Monitoring AC Corrosion in Buried Pipelines

AC corrosion in buried pipelines is increasingly acknowledged as being a significant cause of corrosion and threat to the pipeline integrity. The AC voltage is typically induced on the pipeline by parallel overhead high voltage transmission power lines. In NACE, task group TG 430 has been formed and assigned to prepare a standard document on how to assess, mitigate, and monitor corrosion caused by alternating current on buried cathodically protected pipelines.

Through 15 years of research conducted as joint industry programs, computer aided monitoring concepts have been designed and systemized. The research and monitoring efforts have been based on equal combinations of laboratory research and on-line measurements at major European operators. Investigations have systematically included both corrosion rate measurements and measurements of any sort of electrical quantity that may influence the corrosion (AC voltage, AC current density, DC potential, DC current density, spread resistance of coating fault).

The presentation will particularly discuss the interrelation between the electrical characteristics as well as compare these electrical characteristics with corrosion rates measured simultaneously. The cases clearly indicate the inadequacy of electrical measurements alone (for instance 30 A/m2 criterion on coupons). The systemized data managing system is presented in greater details and examples given on how this system has not only diagnosed AC corrosion risk but also suggested individually customized safe conditions.  

Keywords: AC corrosion rate, monitoring, electrical parameters, corrosion probes, data management, criteria, diagnostics.