Magnetic Particle Testing

Mt (magnetic particle testing)
it is a non-destructive testing (ndt) process for detecting surface and slightly subsurface discontinuities in ferromagnetic materials such as iron, nickel, cobalt, and some of their alloys. The process puts a magnetic field into the part. The piece can be magnetized by direct or indirect magnetization.
Direct magnetization
direct magnetization occurs when the electric current is passed through the test object and a magnetic field is formed in the material.
Indirect magnetization
indirect magnetization occurs when no electric current is passed through the test object, but a magnetic field is applied from an outside source.
Dry particle inspection
in this magnetic particle testing technique, dry particles are dusted onto the surface of the test object as the item is magnetized. Dry particle inspection is well suited for the inspections conducted on rough surfaces. When an electromagnetic yoke is used, the ac or half wave dc current creates a pulsating magnetic field that provides mobility to the powder. The primary applications for dry powders are unground welds and rough as-cast surfaces. Dry particle inspection is also used to detect shallow subsurface cracks. Dry particles with half wave dc is the best approach when inspecting for lack of root penetration in welds of thin materials. Half wave dc with prods and dry particles is commonly used when inspecting large castings for hot tears and cracks.
Wet suspension inspection
wet suspension magnetic particle inspection, more commonly known as wet magnetic particle inspection, involves applying the particles while they are suspended in a liquid carrier. Wet magnetic particle inspection is most commonly performed using a stationary, wet, horizontal inspection unit but suspensions are also available in spray cans for use with an electromagnetic yoke.