The potential and current fluctuations imposed on pipelines by telluric currents have been observed for many years, but only recently have techniques been developed to compensate for this activity.
The magnitude and rate of the potential change caused by telluric activity can render the data recorded from a potential survey useless unless it is properly compensated and corrected. The technique used by Corrosion Service entails the use of Global Positioning System (GPS) synchronized interrupters, stationary dataloggers and field loggers. The information recorded thus can be mathematically processed to determine the true pipe potential for every survey location with a high degree of accuracy.
Photo courtesy NASA / JPL
Related Articles and Publications:
Telluric Current Effects on Corrosion & Corrosion Control Systems on Pipelines in Cold Climates
Author : R.A. Gummow Date : Feb-01 Notes : NACE N.W. Area Conf. (Anchorage)
The impact of telluric current activity on the corrosion control systems on pipelines in northern regions and cold climates is examined. Three specific areas of concern are identified. These factors are; corrosion of the pipe during positive cycles of the telluric disturbances, accurate measurement of cathodic protection performance parameters, and coating damage during the negative cycles of the telluric activity. Corrosion rates are calculated versus the magnitude of the pipe potential change caused by discharging telluric current for different values of the Kp geomagnetic index. Methods of compensating and mitigating telluric current effects are discussed in the context of cathodic protection design and monitoring procedures. The benefits of using potential controlled rectifiers and integrated reference/coupons in mitigating telluric current effects are illustrated.
Practical Telluric Compensation for Pipeline Close Interval Survey
Author : T. Place/O. Sneath Date : Mar-00 Notes : NACE Corrosion 2000
Transient phenomena can significantly affect the accuracy of pipe-to-soil potential (PSP) measurements. One pipeline operator has developed a simple method to improve the accuracy of cathodic protection close interval survey (CIS) measurements through the use of continuous dataloggers at reference locations within the survey area.
Telluric Current Considerations in the CP Design for the Maritimes & NorthEast Pipeline
Author : B. Rix / D.H. Boteler Date : Mar-03 Notes : NACE Corrosion 2001, Paper No. 01317
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 insulating flanges into the pipe created extra sites where large 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 system.