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RADIOGRAPHY

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OBJECTIVES

To:

• understand the principle of radiographic

testing methods

• Know the technique of testing

• Become familiar with standards & codes

• Learn the applications.

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INTRODUCTION 

Radiography:

•

one of the oldest & the most widely used NDT whichuses X-rays or  -rays radiation to examine the interiorof the materials.

• gives a permanent film record of defects that is easy

to interpret.• applied for assessing the quality of the welded joints

also.

• can detect flaws or discontinuities in welds such as

cracks, porosity & blow holes, slag, flux or oxideinclusions, lack of fusion between the weld metal &the parent metal, incomplete penetration, tungsteninclusion, etc.

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PROPERTIES OF X- RAYS &  - RAYS 

X- rays are highly penetrating electromagnetic

radiations of wave length shorter than UV-rays (X-

rays: 5 to 0.0004A,  - rays: 0.1 to 0.005A)

These rays have the following properties:

• Invisible electromagnetic radiations.

•

Can penetrate matter. Penetration is less if density ofmatter is more and thickness is more

• Are differentially absorbed.

• Travel in straight lines.

• Produce photochemical effects on films.• May be refracted, reflected and diffracted

• Damage living tissues

• Ionise gases through which it pass.

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PRINCIPLE

• Both X-rays &  -rays are very short wave length

electro magnetic radiation which penetrate opaquematerials & obtain a permanent record of the result

on sensitized film.

• When these rays pass through a material having

defects, the rays passing through the less denser

parts of the object are absorbed to a smaller extent

than the rays passing through the adjacent sound

material (because of difference in density & thicknessof the test piece) & are allowed to fall on a light

sensitive film placed on the back side of the object to

be radiographed.

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Contd-

• After exposure for the prescribed time, the film is

developed. 

• The contrast (difference in density) on the developed

film between the image of an area containing a

defect & the image of a defect free area of thespecimen permits the observer to distinguish the

flaw.

• The film is called exograph, if X-rays are used &

gamma ray graph, if  -rays are used.• Both types of film are called radiograph

(photographic record of defects) 

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GENERATION OF X-RAYS 

• X-rays are produced by an X-ray tube.

• An X- ray tube is an evacuated tube, usually made ofglass, containing an electrically heated filament

which liberates electrons & a tungsten anode.

•

The electrons liberated from the heated filament aremade to impact on the anode with the help of large

PD (50 to 2000KV) between the filament & the

anode.

•  X-rays are emitted due to the impact of high velocityelectrons on the anode.

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Contd-----• Only about 1% of the total electron energy is converted

into X-rays & the rest of it transforms into heat due to

which the anode is heated to a very high temp & a deviceto cool the anode by water or oil is necessary.

• The X-rays come out of the tube through a window in the

form of a beam.

• The intensity of X-rays is directly proportional to thefilament current & the wave length is inversely

proportional to the voltage between the cathode &

anode.

• Both the voltage & the current can be varied due to

which the tube may be adjusted over a wide range of

operating characteristics depending upon the material to

be radiographed.

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GENERATION OF X-RAYS 

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METHOD OF TESTING 

• The X-ray tube, components to be tested & film are set

up as shown in the fig 

• The X-rays are allowed to fall upon the test piece• A cassette containing film is placed behind & in contact

with the component lar to the rays.

• Since most defects possess lesser density than the

sound parent metal, they transmit X-rays or  -rays

better than the sound metal does, therefore the film

appears to be more dark where defects are in line of the

beam.

•  Usually a penetrameter is placed on the side of the

source adjacent to the weld.

• Thickness of the penetrameter is usually 2% of the

thickness of the weld joint.

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MARKING OF RADIOGRAPHIC LOCATION, DIRECTION OF

WELD BEAD AND PLACING OF PENETROMETER

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WELDED COMPONENT

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SETTING UP OF CASSETTE

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X-RAY MACHINE

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RADIOGRAPHY TESTING

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RADIOGRAPHY TESTING

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GENERATION OF  - RAYS 

 rays, are produced by a radioactive isotope

(Radium, Radon, Cobalt, Iridium, Cesium, Thalium,

Europium, Cerium, Xenon, Tantalum, etc).

• The gamma ray source (300 mg) is housed in a lead

or tungsten alloy container of sufficient thickness toprovide necessary protection.

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VARIOUS TYPES OF ISOTOPES FOR RADIOGRAPHY ( - RAYS) 

Co 60 : This has a half-life of 5.3 years. This is used forradiography of thicker sections of steel (between 2 to

6”). 

Ir192 : This has a half-life of 72 days. This is used for 

thin section. Ir192 will give better radiographicsensitivity than Co 60 . 

Cs137 : This half-life of 30 years. Suitable for

radiographic examination of steel sections of  1.5 to2.5 inches.

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 - RAYS

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 - RAYS TESTING

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PRECAUTION

• Every radiation worker and area require some

radiation measurment method in order to

have safty aspect

• There are two type of radiation monitoring

instrument – Personnel monitoring

 – Lab /area monitoring

• Portable unit measuring range upto 20 mr /hr

• TLD  – Thermo Luminenscec Dosimeter

• Film Badge Reader.

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RADIOGRAPHIC FILM

• Basically X-ray film is made of:

 – Base: a transparent blue tinted cellulose derivated

 – Emulsion: consists of gelatin containing microscopic,

radiation sensitive silver halide crystals such as silver

bromide & iodide• Usually, the emulsion is coated on both sides of

the base in layers about 0.0005 inch thick.

Putting emulsion on both sides of the basedoubles the amount of radiation-sensitive silver

halide & thus increases the film speed.

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RADIOGRAPHIC FILM 

• The emulsion layers are thin enough so

developing, fixing & drying can be accomplishedin a reasonable time.

• The emulsion is very sensitive & when x-ray, -

ray strikes it, a change takes place in its physicalstructure.

• The change is of a nature that it cannot be

detected by ordinary physical method. However,when the exposed film is processed

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FILM PROCESSING • When the film is processed, it is exposed to several

different chemicals solutions for controlled periods of

time. Processing film basically involves the followingfour steps.

 – Development - The developing agent gives up

electrons to convert the silver halide grains to

metallic silver. Grains that have been exposed to theradiation develop more rapidly, but given enough

time the developer will convert all the silver ions into

silver metal. Wash the developer away with water

 – Fixing - Unexposed silver halide crystals are removed

by the fixing bath. The fixer dissolves only silver

halide crystals, leaving the silver metal behind.

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Contd-----FILM PROCESSING 

 – Washing - The film is washed with water to

remove all the processing chemicals.

 – Drying - The film is dried for viewing.

• Processing film is a strict science governed by

rigid rules of chemical concentration,

temperature, time, and physical movement.

FILM HANDLING

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FILM HANDLING

X-ray film should always be handled carefully to avoid

physical strains, such as pressure, creasing, buckling,

friction, etc. Whenever films are loaded in semi-flexibleholders and external clamping devices are used, care

should be taken to be sure pressure is uniform.

• Marks resulting from contact with fingers that are moist

or contaminated with processing chemicals, as well ascrimp marks, are avoided if large films are always grasped

by the edges and allowed to hang free.

• Clean towels should be kept close at hand to dry the

hands.• Another important precaution is to avoid drawing film

rapidly from cartons, exposure holders, or cassettes.

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VIEWING RADIOGRAPHS

• Radiographs (developed film exposed to x-ray

or gamma radiation) are generally viewed on a

light-box.

• Because the energy of electromagnetic

radiation is directly related to their frequency,

X rays are much more energetic and

penetrating than light waves as well.

INTERPRETATION OF RADIOGRAPH

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INTERPRETATION OF RADIOGRAPH 

For successful interpretation of a radiograph, one

should have as wide a knowledge of the form of

images characteristics or various defects. A radiograph

contains light & dark areas. The latter representing

parts of the material having a lower density. Various

defects appear on the negatives of a radiographs asfollows:-

• Gas cavities & blow holes appear as well defined

circular dark areas

• Shrinkage cavity appears as a fibrous irregular dark

region having an indistinct outline

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INTERPRETATION OF RADIOGRAPH 

•

Cracks are indicated by darkened areas ofvariable width

• Sand inclusions appear as grey or black spots

of an uneven or granular texture withindistinct boundaries.

• Inclusions in castings appear as dark spots of

definite outline. In light alloys, the inclusions

may be of high density & thus cause light

spots.

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CONDITION FOR GOOD RADIOGRAPHY 

• The distance between the source and the

material under test should be always as greatas in practical.

• The film should be as close as possible to the

object being radiographed.

• The central rays should be as nearly

perpendicular to the film as possible to

minimize distortion.

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ADVANTAGE & DISADVANTAGE OF X-RAY  -RAY

• Advantages:

• Disadvantages:

X-ray - ray•Exposure times much

shorter

•More sensitive & is better

on extremely thin sections.

•suitable for out door

•Portable because the source is small.

•Very suitable for out door work & in

confined spaces, since it requires neither

electric power nor water supply foroperation.

X-ray - ray

•Requires trained operator

•Involves radiation hazards

•Requires trained operator

•Requires more exposure time due to lower

sensitivity which involves more radiation hazards

•involves radiation hazards

•source loses strength continuously

Trained operator is required

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RADIOGRAPHY TESTING

Neutron radiography:-

It is used to solve complex problem that can not be

solved by X-rays or Y-rays. It is used for detecting

internal cracks of very light materials like plastic,rubber components, etc.

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