What Does
Direct Current Voltage Gradient Measurement Mean?
Direct current voltage gradient (DCVG) measurement is a technique used to assess the efficacy of corrosion protection on buried pipelines. Coating faults, holidays, loss of cathodic protection (CP) and other defects can be detected using regular monitoring by DCVG. This method of detection was found by John Mulvany of Australia in the early 1980's and now is universally accepted in the pipeline industry.
It is laid out as a testing method by National Association of Corrosion Engineers (NACE) International Test Method TM-0109-2009.
Trenchlesspedia Explains Direct Current Voltage Gradient Measurement
Pipelines that are buried under the earth are prone to corrosion overtime. If not protected against corrosion using CP and application of protective coating the pipe will degrade faster. Protective coatings may also have inherent defects or may incur small damages during installation. These can become the reason for extensive corrosion at a later date.
DCVG is an electrical method used for locating holidays such as voids, pinpoints, cracks, non-adhesion of coating etc. in a pipeline. To undertake a DCVG survey, equipment such as DCVG, half cells, alignment drawings, pipe locator, radio, etc. are required. In order to easily locate defects in coating, pulsed DC current is needed. This can be obtained from the CP rectifiers using GPS synchronized current interrupters.
Pipelines protected by sacrificial anodes will require installation of a temporary rectifier and interrupter.