MT magnetic method

It belongs to the most used surface non-destructive methods – i.e. search for surface defects and defects that are right under the surface (up to the depth max. ca. 5 mm) in ferromagnetic objects. The ferromagnetic object to be inspected will be magnetised in appropriate way and the ferromagnetic powder will be placed on the surface. In the place of defect there is deformed magnetic field, it comes over the surface and makes so called magnetic flux leakage. The particles of ferromagnetic powder are pulled because of the action of leakage field and they group together in the place of defects. Patterns that are made this way are usually characteristic for the type of detected non-integrity. The sensitivity of the method is the biggest for the surface defects and it significantly decreases with the increasing distance of the subsurface defect from the surface. The characteristic types of defects that can be detected with this method are for example splits, cracks, laps in forgings, doublings on the welding edges of steel sheets, cold laps in castings and some subsurface volume defects.

 

There are many applications of this method that can be divided into two large groups: Stationary testing – testing of new products (forgings, castings, welded parts), Mobile testing – testing of surfaces, welds in terrain or in operation.

 

A special form of this method is also demagnetization of individual components.