The DCVG method is directly connected to the cathodic protection of pipelines. From the impressed current cathodic protection system DC current flows into the coating defects causing a drop of voltage in the soil.
This potential gradient can be detected between two electrodes placed on the soil surface with a sensitive analog mV meter therefore the location of the coating defect can be determined with a precision of 10 – 20 cm.
The size or severity of the coating defect is characterized by a relative number, the so-called % IR number.
This method is also effective in the case of pipelines without cathodic protection by using temporary anodes and CP stations.
At the laying of new pipelines it is recommended to carry out a DCVG Survey immediately after the pipe laying so that the contractor could repair the possible coating defects still under guarantee.
The DCVG method is also suitable for the coating inspection of underground storage tanks.