What type of defects is MPI most effective at detecting?

Magnetic Particle Inspection (MPI) is particularly effective at detecting surface and near-surface defects because the method relies on magnetic fields and ferromagnetic materials. During the inspection, the test piece is magnetized, and when there is a discontinuity such as a crack or void at or near the surface, the magnetic field is disrupted.

This disruption causes magnetic particles, which are applied to the surface, to cluster at the site of the defect, making it visually identifiable. Surface and near-surface defects are critical to detect because they can significantly impact the integrity and safety of components, often leading to catastrophic failures if not found. Other types of defects, such as internal structural defects, would typically require alternative methods like ultrasonic testing or radiographic inspection, as MPI primarily illuminates issues that intersect with the surface of the material. Therefore, MPI’s capability is maximized in detecting defects that are exposed or slightly buried below the surface.