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MT - Magnetic Particle Inspection

Magnetic method - one of the most popular, reliable and productive methods of nondestructive testing surfaces of articles made of ferromagnetic materials in their production and use.

IPC - one of the four classical methods of nondestructive testing, and also one of the oldest NDT methods related to the use of instruments and materials for NDT flaw detection. The first experiments have described the phenomenon of magnetic scattering fields and explained their significance. Subsequently, attempts were made to find a use for this phenomenon and put it in technical practice. In 1868, Englishman Saxby applied compass to determine the defects in the gun barrel. In 1917, the American Hawk iron filings applied to detect cracks in the steel parts.

The essence of the method is as follows: the magnetic flux in the defect-free part of the product does not change its direction; if the way of its areas of decreased permeability, such defects as metal discontinuity (cracks, nonmetallic inclusions, etc.), part of the magnetic field lines coming out from the workpiece outwardly and enters back into it, while having local magnetic poles (N and S) and as a result, the magnetic field above a defect. Since the magnetic field is nonuniform over the defect, the magnetic particles, trapped in this field, a force draws them to the place of greatest concentration of magnetic field lines, that is a defect. The particles in the field of defect magnetized and attracted to each other as magnetic dipoles under the force so that they form a chain structures oriented along the magnetic field lines.

The method of magnetic particle inspection is designed to detect subtle surface and subsurface discontinuities metal - defects propagating deeper into the products. Such defects can be cracked, hairline tears, flakes, lack of fusion pores. The highest probability of detection of defects is obtained in the case where the plane defect makes an angle of 90 ° with the direction of the magnetizing field (magnetic flux). With the reduction of this angle, the sensitivity decreases at angles substantially less than 90 ° defects can not be detected.

Sensitivity MTD defined magnetic characteristics of the material tested article (magnetic induction (B), remanence (Br), maximum magnetic permeability (μmax), coercive force (H0), the surface roughness control, by the intensity of the magnetizing field and its orientation with respect to the plane of the defect, quality flaw detection means and the controlled lighting surface.