The modern approach to interference testing takes into account the effect of foreign voltage gradients on measured pipe to soil potentials when the reference electrode is on the ground surface.

 

Even buried reference electrodes, close to a pipeline, may be influenced by foreign voltage gradients when they are primarily “looking” at a coating defect further down the pipeline.  The use of DCVG surveys to evaluate coating defects in the area of crossings and inspection of polarization and depolarization profiles are considered part of the evaluation of adverse interference cases.

 

The pipe to soil potentials measured on the ground surface at a pipeline crossing are not the sole arbiter of deciding if adverse interference is present.