MPI works by issuing a magnetic field into the component being tested – essentially magnetizing the component. Next, iron particles are applied to the surface either in a dry form or suspended in liquid. Because even the tiniest cracks and fissures will allow some of the magnetism to “leak” out, these particles become attracted to the tiny cracks, building up and providing evidence of a leak, or “indication.” The component may be magnetized by an electrical current, called direct magnetization, or indirectly by applying a magnetic field to the outside of the component. Like ultrasonic testing, this approach requires considerable training and expertise.
