MAGNETIC PARTICLE INSPECTION

Magnetic particle inspection is a sensitive method of locating surface and some sub-surface defects in Ferro-magnetic components. The basics processing parameters depend on relatively simple concepts. In essence, when a ferromagnetic component is magnetized, magnetic discontinuities that lie in a direction approximately perpendicular to the field direction will result in the formation of strong ‘leakage field’.

This leakage field is present at and above the surface of the component, and its presence is visibly detected by the utilization of finely divided magnetic particles. The application of dry or wet particles in a liquid carrier, over the surface of the component, results in a collection of magnetic particle at a discontinuity.

Applications:
• Most weld discontinuities open to or near the surface
• Most suitable for cracks, laps, seams, voids, pits, subsurface holes, and other surface or slightly    subsurface, discontinuities in ferromagnetic materials

Advantages:
• Relatively economical and expedient
• Test equipment is considered portable
• Unlike liquid penetrant, magnetic particle can detect some near surface discontinuities
• Can inspect through thin coatings

Limitations:
• Application only to ferromagnetic materials as well as to surface or near-surface flaws
• Parts should be clean before and after inspection
• Thick coatings may mask rejectable indications
• Some applications require parts to be demagnetized after inspection
• Magnetic particle test requires use of electrical energy for most applications
• Some potential for arc strikes on surface