What are tests in welding ?

3. Magnetic particle test (MT)

Irons and ferritic steels can easily be magnetized by a magnet. Therefore, if there is any defect on or near the surfaces of a weldment, the magnetic poles will be developed on both sides of the defect, producing the leaked magnetic flux . When fine magnetic particles are brought near the periphery of this magnetic flux, the particles are magnetized, and the magnetic poles are developed at both ends of each particle.

The magnetic power acts through the magnetic poles of the particles and defective zone. Consequently, the particles are connected each other to develop a particle pattern like a chain.

 For the magnetic particles, either a dry powder or liquid suspension powder is used.

By using this method, defects such as cracks and porosity which are open to or close to the surface of a weldment can be detected.