Magnetic Particle Inspection
Dye penetrant testing is the easiest and quickest method of surface crack detecting on non-porous surfaces. However dye penetrant only highlights surface cracks. A liquid dye is sprayed onto the surface and capillary action draws the dye into cracks. Fluorescent dyes and UV may be used to better highlight small cracks
Magnetic particle inspection utilises a magnetic field to concentrate mobile magnetic particles at flux concentrations caused by cracks and discontinuities in the material. MPI can detect cracks down to 1-2 mm below the surface.