Magnetic-particle inspection Guide, Meaning , Facts, Information and Description
Magnetic Particle Inspection.Magnetic Particle Inspection processes are used for the detection of defects in Ferrous materials, the detection of defects by magnetism depends on the magnetic susceptibility of a fault is clearly poorer to that of the surrounding material of the specimen. Basically, the magnetic resistance of the defect is greater than the sound material.
The flaw acts in the same way as a discontinuity in the path of the magnetic fluctuation caused to flow in the specimen in such a direction it crosses the main plane of the defect at right –angles, causing the flux to bend around the defect in an alternative direction in the material which surrounds it. This deformation of the flux is not limited to the immediate locality of the defect but extends, in a deteriorating degree, for a considerable distance around it, and out through the surface into the surrounding air if the intensity of the magnetism is high enough.
It is the external field effect, which makes Magnetic Particle Inspection possible. The simplest of these, and the main one, which is generally accepted, is the method, which finely divided iron or magnetic iron oxide, held in suspension in kerosene or other suitable liquid is applied to the specimen. (This ‘Ink’ is usually black in colour and a White Lacquer background should be applied to ensure any defects can be observed. Also the method using a ‘Black Light’ and Fluorescent Ink can used)
The ‘Ink’, which is the term used for the above, can be sprayed or painted over the magnetised specimen. The magnetic particles are attracted by the surface field in the area of the defect and hold on to the edges of the defect to reveal it as a build up of particles.
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