rtfi-ri-2

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 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

Radiographic Film

Supercoat

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.

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.

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.

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

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

• 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

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

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

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

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

• 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 Density

DensityDensity 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 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

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

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?

2.07 - 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)

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

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

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)

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

= 4 x 25 0.25

Min FFD = S x OFD Penumbra

S = 4mmOFD = 25mmFFD = 275Penumbra = 0.25

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

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

Short Film to Object Distance

Small Focus

Large Focus

Short Object to Film Distance

Long Object to Film Distance

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

= 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%

Step / Hole type IQI Wire type IQI

Image Quality Indicators

IQI wire thickness =

Subject thicknes x 2

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.

2502mm3002mm

E2 =5Mins. X 3002

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

100ciMins.5502mm8502mm

E1 =100ciMins. X 5502

E1 = 42 ciMins.

100ciMins.

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.

5002mm8002mm

E2 =100ciMins. X 8002

E2 = 256 ciMins.

E1 = E2 =

100ciMins.

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.

4402mm5002mm

E2 =11mAmin. x 5002

4402E1 =

5mA x 2min 12sec

3.5mA x T

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

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

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 placingA 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 identificationEN 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 3.0Density unacceptable

Density1.2

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

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

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

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

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

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

rtfi-ri-2

film speedexample film

film emulsion

film factors

smaller film factor

slow mixing

silver halide crystals

grain structures

rapid mixing

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