This paper presents the results of a four year laboratory program to determine the correlation between the potential of a pipeline coating defect and a cathodic protection (CP) coupon buried in the same environment. The factors evaluated include exposed steel area, geometry, distance from CP anodes, and temperature. Buried pipelines and electrically bonded CP coupons experience similar effects from CP systems and interference currents (e.g. Telluric and stray). When if is impractical to correct for voltage drops in pipeline potential
measurements by disconnecting all current sources, CP coupons may be
used to ensure that adequate cathodic protection has been achieved. Disconnecting coupons from the pipe removes IR-drop and mixed potential emors from coupon potential measurements. This testing was designed for application to the Trans Alaska Pipeline. Site specific engineering evaluations are recommended for application of these results to other pipelines.
KEYWORDS: cathodic protection, coupon, Telluric current, stray current, interference, lR-drop, monitoring, pipeline