Twi Radiographic Interpretation.(part3) 70705k

Radiographic Interpretation

Part 3. Course Reference WIS 20 Copyright © 2004 TWI Ltd

M.S.Rogers

Radiographic Techniques

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Radiographic Techniques  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) Copyright © 2004 TWI Ltd

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Single Wall Single Image SWSI

Film Film

IQI’s should be placed source side

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Single Wall Single Image Panoramic SWSI panoramic

Film

 IQI’s are placed on the film side  Source inside film outside (single exposure) Copyright © 2004 TWI Ltd

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Double Wall single Image DWSI

Film  IQI’s are placed on the film side  Source outside film outside (multiple exposure)  This technique is intended for pipe diameters over 100mm Copyright © 2004 TWI Ltd

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Double Wall single Image

Identification • Unique identification EN W10

• IQI placing • Pitch marks indicating readable film length

A

B ID MR11

Radiograph Copyright © 2004 TWI Ltd

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Double Wall single Image

Radiograph Copyright © 2004 TWI Ltd

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Double Wall Double Image DWDI

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 Copyright © 2004 TWI Ltd

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Double Wall Double Image

Identification

4

• Unique identification

3 EN W10

• IQI placing • Pitch marks indicating readable film length

1

2 ID MR12

Shot A Radiograph Copyright © 2004 TWI Ltd

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Double Wall Double Image

4

3

1

2

Elliptical Radiograph Copyright © 2004 TWI Ltd

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Double Wall Double Image perpendicular DWDI

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 Copyright © 2004 TWI Ltd

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Intensifying Screens 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 Copyright © 2004 TWI Ltd

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Lead Intensifying Screens  Film placed between 2 intensifying screens  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 Copyright © 2004 TWI Ltd

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Salt Intensifying Screens  Film placed between 2 intensifying screens  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 Copyright © 2004 TWI Ltd

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Fluoromatallic Intensifying Screens  Film placed between 2 intensifying screens  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 Copyright © 2004 TWI Ltd

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Comparison Chart, Intensifying Screens Intensification How factor intensificatio n is achieved

Screen type

Order of image quality

Lead

1

3

2-3

Electrons -ve Beta radiation

Fluorescent

4

1

8-15

Light radiation

Fluorometallic

3

2

5-10

Light radiation

None

2

4

N/A

None

Order of speed

An intensification factor of 3 will reduce exposure from six minutes to two minutes Copyright © 2004 TWI Ltd

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Radiographic Film

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Radiographic Film

Base

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Radiographic Film

Subbing

Base Subbing

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Radiographic Film Supercoat

Emulsion AgBr Subbing

Base Subbing

Emulsion AgBr Supercoat Copyright © 2004 TWI Ltd

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What are the advantages of Double Coated Film?

•Improve contrast

• Reduce the exposure time

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Radiographic Film Film Types Grain size

Speed

Quality

Film Factor

Coarse

Fast

Poor

10

Medium

Medium

Medium

35

Fine

Slow

Good

90

Ultra Fine

V Slow

V Good

200

Note: Some film manufactures my use different film factor systems

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Image Formation When radiation es 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 Copyright © 2004 TWI Ltd

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Film Processing Film processing is carried out using the following

 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 Copyright © 2004 TWI Ltd

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Processing Systems Development Metallic Silver converted into Black metallic silver 3-5 min at 20OC Main Constituents Developing agent metol-hydroquinone Accelerator keeps solution alkaline Restrainer ensures only exposed silver halides converted Preservative prevents oxidation by air 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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Film Processing Development  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 Copyright © 2004 TWI Ltd

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Film Processing Fixer  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 Copyright © 2004 TWI Ltd

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Film Processing Washing / Drying  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 Copyright © 2004 TWI Ltd

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Film Characteristic Curve Sensitometric curve H & D Curve (Hurter & Driffield) The point of solarisation 3.5

Density (Log)

3.0

2.5 2.0 1.0

Maximum 0.5 inherent film density 0.3 Copyright © 2004 TWI Ltd

Log Relative Exposure M.S.Rogers

Film Characteristic Curve Information which can be obtained from a films characteristic curve  The position of the curve on the exposure axis gives information about the films speed

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Film Characteristic Curve

Density A

B

C

D

E

Film A is faster than Film B Film B faster then C

Log Relative Exposure Copyright © 2004 TWI Ltd

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Film Characteristic Curve Information which can be obtained from a films 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

Copyright © 2004 TWI Ltd

M.S.Rogers

Film Characteristic Curve

Density (Log)

Density obtained in a photographic emulsion does not vary linearly with applied exposure Steeper gradient Highest contrast

Log Relative Exposure Copyright © 2004 TWI Ltd

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Film Characteristic Curve Information which can be obtained from a films 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  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

Copyright © 2004 TWI Ltd

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Film Characteristic Curve Shoulder

Density (Log)

Straight line section Toe

Log Relative Exposure Copyright © 2004 TWI Ltd

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Film Characteristic Curve Information which can be obtained from a films 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  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 Copyright © 2004 TWI Ltd

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Changing Density Density achieved 1.5 Density required

Density

2.5

2.5

Determine interval between logs 1.8 - 1.3 = 0.5 Antilog of 0.5 = 3.18 Therefore multiply exposure by 3.18 (measured density is lower than the required density)

Original exposure 10 mA mins NewCopyright exposure © 2004 TWI Ltd

31.8mA mins

1.5

1.3 1.8

Log Relative Exposure M.S.Rogers

Changing Film Obtain Logs for Films A and B at required density

Density

A

B

2.5

Interval between logs = 0.15

Antilog of 0.15 = 1.42 Multiply exposure by 1.42 1.7 1.85

Original exposure 10 mA mins New exposure Copyright © 2004 TWI Ltd

14.2 mA mins

Log Relative Exposure M.S.Rogers

Determination of Exposure  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 Copyright © 2004 TWI Ltd

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Determination of Exposure Gamma exposures are calculated by the use 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 Copyright © 2004 TWI Ltd

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Determination of Exposure 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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Exposure Chart Kilo Volts 100 120 150 180 200 220 250

280

300

6.5

Milli Amps

5.5 4.5 3.5

Chart based on

2.5

• Screen = pb

• Philips 300kV • Dev = to spec

• Density = 2.0

1.5 1.0 0.5 5 Copyright © 2004 TWI Ltd

10

15

20

25

30

35

Material thickness

40

45 50 M.S.Rogers

Density Equivalent Factor st

1 Density Achieved

Density Required 1.50

2.00

2.50

3.0

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.

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Exposure Chart Kilo Volts 100 120 150 180 200 220 250

280

300

6.5

Milli Amps

5.5 4.5 Chart based on

3.5

• Philips 300kV • Screen = pb

2.5

• Dev = to spec • Density = 2.0

1.5

• Material C/S

1.0 0.5 5 Copyright © 2004 TWI Ltd

10

15

20

25

30

35

Material thickness

40

45 50 M.S.Rogers

Exposure Equivalent Chart Radiographic Equivalence Chart 50kv 100kV 150kV 220kV 400kV Mg

0.6

0.6

0.5

0.08

Al

1

1

0.12

0.08

0.45

0.35

Ti Cu

18

1.6

1.4

1.4

Steel

12

1

1

1

1.4

1.3

1.3

Zi Copyright © 2004 TWI Ltd

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Exposure Chart Kilo Volts 100 120 150 180 200 220 250

280

300

6.5

Milli Amps

5.5 4.5

Chart based on • Philips 300kV

3.5

• Screen = pb • Dev = to spec

2.5

• Density = 2.0

• Material C/S

1.5

• Film Type

1.0 0.5 5 Copyright © 2004 TWI Ltd

10

15

20

25

30

35

Material thickness

40

45 50 M.S.Rogers

Relative Film Exposures Film Speed Chart D7

Agfa CX

Kodak

Fuji

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D4

AX

150 2 2.5

D5

MX

100 3

3.5

80 4

5

6

7

8

10 12 14 M.S.Rogers

Relative Film Exposures Change of Film From CX to MX Original Exposure

4 mins

Film factor for CX

2.5

Film factor for MX

10

New Exposure = New film type X original exposure original film New Exposure = 10 x 4 = 16mins 2.5 Copyright © 2004 TWI Ltd

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Exposure Chart Kilo Volts 100 120 150 180 200 220 250

280

300

6.5

Milli Amps

5.5 4.5 Chart based on • Philips 300kV

3.5

• Screen = pb • Dev = to spec

2.5

• Density = 2.0

1.5

• Material C/S • Film Type

1.0

• FFD = 900

0.5 5 Copyright © 2004 TWI Ltd

10

15

20

25

30

35

Material thickness

40

45 50 M.S.Rogers

Exposure Calculation Exposure = intensity x time example 3 mA at 2 minutes = 6 mA minutes 1 mA at 6 minutes = 6 mA minutes

Exposure formula old exposure = old distance2 new exposure new distance2 E1 = D12 E2 D22 Copyright © 2004 TWI Ltd

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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 Copyright © 2004 TWI Ltd

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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 =

Copyright © 2004 TWI Ltd

(600) 2 (500)

2

X

10 = 14.4 mins

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Any Questions

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