Magnetic Particle Testing

The magnetic particle test method of Non-Destructive Examination was developed in the USA, in the 1930s, as a way to check steel components on production lines. The principle of the method is that the specimen is magnetised to produce magnetic lines of force, or flux, in the material.

This testing method is called MT (Magnetic Testing) or MPT (Magnetic Particle Testing), and suitable for the surface / subsurface flaw inspection of ferromagnetic materials.

Principle of MPT is as follows:

• If there is a flaw on the surface, magnetic flux leaks into the air at the position of the flaw.
• Then magnetic particles (dyed or fluorescent encapsulated) are applied to the surface.
• These magnetic particles will migrate to the flaw where the magnetic flux leaks and forms a flaw indication that is several tens of times of actual flaw width.
• The inspector visually identifies the flaw.