A flaw detector finds defects in materials using different physical principles. In an X-ray flaw detector, high-voltage electrons bombard a target of tungsten, platinum or a similar metal, producing bremsstrahlung and characteristic X-rays. As the X-rays pass through the workpiece, differences in material density form an attenuation image. Recorded on film or a digital detector, the image shows the location, shape and size of defects directly.
A magnetic particle inspection machine works on the principle of magnetic flux leakage: it magnetizes the ferromagnetic part, and wherever a crack interrupts the field, magnetic particles gather to form a visible indication of the defect.