Magnetkontrolli

Magnetkontrolli is a family of nondestructive testing methods that use magnetic fields to detect discontinuities in ferromagnetic materials. In international practice, the techniques are most commonly known as magnetic particle inspection (MPI) and magnetic flux leakage (MFL). The core idea is to magnetize the test object so that defects such as cracks, seams, or porosity disturb the magnetic circuit and create a leakage field that can be observed.

The principle relies on magnetization of the component, which can be achieved by yokes, coils, or permanent magnets. When a defect perturbs the magnetic field, leakage fields concentrate at the defect and draw attention to it. MPI reveals surface and near-surface defects by applying ferromagnetic particles, either as a dry powder or in a liquid suspension, often under ultraviolet light for enhanced visibility. MFL uses sensors to detect the stray field or flux leakage in regions of interest, providing a different diagnostic approach, sometimes with quantitative indications of defect size and location.

Procedures typically include surface cleaning, appropriate magnetization in a chosen direction (longitudinal, transverse, or circumferential), application of magnetic indicators, and careful inspection under suitable lighting. After testing, demagnetization and cleaning may be performed to restore material properties and remove residual magnetic effects.

Magnetkontrolli is widely used for steel components and welds in industries such as aerospace, automotive, oil and gas, and manufacturing. It is limited to ferromagnetic materials and is most effective for surface and near-surface defects. Standards governing these methods include ISO 9934 and ASTM E709, among others. Safety considerations include management of strong magnetic fields and the need for trained personnel.