Why is it important to use a clean surface before conducting MPI?

Using a clean surface before conducting Magnetic Particle Inspection (MPI) is crucial because contaminants can obscure flaws and lead to inaccurate results. In MPI, the primary goal is to detect surface and near-surface discontinuities, such as cracks or voids, in ferromagnetic materials. If the surface is contaminated with dirt, grease, or other foreign materials, these contaminants can create a barrier that prevents the magnetic particles from adequately penetrating the flaws and forming visible indications.

Additionally, any foreign material can contribute to false indications or, conversely, mask true indications that could reveal critical defects. A clean surface allows for the proper application of the magnetic field and ensures that the magnetic particles concentrate at the areas of concern, thus maximizing the effectiveness of the inspection and improving the accuracy of the results. This is essential in quality control and safety-critical applications, where undetected defects could lead to catastrophic failures.