Magnetic Particle Testing (MPT/MT)

Magnetic Particle Testing

Magnetic particle testing or MPT is a nondestructive testing method for locating surface and near surface discontinuities in ferromagnetic materials. It depends for its operation on the fact that when the material or part under test is magnetized, discontinuities that lie in a cause leakage field to the direction of the magnetic field will cause a leakage field to be formed at and above the surface of the part. The presence of this leakage field, and therefore the presence of the discontinuity, is detected by the use of finely divided ferromagnetic particle applied over the surface, some of the particle being gathered and held by the leakage field. This magnetically held collection of particle forms an outline of the discontinuity and generally indicates its location, size, shape and extent. Magnetic particles are applied over a surface as dry particles, or as wet particle in a liquid.

Ferromagnetic materials include most of the iron, nickel and cobalt alloys. These materials lose their ferromagnetic properties above a characteristic temperature called the Curie point which is approximately 760◦ C for most of the ferromagnetic material.

Applications

The principal industrial uses of magnetic article testing are final inspection, receiving inspection, in process inspection and quality control, maintenance and overhaul in the transportation industries, plant and machinery maintenance and inspection of large components.

Limitations

Thin coatings of paint and other non-magnetic coverings, such as plating; adversely affect sensitivity of magnetic particle inspection. Other limitations are:

  1. Magnetic particle inspection methods will work only on ferromagnetic materials.
  2. For best results, the magnetic field must be in a direction that will intercept the principle plane of the discontinuity. Sometimes this requires two or more sequential inspections. With different magnetizations.
  3. Demagnetization following magnetic particle testing is often necessary.
  4. Post cleaning to remove remnants of the magnetic particle clinging to the surface may be required after testing and demagnetization.
  5. Exceedingly large currents sometimes are required for very large parts.
  6. Care is necessary to avoid local heating and burning of finished parts or surface at the points of electric contact.
  7. Although magnetic particle indications are easily seen, experience and skill in interpreting their significance are needed.

 

Magnetic particle inspection facilities at 'Trinity NDT', Bangalore, India

  1. Specialized magnetic particle inspection equipments for Aerospace NDT applications
  2. Modern high amperage magnetic particle testing equipments including electromagnetic yokes
  3. Powerful mobile type of prod equipments
  4. 6000 amperes stationery wet horizontal type equipments for inspection of mass production components, coils, solenoids, central conductors with AC, HWDC and FWDC facilities.
  5. High intensity black light kits for fluorescent inspection and demagnetizing equipments
  6. Magnetic particle testing professionals are qualified and certified to MT Level I, II as per ASNT recommended practice SNT-TC-1A, IS:13805 certified by Indian Society for Nondestructive testing (ISNT) and are approved by leading third party inspection authorities
  7. Experienced in house ASNT NDT Level III consultants and experts for providing techniques establishment, procedure preparation, approval and consultancy services.
  8. ASNT NDT Level III trainers for conducting in house or external NDT Level 1, 2 training and certification courses on Magnetic particle testing and other NDT inspection methods. Read more about Magnetic Particle Testing personnel Certifications.
  9. Strong team of NDT professionals to provide magnetic particle testing services across India
  10. Sales and Supply of magnetic particle inspection (MPI), powders, consumables and other accessories. Read more about sales of Magnetic particle inspection equipments
 

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