Which types of materials can be inspected using MPI?

Magnetic Particle Inspection (MPI) is a non-destructive testing method specifically designed for detecting surface and near-surface discontinuities in ferromagnetic materials. Ferromagnetic materials, such as iron, nickel, and cobalt, have magnetic properties that allow them to be magnetized. During the MPI process, a magnetic field is applied to these materials, and when a discontinuity, such as a crack or void, is present, it disturbs the magnetic field. This disturbance causes magnetic particles, typically coated in a fluorescent dye or color, to gather at the discontinuity, making it visible under appropriate lighting conditions.

In contrast, materials like plastic, rubber, non-ferrous metals such as aluminum and copper, or composite materials do not exhibit ferromagnetic properties. Therefore, they cannot be effectively inspected using MPI. These materials either do not respond to magnetic fields or lack the necessary characteristics to reveal defects in the same manner as ferromagnetic materials. This specialization in ferromagnetic materials is what makes MPI an effective tool in various industries, particularly in manufacturing and maintenance of metal components.