TWI - Radiography Inspection Part 4 refresher

Radiography Testing

1. 23 Sep 02
Radiography
Part 4.
Course Reference WIS 20

2. 23 Sep 02
Determination of Exposure
Wavelength - Gamma fixed, X-ray
variable
Intensity - Gamma curries fixed, X-ray mA
variable
Film density to be achieved
Film speed
Source to film distance
Material type
Material thickness

3. 23 Sep 02
Determination of Gamma
Exposures
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

4. 23 Sep 02
Determination of X-ray
Exposures
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

5. 23 Sep 02
Exposures Charts
5101520253035404550
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
300280250220200180150120100
M
illi A
m
p
s
Material thickness
Kilo Volts

6. 23 Sep 02
Density Equivalent Factors
Density Required
1.50 2.00 2.50 3.0
1
st
Density
Achieved
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.

7. 23 Sep 02
Exposures Charts
5101520253035404550
0.5
1.0
1.5
2.5
3.5
4.5
5.5
6.5
300280250220200180150120100
M
illi A
m
p
s
Material thickness
Kilo Volts
Chart based on
•Philips 300kV
•Screen = pb
•Dev = to spec
•Density = 2.0
•Material = C/S

8. 23 Sep 02
Exposure Calculations
50kv100kV150kV220kV400kV
Mg 0.60.60.50.08
Al 1 1 0.120.08
Ti 0.450.35
Cu 18 1.61.41.4
Steel 12 1 1 1
Zi 1.41.31.3
Radiographic Equivalence Chart

9. 23 Sep 02
Exposures Charts
5101520253035404550
0.5
1.0
1.5
2.5
3.5
4.5
5.5
6.5
300280250220200180150120100
M
illi A
m
p
s
Material thickness
Kilo Volts
Chart based on
•Philips 300kV
•Screen = pb
•Dev = to spec
•Density = 2.0
•Material = C/S
•Film type = D7

10. 23 Sep 02
Relative Film Exposures
Film Speed Chart
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

11. 23 Sep 02
Exposure Calculation
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

12. 23 Sep 02
Exposures Charts
5101520253035404550
0.5
1.0
1.5
2.5
3.5
4.5
5.5
6.5
300280250220200180150120100
M
illi A
m
p
s
Material thickness
Kilo Volts
Chart based on
•Philips 300kV
•Screen = pb
•Dev = to spec
•Density = 2.0
•Material = C/S
•Film type = D7
•FFD = 900

13. 23 Sep 02
Exposures Calculations
Exposure = intensity x time
example3 mA at 2 minutes = 6 mA minutes
1 mA at 6 minutes = 6 mA minutes
Exposure formula
old exposure = new distance
2
new exposure new distance
2
E1 = D1
2
E2 D2
2

14. 23 Sep 02
Radiographic Techniques

15. 23 Sep 02
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)

16. 23 Sep 02
Single wall single image SWSI
IQI’s should be placed source side
Film
Film

17. 23 Sep 02
Single wall single image SWSI
panoramic
•IQI’s are placed on the film side
•Source inside film outside (single exposure)
Film

18. 23 Sep 02
Film
Double wall single image DWSI
•IQI’s are placed on the film side
•Source outside film outside (multiple exposure)
•This technique is intended for pipe diameters
over 100mm

19. 23 Sep 02
Double wall single image DWSI
Radiograph
Identification
ID MR11
•Unique identification
EN W10
•IQI placing
A B•Pitch marks
indicating readable
film length

20. 23 Sep 02
Film
Double wall double image DWDI
elliptical exposure
•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

21. 23 Sep 02
Double wall double image DWDI
Shot A Radiograph
Identification
ID MR12
•Unique identification
EN W10
•IQI placing
1 2
•Pitch marks
indicating readable
film length
4 3

22. 23 Sep 02
Film
Double wall double image DWDI
perpendicular exposure
•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

23. 23 Sep 02
Density requirement 2.0 to 3.0
Density unacceptable
Density
1.2
Density
1.2
Density
3.0
Density
3.0
Sandwich Technique

24. 23 Sep 02
LEAD
SCREENS
FILM A
FILM B
FILM A: Fine Grain Medium Speed
FILM B: Very Fine Grain-Slow Speed
FILM A
FILM B
Density
2.0
Density
2.0
Density
3.0
Density
3.0
Sandwich Technique
Density 2.0 to 3.0 acceptable

25. 23 Sep 02
t = 50
d ?
Defect
b = 30
a = 15
Lead Marker
Tube Shift
Source
Defect Images
Lead Marker Images
Source
Parallax or tube shift Technique
d = t x a
b
d = 50 x 15
30
d = 25mm

26. 23 Sep 02
Radiographic Films

27. 23 Sep 02
Radiographic Film
Base

28. 23 Sep 02
Radiographic Film
Base
Subbing
Subbing

29. 23 Sep 02
Radiographic Film
Base
Subbing
Subbing
Emulsion AgBr
Emulsion AgBr
Supercoat
Supercoat

30. 23 Sep 02
Film Types
Grain SizeSpeed Quality Film factor
CoarseFast Poor 10
MediumMedium Medium 35
FineSlow Good 90
Ultra FineV.Slow V.Good 200

31. 23 Sep 02
Image formation
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 the amplified by the
developer, the developer completely converts
the affected crystals into metallic silver
3.The radiograph attains its final appearance by
fixation

32. 23 Sep 02
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

33. 23 Sep 02
Film Processing
Development
Supplied as a liquid concentrated alkali mixed to
1 part developer to 4 parts water
Developer temperatures for manual processing
20
o
C
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

34. 23 Sep 02
Film Processing
Fixer
Supplied as a liquid concentrated acid mixed to 1
part fixer to 3 parts water
Fixing temperatures for manual processing 20
o
C
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

35. 23 Sep 02
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
Film Processing
Washing / Drying

36. 23 Sep 02
Characteristic curve
Sensitometric curve
H & D Hunter & Driffield curve
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

37. 23 Sep 02
Characteristic Curves
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

38. 23 Sep 02
Characteristic Curves
Log Relative Exposure
Density
A B C D E
Film A is faster than
Film B
Film B faster then C

39. 23 Sep 02
Characteristic Curves
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

40. 23 Sep 02
Characteristic Curves
Log Relative Exposure
Density
(Log)
Density obtained in
a photographic
emulsion does not
vary linearly with
applied exposure
Steeper gradient
Highest contrast

41. 23 Sep 02
Characteristic Curves
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

42. 23 Sep 02
Log Relative Exposure
Density
(Log)
Shoulder
Toe
Straight line
section
Characteristic Curves

43. 23 Sep 02
Characteristic Curves
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