What is the primary type of material that MPI is used to inspect?

Magnetic Particle Inspection (MPI) is specifically designed for the detection of surface and near-surface discontinuities in ferromagnetic materials. These materials, such as iron, cobalt, and nickel, possess magnetic properties that allow them to be magnetized and respond effectively to the inspection process. When a magnetic field is applied to a ferromagnetic component, any discontinuities present can disturb the magnetic field. This disturbance causes magnetic particles, applied as a fine dry powder or in a suspension, to cluster around the discontinuity, making it visible under proper lighting conditions.

In contrast, while all types of materials can be inspected by various methods, MPI is particularly effective only with ferromagnetic substances. Non-ferromagnetic materials will not respond to the magnetic fields used in this inspection method, making it unsuitable for them. Additionally, composite materials also do not possess the required magnetic properties necessary for this process. Thus, ferromagnetic materials are the primary focus of MPI, as they allow for effective detection and analysis of flaws that could otherwise compromise the integrity of the component.