a brief description of ndt techniques - copy

8/2/2019 A Brief Description of NDT Techniques - Copy

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By

AVINASH RANJAN

(1SI08ME022)


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Non-destructive testing is the testing of materials,for surface or internal flaws or metallurgicalcondition, without interfering in any way with theintegrity of the material or its suitability forservice.

Major types of NDT1. Radiography.

2. Magnetic Particle Inspection.3. Dye Penetrant Testing.

4. Ultrasonic Testing.

5. Eddy Current and Electro-magnetic Testing.


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Top view of developed film

X-ray film

The part is placed between the radiation

source and a piece of film. The part willstop some of the radiation. Thicker and

more dense area will stop more of the

radiation.

= more exposure

= less exposure

The film darkness (density)

will vary with the amount ofradiation reaching the filmthrough the test object.

Defects, such as voids,cracks, inclusions, etc., can be

detected.


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Advantages Suitable for any material.

Information is presented

pictoriallyDisadvantage There is an upper limit of

thickness through which theradiation can penetrate

The operator must have access toboth sides of an object

Highly skilled operator isrequired because of the potentialhealth hazard of the energeticradiations

Application

Can be used in anysituation when one

wishes to view theinterior of an object

To check for internalfaults and construction

defects, e.g. faultywelding

To see through what isinside an object


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The magnetic flux line close to the surface of aferromagnetic material tends to follow the surfaceprofile of the material

Discontinuities (cracks or voids) of the materialperpendicular to the flux lines cause fringing of themagnetic flux lines, i.e. flux leakage

The leakage field can attract other ferromagnetic

particles MPI uses magnetic fields and small magnetic

particles, such as iron filings to detect flaws incomponents


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Cracks just below the

surface can also berevealed

The magnetic particles form a

ridge many times wider than the

crack itself, thus making theotherwise invisible crack visible


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Advantage

fast, simple andinexpensive

direct, visibleindication onsurface

can be used onpainted objects

Limitations

Only good forferromagnetic

materials objects must be

demagnetized

before and after theexamination

the currentmagnetization maycause burn scars onthe item examined


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Liquid penetration inspection is a method that is used to

reveal surface breaking flaws by bleed out of a colored orfluorescent dye from the flaw.

The technique is based on the ability of a liquid to be drawninto a "clean" surface breaking flaw by capillary action.

Advantage: The method has high sensitive to small surface

discontinuities.

The method has few material limitations

Large areas and large volumes of parts/materials can beinspected rapidly and at low cost.

Parts with complex geometric shapes are routinelyinspected.


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1. SurfacePreparation

2. Penetrant Application

3. Penetrant Dwell

4. Excess Penetrant Removal

5. Developer Application

6. Indication Develop .

Basic processing steps of LPI


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The most commonly usedultrasonic testing technique is pulse

echo, whereby sound is introducedinto a test object and reflections(echoes) from internal imperfectionsor the part's geometrical surfacesare returned to a receiver.

The time interval between thetransmission and reception of pulsesgive clues to the internal structure ofthe material.

In ultrasonic testing, high-frequency sound waves are transmitted

into a material to detect imperfections or to locate changes inmaterial properties.


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High frequency sound waves are introduced into a

material and they are reflected back from surfaces orflaws.

Reflected sound energy is displayed versus time, andinspector can visualize a cross section of the specimen

showing the depth of features that reflect sound.

plate

crack

0 2 4 6 8 10

initialpulse

crack

echo

back surfaceecho

Oscilloscope, or flaw

detector screen


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Eddy current testing can be used on all electrically

conducting materials with a reasonably smooth surface.

The test equipment consists of a generator (AC power

supply), a test coil and recording equipment, e.g. a

galvanometer or an oscilloscope

Used for crack detection, material thickness measurement

(corrosion detection), sorting materials, coating thickness

measurement, metal detection, etc.


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When a AC passes through atest coil, a primary magneticfield is set up around thecoil

The AC primary fieldinduces eddy current in thetest object held below thetest coil

A secondary magnetic fieldarises due to the eddycurrent


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Conductivematerial

CoilCoil'smagnetic field

Eddycurrents

Eddy current'smagnetic field

Eddy Current Instruments

Voltmeter


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APPLICATIONS


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Probe

Signals produced

by variousamounts ofcorrosionthinning.

Periodically, power plants are

shutdown for inspection.Inspectors feed eddy currentprobes into heat exchangertubes to check for corrosiondamage.

Pipe with damage


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Electromagnetic devicesand visual inspections areused to find broken wiresand other damage to thewire rope that is used inchairlifts, cranes and otherlifting devices.


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Aircraft engines are overhauled

after being in service for a periodof time.

They are completely disassembled,cleaned, inspected and thenreassembled.

Fluorescent penetrant inspection

is used to check many of the partsfor cracking.


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Special cars are used to inspect

thousands of miles of rail to findcracks that could lead to aderailment.


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NDT is used to inspect pipelinesto prevent leaks that could

damage the environment. Visualinspection, radiography andelectromagnetic testing are someof the NDT methods used.

Remote visual inspection usinga robotic crawler.

Radiography of weld joints.

Magnetic flux leakage inspection.This device, known as a pig, isplaced in the pipeline and collectsdata on the condition of the pipe as itis pushed along by whatever is beingtransported.


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Thank

you

a brief description of ndt techniques - copy

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