AC Voltage Gradient (ACVG)
The ACVG method employed by RYSCO Corrosion Services is a variation of the Pearson technique for detecting coating faults on buried pipelines. The technique involves the induction of an AC current on the pipeline, which is then assessed by two technicians wearing metal cleats. The metal cleats provide electrical contact points with the ground, both over the pipeline and at a 3m distance perpendicular to the pipeline. The voltage gradient is then measured between the two contact points and adjusted for relative distance from the transmitter. A coating fault will result in a higher voltage gradient between the over the pipeline contact and the 3m contact than a location where there is no coating fault.
The method employed by RYSCO Corrosion Services is considered a modified Pearson technique due to the elimination of audible tones and interpretation of acoustic data. Measurement in the modified technique is considerably more analytical as due to the use of electronic measurement, and the recording of actual AC voltage gradient magnitudes in millivolts (mV). During analysis of the data, RYSCO Corrosion Services will look for increases in the normalized Vm measurement to indicate voltage leakage from the pipeline. Interferences from the poor contact are confirmed and correlated to ACCA data to indicate coating anomalies.
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