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Magnetic Particle Testing, MT

Testing method where the material is magnetized and coated with a ferromagnetic powder to detect defects at and just below the surface.

Beskrivning
Illustration of Magnetic Particle Testing, MT

The process

The material [1] to be tested must first be cleaned so the powder which will then be applied to the surface is not absorbed by the contamination. A magnetic yoke [2] creates a magnetic field in the surface of the material and in a ferromagnetic powder sprinkled gently over the surface and then blown gently away. The powder collects at defects [3] as a result of disturbances in the direction of the magnetic field lines.

In order to detect any cracks in the surface, the material is analyzed based on powder behavior and dispersal. This process can be repeated 2-5 times in which the yoke is placed differently each time to create magnetic fields with different directions.

Magnetic Particle Testing, MT
Process films
Advantages and disadvantages
In comparison with alternative methods
Quick method: Relatively straightforward
Provides direct indication of defects
Displays defects on and near the surface
Can be adapted for use in the workshop or on site
Large or small objects can be examined
Complicated preparation is not necessary
Messy process
Requires access to electricity
Difficult to sometimes determine whether the magnetic field is strong enough or not
Can not be used if a thick layer of color exist on the object
Subsequent demagnetization is usually required
Each item must be examined in two directions