NON-DESTRUCTIVE TESTING TECHNIQUES CLASS NOTES
NON-DESTRUCTIVE TESTING
TECHNIQUES CLASS NOTES
Non-destructive testing (NDT) is a
technique to evaluate the properties
of a material without causing any
damage to the component being
tested. It determine the external
(surface) and or internal defect.
It takes less time as compared to
destructive testing. Thus it saves
time and money. It is applicable to
all spheres of life. Some of the most
important are inspection of welded joint,
human x-rays and ultra-sound testing.
Non-destructive testing (NDT) is also
said as Nondestructive
examination (NDE) or Nondestructive
inspection (NDI) or Nondestructive
evaluation (NDE)
Techniques
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Visual Testing Technique
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Dye Penetration Technique
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Magnetic –Particle Technique
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Ultrasonic Testing Technique
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Eddy Current Testing Technique
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Radiographic Testing Technique
Visual testing
It uses the followings:
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Visual inspection by the naked eye
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Mirrors
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Magnifying glasses
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Microscopes (optical and electron microscopes)
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Closed circuit television (CCTV)
Dye Penetration Technique
Most commonly used method. It detects the surface and internal cracks. This test uses three fluids. These are
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Cleaner to clean the surface
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Penetrating dye to penetrate in the crack
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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.
Radiographic Testing
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
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Firstly it is easy and fast.
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Secondly it is economical. There is no harm to the material.
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Thirdly it increases the safety and reliability of a product.