Due to large repair workload and cost, the detection of coating has a great guidance to a major overhaul of buried pipelines. Direct current voltage gradient (DCVG) and close interval potential survey (CIPS) techniques have already been widely used in this area and the theories are introduced in this paper. Based on the above two detection principles, a set of detection instrument for coating defects of buried pipelines is developed, and the detailed hardware and software designs of the instrument is also provided. In this instrument, pipe/soil potential is used to detect coating defects and IR drop (the product of soil current and resistance) is eliminated during potential measurement using instantaneous CP (cathode protection) current cut method. The detection results saved in Flash can be displayed on LCD of the instrument or transferred to the computer for graph plotting. Through the field application examples, it is indicated that the device designed in this article has a very high precision in defects positioning and a broad prospect of application.

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