Magnetic Particle Inspection MPI or Magnetic Particle Testing MT is the method for finding Linear Defects  in Ferro Magnetic Materials by utilization of Magnetic Field.

Magnetic particle inspection

Only ferromagnetic materials can be inspected using MPI test. The materials with major content as Ferrous or Cobalt or Nickel is called as ferromagnetic material.

Magnetic Particle Inspection utilizes wide range of machines such as :

  • Yoke
  • Prod
  • Head Shot Machine
  • Central Conductor
  • Rigid Coils
  • Wire Wrap

The MPI test method is used to find the Surface and Sub Surface defects only. MPI testings does not detects internal defects.


To find internal defects Magnetic Particle Inspection(MPI) testing is followed by internal defect detection  method such as Ultrasonic testing or Radiographic testing method.

FAQ: How much deep does MPI testing finds defects ?

Magnetic Particle Testing Method detects surface and sub surface defects upto 8mm approximately. To find deeper defects a high current (high Amps) should be used in order to produce deeper and stronger magnetic field.

  • AC current  for a electromagnetic Coil finds out Surface defects
  • DC current for a electromagnetic coil finds out Sub Surface defects

MPI testing method can be done as Visible and Fluorescent method

FAQ: Which is best, Fluorescent or Visible MPI ?

Ans: Fluorescent MPI is more sensitive than Visible method.

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