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Industrial Radiographic Film Interpretation
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Radiographic Interpretation
PART 2
Duties of a Radiographic Interpreter Mask of any unwanted light from viewer Ensure the background light is subdued Check the radiograph for correct
identification Assess the radiographs density Calculate the radiographs sensitivity Check the radiograph for any artifacts Assess the radiograph for any defects
present State the action to be taken, acceptable,
rejectable or repair
Radiographic Films
Radiographic Film
Base
Base must be :-• Transparent - To allow white light to go through• Chemically inert• Must not be susceptible to expansion and
contraction• High tensile strength• Flexibility
cellulose triacetate / polyester
Subbing layer - the adhesive between the emulsion and base
- The material for this is gelatine + a base solvent
Subbing
Subbing
Base
Radiographic Film
Base
Supercoat
Supercoat
Subbing
Subbing
Radiographic Film
The Emulsion
• Consist of millions of silver halide crystal (silver bromide)
• The size usually 0.1 & 1.0 µm suspended in gelatin binding medium
• Is produced by mixing solution of silver nitrate & salt, such as potassium bromide
• The rate & temperature of mixing governs its grain size
• Size & distribution of the crystal effect the quality / appearance of final radiograph (large grain more sensitive to radiation)
What are the advantages of Double Coated Film?
• Improve contrast • Reduce the exposure time
Radiographic Film
Image formationWhen radiation passes through an object it is differentially absorbed depending upon the materials thickness and any differing densitiesThe 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 black metallic silver
3. The radiograph attains its final appearance by fixation
Film TypesGrain SizeSpeed Quality Film factor Coarse Fast Poor 10Medium Medium Medium 35Fine Slow Good 90Ultra Fine V.Slow V.Good 200Film emulsion produced by mixing solutions of nitrate and salt such as potassium bromide.• The rate and temperature determine the grain structures
1. Rapid mixing at low temperature - Finest grain structure
2. Slow mixing at high temperature - Large grain structure
Film Factor
• Is a number relates to the speed of particular film• Is obtained from a films characteristic curve• SCRATA scale often used for film factors :
Smaller film factor - faster the film speed
Example • Film factor of 10 will be twice as fast compared to a film
factor of 20.• A film factor of 20 took 4min. to expose, 2min will require
for a film factor of 10 to gives the same density
Film Type100kV 200kV Iridium 192 Cobalt
NoScreens
PbScreens
PBScreens
RFactor
PbScreens
RFactor
KODAK R (single) 20 20 20
FUJI IX25 35 30
KODAK R (double) 35 35 35 25
AGFA D2 30 40
FUJI IX29 35 45
FUJI IX50 60 55 50 5.0 50 14.0
AGFA D3 55 45 40 30
FUJI IX59 60 75
FUJI IX80 100 100 100 2.5 100 5.0
KODAK M 90 75 60 5.0 45
KODAK B 105 95 100 75
AGFA D4 70 70 65 55
KODAK T 140 115 100 75
AGFA D5 120 115 105 95
FUJI IX100 200 190 210 1.0 210 2.0
KODAK AA 200 200 150 1.1 150
AGFA D7 220 180 170 155
FUJI IX150 370 340 400 0.6 410 0.9
KODAK CX 300 250 200 255
AGFA D8 315 260 265 260
CharacteristicsD2 Extremely fine-grained film with low speed and high contrast. Ideal for exposures where
the finest possible detail is required.
D3S.C.
Single-emulsion film with very high image quality, maximum perceptibility, high contrast and pleasant image tint. The ideal film for sharp enlargements. The colorless back coating prevents curling to guarantee a film that remains flat under all conditions.
D3 An ultra fine-grained film with low speed and high contrast that obtains a high detail perceptibility. D3 meets the requirements of the nuclear industry.
D4 The ideal standard film for high quality applications. An extra fine grain film with average speed and high contrast.
D5The fastest film for fine detailed applications. A fine grain, moderate speed film with high contrast. High image quality, excellent consistency and homogeneity, pleasant image tint and a shiny surface.
D7
The ideal standard film for those applications where the emphasis is on short exposure time. A fine grained film with excellent image quality and high contrast. D7 is a high speed film used for high energy applications, with particularly good consistency, homogeneity, a pleasant image tint and shiny surface.
D8Ultra-high speed fine grain film, with moderate contrast designed for exposures with or without metal screens. If a higher speed is required. D8 also can be used with fluorometallic (RCF) or fluorescent screens (bivalent type).
D6RD6R, an extra-fine grain film, can be processed both in a standard 8 min. cycle and in a short 2 min./90 sec. cycle. Designed for exposures with or without metal screens, flourometalic (RCF), and fluorescent screens (bivalent type).
Film Features
lx 25Fuji's finest grain, high contrast ASTM Class 1 film having maximum sharpness and discrimination characteristics. It is suitable for new materials, such as carbon fiber reinforced plastics, ceramic products, and micro electric parts. lx25 is generally used in direct exposure techniques or with lead screens. lx25 is recommended for automated processing only.
lx 50
An ultra-fine grain, high contrast ASTM E94 Class 1 film having excellent sharpness and high discrimination characteristics. It is suitable for use with any low atomic number material where fine image detail is imperative. Its ultra-fine grain makes it useful in high energy, low subject contrast applications where high curie isotopes or high output X-ray machines permit its use. Wide exposure latitude has been demonstrated in high subject contrast applications. IX 50 is generally used in direct exposure techniques or with lead screens.
lx 80
An extremely fine grain, high contrast ASTM Class 1 film suitable for detection of minute defects. It is applicable to the inspection of low atomic number material with low kilovoltage X-ray sources as well as inspection of higher atomic number materials with high kilovoltage X-ray or gamma ray sources. Wide exposure latitude has been demonstrated in high subject contrast applications. IX 80 is generally used in direct exposure techniques or with lead screens.
lx 100
A very fine grain, high contrast ASTM Class 2 film suitable for the inspection of light metals with low activity radiation sources and for inspection of thick, higher density specimens with high kilovoltage X-ray or gamma ray sources. Wide exposure latitude has been demonstrated in high contrast subject applications. Although IX 100 is generally used in direct exposure techniques or with lead screens, it is suitable for use with fluorescent or fluorometallic screens.
lx 150A high speed, fine grain, high contrast ASTM Class 2 film suitable for inspection of a large variety of specimens with low-to-high kilovoltage X-ray and gamma ray sources. It is particularly useful when gamma ray sources of high activity are unavailable or when very thick specimens are to be inspected. It is also useful in X-ray diffraction work. IX 150 is used in direct exposure techniques or with lead screens.
Processing Film
Dev
elop
er
Stop
bath
Fixe
r Running water
Processing Systems
Manual System
Development Metallic Silver converted into Black metallic silver
3-5 min at 20OC
Main ConstituentsDeveloping agent metol-hydroquinoneAccelerator keeps solution alkalineRestrainer ensures only exposed silver halides convertedPreservative prevents oxidation by air
Processing Systems
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
Stop Bath
3% Acetic acid - neutralises the developer
Processing Systems
Fixer
• Sodium thiosulphate or ammonium thiosulphate Functions:- 1. Removes all unexposed silver grains 2. Hardens the emulsion gelatin
• Clearing time - The time taken for the radiography to loose its milky appearance.
• Fixing time - Twice the clearing time
Processing Systems
Processing Systems
Running water
• Films should be washed in a tank with constant running water for at least 20 minutes.
• Insufficient washing the film can caused the yellow fog appears.
SENSITOMETRY
Characteristic Curves• Increasing exposures applied to successive
areas of a film• After development the densities are measured• The density is then plotted against the log of the
exposure
Characteristic curve
Sensitometric curve
Hunter & Driffield curve
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0 0.5 1.0 1.5 2.0 2.5 3.0
Density
Toe portion
Average gradient- Straight line
Shoulder
Base fog0.3
Characteristic Curves
The relationship between exposure time and resultant film density is non-linear
The gradient of the film characteristic curve is a measure of film contrast
Characteristic Curves
Characteristic Curves
Information which can be obtained from a films characteristic curve
• The position of the curve 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 contrast will be at its highest.
• New exposure time can be determined for a change of film type
Characteristic Curves
Log Relative Exposure
Density (Log)
Density obtained in a photographic emulsion does not vary linearly with applied exposure
The steeper the slope the greater the contrast
Characteristic Curves
Log Relative Exposure
Density
A B C D E
Film A is faster than Film B
Film B faster then C
Information which can be obtained from a films characteristic curve
• The position of the curve axis gives information about the films speed
• Film A is coarse grain & is faster than Film B & C
• Film B is fine grain and it’s speed is intermediate between Film A & C
• Film C is ultra-fine grain and is the slowest of the three
• A “fast” film requires a shorter exposure time than a “slow” film
Characteristic Curves
Information which can be obtained from a films characteristic curve
• The position of the curve 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 contrast will be at its highest.
• New exposure time can be determined for a change of film type
Changing Density
Log Relative Exposure
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 = 3.16
Therefore multiply exposure by 3.16
(measured density is lower than the required density)
Original exposure 10 mA mins
New exposure 31.6mA mins
Using D7 Film a density of 1.5 was achieved using an
exposure of 10 mAmin
What exposure is required to achieve a
density of 2.5?
1.63 - 1.31 = 0.32 Antilog 0.32 = 2.1Original Exposure = 10 mAminNew Exposure = 2.1 X 10 = 21 mAmin
Characteristic Curves
Information which can be obtained from a films characteristic curve
• The position of the curve 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 contrast will be at its highest.
• New exposure time can be determined for a change of film type
Changing Film
Obtain Logs for Films A and B at required density
Interval between logs 1.85 – 1.7= 0.1
Antilog of 0.15 = 1.42Multiply exposure by 1.42
Original exposure = 10 mA mins
New exposure = 10mAmins. X 1.42 = 14.2 mA mins
Log Relative Exposure
Density
1.7 1.85
2.5
A B
Using D7 Film a density of 2.5 was achieved using an
exposure of 10 mAmin
What exposure is required to achieve a density of 2.5 using
MX film?
2.07 - 1.63 = 0.44 Antilog 0.44 = 2.75Original Exposure = 10 mAminNew Exposure = 2.75 X 10 = 27.5 mAmin
National standards generally limit the base fog level of unexposed radiographic film to 0.3.
If the base fog level exceeds this value film contrast can be quite severely affected.
Fog level can be checked by processing a sample of the unexposed film.
BASE FOG LEVEL (AFFECTS FILM CONTRAST)
Characteristic Curves
BASE FOG LEVEL (AFFECTS FILM CONTRAST)Characteristic Curves
Effect of film fogging on the film characteristic curve
(The dotted lines show the average gradient between a film density of 1.5 and a film density of 2.5 for film having a base fog level of 0.1 and 0.5 respectively.
The average gradient with a base fog level of 0.1 is about 3.6 while that for a base fog level of 0.5 is about 2.7.
This decrease in average gradient is indicative of a reduction in film contrast.)
RADIOGRAPHIC DEFINITIONDEFINITION • Is the sharpness of the dividing line between areas of different density
• Usually is not measured exclusively, normally assessed subjectively
• Measured by the use of Duplex type III IQI (Bs EN 462:P5)
Radiographic DefinitionDefinition measured by the use of a type III I.Q.I.
Alternative terms given
• Duplex type
• Cerl type B
• EN 462 part 5
Consists of pairs of parallel platinum or tungsten wires of decreasing thicknesess
The gap same as the thickness wire
EN 4
6 2-5
Geometry Unsharpness ( Ug)• Also known as Penumbra is the unsharpness on the
radiograph caused by the geometry of the radiation in relation to the object/subject
• Always exists & borders all density fieldsInherent unsharpness (Ui) • Unsharpness of the radiographs caused by stray
electrons transmitted from exposed crystal which have affected adjacent crystal
• Always exists; depending on grain size, distribution & energy used
• Increases with a reduction in wavelenght
Radiographic Definition
Radiographic Definition
Geometric unsharpness Inherent unsharpness
• FFD/SFD too short• OFD too large/screen film contact• Source size too large• Vibration/movement• Abrupt thick. Changes in specimen
• Coarse grain film• Salt screens• Radiation quality• Development
DEFINITION
Geometry of Image Formation
Penumbra Ug)
Ug= F x ofd fod
(Ug = 0.25mm)
ofd
Focal spot size, F
fodffd
To minimise penumbra Source size as small as possible
Source to object distance as long as possible
Object to film distance as small as possible
Penumbra (Ug)
Penumbra = S x OFD FFD - OFD
S = 4mmOFD = 25mmFFD = 275
= 4 x 25 275 - 25
Penumbra = 0.4mm
Penumbra Calculations
Penumbra Calculations
= 4 x 25 0.25
+ 25
Min FFD = S x OFD Penumbra
S = 4mmOFD = 25mmFFD = 275Penumbra = 0.25
+ OFD
Min FFD = 425mm
Inherent Unsharpness
Exposed radiographwith crack like indication
Stray electrons fromexposed crystals
Adjacent crystalsaffected by stray electrons
- -
-
--
--
- -
-
Inherent Unsharpness
Large film grain size increased inherent Unsharpness
Short wavelength increased inherent Unsharpness
Loose film crystal distribution increased inherent Unsharpness
Determination of focal spot size
FOCAL SPOT SIZE
DETERMINED BY
Image Dimension minus (2 X Hole Size)
4 mm - (2 X 0.25) = 3.5 mm
X- RAY TUBE
LEAD SHEET ~ 4 mm W.T.0.25 mm Dia HOLE
FILM AND CASSETTE
LARGEST IMAGE DIMENSION e.g. 4mm
FOCAL SPOT
DEVELOPED FILM
250 mm
250 mm
Measurement of the longest linear dimension of the image
Placed a lead sheet approx. 4mm thick containing a small hole about 0.25mm dia, exactly halfway between the focal spot & radiographic film
Geometric Unsharpness
Geometric UnsharpnessLong Film to Focal Distance
Geometric Unsharpness
Short Film to Object Distance
Small Focus
Geometric Unsharpness
Large Focus
Geometric Unsharpness
Short Object to Film Distance
Geometric Unsharpness
Long Object to Film Distance
Geometric Unsharpness
Intensifying Screens
Radiographic film is usually sandwiched between two intensifying screens
There are three main types of intensifying screens
•Lead screens
•Fluorescent screens
•Fluorometallic screens
Film placed between 2 intensifying screensIntensification action achieved by emitting particulate/beta radiation (electrons)
Generally lead of 0.02mm to 0.15mmFront screen shortens exposure time and improves quality by filtering out scatterBack screen acts as a filter only
Lead Intensifying Screens
Intensification action achieved by emitting Light radiation (Visible or UV-A)
Intensification action twice that of lead screensNo filtration action achievedSalt used calcium tungstateFilm placed between 2 intensifying screens2 types –
1. high definition (fine grain screen)2. high speed or rapid screen
Salt Intensifying Screens
Film placed between 2 intensifying screensIntensification action achieved by emitting light
radiation (Visible or UV-A) and particulate radiation electrons)
High costFront screen acts as a filter and intensifierSalt used calcium tungstateScreen type
1. Type 1 – x-rays up to 300kV
2. Type 2 – x-rays 300-1000kV, Ir 1923. Type 3 – Co60
Fluorometallic Intensifying Screens
Latitude – Range of thicknessWide latitude radiographic films meet the applications for a variety of multi-thickness subjects. (fuji IX 29 & 59)
Film Latitude
Wide latitudePoor contrastGood definition
Low latitudeGood contrastPoor definition
Scatter
• Radiation emitted from any other source than that giving the primary desired rectilinear propagation (straight line)
• Scatter will lead to - poorer contrast - poorer definition and - create spurious indications
• It may also cause radiological protection problems
Scatter
• Internal scatter originating within the specimen
• Side scatter walls and nearby objects in the path of
the primary beam• Back scatter materials located behind the film
Scatter
• Internal scatter originating within the specimen
Scatter• Side scatter walls and nearby objects
in the path of the primary beam
Scatter
• Back scatter materials located behind the film
SCATTER
Control of Scatter
• Collimation• Diaphragms• Beam filtration• Masking or Blocking• Grids• Filters• Increased beam energy
COLLIMATION
• provide radiation safety to the operating personnel and general public by directing the emerging radiation beam to the useful area of exposure.
• X-ray equipment is always to some extent self-collimated
• which is turn results in radiographs with better sensitivity.
• In gamma radiography collimators consisting of hollowed out blocks of lead weighing around 2.5 kg are common.
• collimators for gamma radiography are made from tungsten or tantalum.
• The principle of collimation is if there is less radiation then there will be proportionally less scatter.
Diaphragms • They consist of a sheet of lead which has
a hole cut in it the same shape as the object which is being radiographed.
• shield out all unwanted radiation, the set up for radiography must however, be extremely accurate if the use of a diaphragm is to be successful.
• Diaphragms are therefore more likely to be seen where a fully automated technique is in use that allows for a very high degree of repeatability in the set up accuracy.
Shutters and masks
• consists of placing sheets of lead, bags of lead shot or barium putty or any other radiation absorbing material around the object which is being radiographed in order to reduce the undercutting effect of side scatter.
• limit the radiation beam as it is directed toward the part, thereby decreasing scatter radiation by narrowing and decreasing beams to a specific location.
• Shutters are usually mounted on the front of the image intensifier and help keep radiation not passing through the part from impinging on image intensifier screen and causing phosphor blooming.
GRIDS• limited to medical radiography. • A grid consists of a matrix of parallel metal bars which is set
in oscillation during exposure such that the grid itself does not produce a radiographic image.
• effective method of reducing the effects of side scatter, but grids are very rarely a practical option for industrial situations.
• In order to be effective the grid must be placed as close as possible to the film.
• In microfocus x-radiography it may be placed between the film and the object.
SensitivitySensitivity• Defined as the smallest indication or detail can be seen
on the radiographs.
• It is a function of the contrast and the definition of the radiographic image.
• A general term of sensitivity can be determine as an overall assessment of the quality on a radiographic image which relates to the ability radiographic techniques to detect fine discontinuities. .
• Image quality is determined by a combination of variables: radiographic contrast and definition.
IQI sensitivityThe image on a radiograph which is used to determine the quality level
Defect sensitivityAbility to assist the sensitivity and locate a defect on a radiograph(Depend on the defect orientation)
Sensitivity
Ideally IQI should be placed on the source side IQI sensitivity is calculated from the following formula
Sensitivity % = Thickness of thinnest step/wire visible x 100Object Thickness
IQI Sensitivity
Image Quality IndicatorsThickness BS 3971 DIN 54 109 BS EN 462-2 BS EN 462-1
(mm) STEP WIRE WIRE (DIN 62) STEP/HOLE WIRE1-6 7-12 13-18 4-10 9-15 15-21 1-7 6-12 10-16 H 1 H 5 H 9 H 13 W 1 W 6 W 10 W 13
0.050 70.063 7 60.08 6 50.10 5 7 7 40.125 6 4 6 6 6 30.150.16 5 3 5 5 5 20.20 4 2 7 4 4 4 10.25 3 1 6 7 3 3 7 30.300.32 2 5 6 2 2 6 6 20.350.40 1 4 5 1 1 5 5 10.50 6 3 4 4 40.600.63 5 2 3 3 30.750.80 4 1 7 7 2 2 6 7 20.901.00 3 6 6 1 1 5 6 11.201.25 2 5 5 4 51.50 1 41.60 4 3 41.80 32.00 6 2 3 2 6 32.50 5 1 2 1 5 23.003.20 4 1 4 14.00 3 35.00 2 26.30 1 1
IQI Sensitivity
A Radiograph of a 16mm thick but weld is viewed under the correct conditions, 5 wires visible on the radiograph IQI pack 6-12 Din 62, what is the IQI sensitivity?
Sensitivity = Thickness of thinnest wire visible X 100 Total weld thickness
Sensitivity = 0.4 X 100 16
Sensitivity = 2.5 %
IQI SensitivityUsing the same IQI pack 6-12 Din 62, How many IQI wires must be visible to give an IQI sensitivity of 2 %, thickness of material 16mm
Sensitivity % = Thickness of thinnest step/wire visible x 100
Total object thickness
2 = Thickness of thinnest step/wire visible x 100
16 = 2 x16
100
= 0.32 ( 6 wire visible)
Thickness of thinnest step/wire visible
Image Quality Indicator
Image Quality Indicators IQI’s / Penetrameters are used to measure radiographic sensitivity
and the quality of the radiographic technique used.
They are not used to measure the size of defects detected
Standards for IQI’s include:
BS EN 462-1 – Wire TypeBS EN 462-2 – Step/wedge Type BS EN 462-3 – Classes for ferrous mat. BS EN 462-4 – IQI values & tables BS EN 462-5 – Duplex WireType
BS 3971DIN 54 109ASTM E747
BS EN 462-1 wire type IQIs each consist of 7 wires taken from a list of 19 wires.
Each of these groupings is available in any of 4 types of material;
‘FE’, for Steel or stainless steel ‘CU’, for copper, tin, zinc and their alloy‘AL’ for Aluminium‘TI’. for Titanium
Four standard wire groupings are available,
designation ‘W1’, wires 1 to 7, designation ‘W6’, wires 6 to 12, designation ‘W10’, wires 10 to 16designation ‘W13’, wires 13 to 19.
EN 462-1 wire type IQIs
Designation Diameter
W1 3.2W2 2.5W3 2.0W4 1.6W5 1.25
W6 1.0W7 0.8W8 0.63
W9 0.5W10 0.4
W11 0.32
W12 0.25
W13 0.2
W14 0.16
W15 0.125
W16 0.1
W17 0.08
W18 0.063
W19 0.05
Easy to remember the wire diameters: Remember the diameters of the first three, 3.2, 2.5 and 2.0 mm divide by halve from the remaining value.
BS EN 462-1 wire diameters
The series consists of 21 wires ranging from 0.08 mm to 8.1 mm in diameter; there are 4 overlapping groups of 6 wires, each designated by a letter (A, B, C or D)
IQI type WIRE DIAMETERS
A 0.08 0.1 0.13 0.16 0.2 0.25
B 0.25 0.33 0.4 0.5 0.63 0.81
C 0.81 1.0 1.27 1.6 2.0 2.5
D 2.5 3.2 4.0 5.1 6.3 8.1
ASTM E 747
BS EN 462-2 Step-hole IQIs
Classification of radiographic techniques
The radiographic techniques are divided into two classes:— class A: basic techniques;— class B: improved techniques.
Class B techniques will be used when class A might be insufficiently sensitive.Better techniques compared to class B are possible and may be defined by specification of all appropriate test parameters.
The choice of radiographic technique shall be defined by specification.If, for technical reasons, it is not possible to meet one of the conditions specified for class B, such as type of radiation source or the source-to-object distance, f, it may be defined by specification that the condition selected may be that specified for class A. The loss of sensitivity shall be compensated by an increase of minimum density to 3,0 or by the choice of a higher contrast film system.
Because of the better sensitivity compared to class A, the test specimen may be regarded as tested within class B.
This does not apply if the special SFD reductions as described in 6.6 for test arrangements 6.1.4 and 6.1.5 are used.
CLASS ‘A’ RADIOGRAPHY1. Single Wall Technique Source Side IQI
Thickness Required wire Wire diameter Average Sensitivity
≤ 1.2 18 0.063 > 5.25%
> 1.2 ≤ 2 17 0.08 5%
> 2 ≤ 3.5 16 0.1 3.64%
> 3.5 ≤ 5 15 0.125 2.94%
> 5 ≤ 7 14 0.16 2.67%
> 7 ≤ 12 13 0.2 2.1%
> 12 ≤ 18 12 0.25 1.67%
> 18 ≤ 30 11 0.32 1.33%
> 30 ≤ 40 10 0.4 1.14%
> 40 ≤ 50 9 0.5 1.11%
> 50 ≤ 60 8 0.63 1.14%
> 65 ≤ 85 7 0.8 1.07%
> 85 ≤ 120 6 1.0 0.98%
> 120 ≤ 220 5 1.25 0.74%
> 220 ≤ 380 4 1.6 0.53%
> 380 3 2.0 < 0.53%
CLASS ‘B’ RADIOGRAPHY1. Single Wall Technique Source Side IQI
Thickness Required wire Wire diameter Average Sensitivity
≤ 1.5 19 0.05 > 3.33%
> 1.5 ≤ 2.5 18 0.063 3.15%
> 2.5 ≤ 4 17 0.08 2.46%
> 4 ≤ 6 16 0.1 2.0%
> 6 ≤ 8 15 0.125 1.79%
> 8 ≤ 12 14 0.16 1.6%
> 12 ≤ 20 13 0.2 1.25%
> 20 ≤ 30 12 0.25 1.0%
> 30 ≤ 35 11 0.32 0.98%
> 35 ≤ 45 10 0.4 1.0%
> 45 ≤ 65 9 0.5 0.91%
> 65 ≤ 120 8 0.63 0.68%
> 120 ≤ 200 7 0.8 0.5%
> 200 ≤ 350 6 1.0 0.36%
> 350 5 1.25 < 0.36%
7FE12
Step / Hole type IQI Wire type IQI
Image Quality Indicators
EN 4
62-5
Image Quality Indicators
IQI wire thickness =
Subject thicknes x 2
100
4T dia
ASME Image Quality Indicators
1 Hole visible = 4T2 Holes visible = T3 Holes visible = 2T
IQI Sensitivity
Minimum Penetrmeter Thickness 0.5mm(2% of the weld thickness)Minimum Diameter for 1T Hole 0.5mmMinimum Diameter for 2T Hole 1.0mmMinimum Diameter for 4T Hole 2.00mm
Penetrmeter Design T dia2T dia
17 12mm
38mm T
Wire Type IQI
Step/Hole Type IQI
Image Quality Indicators
It is important that IQIs are placed
Placement of IQI• IQI must be placed on the maximum thickness of weld • Thinnest required step or wire must be placed at the
extreme edge of section under test • IQI must be placed at the source or film side and at a
position within the diagnostic film length (DFL) in accordance with the requirements of the contract specification.
• In case of access problem , IQI has to placed on the film side of the object, letter ‘FS’ should be placed beside the IQI.
• IQI material chosen should have similar radiation absorption/transmission properties to the test specimen
Exposure Control
For FFD/SFD change
E1 D1 2
E2 D2 2=
E1 = New exposure time
E2 = Original exposure time
D1 = New FFD
D2 = Original FFD
Exposure control
For FFD/SFD change
Example: Calculate new exposure time for FFD = 300mm Original exposure at 250mm was 5 min
Exposure control
E1 D1 2
E2 D2 2
=5min.
E2
2502mm3002mm
=
E2 =5Mins. X 3002
2502
E2 =
E1 =
E2 =
D12 =
D22 =
5min.
?
250mm
300mm
If a good radiograph was produced using an exposure of 100 curie minutes at a source to film distance of 850 mm what exposure will produce a good radiograph if the source to film distance is changed to 550 mm (assuming that all other factors remain equal)?
E1 D1 2
E2 D2 2
=E1
100ciMins.5502mm8502mm
=
E1 =100ciMins. X 5502
8502
E1 = 42 ciMins.
E1 =
E2 =
D12 =
D22 =
?
100ciMins.
550mm
850mm
An exposure chart for iridium 192 that has been constructed for SFD = 500 mm gives an exposure of 100 Ci-min for 25 mm of steel. The specification calls for a minimum SFD = 800 mm. If all other factors remain equal what exposure is needed at the specified minimum SFD?
E1 D1 2
E2 D2 2
=100ciMins.
E2
5002mm8002mm
=
E2 =100ciMins. X 8002
5002
E2 = 256 ciMins.
E1 = E2 =
D12 =
D22 =
100ciMins.
?
500mm
800mm
A radiographic technique produces a good radiograph, the settings are:kV =175, mA = 5, FFD = 440 mm and Exposure time = 2 mins 12 secsWhat exposure time will be required if the settings are changed as follows?kV = 175,mA = 3.5, FFD = 500
E1 D1 2
E2 D2 2
=11mAmin.
E2
4402mm5002mm
=
E2 =11mAmin. x 5002
4402E1 =
E2 =
D12 =
D22 =
5mA x 2min 12sec
3.5mA x T
440mm
500mm
E1 = mA X Time (mA.min)
= 5 x 2.2
= 11mAmin.
3.5mA x T = 14.2mAmin. T = 14.2mAmin.
3.5mAExposure time = 4min 3sec
Exposure calculation
E = Intensity X Time (mA.min) – X-Ray
E = Intensity X Time (ci.mins) – Gamma Ray
Example for X-ray
E = exposure (mA.min)I = Tube current (mA)T = Exposure time (min)
Exposure calculation
In one radiographic operation, an-x-ray machine is set at 5mA and the radiographic film is exposed for a period of 15 minutes. What is the total exposure received by the film?
Solution:
Given,
Tube current (mA) = 5mA
Exposure time (t) = 15 minutes
Exposure ( E) = Intensity(mA) X T(min.)
= 5 X 15
= 75 mA.min
A satisfactory radiograph is produced in 3 minutes at 8 mA. Assuming that all other factors remain the same, what exposure time is required if the mA is reduced to halved?
Original exposure
E = mA x t = 8mA x 3min = 24mAmin.
After reduced exposure
E = mA x T24mA = 4mA x TT = 24mAmin.
4mA = 6min.
Radiographic Techniques
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)
Single wall single image SWSI
IQI’s should be placed source side
Film
Film
Single wall single image SWSI panoramic
• IQI’s are placed on the film side• Source inside film outside (single
exposure)
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
Film
Double wall single image DWSI
Radiograph
Identification
ID MR11
• Unique identification EN W10
• IQI placingA B• Pitch marks indicating
readable film length
Double wall double image DWDI elliptical exposure
Film
• IQI’s are placed on the source 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 image DWDI
Shot A Radiograph
Identification
ID MR12
• Unique identificationEN W10
• IQI placing
1 2• Pitch marks indicating readable film length
4 3
Double wall double image (DWDI) perpendicular exposure
Film• IQI’s are placed on the source 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
Density requirement 2.0 to 3.0Density unacceptable
Density1.2
Density1.2
Density3.0
Density3.0
Sandwich Technique
FILM AFILM B
FILM A: Fast film - Thicker sectionFILM B: Slow film - Thinner section
LEAD SCREENS
FILM AFILM B
Density2.0
Density2.0
Density3.0
Density3.0
Sandwich Technique
Density 2.0 to 3.0 acceptable
Interpretation conditions
Duties of a Radiographic Interpreter Mask of any unwanted light from viewer Ensure the background light is subdued Check the radiograph for correct
identification Assess the radiographs density Calculate the radiographs sensitivity Check the radiograph for any artifacts Assess the radiograph for any defects
present State the action to be taken, acceptable,
rejectable or repair
Viewing conditions
• Darkened room• Clean viewer• Minimum adequate illumination from the viewer is
3000cd/m2
• Eyesight must be adjusted to the darkened conditions• Comfortable viewing position and environment• Avoid fatigue
Radiographic Quality
Density - relates to the degree of darkness
Contrast - relates to the degree of difference in density between adjacent areas on a radiograph
Definition - relates to the degree of sharpness
Sensitivity - relates to the overall quality of the radiograph
Factors Influencing Sensitivity
Sensitivity
Contrast Definition
Radiographic Quality
• Density• Contrast
The ability to differentiate areas of different film density
Contrast
Radiographic contrast :- The density difference on a radiography between two areas- usually subject and the background (overall)
Subject contrast :- Contrast arising from variation in opacity within an irradiated area
Film contrast :- The slope of characteristic curve of the film at specified density. ( Type of film being used, fine grain or large grain)
Radiographic ContrastInsufficient
Contrast• kV too high• Over exposure
compensated for by shortened development
• Incorrect film - screen combination
Excessive Contrast• kV too low• Incorrect
developer
Factors Influencing Sensitivity
Density
Sensitivity
Contrast Definition
Film Energy Subject contrast
Processing
Factors Influencing SensitivitySensitivity
Definition
Density Film Energy Object contrast
Processing
Time Temperature Type Strength Agitation
Contrast
Film Contrast Subject Contrast
Film type Density Processing Scatter Wavelength Screens
Radiographic Contrast
Factors Influencing Sensitivity
Sensitivity
Definition
Film speed
Screens Energy Vibration ProcessingGeometry
Contrast
Factors Influencing SensitivitySensitivity
Contrast Definition
Film speed
Screens Energy Vibration Processing
Time Temperature Type Strength Agitation
Geometry
Radiographic Contrast
Poor contrast
Poor contrast
High contrast
Radiographic Density
* Greater contrast is achieved at higher density
The DEGREE OF DARKENING of a processed film is called FILM DENSITY.Film Density is a logarithmic unit:
Where I1 is the incident light intensity and I2 is the transmitted light intensity
Thus if Film Density = 2, the incident light intensity is 100x greater than the transmitted intensity
Radiographic Density
Lack of Density
Under exposure
Developer temp too low
Exhausted developer
Developer too weak
Insufficient development
time
Excessive Density
Over exposure
Excessive development
Developer temp too high
Too strong a solution
Measuring Radiographic Density
Density is measured by a densitometer A densitometer should be calibrated using a
density strip
4.0 3.5 3.0 2.5 2.0 1.5 1.0
What is a good radiograph? A good radiograph satisfies the inspection requirement
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