What is the proper procedure to prepare a surface for magnetic particle testing?

Preparing a surface for magnetic particle testing is crucial to obtaining accurate results. The most important step is to clean the surface of any contaminants, such as oil, grease, dirt, rust, or paint, that could interfere with the adherence of the magnetic particles to the defects being tested. Residual contaminants can mask flaws or cause false indications, leading to misleading results. Proper cleaning ensures that the magnetic field can properly penetrate and highlight any discontinuities present in the material.

While other options might seem relevant, such as sanding or heating, these actions could potentially alter the surface and are not standard preparatory steps for magnetic particle testing. A coating for protection is also not appropriate for this testing method, as any protective layer could obscure the magnetic particles from interacting with subsurface flaws. Therefore, the primary focus should always be on ensuring a contaminant-free surface to ensure valid and reliable testing outcomes.