Magnetic Particle

Magnetic Particle Testing (MT)

"An electromagnetic yoke is a very common piece of equipment that is used to establish a magnetic field.."

The Magnetic Particle Examination (MT) method may be applied to detect cracks and other discontinuities on or near the surface of ferromagnetic materials.

This method involves magnetizing an area to be examined, and applying ferromagnetic particles to the surface. The particles will form patterns on the surface where cracks and other discontinuity cause distortions in the normal magnetic field. These fields are usually characteristic of the type of discontinuity detected.

Magnetic Particles are available in a dry mix or a wet solution and treated to impart color or fluorescent pigments in order to make them highly visible against the background of the surface being examined. The wet magnetic particle testing method is generally more sensitive than the dry because the suspension provides the particles with more mobility and makes it possible for smaller particles to be used. The wet method also makes it easy to apply the particles uniformly to a relatively large area.

A variety of equipment exist to establish the magnetic field for MT, Most of the equipment uses an electric current to produce the magnetic field (electromagnetism).

Some equipment is designed to be portable so that inspections can be made in the field, others are designed to be stationary for ease of inspection in the laboratory. Some common types include; portable prod type electrodes that are pressed against the surface of the component being inspected, multi-turn coils or cables with current passing through them can be wrapped around the part to be examined, or electromagnetic yokes that can be powered with alternating current from a wall socket or by direct current from a battery pack.