Magnetic Particle Inspection

Surface defects in ferromagnetic metals.

Magnetic Particle Inspection (MPI) or Magnetic Testing (MT) is an NDT method for checking the surface integrity of ferromagnetic materials. The material is magnetized using a handheld yoke or a horizontal MPI bench setup.

Defects in the surface and shallow subsurface cause magnetic field fluxes to "leak". When a liquid containing tiny magnetic particles is applied, these particles accumulate around those discontinuities making them visible to the naked eye.

If necessary a white contrast agent is applied to the material before testing. For high sensitivity, a fluorescent liquid and blacklight can be used. This requires a dark testing environment.

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  • Rapid inspection of large surfaces

  • Relatively low equipment cost

  • Detection of surface and near-surface defects

  • Immediate interpretation of indications

  • Can be used in workshop and on site

  • Surface preparation is less critical than with Penetrant Testing (PT)

  • This method is typically ‘colour-contrast’ with white contrast paint and black ink. However, for high sensitivity, a fluorescent ink and blacklight can be used. This requires a dark testing environment.


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Ultrasonic Inspection (UT)Dye Penetrant Inspection (PT/DPI)Radiographic / X-ray Inspection (RT)Magnetic Particle Inspection (MT/MPI)Welding Inspection
Visual Inspection (VT)Vendor InspectionPhased Array Inspection (PAUT)Hardness Testing (HT)Positive Material Identification (PMI)Hiring of Inspection Personnel


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