Influence of Cl(−) ions on anodic polarization behaviour of API X80 steel in high potential/current density conditions in Na(2)SO(4) solution

Pipeline steel has considerable risk of corrosion in the high voltage direct current interference cases. Thus, under high potential/current density conditions, the anodic polarization behaviour of X80 steel in Na(2)SO(4) solution and the influence of Cl(−) ions were investigated using reversed potentiodynamic polarization, the current interrupt method, galvanostatic polarization, scanning electron microscopy, and X-ray photoelectron spectroscopy. In the Na(2)SO(4) solution free of Cl(−) ions, steel was passivated above 0.120 A cm(−2) and the potential increased from −0.32 V to 1.43 V. The passive film was composed of Fe(3)O(4), γ-Fe(2)O(3), and FeOOH. The addition of Cl(−) ions observably influenced the passivation by attacking the passivate film. Low concentration of Cl(−) ions (<5 mg L(−1) NaCl) could set higher demands of current density to achieve passivation and increase the requirement of potential to maintain passivation. A high concentration of Cl(−) ions (>5 mg L(−1) NaCl) completely prevented passivation, showing strong corrosiveness. Thus, the X80 steel was corroded even under high-current-density conditions. The corrosion products were mainly composed of Fe(3)O(4), α-Fe(2)O(3), and FeOOH.