rtfi class

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 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

Supercoat

Subbing

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

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

• 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).

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).

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.

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.

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.

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.

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.

Features Film

Processing FilmProcessing Film

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

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

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

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 Curves

Information which can be obtained from a films characteristic curve

• The position of the curve axis gives information about the films

• 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

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

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

Changing DensityChanging Density

Density Density achieved 1.5

Density required 2.5

Determine interval between logs

1.8 - 1.3 = 0.5

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

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

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)

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

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

2mm dia.

2mm length

S = 2² + 2² = 2.82mm

Calculation of geometric unsharpness (Ug

Focal / Source SIZE

FFD / SFD FOD / SOD

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)

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

Min FFD = S x OFD Penumbra S = 4mm OFD = 25mm FFD = 275 Penumbra = 0.25

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

Short Object to Film Distance

Long Object to Film Distance

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

2 types – 1. high definition (fine grain screen)

2. high speed or rapid screen

Salt Intensifying ScreensSalt 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.

• 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

Step / Hole type IQI Wire type IQI

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

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

Single wall single image SWSI panoramic

• IQI’s are placed on the film side • Source inside film outside (single

exposure)

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

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

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

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 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 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

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.

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

Sensitivity

Contrast Definition

Film speed

Screens Energy Vibration Processing

Time Temperature Type Strength Agitation

Geometry

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

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.

Lack of Density

Under exposure

Developer temp too low

Exhausted developer

Developer too weak

Insufficient development

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?

rtfi class

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