Investigation of High pH Corrosion Under Alternating Current Interference

This paper investigates the possible alternating current (AC) corrosion mechanism as dihypoferrite dissolution at high pH under an alternating voltage perturbation and compares polarization behavior of three commonly used pipeline steels, X52, X65, and X70. The methods used are polarization scans at various interference levels, weight-loss coupons, and ER-probe corrosion rate measurements. It is found that AC enhances the stability region of dihypoferrite in the Pourbaix diagram, leading to corrosive conditions for all investigated steels, but that within the investigated steel types, the alloy is of less importance. A mechanistic model for AC corrosion that considers a soluble ion and the role of hydrogen evolution is presented.