AC-Induced Corrosion and Interactions with Cathodic Protection

For many years, the tribal knowledge within the corrosion community was that alternating currents (AC) had little or no detrimental effects on the corrosion of metal structures. More recently, it has been recognized that AC-induced corrosion can have major deleterious effects. An exemplar of the problem is buried pipelines that are co-located with high-voltage transmission lines for electrical distribution, although other applications are likely to apply where there is a combination of alternating currents and cathodic protection. . The controlling parameters are not fully defined, and their relationship to corrosion rates is not well established. For Induced AC plus DC for cathodic protection, the trends are to exacerbate the problem with greater magnitude of induced current density, fewer and smaller coating defects (holidays) and higher levels of cathodic protection. The objective of this work is to examine the effects of AC-induced corrosion and interactions with cathodic protection under controlled laboratory conditions. The findings will better inform mitigation methods, monitoring techniques, risk assessment and integrity management.