Electrochemical behavior of X70 pipeline steel in SRB-containing environment under hydrogen-charged conditions

Objective  High-strength pipeline steel is highly susceptible to electrochemical corrosion in the marine environment containing sulfate reducing bacteria (SRB). If a large number of hydrogen atoms are infiltrated into the pipeline steel, the corrosion will be more serious, so it is necessary to investigate the electrochemical corrosion of X70 pipeline steel in the SRB environment under hydrogen-charged conditions.

Method  The electrochemical behavior of X70 pipeline steel under hydrogen-charged conditions in a simulated marine solution containing SRB of the South China Sea was systematically studied by electrochemical and surface analysis techniques. Through simulating the diffusion of different concentrations of hydrogen atoms into α-Fe, differential charge density maps and Fe—Fe bond energies, the effects of different concentrations of hydrogen atoms entering between Fe atoms were analyzed.

Result When SRB were present, corrosion levels rose in tandem with increases in hydrogen charging. Additionally, higher hydrogen charging current density and longer hydrogen charging duration could promote forward corrosion.

Conclusion  The simulation of the South China Sea marine solution reveals that hydrogen is an important factor in the corrosion of X70 pipeline steel. The results of first principle calculations indicate that the presence of hydrogen atoms decreases the charge density between iron atoms, thereby weakening the Fe—Fe bonds in close proximity to the hydrogen atoms. As a consequence, in a corrosive environment, the structural integrity of the entire system will fail at these weakened locations, making them more susceptible to corrosion.