Abstract
Despite the existing body of research data and some empirical evidence apparently implicating AC currents as deleterious to the buried pipelines, there remained a need to further investigate the issue, especially the conditions at which AC currents may pose a threat to underground structures and cathodic protection requirements needed to mitigate the possible adverse AC current effects. Of a particular interest were the following two issues: (1) the effect of AC current density on the corrosion rate and (2) cathodic polarization requirements necessary to mitigate the impact of AC current. This paper describes an extensive laboratory-based study of carbon steel specimens exposed to soils under the influence of AC and CP polarization. The primary conclusions are that AC corrosion may take place even at AC current densities considered ‘safe’. To overcome the effects of the AC currents, the current needs to be mitigated first; mitigation of AC potentials to values below 15V may not be sufficient with respect to AC current densities at the coating holidays. Application of increased cathodic protection current (>150 mV of polarization) may be required to control AC corrosion.
