Corrosion Rate Measurement and Oxide Investigation of AC Corrosion at Varying AC/DC Current Densities

Corrosion of pipelines under cathodic protection (CP) caused by induced alternating current (AC) is highly dependent on the cathodic current density. This study uses electrical resistance probes to produce a corrosion rate map of the AC/DC current density domain, using a galvanostatic CP system subject to varying AC voltage interference levels. Two corrosion domains are recognized at high or low CP, respectively. X-ray photoelectron spectroscopy is utilized for analysis of surface oxides, being primarily magnetite and ferrous hydroxide. The results are discussed in a Pourbaix diagram context.