Dcvg – Analysis of Practical Limits and Suggestions for Improvements

This paper examines the practical limits of the DCVG (Direct Current Voltage Gradient) method for the detection of coating defects. The approach is based on the combination of numerical calculations and the development of a calibration electrode (pen) with series resistance which can be used in the field to simulate coating defects. The DCVG profile (shape) caused by this pen is determined by the pen depth while the maximum DCVG value depends on the pen current, which can be controlled using a series resistance. Using an automatic optimization algorithm, an analytical formula for both the optimum pen depth and series resistance has been obtained. It has been demonstrated that using these values, a very good agreement between the DCVG profiles of the different coating defect situations and the pen has been obtained. Also it has been proven that the obtained formulas can be extended to deal with different coating defect sizes and changing local soil resistivity (e.g. due to the presence of cathodic protection reaction products). The calibration approach will be used to demonstrate the practical limits of the DCVG method to detect coating defects in different situations, including the effect of stray currents.