Non Destructive Testing

Magnetic Particle Inspection applies only to ferromagnetic parts. It only detects surface-breaking or shallow sub-surface (approx. 1 mm) discontinuities, such as cracks or quenching cracks. Painted parts can be inspected provided the paint layer is less than 50 µm.

This method is sensitive to the orientation of discontinuities on the surface. Thus, detecting a crack in the longitudinal or transverse direction does not exactly require the same technique.

Magnetic Particle Inspection works as follows: the area to be inspected is magnetized, causing the magnetized field to leak into a discontinuity. This causes ferromagnetic particles to be attracted to a discontinuity and form what is known as an indication.

Various types of material are available in the field. Some are portable and can enable on-site testing. Magnetization is usually achieved by passing a current through the part to be inspected, inducing a magnetic field. Alternatively, the area of the part to be inspected can be placed in a magnetic field.

The surface to be inspected is then sprayed or dusted with colored or fluorescent ferromagnetic particles which will stick to the discontinuities.

Finally, the part is observed under suitable lighting, either visible or UV-A, to detect any indications, which will appear as lines or spots.

At the end of the test, it may be necessary to demagnetize the part, otherwise subsequent machining steps could be disturbed, or the part could malfunction during use.

Indications are assessed according to acceptance criteria. Should they exceed the authorized limits, we use the term “defect” and the part is declared non-conforming.