The most widely used Non-Destructive Inspection methods to metal castings are visual inspection, magnetic particle, dye penetrant, ultrasonic inspection and radiography inspection.
Visual Inspection
Visual Non-Destructive inspection is the act of collecting visual data on the status of a material. Visual inspection is the most basic way to examine a material or object without altering it in any way.
Magnetic Particle and Dye Penetrant
The magnetic particle technique uses the concentration of magnetic flux along a crack to attract particles that make the crack more visible. It only works on ferrous materials.
Dye penetrant methods work on ferrous and nonferrous materials. They use a low viscosity liquid that gets drawn into cracks by capillary action. After being allowed to soak, the surface is wiped clean and the dye makes the cracks show up.
magnetic particle
dye penetrant
Ultrasonic Inspection
There are various ways of performing ultrasonic inspections: selection depends on the type of defects being sought and the speed or process rate needed.
Ultrasound is generally very effective for finding internal cracks, porosity, and inclusions but the equipment can be expensive and needs a trained operator.
Ultrasonic Inspection
Radiography Inspection
Radiography Non-Destructive Inspection is the act of using gamma- or X-radiation on materials to identify imperfections. 
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