A linear anode was used as the current source for GIS and DCVG testing and the five vertical anodes in the southwest corner of the facility were used as the current source for the signal in the PCM and ACVG testing.
Table 1 is a summary or the ACVG and DCVG indication data by approximate location against those found in the baseline-isolated survey.
It is likely that the same relative current splits occurred during the ACVG surveys.
The ACVG and PCM surveys were also affected by the parallel cable in close proximity to the buried pipe by what appeared to be a self-canceling of the signal along the parallel cable.
Both the ACVG and DCVG methods are affected by the connection to grounding elements, particularly when the pipeline is grounded at both ends.
This is as simple as moving the ACVG
probes around to pinpoint the highest pressure or greatest voltage, and if it is not directly over the pipe, we can safely rule it as a foreign metal object or interference for the survey.