Introduction to NDT Methods

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Nondestructive Tests

Prepared by:

Mostafa Mohammed Ahmed Aref

TWI


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We use Non Destructive Testing (NDT) when we wish to

assess the integrity of a structure without destroying it

Types of NDT used are:

Dye penetrant inspection (PT)

Magnetic particle inspection (MT)

Radiographic inspection (RT)

Ultrasonic inspection (UT)

Introduction


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Dye penetrant inspection(PT)


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Surface breaking defects only detected

Penetrant applied to the component and drawn

into the defects by capillary action

Applicable to all non- porous materials.

Introduction


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Procedure


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Two types of penetrants are:

1) ColourColour contrastcontrast 2) Fluorescent PenetrantFluorescent Penetrant

Any penetrant that has been drawn into a crack by capillary

action will be drawn out into the developer

Once the contact time has elapsed, the penetrant isremoved and a developer is then applied

First the work must be cleaned thoroughly, then a

penetrant is applied for a specified time

Procedure


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Apply Penetrant Clean then apply Developer Result

Method


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Magnetic particle inspection(MT)


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Surface and slight sub-surface detection

Relies on magnetization of component being tested

Ferro-magnetic materials only can be tested

Methods of applying a magnetic field, yoke, permanent magnetand prods.

Any defect which interrupts the magnetic field, will create aleakage field, which attracts the particles

Introduction


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Collection of ink

particles due to

leakage field

Prods

DC or AC

Electro-magnet

(yoke) DC or AC

Crack like

indication

Crack likeindication

Method


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The types of magnetic media used are:

1) Wet ink1) Wet ink 2)2) Dry powderDry powder 3)3) Fluorescent inkFluorescent ink

The weld length must be crossed at 90by the magnetic field

A magnetic ink is applied which will concentrate in areas of

flux leakage, as those caused by flaws

First the work must be cleaned and a whitener applied for

contrast. A magnetic flux is then applied by permanent magnet,

electro magnet, or straight current

Procedure


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Contrast paint Magnet & Ink Result

Method


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Radiographic inspection(RT)


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Radiation is transmitted to varying degrees dependant upon

the density of the material through which it is travelling

Thinner areas and materials of a less density show as darkerareas on the radiograph

Thicker areas and materials of a greater density show as

lighter areas on a radiograph

Applicable to metals, non-metals and composites

Introduction


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The 2 types of radiation used in industrial radiography:

1) X rays (from Cathode Ray Tube)

2) Gamma rays (from a Radioactive Isotope)

Any imperfections in line with the beam of radiation will be

shown on the film after exposure and development

A film is placed inside a cassette between lead screens.

It is then placed to the rear of the object to be radiographed

A radiographic source, is exposed to the work and film for a

pre-calculated time

Procedure


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Source

Radiation beamImage quality indicator

Test specimenRadiographic film

Method


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Source

Radiation beamImage quality indicator

Radiographic film with latent image after exposure

Test specimen

Method


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Ultrasonic inspection(UT)


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This detection method uses high frequency sound waves,

typically above 2MHz to pass through a material

A probe is used which contains a piezo electric crystal totransmit and receive ultrasonic pulses and display the signals on

a cathode ray tube or digital display

The actual display relates to the time taken for the ultrasonic

pulses to travel the distance to the interface and back

An interface could be the back of a plate material or a defect

Introduction


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Any imperfections will rebound the sound waves causing a

signal to occur on the cathode ray tube

A probe is then applied with the correct angle for the weld

preparation and sound waves are transmitted

First the work must be cleaned thoroughly, then a couplant is

applied to increase sound transmission

Procedure


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Apply Couplant Sound wave

Signal reboundedSignal rebounded

from Lack of fusionfrom Lack of fusion

CRT display

Result

Method


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defect

0 10 20 30 40 50

defect

echoBack wall

echo

CRT DisplayCompression Probe

Material Thk

initial pulse

Method


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Introduction to NDT Methods

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