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Journal of Chinese Society for Corrosion and protection  2024, Vol. 44 Issue (2): 512-518    DOI: 10.11902/1005.4537.2023.091
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Discussion on DC Voltage Gradient (DCVG) Measurement and %IR Calculation of Buried Coating Pipeline
LIU Guo()
Beijing Cathtop Technology Co., Ltd., Beijing 100028, China
Cite this article: 

LIU Guo. Discussion on DC Voltage Gradient (DCVG) Measurement and %IR Calculation of Buried Coating Pipeline. Journal of Chinese Society for Corrosion and protection, 2024, 44(2): 512-518.

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Abstract  

The direct current voltage gradient method (DCVG) is an indirect measurement method used to evaluate defects in anti-corrosion coatings of pipeline. The implementation of DCVG detection has certain requirements for the DC test current and the setting of interrupters, but these technical details are often ignored in actual on-site work. %IR is a parameter used in the DCVG method to evaluate the severity of pipeline coating damage. There are many misconceptions in the calculation and application of this parameter in the pipeline industry, such as the incorrect selection of the test current and on-off period, and lack of consideration of factors such as soil resistivity and burial depth of the pipe. This article has conducted research and discussion on the testing current requirements of DCVG and the principle and calculation method of %IR, clarified the signal strength requirements for conducting DCVG inspection, analyzed the factors that affect the %IR value, and pointed out that it's uncertain to evaluate the size and severity of coating defects using %IR.

Key words:  direct current voltage gradient method      %IR      anti-corrosion coating      cathodic protection      external inspection     
Received:  27 March 2023      32134.14.1005.4537.2023.091
ZTFLH:  TG174  
Corresponding Authors:  LIU Guo, E-mail: Liuguo@cathtop.com

URL: 

https://www.jcscp.org/EN/10.11902/1005.4537.2023.091     OR     https://www.jcscp.org/EN/Y2024/V44/I2/512

Fig.1  Schematic diagram of detection of pipeline coating defect by DCVG
Fig.2  Schematic diagram of voltage drops SOL and SCD along soil
Fig.3  Measurement and acquisition method of SOL
Fig.4  Presentation of DCVG data and %IR calculation
Fig.5  Schematic diagram of calculation method of%IR in GB/T 19285-2014
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