Understand the AC induced pitting corrosion on pipelines in both high pH and neutral pH carbonate/bicarbonate solutions

In this work, the alternating current (AC) induced corrosion and pitting corrosion of X65 pipeline steel was studied in both high pH and neutral pH carbonate/bicarbonate solutions. A real-time AC/DC (direct current) signal data acquisition technique coupled with polarization curve measurements and surface characterization was used for mechanistic studies. Pitting corrosion can be initiated on the steel at sufficiently high AC current densities in both solutions. Mechanistic models are proposed to illustrate the pitting initiation in the presence of AC, where AC can affect passive film or corrosion product layer formed on the steel as well as the charge distribution in double layer charge. In the high and neutral pH solutions, the critical AC current densities to initiate pitting are approximately 0.03 A/cm2 and 0.02 A/cm2, respectively.