Direct Current Voltage Gradient Meter (DCVG) - cathtect.com

1 Direct Current Voltage Gradient Meter (DCVG)27 YaronAvenue l Lea Glen l Roodepoort l 1709 l South Africa T:+27 11 674 1502 l F: +27 11 674 1605 l C: +27 82 828 7244 l E: Theory 1 Advantages 3 Operating and Maintenance Manual 27 YaronAvenue l Lea Glen l Roodepoort l 1709 l South Africa T:+27 11 674 1502 l F: +27 11 674 1605 l C: +27 82 828 7244 l E: , YaronAvenue l Lea Glen l Roodepoort l 1709 l South Africa T:+27 11 674 1502 l F: +27 11 674 1605 l C: +27 82 828 7244 l E: Accuratedefectlocation Revealsrelativedefectsize. Canbecombinedwithothertechniques (DCVG) : Inputfilteringtoremoveinterferencecaused byhighvoltageoverheadACpowerlinesandstra ytractioncurrents Shieldingwhichpreventsinstabilitycausedb ywindinducedstatic CommonACadaptorandchargerwhichplugsintos urveymeter, inbatterychargingcircuitsandrechargeable batterypacksTechniqueAnimpressedcurrentc athodicprotectionsystemmaybeusedasaDCsou rce, anode maybeanyelectricallyremote, , anode Current flows through the soil to the exposed metal causes a Voltage Gradient in the soil.

2 The Gradient is more concentrated the closer it gets to the coating potential Gradient is detected as it appears and disappears (due to the switching of the CP system) by placement of the probes 1 2 meters apart along the pipeline. As Current is travelling through the soil to the defect and the Current is ON for half ( sec) the time is OFF the Meter points the surveyor in the direction of the Current flow and towards the defect, the Meter needle flicks .The defect once pinpointed is sized, the relative size is expressed as a percentage (%IR) of the signal applied to the pipeline.

3 The signal is the difference between the pipe-to-soil ON and OFF potentials measured at adjacent test points during the survey. Themagnitudeofthegradientaroundadefectis dependantonmanyfactors, YaronAvenue l Lea Glen l Roodepoort l 1709 l South Africa T:+27 11 674 1502 l F: +27 11 674 1605 l C: +27 82 828 7244 l E.