The recording and analysis of close interval potential survey (CIS) data on pipelines is a very common means of assessing the cathodic protection (CP) levels and overall CP system performance in mitigating external corrosion.
The C.I.S. is based on recording pipe to soil potentials at regular intervals over the pipeline with the reference electrode(s) located on the ground surface. What happens when the survey records data through a foreign pipeline crossing? Can we believe the potentials recorded on the ground surface or are they contaminated by voltage gradients that may exist around the foreign pipeline?
This paper discusses historical field data recorded by the author in conjunction with recent testing undertaken on a simulated pipeline crossing installed in an aqueous environment. The effects of reference electrode location, varying current densities and the resultant voltage gradients emphasize the likelihood of potential errors in the CIS through foreign line crossings.1
Key Words: cathodic protection, close interval surveys, CIS, polarization, waveforms, foreign pipeline crossing, voltage gradient, -0.85V criterion, reference electrode, current density, bare pipeline