Pipe-to-Soil potentials measured at permanently installed test points  often spaced at 1-kilometer intervals along the pipeline do not accurately consider the Pipe-to-Soil potentials along the entire route or between test points.

When performing a close interval potential survey incorporating GPS location, pipe-to-soil potentials are measured at intervals of between 1-3 meters, providing an accurate Pipe to Soil potentials profile for the entire pipeline length. A connection to the pipeline at an above ground test station via a trailing insulated copper wire mounted on a reel carried by the surveyor connected to a high input impedance voltage datalogger equipment the surveyor operates. Portable reference electrodes wired to the datalogger are then placed at known spacing across the top of the pipeline to obtain the Pipe to Soil potential readings.

Pipe-to-soil potentials measurements when cathodic protection current is applied are termed ‘On’ Potentials’.  ‘On’ Potentials are effected by the cathodic protection current flow creating a measurement error known as the ‘IR’ error, derived from Ohm’s Law: V = I x R volts. ‘IR’ errors become  reduced if all sources of cathodic protection current flow on  the pipeline are synchronously interrupted/disconnected with the pipe-to-soil measurement taken immediately after the currents have stopped flowing.  These interrupted/disconnected current flow readings are called ‘Off’ Potentials.

Upon completing the survey collected data is displayed graphically in a plot of potential against distance with notes added as required.