MAGNETIC TESTING (MT)
MPI (Magnetic Particle Inspection) is a method that can be used to find surface and near surface flaws in ferromagnetic materials such as steel and iron it is primarily used for crack detection.
During Magnetic Particle Inspection the specimen is magnetised either locally or overall and if the material is sound the magnetic flux is predominantly inside the material. If however during the Magnetic Particle Testing there is a surface-breaking flaw, the magnetic field is distorted, causing local magnetic flux leakage around the flaw.
This leakage flux is displayed by covering the surface with very fine iron particles applied either dry or suspended in a liquid. The particles accumulate at the regions of flux leakage, producing a build-up, which can be seen visually even when the crack opening is very narrow. Thus, during Crack Testing a crack is indicated as a line of iron powder particles on the surface.
Magnetic Particle Testing is suitable to test at all ferrous metals, such as carbon steel, low-alloy and cast iron. The main use of Magnetic Particle Testing is for welds and heat affected zones.