Magnetic particles test (MT)

Principle of the method
This technique makes use of a particular characteristic of ferrous alloys: the ferromagnetism, that is the capability of concentrating the field to highlight the defects of the magnetic field flux lines near a surface defect.

Near an irregularity such as a microcrack, the flux lines of the magnetic field locally divert and create a magnetic field anomaly at the edges of the defect. When the defect reaches the surface, some of the magnetic field flux lines are scattered beyond the surface; to highlight the defect, just spray the surfaces with suitable coloured or fluorescent ferromagnetic powder suspensions. The particles that concentrate and line up along the magnetic field flux line are made visible by Wood lamp.

The magnetic-particle test is particularly suitable for pointing out surface or subcortical defects: such as cracks, inclusions, pinching, etc., while it is completely useless in case of inner defects. Also the sensitivity to round defects is rather low. The minimum dimension of the detectable defect depend above all on its distance from the surface and the detecting limit is anyway better than the one of penetrating fluids. It is a sensitive method that can be applied for semi-finished or finished parts, sheets, forgings, butt-to-butt welding, fillet welding, structural works and mechanical parts. TEC Eurolab S.r.l. is able to carry out this check using a table magnetoscope or working at the customers’ by a portable yoke or a pillar-magnetoscope.
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