TWI Radiographic Interpretation.(Part3)

M.S.RogersCopyright © 2004 TWI Ltd

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Part 3.

Radiographic InterpretationRadiographic Interpretation

Course Reference WIS 20


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G Y Radiographic Radiographic

TechniquesTechniques


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G Y Single Wall Single Image (SWSI)

- film inside, source outside

Single Wall Single Image (SWSI) panoramic

- film outside, source inside (internal exposure)

Double Wall Single Image (DWSI)

- film outside, source outside (external exposure)

Double Wall Double Image (DWDI)

- film outside, source outside (elliptical exposure)

Radiographic TechniquesRadiographic Techniques


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IQI’s should be placed source side

Film

Film

Single Wall Single ImageSingle Wall Single Image

SWSI


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IQI’s are placed on the film side

Source inside film outside (single exposure)

Film

SWSI panoramic

Single Wall Single Image PanoramicSingle Wall Single Image Panoramic


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Film

IQI’s are placed on the film side Source outside film outside (multiple exposure) This technique is intended for pipe diameters over

100mm

Double Wall single ImageDouble Wall single Image

DWSI


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Radiograph

Identification

ID MR11

• Unique identificationEN W10

• IQI placing

A B• Pitch marks indicating readable film length



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Radiograph



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Film

IQI’s are placed on the source or film side Source outside film outside (multiple exposure) A minimum of two exposures This technique is intended for pipe diameters less than

100mm

Double Wall Double ImageDouble Wall Double Image

DWDI


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Shot A Radiograph

Identification

ID MR12

• Unique identification EN W10

• IQI placing

1 2• Pitch marks indicating readable film length

4 3



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Elliptical Radiograph

1 2

4 3



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Film

IQI’s are placed on the source or film side Source outside film outside (multiple exposure) A minimum of three exposures Source side weld is superimposed on film side weld This technique is intended for small pipe diameters

Double Wall Double Image perpendicularDouble Wall Double Image perpendicular

DWDI


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G Y Radiographic film is usually sandwiched between two

intensifying screens

There are three main there are three main types of intensifying screens

Lead screens

Fluorescent screens

Fluorometallic screens

Intensifying ScreensIntensifying Screens


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Intensification action achieved by emitting

particulate radiation (electrons/beta)

Generally lead of 0.02mm to 0.15mm

Front screen shortens exposure time and

improves quality by filtering out scatter

Back screen acts as a filter only

Lead Intensifying ScreensLead Intensifying Screens


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Intensification action achieved by emitting

Light radiation (Visible or UV-A)

Intensification action twice that of lead

screens

No filtration action achieved

Salt used calcium tungstate

Salt Intensifying ScreensSalt Intensifying Screens


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Intensification action achieved by emitting light

radiation (Visible or UV-A) and particulate

radiation electrons)

High cost

Front screen acts as a filter and intensifier

Salt used calcium tungstate

Fluoromatallic Intensifying ScreensFluoromatallic Intensifying Screens


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image quality

None

Fluorescent

Fluorometallic

Order of speed

Intensification factor

How intensification

is achieved

Electrons -veBeta radiation

1

4

3

Lead

2

3

1

2

4

2-3

8-15

5-10

N/A

Light radiation

Light radiation

None

An intensification factor of 3 will reduce exposure from six minutes to two minutes

Comparison Chart, Intensifying ScreensComparison Chart, Intensifying Screens


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Radiographic FilmRadiographic Film


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Base



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Base

Subbing

Subbing



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Base

Subbing

Subbing

Emulsion AgBr

Emulsion AgBr

Supercoat

Supercoat



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G YWhat are the advantages of Double Coated Film?

•Improve contrast

• Reduce the exposure time


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Grain size Speed Quality Film Factor

Coarse

Medium

Fine

Ultra Fine

Fast

Medium

Slow

V Slow

Poor

Medium

Good

V Good

10

35

90

200

Note: Some film manufactures my use different film factor systems



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When radiation passes through an object it is differentially

absorbed depending upon the materials thickness and any

differing densities

The portions of radiographic film that receive sufficient

amounts of radiation undergo minute changes to produce the

latent image (hidden image)

1. The silver halide crystals are partially converted into

metallic silver to produce the latent image

2. The affected crystals are then amplified by the

developer, the developer completely converts the

affected crystals into metallic silver

3. The radiograph attains its final appearance by fixation

Image FormationImage Formation


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Developer tank - alkali

Stop bath or rinse tank - slightly acidic

Fixer tank - acidic

Final wash tank - running water

Wetting agent - detergent

Drying - drying cabinet or drying room

Film ProcessingFilm Processing


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DevelopmentDevelopment Metallic Silver converted into Black metallic silver

3-5 min at 20OC

Main ConstituentsMain Constituents Developing agent metol-hydroquinone Accelerator keeps solution alkaline Restrainer ensures only exposed silver halides converted Preservative prevents oxidation by air

Processing Systems

Replenishment Replenishment

Purpose – to ensure that the activity of the developer and the

developing time required remains constant

Guideline – 1. After 1m2 of film has been developed,

about 400 ml of replenisher needs to be added


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Supplied as a liquid concentrated alkali mixed to 1 part developer to 4 parts water

Developer temperatures for manual processing 20oC

Development times are 4 to 5 minutes During the development process agitation should

take place to avoid bromide streaking Replenishment may be added to maintain

development times and the activity of the developer



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Supplied as a liquid concentrated acid mixed to 1 part fixer to 3 parts water

Fixing temperatures for manual processing 20oC

Fixing times are twice the clearing time, clearing time about 3 minutes, fixing time about 6 minutes

During the fixing process agitation should take place to avoid light spots on the radiograph

When fixing times exceed 10 minutes the fixer should be replaced, replenishment is not normally added



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G Y After washing in running water the films may be placed in a

wetting agent to reduce surface tension this results in even

drying, preventing black streaky marks on the radiograph

Before drying excess water should be removed with the use

of a squeegee

Drying should take place in a dust free environment

Typical drying times in a drying cabinet 15 minutes

Typical drying times in a drying room 45 minutes Care should be taken not to allow drops of water to appear

on the drying films, this may cause black marks to appear

on the radiograph

Washing / Drying



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Sensitometric curve

H & D Curve (Hurter & Driffield)

Log Relative Exposure

Density (Log)

The point of solarisation

0.5

1.0

2.0

2.5

3.0

3.5

Maximum inherent film density 0.3

Film Characteristic CurveFilm Characteristic Curve


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films characteristic curve The position of the curve on the exposure axis

gives information about the films speed



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Density

A B C D E

Film A is faster than Film B

Film B faster then C



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characteristic curve

The position of the curve on the exposure axis gives

information about the films speed

The gradient of the curve gives information on the films

contrast



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Density (Log)

Density obtained in a photographic emulsion does not vary linearly with applied exposure

Steeper gradientHighest contrast



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G Y Information which can be obtained from a films characteristic

curve




contrast

The position of the straight line portion of the curve against

the density axis will show the density range within which the

film is at its optimal



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Density (Log)

Shoulder

Toe

Straight line section



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characteristic curve




contrast

The position of the straight line portion of the curve against

the density axis will show the density range range within

which the film is at its optimal

A new exposure can be determined for a change of film

type



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Changing DensityChanging Density


DensityDensity achieved 1.5

Density required 2.5

Determine interval between logs

1.8 - 1.3 = 0.5

2.5

1.5

1.3 1.8

Antilog of 0.5 = 3.18

Therefore multiply exposure by 3.18(measured density is lower than the required density)(measured density is lower than the required density)

Original exposure 10 mA mins

New exposure 31.8mA mins


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Changing FilmChanging Film


Density Obtain Logs for Films A and B at required density

Interval between logs = 0.15

1.7 1.85

Antilog of 0.15 = 1.42

Multiply exposure by 1.42

Original exposure 10 mA mins

New exposure 14.2 mA mins

2.5

A B


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G Y Wavelength - Gamma fixed, X-ray variable

Intensity - Gamma curies fixed, X-ray mA variable

Film density to be achieved

Film speed

Source to film distance

Material type

Material thickness

Determination of ExposureDetermination of Exposure


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of a gamma calculators/slide rule

Gamma calculators take into consideration Film density to be achieved Source type Activity of the source Film speed Source to film distance Material type Material thickness



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G Y X-ray exposures are less straight forward

because the wavelength and intensity are variable

X-ray exposures are determined by the following

By using exposure charts

By reference to previous exposure records

By trial and error test shots

By a combination of the above



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5 10 15 20 25 30 35 40 4550

0.5

1.0

1.5

2.5

3.5

4.5

5.5

6.5

Chart based on

• Philips 300kV

• Screen = pb

• Dev = to spec

• Density = 2.0

300280250220200180150120100M

illi A

mps

Material thickness

Kilo VoltsExposure ChartExposure Chart


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1.50 2.00 2.50 3.0

1st DensityAchieved

0.50 5.00 7.50 10.00 12.00

0.75 2.60 3.90 4.90 6.00

1.00 1.75 2.50 3.33 4.00

1.50 1.00 1.40 1.90 2.40

2.00 0.75 1.00 1.25 1.60

2.50 0.55 0.80 1.00 1.20

2.75 0.50 0.70 0.95 1.10

3.00 0.45 0.60 0.80 1.00

3.50 0.38 0.55 0.70 0.86

3.75 0.36 0.53 0.65 0.80

4.00 0.35 0.50 0.60 0.75

Multiply 1st exposure by the above factors to achieve the density required.

Density Equivalent FactorDensity Equivalent Factor


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5 10 15 20 25 30 35 40 4550

0.5

1.0

1.5

2.5

3.5

4.5

5.5

6.5

Chart based on

• Philips 300kV

• Screen = pb

• Dev = to spec

• Density = 2.0

• Material C/S

300280250220200180150120100M

illi A

mps

Material thickness



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50kv 100kV 150kV 220kV 400kV

Mg 0.6 0.6 0.5 0.08

Al 1 1 0.12 0.08

Ti 0.45 0.35

Cu 18 1.6 1.4 1.4

Steel 12 1 1 1

Zi 1.4 1.3 1.3

Radiographic Equivalence Chart

Exposure Equivalent ChartExposure Equivalent Chart


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5 10 15 20 25 30 35 40 4550

0.5

1.0

1.5

2.5

3.5

4.5

5.5

6.5

Chart based on

• Philips 300kV

• Screen = pb

• Dev = to spec

• Density = 2.0

• Material C/S

• Film Type

300280250220200180150120100M

illi A

mps

Material thickness



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Agfa

Kodak

Fuji

2 2.5 3 3.5 4 5 6 7 8 10 12 14

150 100 80

CX AX MX

D7 D5 D4

Relative Film ExposuresRelative Film Exposures


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Original Exposure 4 mins

Film factor for CX 2.5

Film factor for MX 10

New Exposure = New film type X original exposureoriginal film

New Exposure = 10 x 4 = 16mins2.5

Relative Film ExposuresRelative Film Exposures


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5 10 15 20 25 30 35 40 4550

0.5

1.0

1.5

2.5

3.5

4.5

5.5

6.5

Chart based on

• Philips 300kV

• Screen = pb

• Dev = to spec

• Density = 2.0

• Material C/S

• Film Type

• FFD = 900

300280250220200180150120100M

illi A

mps

Material thickness




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example 3 mA at 2 minutes = 6 mA minutes1 mA at 6 minutes = 6 mA minutes

Exposure formula

old exposure = old distance2

new exposure new distance2

E1 = D12

E2 D22

Exposure CalculationExposure Calculation


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Exposure control• For FFD/SFD change

T1 D1 2

T2 D2 2

=

T1 = New exposure time

T2 = Original exposure time

D1 = New FFD

D2 = Original FFD


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Exposure control• For FFD/SFD change

Example:

Calculate new exposure time for FFD = 600 mm

Original exposure at 500mm was 10 min

T1 =(600) 2

(500) 2 X 10 = 14.4 mins


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G Y Any QuestionsAny Questions

??

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TWI Radiographic Interpretation.(Part3)