THE HIGH VOLTAGE TESTING OF DIELECTRIC COATINGS THICKNESS

Abstract

The technology of applying many coatings (including paints and varnishes) involves the layering of visually indistinguishable layers that make up the coating system. However, in case of application technology violation, the number of coating layers (thickness) may not correspond to the declared. Thus, in a number of cases, it is necessary to control the number of layers of the final coating system. One of the most common methods for monitoring the continuity of coatings is the high voltages spark method of non-destructive testing. The method involves the application of a high voltage U between the electrode installed on the surface of the coating and the conductive substrate. The revealing of defect coating area provide by registering the coating breakdown. The analysis shows that the development of methods for detecting not only discontinuities, but also unacceptable thinning of dielectric coatings due to their spark breakdown, seems to be a promising direction in the development of high voltages spark testing. In relation to pulsed high voltages spark testing, the electrical mechanism of the breakdown of dielectrics based on quantum-mechanical concepts, the conditions of its occurrence, and the main relations obtained for calculating the electric strength Es and breakdown voltage Us for protective dielectric coatings are considered in detail. Comparative results of an experimental study of the proposed algorithms for calculating Es and Us, as well as methods for identifying (tolerance control) sections of paint coatings with an unacceptable minimum thickness and coating bubbles, are presented. The application of the proposed algorithms and methods will allow one hundred percent control of the continuity and unacceptable thinning of paint and varnish and similar dielectric protective coatings of the external and internal surfaces of pipelines, as well as various large area facilities.