.243 kJ/mol and 3.826–3.327 kJ/mol, respectively. Accompanied by a corresponding decrease in corrosion resistance. At the same test temperature, the weld joint of X80 pipeline steel demonstrated inferior corrosion resistance relative to its base metal, which was reflected by a higher corrosion current density and lower polarization resistance. Throughout the tested temperature range, the corrosion process of both the base metal and weld joint of X80 pipeline steel was dominated by cathodic diffusion control.