Detection of leakage field :

Detection of leakage field :
Finely divided iron particles are used for detection of leakage field. Leakage  field at the surface collects and hold the iron particles together to form visible indication patterns.

  • Flaws at or near the surface disturb the magnetic flux flow and produce leakage field at surface above the flaw.
  • Magnetic particle build up at the leakage field produces recognizable patterns which are interpreted.
  • Color of the particles must be chosen to provide adequate contrast against the part’s natural color.

Discontinuities at or near the surface produce magnetic leakage field on the surface

Discontinuities at or near the surface produce magnetic leakage field on the surface :
Magnetic flux in a magnetized part pass through the body of the part. Discontinuities at or near the surface of the part disturb the normal flow of magnetic flux and leakage flux fields are produced on the surface above the discontinuities. These leakage fields attract  iron particles and are detected by applying iron powders.

What is magnetic particle testing?

What is magnetic particle testing?

This method is used for the detection of surface and near-surface flaws in ferromagnetic materials and is primarily used for crack detection. The specimen is magnetised either locally or overall, and if the material is sound the magnetic flux is predominantly inside the material. If, however, 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, a crack is indicated as a line of iron powder particles on the surface.