MPI (Magnetic Particle Inspection) is used for the detection of surface and near-surface flaws in ferromagnetic materials like iron, nickel, cobalt and gadolinium.
During inspection a permanent magnet, electromagnet or electromagnetic coil is used to apply a magnetic field to the test item, with flaws being revealed by the distortion of magnetised flux.
The component surface is first magnetised in at least two perpendicular directions at 90 degrees to each other, ensuring complete inspection in both planes. The process consists of spraying fine magnetic particles within a carrier fluid onto the component. Particles are then attracted to the area of flux leakage, creating a visible flaw indication.
To ensure clear contrast visibility, white paint is mixed with black magnetic particle ink. A further option uses dry powder application for hot surfaces where wet ink is less effective. The most sensitive process for revealing finer imperfections uses fluorescent particles viewed under UV light.
Types of electrical currents used for MPI
There are several types of electrical currents used in MPI. For a proper current to be selected considerations is given to the part geometry, material, the type of discontinuity being looked for, and how far the magnetic field needs to penetrate into the part.
Each method of magnetizing has its pros and cons. AC is generally the best for discontinuities on the surface, while some form of DC is better for subsurface defects.
See a complete range of the standards used by ITCL for Dye Penetrant Testing – here
We pride ourselves on the high quality of application and testing by our experienced technicians. Our workforce is fully qualified to current standards and work to approved procedures and control checks. Environmental and health & safety issues are of paramount concern to all staff working on your site, with expert consultation always available.
ITCL offers a comprehensive 24hr in-house and on-site service.
Contact a member of the ITCL team on 0151 356 7118 for more information.