What condition must be met for magnetic particle inspection (MPI) to be effective?

Magnetic Particle Inspection (MPI) is a non-destructive testing method that relies on the ability of magnetic fields to reveal surface and near-surface discontinuities in ferromagnetic materials. For MPI to be effective, the material under inspection must be magnetized. This magnetization creates a magnetic field that allows fine magnetic particles—applicable in both dry and wet forms—to concentrate at the sites of indications, such as cracks or other discontinuities, thus revealing them visually.

Magnetization can be achieved using various methods, such as using an electric current or permanent magnets. When the material is magnetized correctly, any defects present will disrupt the magnetic field lines, causing the magnetic particles to cluster at those points of leakage, making the defects visible.

While factors such as temperature or surface finish may influence the effectiveness of the inspection and the definition of clarity of indications, the primary condition for the MPI method to work is that the material must be in a magnetized state. Without proper magnetization, the detection of discontinuities would not be possible.