Rolled Waterproofing Coating Delamination Detection by High-Voltage Testing

This study assesses the possibility of identifying non-through defects in dielectric coatings, specifically interfacial defects located at the metal–coating boundary, by means of high-voltage non-destructive testing. It is demonstrated that partial discharges causing characteristic distortions of the applied test-voltage pulse can be used as a reliable diagnostic feature of such defects. Using an equivalent capacitive representation of a defective coating, a relationship is established between the apparent charge and the geometry of the air-filled gap. The proposed approach is supported by COMSOL simulations of the electric-field distribution and by experiments performed on Plexiglas specimens containing blind holes of different depths. In addition, a method is developed for isolating the partial-discharge signal based on a weighted sum of increments in the root-mean-square deviations of the second derivative of the voltage waveform. The resulting relationships enable estimation of the residual coating thickness in the defect region.