On the Use of Lateral or Side-Drain Potentials to Indicate Earth Current Direction on Bare Pipelines

Abstract So called lateral or side-drain potentials measured over and/or transverse to a buried pipe have been used to assess "hot spots” (current discharge area) on unprotected pipe. In some cases, side-drain potentials have been used to indicate the direction of cathodic protection current on bare pipelines based on the net cathodic current criterion recommended by NACE. Research conducted for A.G.A. has shown by computer simulation and field measurements that the current (direction and magnitude) at the pipe is linearly related to the ground-level, transverse potential gradient. The research also has shown that the lateral distance of the reference electrode(s) is important for correct interpretation of current direction, particularly with distributed-anode protection systems. Further, there are minimum values for the transverse potential gradient that must be exceeded to have confidence that the net current on the pipe is all cathodic.