Magnetic particle inspection MT

The magnetic particle non-destructive testing method is intended to detect defects that are not visible on the surfaces and under them. Detection of defects is possible if they come to the surface of the product or lie at a shallow depth (no more than 2 mm). Defects detected by the magnetic method include such defects as cracks, hairs, non-metallic inclusions, inconsistencies, and flocs.

Magnetic methods are based on the study of magnetic stray fields around products made of ferromagnetic materials after magnetization. At the locations of defects, a redistribution of magnetic fluxes and the formation of magnetic stray fields are observed. The task of magnetic particle inspection is to create a magnetic field above the defect and to detect a defect on the product by the presence of a magnetic stray field.

The magnetic powder non-destructive testing method is used only to control objects (products) created from ferromagnetic materials. When using the method of magnetic particle testing over defects, ferromagnetic particles are applied to the controlled areas, which are suspended in a liquid (wet method) or in air (dry method). Particles of ferromagnetic powder that fall into the zone of action of the magnetic field of scattering attract and settle on the surface near the locations of discontinuities. The width of the band along which the deposition of the magnetic powder occurs can significantly exceed the actual width of the defect. As a result, even very narrow cracks  on the settled powder particles can be identified with the naked eye. Registration of the obtained indicator drawings is carried out visually or with the help of image processing devices.