What type of defects is magnetic particle testing (MT) especially effective at detecting?

Magnetic particle testing (MT) is particularly suitable for finding surface and near-surface defects in ferromagnetic materials due to the principles involved in the technique. When a ferromagnetic material is magnetized, any discontinuities or flaws present can disrupt the magnetic field, causing localized leakage fields. This disruption is visible as indications when magnetic particles are applied, making it easier to detect defects that are close to the surface.

Surface and near-surface defects, like cracks, laps, and seams, can be identified effectively because the MT method is designed to highlight disruptions in the magnetic field that those defects cause. Ferromagnetic materials, such as iron, nickel, and cobalt, are necessary for this method; hence, the effectiveness of MT is specifically tied to these types of materials and the type and location of flaws being tested.

The other options do not align with the capabilities of MT. Subsurface cracks in non-ferromagnetic materials would not be detectable using magnetic particle testing because the method relies on magnetic properties, which non-ferromagnetic materials lack. Delaminations in composites and internal voids in cast metals are also beyond the scope of MT, as these defects neither interfere with the magnetic field in a manner detectable by this technique nor are they