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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

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