Magnetic particle testing (MT) is a non-destructive testing (NDT) method used to detect surface and near-surface discontinuities in ferromagnetic materials. This technique is based on locally magnetizing the inspection area and observing the distribution of magnetic particles, which accumulate at disruptions in the magnetic field—such as cracks, seams, and other structural defects.
Fine ferromagnetic powder—either dry or suspended in a liquid—is applied to the surface during or immediately after magnetization. Structural defects cause a magnetic flux leakage, which attracts and holds finely divided magnetic particles, making flaws clearly visible.
MT is used to detect: fatigue cracks, manufacturing defects, laps, folds, slag inclusions, porosity, and other surface-breaking or shallow subsurface discontinuities. The method is particularly applied to steel components subject to variable or cyclic loads, such as forgings, castings, welded joints, load-bearing connections, and machine parts. It is widely used in welding, power generation, transportation, as well as for inspecting lifting equipment and pressure vessels.
There are two primary MT techniques:
Before testing, the surface must be meticulously prepared by removing contaminants, oils, and coatings that could disturb the magnetic field distribution and mask discontinuities.