Magnetic Particle Testing (MPT), also known as Magnetic Particle Inspection (MPI), is a non-destructive testing (NDT) method used for detecting surface and near-surface discontinuities in ferromagnetic materials such as iron, nickel, and cobalt. The process involves magnetizing the test piece and applying magnetic particles, which could be dry or suspended in a liquid, to the surface. Any discontinuities present, like cracks or voids, will disrupt the magnetic field, causing the particles to accumulate at the site of the irregularity.
Here’s a general overview of the process:
- Preparation: The surface of the test material is cleaned to remove any dirt, paint, or other substances that could interfere with the test.
- Magnetization: The test material is magnetized using either a direct or indirect method. The direct method involves passing an electric current through the test material, while the indirect method uses a magnetic yoke or similar device to induce a magnetic field.
- Application of Magnetic Particles: Magnetic particles, usually in the form of a dry powder or a liquid suspension, are applied to the surface of the test material.
- Inspection: The test material is examined under appropriate lighting conditions. Accumulations of magnetic particles at irregularities will be visible as they cluster along lines of magnetic flux leakage, indicating defects.
- Demagnetization: After the inspection, the test material is usually demagnetized to remove any residual magnetism.
- Reporting: The findings of the inspection are recorded, and a determination is made regarding the material’s fitness for its intended use.
Magnetic Particle Testing is widely used in various industries, including automotive, aerospace, and manufacturing, to ensure the integrity of materials and to identify potential weaknesses before they lead to failure.