Most commonly used method. It detects the surface and internal cracks. This test uses three fluids. These are
Cleaner to clean the surface
Penetrating dye to penetrate in the crack
Developer to pull out the penetrating dye
Magnetic –particle technique
Determines the surface defects (discontinuity, crack or foreign material) in magnetic materials like iron and ferrite steel. Magnetize the component with the help of MPT equipment. Then spray finally divided iron particles over the surface. The portion not having iron particles is defective. This method tests welded joint and gas pipes.
Ultrasonic testing technique
Locate the internal defects. Introduce high frequency sound waves in the component. These sound waves reflected back from the surface and the defective portion. Inspection of the photographic plate clearly points the defective portions.
Eddy current testing technique
It finds surface defects. Produce Eddy currents by a coil carrying AC current by induction. It determines the crack, corroded surface, thin material thickness, thickness of thin coating and measurement of conductivity.
Determines the internal defects. It uses high energy photons (short wavelength electro-magnetic radiations). It is same as X-ray in medical radiography. However the wavelength used here is different.
ADVATAGES OF NON-DESTRUTIVE TESTING
Firstly it is easy and fast.
Secondly it is economical. There is no harm to the material.
Thirdly it increases the safety and reliability of a product.
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