as 2177 1 1994 non destructive testing radiography of weld

radiography of weld

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of Metals and Materials It was approved on behalf of the Council of StandardsAustralia on 14 June 1994 and published on 22 August 1994.

The following interests are represented on Committee MT/7:

Australian Institute for Non-Destructive TestingAustralian Nuclear Science and Technology OrganizationAustralian Pipeline Industry Association

AUSTROADSBureau of Steel Manufacturers of AustraliaDepartment of Defence

Electricity Supply Association of AustraliaMetal Trades Industry Association of AustraliaNational Association of Testing Authorities, AustraliaRailways of Australia Committee

Society of Automotive Engineers—AustralasiaWelding Technology Institute of AustraliaWorkCover Authority of N.S.W

Additional interests participating in preparation of Standard:

Non-destructive testing service organizationsRoyal Melbourne Institute of Technology

Review of Australian Standards To keep abreast of progress in industry, Australi an Standards are subject

to periodic review and are kept up to date by the issue of amendments or new editi ons as necessary It is important therefore that Standards users ensure that they are in possession of the latest editi on, and any amendments thereto.

Full detail s of all Australi an Standards and related publications will be found in the Standards Australi a Catalogue of Publications; this information is supplemented each month by the magazine ‘The Australi an Standard’, which subscribing members receive, and which gives details of new publications, new editi ons and amendments, and of withdrawn Standards.

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First publi shed in part as AS B164 — 1965.

AS B230 fi rst publi shed 1967.

AS B237 fi rst publi shed 1967.

AS B164 — 1965, AS B230— 1967 and AS B237 — 1967 revised, amalgamated and redesignated

This Standard was prepared by the Standards Australia Committee on Non-destructive

Testing of Metals and Materials to supersede AS 2177.1 — 1981, Radiography of welded

butt joints in metal, Part 1: Methods of test.

The second Standard in the series is AS 2177.2—1982, Radiography of welded butt joints

in metal, Part 2: Image quality indicators (IQI) and recommendations for their use.

In this edition, cognizance was taken of the following International Standard during therevision of the clauses on gamma-ray sources, radiographic density and film coverage:

ISO 1106/3 Recommended practice for radiographic examination of fusion welded

joints — Part 3: Fusion welded circumferential joints in steel pipes of up

The term ‘informative’ has been used in this Standard to define the application of theappendices An ‘informative’ appendix is not an integral part of a Standard and isincluded for information and guidance only

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Page

FOREWORD 5

SECTION 1 SCOPE AND GENERAL 1.1 SCOPE 6

1.2 REFERENCED DOCUMENTS 6

1.3 DEFINITIONS 6

1.4 TEST METHOD DESIGNATION 6

1.5 SAFETY PRECAUTIONS 7

1.6 QUALIFICATION OF PERSONNEL 7

SECTION 2 EQUIPMENT AND ACCESSORIES 2.1 GENERAL 8

2.2 X-RAY EQUIPMENT 8

2.3 GAMMA-RAY SOURCES 8

2.4 INTENSIFYING SCREENS 8

2.5 CASSETTES 9

2.6 FILTERS 9

2.7 IMAGE QUALITY INDICATORS 9

2.8 FILMS 10

2.9 FILM PROCESSING FACILITIES 10

2.10 VIEWING FACILITIES 10

SECTION 3 TEST METHOD REQUIREMENTS 3.1 GENERAL 11

3.2 SURFACE PREPARATION 11

3.3 PLACEMENT OF IMAGE QUALITY INDICATORS 11

3.4 GEOMETRIC UNSHARPNESS 12

3.5 RADIOGRAPHIC DENSITY 12

3.6 FILM COVERAGE 12

3.7 BACK-SCATTER PROTECTION 16

3.8 RADIOGRAPHIC IDENTIFICATION 16

3.9 RECOMMENDED TUBE VOLTAGES 17

3.10 FILM LOCATION 17

3.11 MASKING 18

3.12 RADIOGRAPHIC PROCEDURAL REQUIREMENTS 18

3.13 PROCESSING OF RADIOGRAPHS 20

3.14 VIEWING OF RADIOGRAPHS 20

3.15 STORAGE OF RADIOGRAPHS 21

SECTION 4 PRESENTATION OF TEST DATA 4.1 SCOPE OF SECTION 22

4.2 RECORD OF TEST 22

4.3 TEST REPORT 22

APPENDICES

A PURCHASING GUIDELINES 24

B GUIDANCE FOR THE USE OF THIS STANDARD 26

C RADIOGRAPHIC EQUIVALENCE FACTORS 41

In the methods described in this Standard, the photographic film is generally placedparallel to and in contact with one surface of the weld The source of ionizing radiation islocated on the remote side of the weld and at a calculated distance from it For hollowproducts the radiation may be required to penetrate both walls of the product

Radiographic sensitivity is affected by parameters which include radiation energy (kilovolt

or isotope spectrum), the film/screen combination, scattered radiation control, andexposure geometry (source-to-film distance and effective source size) Although thehighest radiographic sensitivity is usually achieved using X-rays, their use is limited bythe thickness of the workpiece

For the radiography of hollow components, either single-wall or double-wall methods areused Although the radiographic sensitivity obtained when using single-wall methods isgenerally superior to that obtained when using double-wall methods, other factors such asdiameter, thickness and accessibility may influence the choice of method

STANDARDS AUSTRALIA

Australian Standard Non-destructive testing—Radiography of welded butt joints in metal

Part 1: Methods of test

S E C T I O N 1 S C O P E A N D G E N E R A L

gamma-ray radiographic testing of welded butt joints in metal products It does not coverneutron radiography and does not specify the permissible defect levels used for theacceptance/rejection criteria of welds The individual methods of test and the permissibledefect levels should be specified in the relevant product or application Standard

1929 Non-destructive testing—Glossary of terms

2177 Radiography of welded butt joints in metal

2177.2 Part 2: Image quality indicators (IQI) and recommendations for their use

2243 Safety in laboratories

2243.4 Part 4: Ionizing radiations

3669 Non-destructive testing — Qualification and registration of personnel — Aerospace

3998 Non-destructive testing — Qualification and certification of personnel — General

engineeringZ5 Glossary of metal welding terms and definitions

Z5.2 Part 2: Terminology of and abbreviations for fusion weld imperfections as

(b) By a number 1, 2 or 3 to indicate the film type, as follows:

(i) Type 1: Very fine grain, very high contrast, low speed

(ii) Type 2: Fine grain, high contrast, medium speed

(iii) Type 3: Medium grain, medium contrast, high speed

(c) By a solidus (/) followed by one or two letters to indicate whether testing is

required through a single plate or wall (S), or through a double wall (DW), and inthe latter case, by the addition of another letter to indicate whether a single image

of the weld (S) or a double image of the weld (D) is required

Examples of designation : XR1/S, XR2/DWS, GR3/DWD.

ionizing radiation can be injurious Adequate precautions shall be taken to protect testingpersonnel and any other persons in the vicinity, when X-ray equipment or radioactivesources are being used

NOTE: The use of radioactive substances and irradiating apparatus is controlled by variousstatutory regulations Reference should be made to the ‘Code of Practice for the Safe Use ofIndustrial Radiography Equipment (1989)—Radiation Health Series No 31’, issued by theNational Health and Medical Research Council

Reference should also be made to AS 2243.4 for ionizing radiation safety precautions

to this Standard should have recognized qualifications in the specific area of test

NOTE: The Australian Standards for personnel qualification are AS 3669 and AS 3998

S E C T I O N 2 E Q U I P M E N T A N D A C C E S S O R I E S

delineating the boundaries and contours of discontinuities likely to be present in welds,and of producing radiographs with satisfactory image quality

particular metal or alloy concerned For the testing of steel of thickness up to 75 mm,X-ray equipment capable of operating at voltages up to 400 kV is required For steelthicknesses above 75 mm, high voltage equipment capable of operating up to themega-electronvolt (MeV) range is required The focal spot (source) size should be knownfor the calculation of geometric unsharpness (see Appendix B)

radiography of steel welds having thicknesses below the limits given in Table 2.1

NOTE: As a general guide, methods using gamma-rays are usually less sensitive than methodsusing X-rays and should be limited to applications where the shape, thickness or accessibility ofthe welds makes X-ray examination impracticable

RECOMMENDED GAMMA-RAY SOURCES AND

STEEL THICKNESS RANGES

40 (30)

20 (5) 6

NO TE: In certain cases, it may be permitted to use gamma-ray sources for lesser thicknesses than those given, when X-ray equipment cannot be used on account of unfavourable geometry, e.g single-wall exposures of tubes of small diameter using the source inside and the film placed outside of the tube, or if the use of gamm a-rays makes a more suitable radiation beam direction possible The lesser thicknesses applicable for these special cases are shown in brackets (see also Paragraph B2 of Appendix B).

2.4.1 General Metal intensifying screens reduce scattered radiation, improve definitionand reduce exposure time Screens shall not contain defects such as dents, creases,scratches and contamination by dirt and grease which may produce spurious images on theradiographic film

Fluorometallic screen/film combinations may be used where it can be demonstrated thatthe required image quality indicator (IQI) sensitivity can be achieved

NOTES:

1 When cleaning screens, foreign material such as grease and lint should be removed withcare from the surface, to prevent damage

2 The use of fluorescent screens is not recommended because of their inherent unsharpnessfactor, which may prevent achievement of the required sensitivity.

3 Rolls of paper-backed film supplied in commercial packs with integrated metal intensifyingscreens may be used provided the lead screen thickness complies with Table 2.2

shall be in accordance with the requirements of Table 2.2 The use of screens ofminimum thickness may result in loss of image quality

REQUIREMENTS FOR USE OF METALLIC

INTENSIFYING SCREENS

Radiation source

X-radiation potential (kV),

or isotope type

Screen material

Minimum front screen thickness mm

Minimum back screen thickness mm

>120 ≤ 400

Lead Lead

Not required 0.02

Not required 0.02 Gamm a-

0.02 0.02 0.2 0.2

0.02 0.02 0.2 0.2

will not interfere with the quality or sensitivity of the radiographs Adequate precautionsare required to ensure good film-to-screen contact within the cassette

than the test piece (test object), used to absorb softer radiation preferentially Their use isrecommended when it can be shown that they produce improvements in radiographicquality They are used in the following two ways:

(a) At the source of radiation to absorb the softer components of primary radiation andthus improve image quality

(b) Between the test piece and the radiographic film to absorb scattered radiation fromthe test piece

a means of assessing the image quality of the radiograph The IQI shall have the same orlower attenuation characteristics as the metal under test (see AS 2177.2), and shall be one

of the following types:

(a) Wire-type (W) Wire IQIs comprise wires of steel, aluminium, copper or magnesium

of different diameters set in a flexible mount

(b) Step-hole type (SH) Step-hole IQIs are manufactured from various metals and

contain steps perforated with holes, the diameters of which are related to stepthickness

(c) Plaque-hole type (PH) Plaque-hole IQIs are manufactured from various metal alloys

and consist of a single thickness plaque perforated with holes, the diameters ofwhich are related to the plaque thickness

The IQI and sensitivity requirements shall be those which are specified in the relevantproduct or application Standard

Where a separate indication of contrast is required when using a wire IQI, it isrecommended that a step wedge or similar contrast indicator be used For high-sensitivityradiography using gamma-rays, the contrast should be assessed with a plaque-hole IQI, astep-hole IQI or a contrast meter.

Requirements for IQI are specified in AS 2177.2

NOTE: The IQI sensitivity is a means of assessing radiographic quality but not a measure ofdetectable discontinuity size

X-ray films shall be free from mechanical, chemical or other blemishes which may mask

or be confused with the image of any discontinuities in the test area

which meet the quality requirements specified in Clause 3.13

exposed X-ray film, it is essential that the processor is installed, maintained andcontrolled in accordance with the manufacturer’s instructions to ensure consistency andquality of processing It is important that film characteristics be compatible withprocessing solutions and conditions

designed, maintained, controlled and monitored processing facility

radiographs by diffused light in a darkened room The illuminated area of the viewingscreen shall be equipped with masks to exclude any extraneous light from the eyes of theviewer when viewing radiographs smaller than the screen, or to cover low density areaswithin a radiograph

The brightness of an illuminated radiograph shall be not less than 30 cd/m2 and shall bepreferably greater than 100 cd/m2 To achieve the minimum value of 30 cd/m2, theminimum brightness of the illuminator for the acceptable viewing of a range ofradiographic densities shall be in accordance with Table 2.3

TABLE 2.3 FILM DENSITY/ILLUMINATOR BRIGHTNESS RELATIONSHIP

Density of radiograph

Minimum illuminator brightness cd/m 2

1.5 2.0 2.5 3.0 3.5

S E C T I O N 3 T E S T M E T H O D R E Q U I R E M E N T S

welded steel butt joints in metal products and advice on their application are given inTable 3.1

Table 3.2 lists the wire IQI sensitivities which should be achievable for various weldmetal thicknesses in steel, when using the test methods specified in Table 3.1

The method to be used, the required sensitivity and other parameters to be achievedshould be specified in the relevant product or application Standard

can mask the radiographic images of discontinuities and thus interfere with theinterpretation of radiographs

If uncertainties in the interpretation of a radiograph arise, the weld reinforcement should

be dressed to remove any surface irregularities If after dressing, visual inspection andtesting by other appropriate non-destructive testing methods, the weld is considered to besatisfactory, no additional radiograph need be taken If any uncertainties remain, anotherradiograph shall be taken In either case, the actions taken shall be recorded

NOTE: For method XR1 (see Table 3.1), where the highest level of discontinuity detection isrequired, it may be necessary to dress the weld reinforcement to such a degree that resultingradiographic images due to surface irregularities cannot mask or be confused with the image ofany discontinuity

Backing strips used during the welding process and not forming part of the finishedproduct shall be removed prior to radiographic testing

require-ments apply for the location of image quality indicators:

(a) Plaque-hole or step-hole IQIs shall be placed adjacent to the weld at one or bothends of each section to be radiographed

(b) Wire IQIs shall be placed transversely across all welds at one or both ends of eachsection to be radiographed In certain circumstances it may be necessary to offsetthe IQI

(c) The entire IQI shall be placed in intimate contact with the surface facing the source

of radiation, with the thinnest element more remote from the central beam

(d) Where the surface facing the source of radiation is inaccessible, the IQI may beplaced on the film side of the workpiece in a position specified by the product orapplication Standard If not so specified, one of the following methods may be used

to determine the required film-side IQI sensitivity:

(i) Method A Make an exposure on a representative sample with the required

source-side IQI in place, and a thinner IQI element in place on the filmside Provided that the required sensitivity is achieved by the IQI on thesource side, the first discernible IQI element on the film side shall be used asthe sensitivity requirement

(ii) Method B For double-wall, double-image exposures of pipe with an outside

diameter equal to or less than 90 mm, choose the IQI for single-wallthickness and place it on the source side

(e) If the IQI is placed on the film side (see Item (d)), a lead marker in the form of theletter ‘F’ shall be positioned beside the film side IQI; this shall be stated in thereport

(f) When radiographing a circumferential joint by means of a central source, usingcomplete encirclement film, a minimum of three IQIs placed at equal intervalsaround the circumference shall be used, unless otherwise specified in the relevantproduct or application Standard.

(g) If the weld reinforcement or backing strip has not been removed prior toradiography, a shim of material with absorbance equal to or greater than that of thematerial under test shall be placed under the IQI so that the total thickness under theIQI is approximately the same as the total thickness through the weld, includingreinforcement or backing strip To ensure that its image is readily identifiable in theradiograph, the shim shall be of larger area than the IQI

to the radiography of welds are specified, as follows:

(a) For method designations XR1 and XR2: Ug= 0.2 mm max

(b) For method designations XR3, GR1, GR2 and GR3: Ug= 0.4 mm max

Where accessibility or limitations of equipment prevent the achievement of the Ug

requirement for methods XR1 and XR2, the geometric unsharpness may exceed 0.2 mm

if permitted by the relevant product or application Standard However, in no case shall avalue of 0.4 mm be exceeded

NOTE: The actual geometric unsharpness values may be calculated using Equation B(1) orB(2) in Paragraph B10.3, or using the nomogram given in Figure B6, in Appendix B

corresponding to all the areas under examination shall be not less than 1.7 for X-raytesting or 2.0 for gamma-ray testing, except when permitted by the relevant product orapplication Standard or required for special configurations

The fog density of a processed film shall not exceed 0.3

consideration at each exposure shall be determined by the difference between thethickness of the material penetrated in the centre of the radiation beam and that at theextremities of the film measured in the direction of the beam at those points The values

of film density resulting from this variation of thickness shall be not lower than thosespecified in Clause 3.5, and not higher than those allowed by the available illuminator,provided that suitable masking is possible

NOTE: The detection of planar-type defects such as cracks and lack of side-wall fusionbecomes less certain as the beam spread increases The use of other non-destructive testingmethods such as ultrasonic, magnetic particle, liquid penetrant and eddy current testing should

be considered for the detection of this type of defect (see Paragraph B1 of Appendix B)

Figure 3.1 gives schematic arrangements for source and film placement for the variousmethods of radiographing welded pipe

heat-affected zone adjacent to the weld are fully covered

NOTE: For the purpose of this Standard, the heat-affected zone is considered to extend for

6 mm either side of a weld

TABLE 3.1 SUMMARY OF RADIOGRAPHIC METHODS FOR TYPICAL WELDED

STEEL BUTT JOINT APPLICATIONS

Radiographic

method designation

Radiation source

Nature of exposure

Double-wall, single-image Double-wall, double-image

1 (very fine grain)

1 (very fine grain)

1 (very fine grain)

Where a very high level of sensitivity is required

As for XR 1/S where internal access is not practicable

As for XR 1/DW S where the pipe diameter is ≤ 90 mm

Double-wall, single-image Double-wall, double-image

2 (fine grain)

2 (fine grain)

2 (fine grain)

High sensitivity, general use

As for XR 2/S where internal access is not practicable

As for XR 2/DW S where the pipe diameter is ≤ 90 mm

Double-wall, single-image Double-wall, double-image

3 (medium grain)

3 (medium grain)

3 (medium grain)

Sensitivity slightly less than for XR 2/S.

For use when the detection of fine discontinuities is not required

As for XR 3/S where internal access is not practicable

As for XR 3/DW S where the pipe diameter is ≤ 90 mm

Double-wall, single-image Double-wall, double-image

1 (very fine grain)

1 (very fine grain)

1 (very fine grain)

For optimum sensitivity which is generally below that achievable by X-ray methods

As for GR 1/S where internal access is not practicable

As for GR 1/DW S where the pipe diameter is ≤ 90 mm

Double-wall, single-image Double-wall, double-image

Double-wall, single-image Double-wall, double-image

TABLE 3.2 READILY ACHIEVABLE WIRE IQI SENSITIVITIES FOR STEEL—

EXPRESSED AS SMALLEST WIRE VISIBLE ON RADIOGRAPH WITH

CORRESPONDING SENSITIVITY VALUE

Radiographic test method designation

Wire number (smallest wire visable)

Sensitivity, % Weld metal thickness, mm

1.7

15 1.4

14 1.3

13 1.1

12 1.0

11 1.1

10 1.0

9 0.9

8 0.9

2.1

14 1.8

13 1.7

12 1.4

11 1.3

10 1.3

9 1.3

8 1.3

7 1.1

6 1.1

2.7

13 2.2

12 2.1

11 1.8

10 1.7

9 1.7

8 1.6

7 1.6

6 1.4

5 1.4

4 1.3

3.3

12 2.8

11 2.7

10 2.2

10 1.7

9 1.7

8 1.6

7 1.6

6 1.4

5 1.4

4 1.3

3 1.3

2 1.3

1 1.3

1 1.1

5.3

11 3.6

10 3.3

9 2.8

9 2.1

8 2.1

7 2.0

6 2.0

5 1.8

4 1.8

3 1.7

2 1.7

1 1.6

1 1.3

1 1.1

4.5

9 4.2

8 3.5

7 3.3

6 3.3

5 3.1

4 3.2

3 2.9

2 2.8

1 2.7

1 2.1

1 1.6

1 1.3

1 1.1 NOTES:

1 The values of sensitivity given are not necessarily the optimum values which can be achieved, but are included for information and comparative purposes and should not be taken as mandatory requirements for any particular method Sensitivity values quoted for gamma-ray methods are for Iridium-192 ( 1 92

Ir) for the thickness range of 10 mm to 90 mm , and for Cobalt-60 ( 6 0

Co) for thicker sections

up to 200 mm (see Table 2.1) Sensitivities quoted for gamma-ray methods for thicknesses of less than 10 mm and more than 200 mm are included for information only Attention is drawn to the improved sensitivity which can be obtained with Ytterbium-169 ( 1 69

Yb) in the range 6 mm to 20 mm

2 The sensitivity values have been rounded to nearest 0.1%.

FIGURE 3.1 SCHEMATIC ARRANGEMENTS OF DIFFERENT TEST METHODS FOR

THE RADIOGRAPHY OF WELDS IN PIPE SHOWING SOURCE AND

FILM PLACEMENT POSITIONS

3.6.3 Film overlap When 100% radiography is specified, the film shall be placed sothat all sections of a weld are examined Where strip film is used, sufficient lead markers

in the form of arrows, shot and other symbols shall be present for location purposes and

to identify the beginning and the end of films (see Figure 3.2) Extra film lengths should

be provided to overlap each end of film to ensure full coverage and to ensure that thelocation marks are recorded

reduced by confining the radiation beam to the smallest practical cross-section and byplacing lead behind the film In many cases, a back lead screen or a lead sheet in theback of a cassette or film holder will provide adequate protection against back-scatteredradiation Where back-scatter is likely to affect adversely the quality of a radiograph, asheet of lead not less than 1.5 mm thick should be placed behind the film/screencombination

NOTE: If there is any doubt about the adequacy of protection against back-scattered radiation,

a characteristic lead symbol (frequently a 3 mm thick letter B) should be attached to the back ofthe cassette or film holder and a radiograph made in the normal manner The appearance of animage of this symbol on the radiograph indicates that the protection against back-scatteredradiation is insufficient and additional precautions are needed

corresponding section of weld under test Markers in the form of lead arrows, lead shot,

or other symbolic shapes may be used to supplement the marking system

Identification markers shall be placed alongside the weld at a distance not closer than

6 mm from the edge of the weld (see Figure 3.2), and be comprised of suitable symbols toidentify the following:

(a) The job or workpiece correlation number

(b) The joint designation

(c) The section of the weld joint

The identification marks shall not mask the heat-affected zone or be detrimental to theproduct

ON A WELDED WORKPIECE

3.9 RECOMMENDED TUBE VOLTAGES For method XR1, the recommendedmaximum tube voltages for the radiography of various weld thicknesses of aluminium,copper, lead, steel, iron and nickel are given in Figure 3.3.

For methods XR2 and XR3, higher tube voltages may be used, however it isrecommended that the values determined from Figure 3.3 should not be exceeded by morethan 25%, unless otherwise specified in the relevant product or application Standard

NOTES:

1 The tube voltages for various weld thicknesses of metals and alloys other than steel may bedetermined by calculating the radiographic equivalent thickness of steel using theradiographic equivalence factors listed in Table C1 of Appendix C The graph for steelshown in Figure 3.3 may then be used to determine the maximum X-ray tube voltage

2 Exposures should be carried out at the lowest tube voltage consistent with a reasonableexposure time, because low tube voltages usually give improved image contrast andtherefore better IQI and discontinuity sensitivity (see Appendix B)

OF X-RAYS FOR VARIOUS WELD THICKNESSES OF COMMON METALS

AND ALLOYS WHEN USING METHOD XR1

3.10 FILM LOCATION

3.10.1 Object-to-film distance The distance between the workpiece and the film should

be as small as possible Where a gap between the surface of the object and the filmcassette is unavoidable, the total object-to-film distance is calculated as object thicknessplus gap

3.10.2 Source-to-film distance The minimum value of source-to-film distance (F) is a

function of—

(a) the effective source size (S);

(b) the total object thickness (t); and

(c) the geometric unsharpness (Ug) required

The minimum source-to-film distance (F) for an effective source size (S) of 2 mm may be

obtained from Figure 3.4 which is derived from Equation B(1) of Paragraph B10.3

From Figure 3.4, the following relationships between F and t are evident:

(i) For methods XR1 and XR2: F = 11 t.

(ii) For methods XR3, GR1 and GR2: F = 6 t.

To avoid excessively small values of F, a minimum value of 50 mm shall be used.

NOTE: As an alternative, the source-to-film distance may be calculated by the use of either theEquation B(1) or the nomogram (see Figure B6)

the areas irradiated to those under test

surfaces, the beam of radiation should be directed to the centre of the section under testand be normal to the plate surface at that point As an exception, tests for discontinuitiesoccurring at the fusion face, e.g lack of side-wall fusion, are best carried out by directingthe beam along the fusion face

NOTE: Where directional X-ray machines are used, the axis of the X-ray tube should betransverse to the centreline of the weld

3.12.2 Testing of circumferential welds in curved surfaces

(a) For single-wall, single-image (S) exposures Where a 360° emitting source is usedfor S exposures, the beam of radiation should be directed to the centre of the sectionunder test The beam should be within 90 ±5° to the pipe surface at that point, orwithin ±5° of the bisector of the angle between abutting surfaces

Other beam directions should be used when these are known to be necessary todetermine the position and extent of a particular defect, e.g defects at a fusion face,for which the beam may be directed along that face

Figure 3.1 shows schematic arrangements of the beam alignments for various sourcepositions

Where internal source X-radiography is used in piping, the beam of radiation shouldemanate from a conical anode capable of orthogonal emission relative to the axis ofthe pipe

(b) For double-wall, single-image (DWS) exposures For DWS exposures, the source of

radiation should be positioned to ensure that the centre of the projected beam passesthrough the centre of the test area If necessary, the source of radiation may beoffset to avoid superimposing the images of the welds (see Figure 3.1(b))

(c) For double-wall, double-image (DWD) exposures For DWD exposures, the source

of radiation should be positioned so that the centre of the projected beam passesthrough the centre of the pipe, in the plane of the weld To avoid superimposition ofthe images of the welds, the source of radiation should be offset from the plane

through the weld The film should be correspondingly offset in the oppositedirection to ensure that the axis of the beam passes through its centre (seeFigure 3.1(c)).

As this method is recommended for the testing of pipes of 90 mm diameter or less,

it is necessary to take at least two radiographs at 90° to each other to obtain fullcoverage

TO MINIMUM SOURCE-TO-FILM DISTANCE (F) FOR

A 2 mm EFFECTIVE SOURCE SIZE