Anodic electrochemical behavior of X80 pipeline steel in NaHCO₃ solution

X80 steel has the potential to be widely used for building the gas transmission pipelines because of its high-intensity and high-toughness. Its corrosion performance is a key problem for the life expectancy, especially in soil environment. The anodic electrochemical behavior of X80 pipeline steel in NaHCO₃ solution was studied using potentiodynamic polarization curve, dynamic electrochemical impedance spectroscopy (DEIS) as well as SEM observation. The results show that the shape of the polarization curves changes with HCO₃^- concentration. The corrosion rate of X80 pipeline steel first increases and then decreases with the increase of HCO₃^- concentration. 0.009 mol/L is the critical concentration of HCO₃^- for forming the 'passive' film of the X80 pipeline steel. There is no anodic current peak in the solution when HCO₃^- concentration is below 0.009 mol/L, and one anodic current peak below 0.05 mol/L and two anodic current peaks above 0.1 mol/L. The results of the DEIS measurements are in complete agreement with the potentiodynamic polarization curve. The corrosion products chane with polarization potential and two equivalent circuits are used to explain the experimental spectra of X80 pipeline steel in the whole corrosion process. Therefore, the combination of dynamic polarization cure and DEIS methods can be well used to investigate the corrosion behavior of X80 pipeline steel in NaHCO₃ solution at various potentials. In addition, different corrosion products forming at various potentials and the corrosion mechanisms of X80 pipeline steel are briefly analyzed.