Magnetic particle testing

We provide single and serial testing of your components for surface defects and near-surface defects with magnetic particle testing

Non destructive testing with magnetic particle testing (MT)

What is magnetic particle testing?

Magnetic particle testing is used to detect surface defects and near-surface defects on ferromagnetic materials such as steel or iron materials. Magnetic particle inspection makes use of the laws of magnetization. This is because defects in the material produce changes in magnetic flux.

How does magnetic particle testing work?

Surface inspection by magnetic particle testing makes use of magnetism. A magnet (e.g. a yoke magnet) is used to magnetize the component. A component without surface defects is magnetically homogeneous. This means that the magnetic field lines run parallel and the component has the same magnetic properties at every point.
However, if there is a defect in the component, the magnetic field lines avoid the defect. This is because magnetic field lines always seek the path of least resistance. This results in stray fields on the material surface. Ferritic magnetic powder accumulates at these stray fields. This magnetic powder accumulates above the crack and becomes visible as a “bead” if this is fluorescent or if the surface is coated with white background paint.

Test procedure of a fluorescent MT:

Step 01

Magneti­zation of the component

with the aid of a magnet.

Step 02

Applying magnetic powder

the component surface is then sprayed with a mixture of oil, a fluorescent dye and a magneti­zable powder. At defect-free areas, the mixture flows off almost completely. At defect locations, however, the magnetic powder accumulates over the defect due to the stray flux.

Step 03

Viewing the component under UV light

the fluorescent dye on the magnetic powder thus allows defects to be clearly seen under ultraviolet light.

Step 04

Demagneti­zation of the component

To prevent undesirable effects in further processing, the component is demagnetized after the inspection, if necessary.

When is magnetic particle inspection used?

Magnetic particle inspection is used to detect defects on the surface and near-surface defects in the material.

Detectable defects are:

  • Cracks
  • Lines of slag

Special requirements:
The material to be tested must be magnetizable (ferromagnetic).

Smallest detectable defect:
From 0.01 mm crack width x 0.1 mm crack depth

Detectable defect location:
Surface defects as well as defects up to approx. 0.2 mm below the surface

* The specifications depend on the geometry and physical properties of the material to be tested and are therefore only intended as a guideline

Magnetic particle Testing with VOGT Ultrasonics

We test your components either single or in series in our VOGT test center in Burgwedel (Hanover) or directly at your site.