Magnetic Particle Testing (MPT) is a kind of Surface Testing method.
This NDT method is based on principle of Magnetic Flux Leakage in air. MPT can only be carried out upon ferromagnetic material (Materials with high magnetic permeability).
During magnetic particle testing, a ferromagnetic test specimen is magnetized with a strong magnetic field created by a magnet or special equipment. If the specimen has a discontinuity, the discontinuity will interrupt the magnetic field flowing through the specimen and a leakage field will occur.
Finely milled iron particles coated with a dye pigment are applied to the test specimen with or without carrier fluid. These particles are attracted to leakage fields and will cluster to form an indication directly over the discontinuity. This indication can be visually detected under proper lighting conditions.
There are various type of equipment’s based on magnetic field applied :
- Yoke – Longitudinal magnetic field
- Prod method – Circular magnetic field
- Head shot / Clamp method – Circular magnetic field
- Cable Wrap Method – Longitudinal Magnetic field
- Central Conductor Method – Circular magnetic field
- MPT Test Bench – Circular + Longitudinal (Combined) field
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- Can detect both surface and near sub-surface defects.
- Can inspect parts with irregular shapes easily.
- Fast method of inspection and indications are visible directly on the specimen surface.
- Considered low cost compared to many other NDT methods.
- Is a very portable inspection method especially when used with battery powered equipment.