A Direct Current Voltage Gradient (DCVG) survey is an above ground non-intrusive survey technique. The measurement technique detects voltage gradients as a result of current flow in the soil, generally associated with a holiday or defect in the pipeline coating but it is not a measure of the adequacy of the cathodic protection system.

A DC is impressed, either from the installed ICCP system, or a temporary system. As a result of current flow through resistive soil, DC voltage gradients are created. At locations where there are coating defects, the resistance is lower, resulting in higher current flow, and hence increased voltage gradients