Magnetic - particle testing MT
The magnetic-particle method (MT) together with the penetration method is included in non-destructive surface tests..
The MT tests cover both welded joints, castings and forgings made of ferromagnetic materials. The method consists in detecting the magnetic flux of the scattering field, appearing in places of discontinuity. For magnetizing, permanent magnets, yoke solenoids, and magnetizing coils are used depending on the needs. It is also possible to magnetize with direct current flow. These tests allow to detect the most dangerous surface and subsurface defects such as cracks, porosities, laps, sticking.
This is a very fast and effective method of non-destructive inspection. Together with the ultrasonic method, it belongs to the basic control system of welded joints at the stage of their manufacture or in operation. In contrast to penetration tests, MT tests make it possible to detect discontinuities in the magnetic field under the test surface (up to about 2 mm deep). Within the method, two test techniques can be distinguished: color and fluorescence.
The color technique uses white primer and the black suspension of the magnetic, he observation is carried out in white light of the appropriate intensity. Fluorescence technique uses fluorescent suspensions and the observation is carried out using ultraviolet light. The fluorescence technique is characterized by a slightly higher sensitivity of the test compared to the color technique. In the case of magnetic - particle tests, it is necessary to prepare the surface for testing thoroughly and to remove the paint coatings.