2168.2-2009 Computerized Radiography Testing of Mettalic Materials Using X-Rays and Gamma Rays

AS 2168.2—2009 2168.2—2009

A S 2 1 6 8 .2 — 2 0 0 9

Australian Standard

) d e t n i r p n e h w d e e t n a r a u g t o n y c n e r r u c t n e m u c o D ( 3 1 0 2 r p A 3 0 n o D T L Y T P A I L A R T S U A S A T I R E V U A E R U B y b d e s s e c c A

®

Non-destructive testing—Comput testing—Computerized erized radiography Part 2: Testing of metallic materials using X-rays and gamma rays

This Australian Standard® Standard® was prepared by Committee MT-007, MT-007, Non-destructive Testing of Metals and Materials. It was approved on behalf of the Council of Standards Australia on 17 June 2009. This Standard was published on on 30 June 2009.

The following are represented represented on Committee MT-007: • • • • • • • • • • • •


•

Australian Aerospace Aerospace Non-Destructive Testing Committee Committee Australian Industry Group Group Australian Institute for for Non-Destructive Testing Australian Nuclear Science Science & Technology Organisation Organisation Australian Pipeline Industry Industry Association Bureau of Steel Manufacturers of Australia Engineers Australia Metals Trade Industry Association National Association of Testing Authorities, Australia New Zealand Non-Destructive Testing Association NSW WorkCover Authority Victorian WorkCover Authority Authority Welding Technology Institute of Australia

This Standard was issued in draft draft form for comment comment as DR 06539. Standards Australia wishes to acknowledge the participation of the expert individuals that contributed to the development of this Standard through their representation on the Committee and through the public comment period.

Australian Standards® are are living documents documents that reflect progress in in science, technology and and systems. To maintain their currency, all Standards are periodically reviewed, and new editions are published. Between editions, amendments may be issued. Standards may also be withdrawn. It is important that readers assure themselves they are using a current Standard, which should include any amendments that may have been published since the Standard was published. Detailed information about Australian Standards, drafts, amendments and new projects can be found by visiting Standards Australia welcomes suggestions for improvements, and encourages readers to notify us immediately of any apparent inaccuracies or ambiguities. Contact us via email at , or write to Standards Australia, GPO Box 476, Sydney, NSW 2001.

AS 2168.2—2009

Australian Standard


®

Non-destructive testing—Computerized radiography Part 2: Testing of metallic materials using X-rays and gamma rays

First published as AS 2168.2—2009.

COPYRIGHT

© Standards Australia All rig hts are res erv ed. No par t o f t his wor k m ay be rep rod uce d o r c opie d i n a ny for m o r b y any means, electronic or mechanical, including photocopying, without the written permission of the publisher. Published by Standards Australia GPO Box 476, Sydney, NSW 2001, Australia ISBN 0 7337 9178 6

AS 2168 .2— 2009

2

PREFACE

This Standard was prepared by the Australian members of the Joint Standards Australia/Standards New Zealand Committee MT-007, Non-destructive Testing of Metals and Materials. After consultation with stakeholders in both countries, Standards Australia and Standards New Zealand decided to develop this Standard as an Australian Standard rather than an Australian/New Zealand Standard. The objective of this Standard is to ensure that the parameter of computed radiography systems as a progression for the next generation of radiographic methods are achieved. In the preparation of this Standard cognizance was taken of the f ollowing Standards: EN 14784 14784-1 14784-2


Non-destructive testing—Industrial computed radiograph with storage phosphor imaging plates Part 1: Classification of systems Part 2: General principles for testing of metallic materials using X-rays and gamma rays

This Standard is one of a series of Standards covering the range radiography of metals and materials. AS 2168 2168.1 2168.2

Non-destructive testing—Computerized radiography Part 1: Systems Part 2: Testing of metallic materials using X-rays and gamma rays (this Standard)

2177

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

2314

Radiography of metals—Image quality indicators (IQI) and recommendations for their use

3507 3507.1 3507.2

Non-destructive testing Part 1: Guide to radiography for ferrous castings Part 2: Radiographic determination of quality of ferrous castings

3669

Non-destructive testing—Qualification and approval of personnel—Aerospace

4749

Non-destructive testing—Terminology of and abbreviations for fusion weld imperfections as revealed by radiography

Statements expressed in mandatory terms in footnotes to tables are deemed to be requirements of this Standard.

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AS 2168 .2—2 009

CONTENTS

Page


1

SCOPE........................................................................................................................ 4

2

REFERENCED DOCUMENTS.................................................................................. 4

3

DEFINITIONS............................................................................................................ 4

4

SAFETY PRECAUTIONS ......................................................................................... 5

5

PERSONNEL QUALIFICATION AND VISION REQUIREMENTS........................ 5

6

CLASSIFICATION OF COMPUTED RADIOGRAPHIC TECHNIQUES................. 6

7

GENERAL REQUIREMENTS................................................................................... 6

8

RECOMMENDED TECHNIQUES FOR MAKING COMPUTED RADIOGRAPHS ........................................................................................................ 7

9

PRESENTATION DATA ......................................................................................... 16

AS 2168 .2— 2009

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STANDARDS AUSTRALIA Australian Standard Non-destructive testing—Computerized radiography Part 2: Testing of metallic materials using X-rays and gamma rays 1 SCOPE

This Standard specifies fundamental techniques of computed radiography with the aim of enabling satisfactory and repeatable results to be obtained economically. The techniques are based on the fundamental theory of the subject and test measurements. This Standard specifies the general rules for industrial computed X-ray and gamma radiography for flaw detection purposes, using storage phosphor imaging plates (IP). It is based on the general principles for radiographic examination of metallic materials on the basis of films, (refer to AS 2177.) 2 REFERENCED DOCUMENTS

) d e t n i r p n e h w d e e t n a r a u g t o n y c n e r r u c t n e m u c o D (

The following documents are referred to in this Standard:

3 1 0 2 r p A 3 0 n o D T L Y T P A I L A R T S U A S A T I R E V U A E R U B y b d e s s e c c A

AS 1929

Non-destructive testing—Glossary of terms

2177

Non-destructive testing—Radiography of welded butt joints in metals

2314

Radiography of metals—Image quality indicators (IQI) and recommendations for their use

2168 2168.1

Non-destructive testing—Computerized radiography Part 1: Systems

2243 2243.4

Safety in laboratories Part 4: Ionizing radiations

2452 2452.1

Non-destructive testing—Determination of thickness Part 1: Determination of wall thickness of pipe by the use of radiography

3507 3507.1

Non-destructive testing Part 1: Guide to radiography for ferrous castings

3669

Non-destructive testing—Qualification and approval of personnel—Aerospace

3998

Non-destructive testing—Qualification and certification of personnel

EN 462 462-5

Non-destructive testing—Image quality of radiographs Part 5: Image quality indicators (duplex wire type), determination of image unsharpness value

3 DEFINITIONS

For the purposes of this Standard the following definitions and those in AS 1929 apply. 3.1 Computed radiography system (CR system)

Complete system of a storage phosphor imaging plate (IP) and corresponding read out unit (scanner or reader), and system software, which converts the information of the IP into a digital image. ©

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AS 2168 .2—2 009

3.2 Computed radiography system class

Particular group of storage phosphor imaging plate systems, which is characterized by a Signal-to-Noise Ratio (SNR) range shown in Table 1 and by a certain basic spatial resolution value (e.g. derived from duplex wire IQ I) in a specified exposure range. 3.3 Nominal thickness (t )

Thickness of the material in the regi on under examination. Manufacturing tolerances do not have to be taken into account. 3.4 Object-to-detector distance (b)

Distance between the radiation side of the test object and the detector surface measured along the central axis of the radiation beam. 3.5 Penetrated thickness (w)

Thickness of material in the direction of the radiation beam calculated on basis of the nominal thickness. For multiple wall techniques the penetrated thickness is calculated from the nominal thickness. 3.6 Effective source size (d )

Size of the source of radiation. ) d e t n i r p n e h w d e e t n a r a u g t o n y c n e r r u c t n e m u c o D ( 3 1 0 2 r p A 3 0 n o D T L Y T P A I L A R T S U A S A T I R E V U A E R U B y b d e s s e c c A

3.7 Source-to-detector distance ( SDD)

Distance between the source of radiation and the detector measured in the direction of the beam. 3.8 Source-to-object distance ( f )

Distance between the source of radiation and the source side of the test object measured along the central axis of the radiation beam. 3.9 Storage phosphor imaging plate systems

Complete system of a storage phosphor imaging plate (IP) and a corresponding read out unit (scanner or reader), which converts the information of the IP into a digital image. 4 SAFETY PRECAUTIONS

Prolonged exposure of any part of the human body to ionizing radiation is hazardous to your health. Adequate precautio ns shall be taken to protect testing personnel and any other persons in the vicinity, when X-ray equipment or radioactive sources are being used. NOTE S: 1

2

The use of radioactive substance and irradiation apparatus is controlled by various statutory regulations. Reference should be made to the Radiation Health Series No. 31 Code of Practice for the safe use of industrial radiographic equipment. Reference should also be made to AS 2243.4 for ionizing radiation safety precautions.

5 PERSONNEL QUALIFICATION AND VISION REQUIREMENTS 5.1 Personnel qualifications

Radiographic testing interpretation for compliance, and report shall be made by personnel having qualification and experience for their job function acceptable to the testing body, the manufacturer and where required by the purchaser. Operators of CR systems shall have documented proof of competency in using the equipment. Operators shall have the qualification detailed below or shall carry out their duties under the supervision of persons responsible for the performance of the test. ww w.s tan dard s.o rg. au

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Qualifications normally acceptable for the radiographic testing or welds or metallic materials include the following: (a)

Certification by the Australian Institute for Non-Destructive Testing (AINDT) Certification Board in accordance with AS 3998 or approval in accordance with AS 3669 in radiographic testing.

(b)

Equivalent qualifications.

5.2 Vision requirements

The personnel shall provide documented evidence of satisfactory vision in accordance with AS 3998 or AS 3669. Subsequent to certification, the tests of visual acuity shall be carried out annually and be verified by the e mplo yer or the responsible agency. 6 CLASSIFICATION OF COMPUTED RADIOGRAPHIC TECHNIQUES

Computed radiographic techniques are subdivided into two classes: (a)

Class A: basic technique.

(b)

Class B: improved technique.

Class B technique will be used when Class A may b e insufficiently sensitive.


NOTE : Be tter tec hniques, comp ared wit h Cla ss B, are possib le and may be agreed betwee n the purchaser and the supplier by specification of all appropriate test parameters.

Before commencing the radiographic examination the type of techniques to be used shall be predetermined. NOTE : The agreement betwee n the purc has er and supp lier should be nego tia ted upon at the time of enquiry or placement of order.

Due to image parameters such as signal-to-noise ratio (SNR), un-sharpness and sensitivity to scattered radiation and hardening, differences exist between film radiographs and computed radiographs. Nevertheless , the perception of flaws using film radiography or computed radiography is comparable by using Class A and Class B techniques, respectively. The perceptibility shall be proven by the use of IQIs according to AS 2314.


If it is not possible for technical reasons to meet one of the conditions specified for the Class B, such as the type of radiation source or the source-to-object distance f , it may be agreed between the contracting parties that the condition selected may be that specified for Class A. The loss of sensitivity shall be compensated for, b y doubling the required minimum exposure time with the goal to increase the minimum SNR by a factor of 1.4 (additional to the SNR required from the plate-scanner classes given by Tables 2 to 3). Because of the resulting improved sensitivity compared to Class A, the test sections may be regarded as examined within Class B. NOTE : This applies only to those IP-sca nner sys tem s whose SNR is not lim ited by the inhomogeneity of the phosphor layer or the scanner dynamic at the required minimum exposure time (see Clause 7.5).

7 GENERAL REQUIREMENTS 7.1 Surface preparation and stage of manufacture

In general, surface preparation is not necessary, but where surface imperfections or coatings might cause difficulty in detecting defects, the surface shall be ground smooth or the coatings shall be removed.

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7.2 Identification of radiographs

Symbols shall be affixed to each section of the object being radiographed. The images of these symbols shall appear in the radiograph outside the region of interest where possible and shall ensure unequivocal identification of the section. 7.3 Marking

Position markings on the object to be examined shall be made in order to locate accurately the position of each radiograph. Where the nature of the material and/or its service conditions do not permit position marking, the location may be recorded by means of accurate sketches or photographs. 7.4 Overlap of phosphor imaging plates

When radiographing an area with two or more separate phosphor imaging plates (IP), the IPs shall overlap sufficiently to ensure that the complete region of interest is radiographed. This shall be verified by a high-density marker on the surface of the object that will appear on each image. 7.5 Image quality indicators


The quality of image shall be verified by use of IQIs, in accordance with the specific application of AS 2314 for the contrast resolution and EN 462-5 for measurement of unsharpness. Therefore two IQIs are always required on each image. The minimum IQI-values are dependent on wall thickness and geometry as defined by AS 2314. This document may be applied to non-ferrous m etals if appropriate IQIs are used. In specific cases, as-agreed minimum IQI-values may be specified in accordance with AS 2314. IQIs of the step-hole type should not be applied because the wire IQIs are more suitable to encourage the operator to compensate for limited sharpness with increased contrast. This compensation can be achieved either by reduction of the source voltage or by longer exposure time to increase the SNR of the computed radiograph. 8 RECOMMENDED TECHNIQUES FOR MAKING COMPUTED RADIOGRAPHS 8.1 Test arrangements

Test arrangements shall be determined from the specific application standards for film radiography, refer to AS 2177, AS 2452.1 and AS 3507.1. 8.2 Choice of X-ray tube voltage and radiation source 8.2.1 X-ray equipment

To maintain good flaw detection sensitivity, the X-ray tube voltage should be as low as possible. The maximum values of tube voltage versus thickness are given in Figure 1.

ww w.s tan dard s.o rg. au

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Y 50 0 40 0 Cu 30 0 Fe

20 0 T i V k , E G A T L O V Y A R X

10 0

Al

80 70 60 50 40 30

20


10 1

2

3

4

5 6 7 8 910

20

30

40 50 6 0

80 10 0 X

PENETRATED THICKNESS ( w ), m m LEGEND: X = pen etr ate d t hick nes s w , in millimetres Y = X-ray voltage, in kilovolts

FIGURE 1

MAXIMUM X-RAY VOLTAGE FOR X-RAY DEVICES UP TO 500 kV AS FUNCTION OF PENETRATED WALL THICKNESS

8.2.2 Other radiation sources

The permitted penetrated thickness ranges for gamma ray sources and X-ray equipment above 1 MeV are given in Table 1.


The value for Ir 192 may be reduced further to 10 mm and for Se 75 to 5 mm penetrated wall thickness. This is the subject of agreement between contracting parties. 192

60

On thin specimens, gamma rays from Ir and Co will not produce computed radiographs having as good a defect detection sensitivity as X-rays used with appropriate technique parameters. NOTE : Due to t he advantage s of g amma r ay sou rces i n handl ing and acce ssi bility , Table 1 giv es a range of thickness for which each of these gamma ray sources may be used when the use of Xrays is not practicable.

In cases where radiographs are produced using gamma rays, the travel time to position the source shall not exceed 10% of t he total exposure time.

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AS 2168 .2—2 009

TABLE 1 PENETRATION THICKNESS RANGE FOR GAMMA RAY SOURCES AND X-RAY EQUIPMENT WITH ENERGY FROM 1 MeV AND ABOVE FOR STEEL, COPPER AND NICKEL-BASE ALLOYS Radiation source

Penetrated thickness range ( w ) mm Test Class A

Tm

170

w

Yb 169 *

1

Se 75 †

10

w

≤

≤

w

2

40

14

≤

w

≤ 40

≤

w

≤ 90

≤

w

≤ 5

15

≤

≤ 12

w

20

≤

w

≤

100

20

Co 60

40

≤

w

≤

200

60

≤

w

≤ 150

30

≤

w

≤

200

50

≤

w

≤ 180

X-ray equipment with energy 4 to 12 MeV

50

≤

w

X-ray equipment with energy > 12 MeV

80

≤

w

*


≤ 5

Ir 192

X-ray equipment with energy 1 to 4 MeV


≤

Test Class B

80

100

For aluminium and titanium the penetrated material thickness range is 10 for Class B.

≤

w

≤ 70

For aluminium and titanium the penetrated material thickness range is 35

≤

w

≤ 120

≤

w

≤

w

for Class A and 25

≤

w

≤ 55

†

for Class A.

8.3 Phosphor imaging plate-scanner systems and screens

For computer radiographic examination, IP-scanner system classes shall be used corresponding to the definitions given in AS 2168.1. The IP system classes are defined in AS 2168.1 by the minimum normalized SNR-v alues (SNR IP x) and are reproduced in Table 2. For different radiation sources and wall thickness ranges, the minimum IP-system classes are given in Tables 3 and 4. These Tables show the recommended screen materials and metal thickness. When using lead screens, good contact between IP and screens is required. Other screen thicknesses and materials ma y also be applied if described in the specification provided the required image quality is achieved. TABLE 2 CR SYSTEM EVALUATION ACCORDING TO THE MINIMUM NORMALIZED SNR AT THE MINIMUM SIGNAL INTENSITY I IPX System Class CEN

Minimum normaliz ed SNR

IP1/Y

130

IP2/Y

117

IP3/Y

78

IP4/Y

65

IP5/Y

52

IP6/Y

43

NOTES : 1

The normalized SNR values of Table 1 are similar to those of EN 584-1. They are calculated by SNR = log (e) (Gradient/Granularity) of Table 1 in EN 5841. The measured SNR values are calculated from linearized signal data.

2

Y is the maximum basic spatial resolution (see Clause 6.3.2).


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The classification statement consists of two values: (a)

The assignment to an IP-class in agreement with Table 1. The measured normalized SNR shall be greater or equal to the assigned value of the minimum normalized SNR in Table 1.

(b)

The measured maximum basic spatial resolution, rounded to the nearest 10 µm step.

The statement shall be given in the following form: IP X/Y NOTE : For example, a sys tem cla ssi fied as IP 3/100 is charact erized by a norm ali zed SNR ≥ 78 (see Table 1) and a maximum basic spatial resolution ≤100 µm.


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TABLE

3

IP-SYSTEM CLASSES AND METAL SCREENS FOR THE COMPUTED RADIOGRAPHY OF STEEL, COPPER AND NICKEL BASED ALLOYS Radiation source

IP system class*

Penetrated wall thickness (w) mm

Type and minimum thickness in mm of metal screen

A

B

Fro nt

Back

X-ray

< 50 kV

4

2

None

None

X-ray

< 50 kV to 150 kV

5

3

Pb 0.1

Pb 0.1

X-ray

> 150 kV to 250 kV

5

4

Pb 0.1

Pb 0.1

X-ray

> 250 kV to 350 kV

X-ray

> 350 kV to 450 kV

Yb 169 , Tm

170

w

< 50

5

4

Pb 0.2

Pb 0.2

w

> 50

5

5

Pb 0.3

Pb 0.3

w

< 50

5

4

Pb 0.3

Pb 0.3

w

> 50

5

5

Pb 0.3

Pb 0.3

<5

5

3

Pb 0.1

Pb 0.1

w

>5

5

4

Pb 0.1

Pb 0.1

w

< 50

5

4

Pb 0.3

Pb 0.3

w

> 50

5

5

Pb 0.4

Pb 0.4

w

< 100

5

4

Fe 0.5 + Pb 1.5

Fe 0.5 + Pb 1.0

w

> 100

5

5

Fe 0.5 + Pb 2.0

Fe 0.5 + Pb 1.0

w

< 100

5

4

Fe 0.5 + Pb 1.5

Fe 0.5 + Pb 1.0

w

> 100

5

5

Fe 0.5 + Pb 2.0

Fe 0.5 + Pb 1.0

w

Ir 192 , S e75

Co

60†

X-ray

> 1 MV

†

©

*

S t a n d a r d s A u s t r a l i a

† In case of multiple screens (Fe + Pb) the steel screen shall be located between the IP and the lead screen. Instead of Fe or Fe + Pb also copper, tantalum or tungsten screen screens may be used in if the image quality can be proven.

Better IP-system classes may also be used.

AS 2168 .2— 2009

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TABLE 4 IP SYSTEM CLASSES AND METAL SCREENS FOR ALUMINIUM AND TITANIUM IP system class* Radiation source Class A

Class B

Type and minimum thickness in mm of front and back screens

X-ray

< 50 kV

0

X-ray

50 kV to 150 kV

0

X-ray

> 150 kV to 250 kV

X-ray

> 250 kV

Yb 169 ,Tm

170

IP 5

Se 75 *

IP3

Pb 0.02 Pb 0.1 Pb 0.02 Pb 0.1

Better IP-system classes may be also used.

8.4 System unsharpness

) d e t n i r p n e h w d e e t n

1 1

Computed radiography systems shall provide sufficient image quality for a certain probability of detection of material discontinuities. Table 4 defines the required maximum un-sharpness (duplex wire IQI-value) and pixel size of the scanner depending on radiation energy and wall thickness. The system unsharpness shall be proven for all exposures by the duplex wire IQI (refer to EN 462-5).

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TABLE 4 IP SYSTEM CLASSES AND METAL SCREENS FOR ALUMINIUM AND TITANIUM IP system class* Radiation source Class A

Class B

Type and minimum thickness in mm of front and back screens

X-ray

< 50 kV

0

X-ray

50 kV to 150 kV

0

X-ray

> 150 kV to 250 kV

X-ray

> 250 kV

Yb 169 ,Tm

170

IP 5

Se 75 *

IP3

Pb 0.02 Pb 0.1 Pb 0.02 Pb 0.1

Better IP-system classes may be also used.

8.4 System unsharpness

Computed radiography systems shall provide sufficient image quality for a certain probability of detection of material discontinuities. Table 4 defines the required maximum un-sharpness (duplex wire IQI-value) and pixel size of the scanner depending on radiation energy and wall thickness.


The system unsharpness shall be proven for all exposures by the duplex wire IQI (refer to EN 462-5).


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TABLE 5 REQUIRED SPATIAL SYSTEM RESOLUTION IN DEPENDENCE ON ENERGY AND WALL THICKNESS Radiation source

Wall thickness ( w) mm

X-ray

w

≤ 50

4

kV

X-ray

w

>50 kV to <150 kV

4

X-ray 4

X-ray

12

Class IPB

Duplex wire IQI number †

Max. pixel* size µm

Duplex wire IQI number†

<4

40

> 13‡

30

>> 13§

≤

w

60

13

40

> 13 ‡

<4

60

13

30

>> 13§

≤

w

< 12

70

12

40

> 13 ‡

w

≥

12

85

11

60

13

<4

60

13

30

>> 13§

70

12

40

> 13 ‡

w

150 kV to <250 kV

Class IPA Max. pixel* size µm

≤

w

< 12

w

≥

12

85

11

60

13

< 50

110

10

70

12

≤

w

250 kV to <350 kV

w

≥

50

125

9

110

10

X-ray

w

< 50

125

9

85

11

350 kV to <450 kV

w

50

160

8

110

10

85

11

60

13

Yb 169 , Tm 170 75

Se , I r

192

≥

— w

< 40

160

8

110

10

w

≥

40

200

7

125

9

Co 60

250

6

200

7

X-ray

250

6

200

7

©

>1 MeV

S t a n d a r d s A u s t r a l i a

* † ‡ §

If magnification technique is used, double wire IQI readout is required only. The given IQI numbers indicate the readout value of the first unresolved wire pair corresponding to EN 462-5. The symbol ‘> 13’ requires the 13 th wire pair to be resolved with a dip separation larger than 20% (see Figure 3 of AS 2168.1). The symbol ‘>> 13’ requires the 13 th wire pair to be resolved with a dip separation larger than 50%.

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8.5 Alignment of beam

The beam of radiation shall be directed to the centre of the area being inspected and should be normal to the object surface at that point, except when it can be demonstrated that certain flaws are best revealed by a different alignment of the beam. 8.6 Reduction of scattered radiation 8.6.1 Filters and collimators

In order to reduce the effect of back-scattered radiation, direct radiation shall be collimated as much as po ssible to the section under examination. With Se 75 , Ir 192 and Co 60 radiation sources, or in case of edge scatter, a sheet of lead can be used as a filter for low energy scattered radiation between the object and the cassette. The thickness of this sheet is 0.5 mm to 2 mm. 8.6.2 Interception of back scattered radiation

If necessary, the IP shall be shielded from back-scattered radiation by an adequate thickness of lead at least 1 mm, or of tin of at least 1.5 mm, placed behind the IP-screen combination.

) d e t n i r p n e h w d e e t n

The presence of back-scattered radiation shall be checked for each new test arrangement by a lead letter B (with a height of minimum 10 mm and a thickness of minimum 1.5 mm) placed immediately behind each cassette. If the image of this symbol records as an image with less intensity than the background on the radiograph, it shall be rejected. If the symbol is not visible the radiograph is acceptable and demonstrates adequate protection against scattered radiation. 8.7 Source-to-object distance

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8.5 Alignment of beam

The beam of radiation shall be directed to the centre of the area being inspected and should be normal to the object surface at that point, except when it can be demonstrated that certain flaws are best revealed by a different alignment of the beam. 8.6 Reduction of scattered radiation 8.6.1 Filters and collimators

In order to reduce the effect of back-scattered radiation, direct radiation shall be collimated as much as po ssible to the section under examination. With Se 75 , Ir 192 and Co 60 radiation sources, or in case of edge scatter, a sheet of lead can be used as a filter for low energy scattered radiation between the object and the cassette. The thickness of this sheet is 0.5 mm to 2 mm. 8.6.2 Interception of back scattered radiation

If necessary, the IP shall be shielded from back-scattered radiation by an adequate thickness of lead at least 1 mm, or of tin of at least 1.5 mm, placed behind the IP-screen combination. The presence of back-scattered radiation shall be checked for each new test arrangement by a lead letter B (with a height of minimum 10 mm and a thickness of minimum 1.5 mm) placed immediately behind each cassette. If the image of this symbol records as an image with less intensity than the background on the radiograph, it shall be rejected. If the symbol is not visible the radiograph is acceptable and demonstrates adequate protection against scattered radiation.


8.7 Source-to-object distance

The minimum source-to-object distance f min depends on the source size d and on the objectto-detector (IP) distance b. The distance f , shall, where practicable, be chosen so that the ratio of this distance to the source sized d , i.e. f/d, is not below the values given by the following equations: For Class A:

f /d ≥ 7.5(b) 2/3

. . . (1)

For Class B

f /d ≥ 15(b) 2/3

. . . (2)

b is in millimetres (mm).


If the distance b < 1.2 t the dimension b in Equations (1) and (2) and Figure 2 shall be replaced by the nominal thickness t . For determination of the source-to-object distance, f min , the nomogram in Figure 2 may be used. The nomogram is based on E quations (1) and (2). In Class A, if planar imperfections have to be detected the minimum distance f mi n shall be the same as for Class B in order to reduce the geometric un-sharpness by a factor of 2. In critical technical applications of crack-sensitive materials more sensitive radiographic techniques than Class B shall be used.

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50 0 mm 40 0 30 0 5000 mm

10 mm 8 7

20 0

2000

300

mm

20 0

1000 10 0

6

80

5

1000

50 0 60

4

50

30 0 50 0 3

40 20 0 30

300 d

a n i

2

20 0

f

b n i m

20

f

10 0

b

50 10


10 0

m

30

8

20

6

50

1

30 20

5 10

4 3

0. 5

10

LEGEND: a = b =

FIGURE 2

5

2

1

Minimum source to obj ect distance f or c lass B Minimum source to obj ect distance f or c lass A

NOMOGRAM FOR DETERMINATION OF MINIMUM SOURCE-TO-OBJECT

DISTANCE f min IN RELATION TO THE OBJECT-IP DISTANCE AND THE SOURCE SIZE

8.8 Maximum area for a single exposure

The ratio of the penetrated thickness at the outer edge of an evaluated area of uniform thickness to that at the centre beam shall not be more than 1.1 for Class B and 1.2 for Class A. The read-out intensities resulting from any variation of penetrated thickness shall not be lower than those indicated in Clause 8.9.


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Australia

AS 2168 .2— 2009

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8.9 Minimum read-out intensity of computed radiographs

Each CR image shall have better or equal SNR than those defined by the system classes mentioned in Tables 2 and 3. As SNR values are not measured regularly, the minimum SNR values are guaranteed by the use of minimum r ead-out intensities I IPx where x represents the IP class. These read-out intensities are analogous to the use of minimum optical densities in film radiography. The definition of minimum read-out intensity is derived from measurements of the particular CR system refer to AS 2168.1 and they are provided by the manufacturer. Each acquired computed radiograph shall be verified in accordance to Table 5. To be classified as Class A or Class B, readings shall be equal or exceed the required values. NOTE : The sam e IP-sca nner sys tem may be used for dif fere nt appl ica tion s, whi ch have to sat isf y different IP-scanner system classes. This results in different minimum read-out intensities and usually in different exposure times.

TABLE 6 READ-OUT INTENSITY OF COMPUTED RADIOGRAPHS


Testing class

Minimum Read-out intensity* for system Class x

A

0.81 I ipx †

0.9 SNR

ipx †

B

1.0 I ipx †

1.0 SNR

ipx †

* A measuring tolerance of

± 5%

Minimum SNR

is permitted.

† Value may be reduced by special agreement of contacting parties.

High intensities may be used with advantage if the IP-scanner system does not already limit the SNR. In order to avoid unduly high background intensities arising from exposure by natural radiation, IPs shall always be erased before use if the last erasure was more than two weeks. If IPs are used for high-energy application or gamma radiography, they shall be checked for sufficient erasure by a test read out. If I IPx values are not available, the achieved testing class can be determined from the IQIreadout values in accordance with AS 2314. No image processing is allowed apart from linear brightness and contrast adjustment.


8.10 Monitor and film viewing conditions

The computed radiographs shall be examined in a darkened room on a monitor or a printed film hardcopy- with a resolution better or equal to the requirements of AS 2177. The monitor shall have a luminance of ≥100 cd/m 2 and a resolution of ≥1280 × 1024 pixel with a pixel size of 150 µ m to 300 µ m. The graphic board shall provide ≥256 grey levels. The software shall provide images, which are always visualized with 256 grey levels. The ratio for displayable luminance (L max /L mi n ) shall be ≥100:1. 9 PRESENTATION DATA 9.1 Record test

The record of test shall include at least the following information:

©

(a)

Name of the laboratory or testin g authority.

(b)

Identification of the component.

(c)

Job reference number

Standards Australia


17


AS 2168 .2—2 009

(d)

Num ber of the product Standard.

(e)

Details of the material under test.

(f)

The number of this Australian Standard, i.e. AS 2168.2, the method designation, or any departures from that method.

(g)

Details (to allow the radiograph to be related to the workpiece or the test specimen).

(h)

The surface condition of the workpiece, including type of preparation.

(i)

Details of the X-ray tube voltage and current, or of the isotope used and its radioactivity.

(j)

The effective source size, in millimetres.

(k)

The source-to-detector (SDD) distance used, in millimetres.

(l)

The nature and thickness, in millimetres, of any screens or filters used.

(m)

Special notes on exposure geometry (if applicable).

(n)

IQI ty pes, model, l ocation and percent sensitivity achieved, refer to AS 2314 and EN 462-5.

(o)

The trade designation of the IP’s Cr system.

(p)

The minimum readout intensity.

(q)

Details of exposure, in milliampere seconds or curie seconds.

(r)

Nom inal thickness.

(s)

The date and place of test.

(t)

The report number (of reference number) as applicable.

(u)

Identification of the testing personnel.

9.2 Test report

For each computed radiograph, or set of computed radiographs, a test report shall be made giving information on the radiographic technique used, and on any other special circumstances which would allow a better understanding of the results. Details concerning form and contents as specified in special application standards or be as required by the purchaser and supplier. If inspection is carried out exclusively to this guideline then the test report shall contain at least the following infor mation: (a)

Name of th e laboratory or testin g authority.

(b)

Identification of the component, including sufficient details to permit subsequent correlation between the report and radiographs.

(c)

Job reference number.

(d)

Num ber of the product Standard.

(e)

Details of the material under test.

(f)

Nom inal thickness.

(g)

Reference to this Australian Standard, i.e. AS 2168.2, the method designation, or any departures from that method.

(h)

Details of the manufacturers process.

(i)

Details of any surface imperfections considered in the assessment of the radiograph.

(j)

IQI t ypes, model, l ocation and percent sensitivity achieved, refer to AS 2314 and EN 462-5.


© Standards

Australia

AS 2168 .2— 2009

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(k)

Details of intensifying screens/filters.

(l)

The minimum readout intensity.

(m)

The trade designation of the IPs, CR system.

(n)

The effective source size, in millimetres.

(o)

Test results.

(p)

A statement of compliance or otherwise with the acceptance criteria as specified in the relevant product Standard or application Standard, if applicable.

(q)

The date and place of testing.

(r)

The report number and the date of issue.

(s)

Name of certification and signature from the responsible person(s).


©

Standards Australia


19

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AS 2168 .2—2 009

AS 2168 .2— 2009

20

NOT ES


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2168.2-2009 Computerized Radiography Testing of Mettalic Materials Using X-Rays and Gamma Rays

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