Magnetism is the ability of matter to attract other matter to itself. The ancient Greeks were the first to discover this phenomenon in a mineral they named magnetite. Later on, Bergmann, Becquerel, and Faraday discovered that all matter including liquids and gasses were affected by magnetism, but only a few responded to a noticeable extent.

MPI uses magnetic fields and small magnetic particles (i.e. Iron filings) to detect flaws in components. The only requirement from an inspect ability standpoint is that the component being inspected must be made of a ferromagnetic material such as iron, nickel, cobalt, or some of their alloys. Ferromagnetic materials are materials that can be magnetized to a level that will allow the inspection to be effective.

method is used to inspect a variety of product forms including castings, forgings, and weldments. Many different industries use magnetic particle inspection for determining a component's fitness-for-use. Some examples of industries that use magnetic particle inspection are the structural steel, automotive, petrochemical, power generation, and aerospace industries. Underwater inspection is another area where magnetic particle inspection may be used to test items such as offshore structures and underwater pipelines.

Magnetic-Particle is a method for locating surface and subsurface discontinuities in ferromagnetic materials. It depends for its operation on the fact that when the material or the part under test in magnetized, magnetic discontinuities that life in a direction generally transverse 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 particles applied over the surface, some of the part. The presence of this leakage field and therefore the presence 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 particles in a liquid carrier such as water or oil.

The method involves three essential steps:

• magnetizing the material or part under test.
• applying the ferromagnetic particles over the surface.
• examining the surface for powder pattern or indication.

Following type of electric current is used:

• Alternating Current.
• Half Wave Rectified Direct Current.
• Full Wave Rectified Direct Current.

Magnetic Particles are available in:

• Black
• Red and
• Yellow colour

As per visibility, magnetic particles are available of two types:

• Visible Magnetic Particles
• Fluorescent Magnetic Particles

As per application, magnetic particles are available of two types:

• Dry Magnetic Particle
• Wet Magnetic Particle