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Telluric Current Considerations in the CP Design for the Maritimes and Northeast Pipeline

Published: 20010311 by NACE International
Author(s): Brian Rix
Co-Author(s): David Boteler

The Maritimes and Northeast Pipeline on the east coast of North America is constructed through an area where large geomagnetic disturbances can be expected. Because of this it was decided to include consideration of telluric current effects in the design of the cathodic protection (CP) system for the new pipeline.

An evaluation was made of the electric fields expected to be produced by geomagnetic disturbances. A computer model was set up to examine the pipeline response to these electric fields. This allowed calculations of the pipe-to-soil potentials produced with different coating resistances and placement of insulating flanges and groundbeds, which therefore allow various cathodic protection schemes to be evaluated before construction. The modeling showed that putting insulation flanges into the pipe created extra sites where pipe-to-soil potentials would be produced. Accordingly it was decided to make the pipe electrically continuous and drain the telluric currents off at the ends of the pipeline using potential-controlled rectifiers. This paper describes the CP system installed to mitigate the telluric current effects and presents observations of telluric currents both before and after commissioning of the CP systems.