Capillary (color) method of control is based on capillary penetration inside the defect of a special indicator liquid, which allows to detect defects that have an exit on the surface of the object under study. The method showed its high efficiency in detecting various types of discontinuities in the size range from 0.1 to 500 μm on the surface of non-ferrous and ferrous metals, ceramics, plastics, alloys and glass. Capillary defectoscopy is widely used to control the integrity of the weld, during leakage, and also in combination with other methods of nondestructive testing in complex monitoring of various critical objects. The main branches of the method are construction, engineering and transport. Advantages of capillary flaw detection are the simplicity of the equipment used, the simplicity of the operations performed and the applicability to a very wide range of materials.
Depending on the type of penetrant, the capillary control method can be divided into two types:
- Method of penetrating solutions (based on the use of a liquid indicator solution as a penetrant).
- The method of filterable suspensions (based on the use of indicator suspension).
The most important advantage of capillary control is that it can detect both through and surface defects and obtain detailed information on their shape, location, extent and orientation. In some cases, you can even determine the causes of the defect. As indicator liquids, so-called organic luminescent substances (substances that give a bright glow under the influence of ultraviolet rays), as well as various types of dyes, are usually used. A necessary condition for the qualitative detection of defects by the method of capillary control is the relative non-contamination of the object of investigation by various foreign substances.