What do magnetic particles indicate in magnetic particle testing?

In magnetic particle testing, the primary purpose is to detect discontinuities in ferromagnetic materials. Magnetic particles are applied to the surface of the material and are attracted to areas where there are disruptions in the magnetic field, such as cracks, seams, or other flaws. These discontinuities can occur both on the surface and just below the surface of the material.

When a magnetic field is applied, the magnetic particles will congregate at these irregularities, making them visible under appropriate lighting conditions. This capability makes magnetic particle testing a valuable non-destructive testing method for evaluating the integrity of materials used in critical applications, ensuring safety and reliability.

While pressure and temperature changes, the presence of voids and porosity, or density and mass variations might be relevant to other testing methods or material properties, they do not accurately describe what magnetic particle inspection is designed to identify. The focus of magnetic particle testing is squarely on detecting surface and subsurface discontinuities.