Pipe line operators can increase the benefit from their spending for CP (cathodic protection) and anti-corrosion coating integrity by demanding greater precision from aboveground surveys. The techniques include CIPS (close-interval potential survey), DCVG (direct-current voltage gradient), Pearson, and current attenuation. Whereas Pearson and current attenuation provide very limited information, DCVG is a very powerful tool to assess in detail the quality of the interdependent relationship between protective coating and CP. Coating quality assessment involves CP measurements and assessment by aboveground direct-current techniques. Reasons for deficient survey data is poor surveyor training and a lack of detailed method statements how to carry out the surveys. Awell-conducted aboveground survey can help to avoid more expensive excavation and maintenance work. CIPS entails recording the pipe-to-soil potential at regular intervals along the complete pipe line route using a trailing cable attached back to the nearest test post for electrical connection to the pipe line. Conventional CIPS methods as well as variations with lateral half-cell, trailing half-cell and a combination of both are discribed. The problem of combining CIPS and DCVG techniques into one-pass method lies in ON/OFF switching frequency differences. The correct way to combine CIPS and DCVG is explained and the major survey measurements are listed up.
Understanding voltage surveys results in reliable coating data
Pipe Line and Gas Industry ; 84 , 3 ; 25-31
2001
7 Seiten, 6 Bilder, 1 Tabelle, 18 Quellen
Article (Journal)
English
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