It is the only simple method to find the surface as well as subsurface discontinuities. It’s an economical procedure. All we want to utilize is some quantity of iron filings. The hazardous situation is almost eliminated unless we go for exposure of UV lamb in fluorescent MPT. The MPT has some constraints in its liabilities they are, its use is promoted only if the testing specimen is made up of ferromagnetic material
Magnetic Particle Testing
Magnetic or electrical current is used to establish a magnetic field in the object. Then dusting the iron powder on the surface of the object. When the magnetic field has applied the iron, filling get aligned along the magnetic lines of forces. If a discontinuity is present on the surface or subsurface of the test specimen the magnetic lines of forces will get disturbed and the magnetic particle will get clustered along the edges of the discontinuity.
Magnetizing equipment
- Electromagnetic Yoke
Electromagnetic yoke Is of the commonly used equipment used to establish the magnetic field. This equipment is made by a piece of soft ferromagnetic steel wrapped by an electrical coil along its overall length. A switch is incorporated in the yoke to activate and deactivate the magnetic field. it can be powered by an AC (from the wall socket) or DC (Battery Pack) means. It has the capacity to generate a very strong magnetic field by touching the poles on the part which is to be inspected.
- Prods
It is handheld equipment introduced to the surface of a component for NDT inspection. The prod is made up of copper with an insulated handle to protect the operator. The prod passes an electric current through the metal. The current passing through the prod will create a circular magnetic field around the prod and this field assists the operator for inspection. It consists of a trigger switch to make the flow of current on/off. A proper contact should be maintained between the prod and the surface because electric arcing will get generated and the part will get damaged quickly.
Limitations
Due to arcing prods are not allowed for aerospace inspection and other critical components.
- Portable cables and conductive cables
Here the test specimen is placed within the coil and a longitudinal magnetic field is generated within the component. The coil is made up of copper and this coil is protected by a molded frame. A switch is provided at the foot space of the operator for easy energizing. In portable coils and cables, the number of wrapping is purely based on the magnetizing force required for a particular inspection
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