Electrochemical behavior of API-X100 pipeline steel in NS4, near-neutral, and mildly alkaline pH simulated soil solutions

The effect of environmental parameters on the electrochemical corrosion of X100 steel in NS4 simulated soil solution is investigated. The parameters examined were pH (4.7-9), purging gas (5% carbon dioxide (CO2)/95% nitrogen (N2), 100% carbon dioxide, and 100% nitrogen), solution temperature (25, 40, and 55 °C), bicarbonate (HCO3-) concentration, chloride (Cl−), and sulfate (SO42-). Overall, corrosion rates of the specimens decreased with pH. Sufficient bicarbonate was critical for the passivation of the steel. Higher chloride/sulfate content prevented stable passivation. Impedance results reveal the involvement of adsorption and parallel adsorption-diffusion in near-neutral and mildly alkaline conditions, respectively.