rtfi class
TRANSCRIPT
Radiographic InterpretationRadiographic Interpretation
PART PART 22
Duties of a Radiographic InterpreterDuties 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 FilmsRadiographic Films
Radiographic FilmRadiographic 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 FilmRadiographic Film
Base
Supercoat
Supercoat
Subbing
Subbing
Radiographic FilmRadiographic 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)
After Exposure Pre-exposure
Un-sensitised : Stable Sensitised : Unstable
During exposure a During exposure a ““latent imagelatent image”” is formed by is formed by ““sensitisedsensitised”” Silver Halide crystalsSilver Halide crystals
LATENT IMAGE LATENT IMAGE
• Silver Bromide crystals are not perfect, they contain “interstitial” silver ions
• When an interstitial silver ion accepts a free electron,
it becomes a silver atom • The silver atom is larger than the ion and exerts a
stress on the crystal lattice • In the presence of developer this stress causes
instability and the crystal breaks down
• The interstitial silver atoms nucleate silver crystals • A single interstitial silver atom is sufficient to cause
an entire silver bromide crystal to convert to metallic silver
• The typical size of a silver bromide crystal in a typical
photographic film emulsion is about 1μm • Sensitisation of a silver bromide crystal can be
caused by just a single photon of x-ray energy
What are the advantages of Double Coated Film?
• Improve contrast
• Reduce the exposure time
Radiographic FilmRadiographic Film
Image formationImage 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 black metallic silver
3. The radiograph attains its final appearance by fixation
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
Film 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
260 265 260 315 AGFA D8
255 200 250 300 KODAK CX
0.9 410 0.6 400 340 370 FUJI IX150
155 170 180 220 AGFA D7
150 1.1 150 200 200 KODAK AA
2.0 210 1.0 210 190 200 FUJI IX100
95 105 115 120 AGFA D5
75 100 115 140 KODAK T
55 65 70 70 AGFA D4
75 100 95 105 KODAK B
45 5.0 60 75 90 KODAK M
5.0 100 2.5 100 100 100 FUJI IX80
75 60 FUJI IX59
30 40 45 55 AGFA D3
14.0 50 5.0 50 55 60 FUJI IX50
45 35 FUJI IX29
40 30 AGFA D2
25 35 35 35 KODAK R (double)
30 35 FUJI IX25
20 20 20 KODAK R (single)
R Factor
Pb Screens
R Factor
PB Screens
Pb Screens
No Screens
Cobalt Iridium 192 200kV 100kV Film Type
D6R, 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).
D6R
Ultra-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).
D8
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.
D7
The 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.
D5
The ideal standard film for high quality applications. An extra fine grain film with average speed and high contrast. D4
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. D3
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 S.C.
Extremely fine-grained film with low speed and high contrast. Ideal for exposures where the finest possible detail is required. D2
Characteristics
A 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.
lx 150
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 100
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 80
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 50
Fuji'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 25
Features Film
Processing FilmProcessing Film
Dev
elop
er
Stop
bath
Fixe
r Running water
Processing Systems
Manual System
DevelopmentDevelopment •Metallic Silver converted into Black metallic silver 3-5 min at 20OC •The developer supplies a source of electrons (-ve ions) which cause the chemical changes in the emulsion.
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
Sodium. Hesametaphosphate. Prevents the formation of scale. Sequestering agent
Potassium bromide. Controls the level of development fogging.
Restrainer
Sodium sulphate. Prevents oxidation of the developer. Preservative
Borax. Sodium carbonate. Sodium hydroxide.
A chemical which gives an alkaline reaction which speeds up development.
Accelerator
Metol. Hydroquinone. Phenidone
Preferentially reduces the exposed silver halide crystals (+ve ions) to black metallic silver.
Developing agent(s)
Chemicals in common use Action Constituents
Developer
• The film are agitated for approximately 20 seconds and then for approximately 10 seconds every minute.
• Agitation allows for fresh developer to flow over the film and prevents the possibility of bromide streaking;
Stop BathStop Bath 3% Acetic acid - neutralises the developer
Processing Systems
FixerFixer • Sodium thiosulphate or ammonium thiosulphate Functions:- 1. Removes all unexposed silver grains 2. Hardens the emulsion gelatin 3. Convert the unwanted unexposed halides into water soluble compounds; then readily dissolved or removed at the final wash stage. • Clearing time - The time taken for the radiography to loose its milky appearance. Fixing time - Twice the clearing time
Processing Systems
Processing Systems
WashingWashing • 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.
•• Usually followed by dipping in a clean water bath Usually followed by dipping in a clean water bath containing a wetting agent which helps to promote even containing a wetting agent which helps to promote even dryingdrying..
•• OverwashingOverwashing will cause swelling and excessive will cause swelling and excessive softening of the film emulsionsoftening of the film emulsion, , a major cause of a major cause of ““dryingdrying marksmarks””..
SENSITOMETRYSENSITOMETRY
Characteristic CurvesCharacteristic 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 fog 0.3
Characteristic CurvesCharacteristic Curves
The relationship The relationship between exposure time between exposure time and resultant film and resultant film density is nondensity is non--linearlinear
The gradient of the The gradient of the film characteristic film characteristic curve is a measure of curve is a measure of film contrast film contrast
Characteristic CurvesCharacteristic 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 CurvesCharacteristic 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 DensityChanging Density
Log Relative Exposure
Density Density 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 densitymeasured 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?
1.631.63 -- 1.311.31 = = 0.320.32 Antilog Antilog 0.320.32 = = 2.12.1
Original Exposure Original Exposure = = 10 10 mAminmAmin
New Exposure New Exposure = = 22..1 1 X X 10 10 = = 21 21 mAminmAmin
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 FilmChanging Film
Obtain Logs for Films A and B at required density
Interval between logs 1.85 – 1.7= 0.1
Antilog of 0.15 = 1.42
Multiply 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?
2.072.07 -- 1.631.63 = = 0.440.44 Antilog Antilog 0.440.44 = = 2.752.75
Original Exposure Original Exposure = = 10 10 mAminmAmin
New Exposure New Exposure = = 22..75 75 X X 10 10 = = 2727..5 5 mAminmAmin
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 CurvesCharacteristic Curves
BASE FOG LEVEL (AFFECTS FILM CONTRAST) Characteristic CurvesCharacteristic 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 DEFINITION
DEFINITION DEFINITION •• Is the sharpness of the dividing line between areas of Is the sharpness of the dividing line between areas of different densitydifferent density
•• Usually is not measured exclusivelyUsually is not measured exclusively, , normally assessed normally assessed subjectivelysubjectively
•• Measured by the use of Duplex type III IQI Measured by the use of Duplex type III IQI ((Bs EN Bs EN 462462::PP55))
Radiographic Definition
Definition 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
62-5
Geometry Unsharpness Geometry Unsharpness ( ( UgUg))
•• Also known as Penumbra is the Also known as Penumbra is the unsharpnessunsharpness on the radiograph on the radiograph caused by the geometry of the radiation in relation to the caused by the geometry of the radiation in relation to the objectobject//subjectsubject
•• Always exists Always exists & & borders all density fieldsborders all density fields
Inherent unsharpness Inherent unsharpness ((UiUi) )
• 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 DefinitionRadiographic Definition
Inherent Unsharpness
Exposed radiograph with crack like indication
Stray electrons from exposed crystals
Adjacent crystals affected by stray electrons
- -
-
- -
- -
- -
-
ug ug
2mm dia.
2mm length
S = 2² + 2² = 2.82mm
Calculation of geometric unsharpness (Ug
Focal / Source SIZE
FFD / SFD FOD / SOD
OFD
Film
Typical maximum penumbra of 0.25 mm is often used.
Two circular objects can be rendered as two separate circles A or as two overlapping circles B depending on the direction of the radiation
Long OFD Short OFD
Long FFD Short FFD
Lack of parallelism
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 Geometry of Image FormationFormation
Penumbra Ug)
Ug= F x ofd fod (Ug = 0.25mm)
ofd
Focal spot size, F
fod ffd
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 = 4mm OFD = 25mm FFD = 275mm
Penumbra CalculationsPenumbra Calculations
Penumbra CalculationsPenumbra Calculations
Min FFD = S x OFD Penumbra S = 4mm OFD = 25mm FFD = 275 Penumbra = 0.25
+ OFD
Inherent Unsharpness
Large film grain size increased inherent Unsharpness
Short wavelength increased inherent Unsharpness
Loose film crystal distribution increased inherent Unsharpness
Geometric Unsharpness
Geometric Unsharpness Long Film to Focal Distance
Geometric Unsharpness
Short Focal to Object Distance
Small Focus
Geometric Unsharpness Geometric Unsharpness
Large Focus
Geometric Unsharpness Geometric Unsharpness
Short Object to Film Distance
Geometric Unsharpness Geometric Unsharpness
Long Object to Film Distance
Geometric Unsharpness Geometric Unsharpness
Intensifying ScreensIntensifying 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 screens
Intensification action achieved by emitting particulate/beta radiation (electrons)
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
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
Film placed between 2 intensifying screens
2 types – 1. high definition (fine grain screen)
2. high speed or rapid screen
Salt Intensifying ScreensSalt 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
Screen type 1. Type 1 – x-rays up to 300kV
2. Type 2 – x-rays 300-1000kV, Ir 192
3. Type 3 – Co60
Fluorometallic Intensifying ScreensFluorometallic Intensifying Screens
Latitude – Range of thickness
Wide latitude radiographic films meet the applications for a variety of multi-thickness subjects. (fuji IX 29 & 59)
Film LatitudeFilm Latitude
Wide latitude Poor contrast Good definition
Low latitude Good contrast Poor definition
ScatterScatter
• 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
ScatterScatter
• 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
ScatterScatter
• Internal scatter originating within the specimen
ScatterScatter
• Side scatter walls and nearby objects in the path of the primary beam
ScatterScatter
• Back scatter materials located behind the film
The presence of back scattered radiation must be checked for each new test arrangement by a lead letter B placed immediately behind each cassette. If the image of this symbol records as a lighter image on the radiograph, it shall be rejected. If the symbol is darker or invisible the radiograph is acceptable and demonstrates good protection against scattered radiation.
Back Scatter NotificationBack Scatter Notification
SCATTER
Control of ScatterControl 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.
Sensitivity
Sensitivity • 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 sensitivity The image on a radiograph which is used to determine the quality level
Defect sensitivity Ability to assist the sensitivity and locate a defect on a radiograph ((Depend on the defect Depend on the defect orientationorientation))
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 100 Object Thickness
IQI Sensitivity
Image Quality Indicators Thickness BS 3971 DIN 54 109 BS EN 462-2 BS EN 462-1
(mm) STEP WIRE WIRE (DIN 62) STEP/HOLE WIRE 1-6 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 7 0.063 7 6 0.08 6 5 0.10 5 7 7 4 0.125 6 4 6 6 6 3 0.15 0.16 5 3 5 5 5 2 0.20 4 2 7 4 4 4 1 0.25 3 1 6 7 3 3 7 3 0.30 0.32 2 5 6 2 2 6 6 2 0.35 0.40 1 4 5 1 1 5 5 1 0.50 6 3 4 4 4 0.60 0.63 5 2 3 3 3 0.75 0.80 4 1 7 7 2 2 6 7 2 0.90 1.00 3 6 6 1 1 5 6 1 1.20 1.25 2 5 5 4 5 1.50 1 4 1.60 4 3 4 1.80 3 2.00 6 2 3 2 6 3 2.50 5 1 2 1 5 2 3.00 3.20 4 1 4 1 4.00 3 3 5.00 2 2 6.30 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
IQI Sensitivity
Using 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
Image Quality IndicatorImage 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 Type BS 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 3971 DIN 54 109 ASTM 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 16 designation ‘W13’, wires 13 to 19.
EN 462-1 wire type IQIs
0.05 W19 0.063 W18 0.08 W17 0.1 W16 0.125 W15 0.16 W14 0.2 W13 0.25 W12 0.32 W11 0.4 W10 0.5 W9 0.63 W8 0.8 W7 1.0 W6 1.25 W5 1.6 W4 2.0 W3 2.5 W2 3.2 W1 Diameter Designation
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)
8.1 6.3 5.1 4.0 3.2 2.5 D
2.5 2.0 1.6 1.27 1.0 0.81 C
0.81 0.63 0.5 0.4 0.33 0.25 B
0.25 0.2 0.16 0.13 0.1 0.08 A
WIRE DIAMETERS IQI type
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.
< 0.53% 2.0 3 > 380
0.53% 1.6 4 > 220 ≤ 380
0.74% 1.25 5 > 120 ≤ 220
0.98% 1.0 6 > 85 ≤ 120
1.07% 0.8 7 > 65 ≤ 85
1.14% 0.63 8 > 50 ≤ 60
1.11% 0.5 9 > 40 ≤ 50
1.14% 0.4 10 > 30 ≤ 40
1.33% 0.32 11 > 18 ≤ 30
1.67% 0.25 12 > 12 ≤ 18
2.1% 0.2 13 > 7 ≤ 12
2.67% 0.16 14 > 5 ≤ 7
2.94% 0.125 15 > 3.5 ≤ 5
3.64% 0.1 16 > 2 ≤ 3.5
5% 0.08 17 > 1.2 ≤ 2
> 5.25% 0.063 18 ≤ 1.2
Average Sensitivity Wire diameter Required wire Thickness
1. Single Wall Technique Source Side IQI CLASS ‘A’ RADIOGRAPHY
< 0.36% 1.25 5 > 350
0.36% 1.0 6 > 200 ≤ 350
0.5% 0.8 7 > 120 ≤ 200
0.68% 0.63 8 > 65 ≤ 120
0.91% 0.5 9 > 45 ≤ 65
1.0% 0.4 10 > 35 ≤ 45
0.98% 0.32 11 > 30 ≤ 35
1.0% 0.25 12 > 20 ≤ 30
1.25% 0.2 13 > 12 ≤ 20
1.6% 0.16 14 > 8 ≤ 12
1.79% 0.125 15 > 6 ≤ 8
2.0% 0.1 16 > 4 ≤ 6
2.46% 0.08 17 > 2.5 ≤ 4
3.15% 0.063 18 > 1.5 ≤ 2.5
> 3.33% 0.05 19 ≤ 1.5
Average Sensitivity Wire diameter Required wire Thickness 1. Single Wall Technique Source Side IQI
CLASS ‘B’ RADIOGRAPHY
7FE12
Step / Hole type IQI Wire type IQI
Image Quality Indicators
EN 4
6 2- 5
Image Quality Indicators Image Quality Indicators
100 2 x
Subject thicknes =
IQI wire thickness
4T dia
ASME Image Quality Indicators ASME Image Quality Indicators
1 Hole visible = 4T
2 Holes visible = T
3 Holes visible = 2T
IQI Sensitivity
Minimum Penetrmeter Thickness 0.5mm (2% of the weld thickness) Minimum Diameter for 1T Hole 0.5mm Minimum Diameter for 2T Hole 1.0mm Minimum Diameter for 4T Hole 2.00mm
Penetrmeter Design T dia 2T dia
17 12mm
38mm T
Wire Type IQI
Step/Hole Type IQI
Image Quality Indicators
It is important that IQIs are placed
Placement of IQIPlacement 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
Radiographic TechniquesRadiographic 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)
Double Wall Double Image (DWDI) - film outside, source outside (superimposed)
Parallax / Tube shift method - to determine the distance/depth of the defect
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 placing A B • Pitch marks indicating
readable film length
Double wall double image DWDI elliptical exposure
• 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
Film
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
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 3.0 Density unacceptable
Density 1.2
Density 1.2
Density 3.0
Density 3.0
Sandwich Technique
It may be used on components where there are substantial thickness differences
FILM A
FILM B
FILM A: Fast film - Thicker section FILM B: Slow film - Thinner section
LEAD SCREENS
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
• The parallax radiographic technique may be used to
determine the depth of defects below the surface • This may be useful to know for repair purposes. • It is a technique more applicable to thick specimens,
eg. over 50mm, but is rarely used • Also known as a Tube Shift Method
Parallax technique
Parallax technique
The beam of radiation shall be directed to the centre of the area being inspected and should be normal to the object surface An appropriate alignment of the beam can be permitted if it can be demonstrated that certain inspections are best revealed by a different alignment of the beam Between the contracting parties other ways of radiographing may be agreed upon.
Alignment of beam
Interpretation conditionsInterpretation conditions
Duties of a Radiographic InterpreterDuties 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 conditionsViewing 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 QualityRadiographic 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 The ability to differentiate areas of different film areas of different film densitydensity
ContrastContrast
Radiographic contrastRadiographic contrast :- The density difference on a radiography between two areas- usually subject and the background (overall) Subject contrastSubject contrast :- Contrast arising from variation in opacity within an irradiated area
Film contrastFilm contrast :- The slope of characteristic curve of the film at specified density. ( Type of film being used, fine grain or large grain)
Radiographic Contrast
Insufficient Contrast • kV too high • Over exposure
compensated for by shortened development
• Incorrect film - screen combination
Excessive Contrast • kV too low • Incorrect developer
Subject contrast is governed by the range of radiation intensities transmitted by the specimen. A flat sheet of homogeneous material of nearly uniform thickness would have very low subject contrast.
Factors Influencing Sensitivity
Sensitivity
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
Contrast Definition
Film speed
Screens Energy Vibration Processing
Time Temperature Type Strength Agitation
Geometry
Radiographic Contrast
Poor contrast
Poor contrast
High contrast
Radiographic DensityRadiographic Density
* Greater contrast is achieved at higher density
The The DEGREE OF DARKENINGDEGREE OF DARKENING of a processed film is of a processed film is called called FILM DENSITYFILM DENSITY..
Film Density is a logarithmic unitFilm Density is a logarithmic unit:: Where IWhere I11 is the incident light intensity and Iis the incident light intensity and I22 is the transmitted light intensityis the transmitted light intensity Thus if Film Density Thus if Film Density = = 22, , the incident light the incident light intensity is intensity is 100100x greater than the transmitted x greater than the transmitted intensityintensity
Radiographic DensityRadiographic Density
The ratio of transmitted light for densities of 1.0 and 2.0 is a factor of 10, i.e. 10 times more light passes through the radiograph for a density of 1.0 than for a density of 2.0. The minimum density in the area of interest, required by specifications is typically between 1.5 and 2.5. The maximum density stated in a specification will typically be 3.0 or 3.5.
Radiographic DensityRadiographic 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 DensityMeasuring Radiographic Density
Density is measured by a densitometer
A densitometer should be calibrated using a density strip A strip of film containing known densities on the same viewer which is to be used for interpreting the radiograph.
4.0 3.5 3.0 2.5 2.0 1.5 1.0
What is a good radiograph?