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7/28/2019 Six Most Common NDT Methods
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Six Most Common NDT Methods
Visual
Liquid Penetrant
Magnetic
Ultrasonic Eddy Current
X-ray
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Visual Inspection Most basic and
common inspectionmethod.
Tools includefiberscopes,borescopes, magnifyingglasses and mirrors.
Portable videoinspection unit withzoom allows inspectionof large tanks andvessels, railroad tankcars, sewer lines.
Robotic crawlers permitobservation inhazardous or tightareas, such as air ducts,reactors, pipelines.
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Liquid Penetrant Inspection A liquid with high surface wetting characteristics is
applied to the surface of the part and allowed time to
seep into surface breaking defects. The excess liquid is removed from the surface of the
part.
A developer (powder) is applied to pull the trapped
penetrant out the defect and spread it on the surface
where it can be seen.
Visual inspection is the final step in the process. The
penetrant used is often loaded with a fluorescent dye
and the inspection is done under UV light to increase test
sensitivity.
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Magnetic Particle InspectionThe part is magnetized. Finely milled iron particles
coated with a dye pigment are then applied to thespecimen. These particles are attracted to magnetic fluxleakage fields and will cluster to form an indicationdirectly over the discontinuity. This indication can bevisually detected under proper lighting conditions.
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Magnetic Particle Crack Indications
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Ultrasonic Imaging
Gray scale image produced using the
sound reflected from the front
surface of the coinGray scale image produced using the
sound reflected from the back surface of
the coin (inspected from heads side)
High r
esolution images can be produced by plotting
signal strength or time-of-flight using a computer-
controlled scanning system.
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High frequency sound waves are introduced into a material andthey are reflected back from surfaces or flaws.
Reflected sound energy is displayed versus time, and inspector canvisualize a cross section of the specimen showing the depth offeatures that reflect sound. f
plate
crack
0 2 4 6 8 10
initial
pulse
crack
echo
back surface
echo
Oscilloscope, or flaw
detector screen
Ultrasonic Inspection (Pulse-Echo)
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Conductivematerial
CoilCoil's
magnetic field
Eddycurrents
Eddy current's
magnetic field
Eddy Current Testing
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Eddy Current TestingEddy current testing is particularly well suited for detecting surface cracksbut can also be used to make electrical conductivity and coating thickness
measurements. Here a small surface probe is scanned over the partsurface in an attempt to detect a crack.
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For More Information on NDT
Ndt Indiahttp://www.ndtindia.org
BA-15, Mangolpuri Industrial Area, Phase-2,
New Delhi, India-110034
Phone : 09560222333
Fax : + 91-11-43852040
Email : info@sigmatest.org
http://www.ndtindia.org/mailto:info@sigmatest.org,clquery@indianbusinesshub.com?subject=Query%20from%20ndtindia.orgmailto:info@sigmatest.org,clquery@indianbusinesshub.com?subject=Query%20from%20ndtindia.orghttp://www.ndtindia.org/Recommended