With the most recent Notice of Proposed Rule Making (NPRM)~((1)) that addresses pipeline integrity and indirect inspections, there is language that relates to Direct Current Voltage Gradient (DCVG) and Alternating Current Voltage Gradient (ACVG) surveys including certain criteria associated with what must be addressed after completing DCVG or ACVG surveys. While generally both DCVG and ACVG are categorized as having the ability to pinpoint indications of coating defects, there can be a major difference in the success of the chosen technique depending on the pipeline conditions. This paper will point out when and why to use either technique including what the criteria of percent IR and Decibel microvolt (dBuV) really mean when conducting these survey techniques.
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