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The Major Differences Between Sham DCVG and True Analogue DCVG.
1) True DCVG has no connection to the pipe, Sham DCVG does.
2) True DCVG locates epicentre of coating fault during survey. Sham does not as data has to be post survey processed.
3) True DCVG enables coating fault severity, current demand, corrosion status and indication of potential metal loss to be determined. An analogue DCVG meter is essential for these calculations. Sham DCVG methods have none of these capabilities, so give very little information about coating faults.
4) Sham techniques take data totally at random with regard to coating fault locations. Even post processing does not give accurate coating fault locations.
5) Sham DCVG suffers from CIPS attenuation steps as trailing cable is moved from test post to test post. This step is not usually corrected for.
6) For best data Sham DCVG requires one half cell to be over the pipeline, hence must locate pipeline before survey. True DCVG is a very accurate pipe locator if a coating fault is present. The True DCVG technique will hold you on the pipeline route.
7) Sham lateral gradient which they call DCVG is taken between 1.5 and 2m which is only a small proportion of the total lateral gradient. In some soils distances of 50m plus to get the full lateral gradient are required. Measurement at small lateral distances are meaningless.
8) Sham DCVG like CIPS does not detect small coating faults. On the true DCVG fault severity scale of 0-100%, the Sham technique does not detect faults below 15% and if CP is weak this can be 30%+. Sham DCVG therefore misses many coating faults. On average this can be more than 50%
9) To analyse data to prioritise faults for repair all data must be be fault specific. True DCVG gives this, Sham DCVG does not. Hence using Computer Programs for analysis of Sham DCVG information is limited. Remember rubbish in, rubbish out for any program.
10) Purveyors of Sham DCVG are trying to cash in on the accuracy and good name of true DCVG, but they do not have the equipment for True DCVG. Also unlike DCVG Ltd, do not possess CIPS equipment specifically designed so CIPS can be done at the same CP pulsing frequency as analogue True DCVG to run the two techniques as a one pass survey.
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