SIST EN ISO 20769-2:2019

SLOVENSKI STANDARD
01-marec-2019
1DGRPHãþD
SIST EN 16407-2:2014
Neporušitvene preiskave - Radiografski pregled korozije in nanosov v ceveh z
rentgenskimi žarki in žarki gama - 2. del: Radiografski pregled preko dveh sten
(ISO 20769-2:2018)
Non-destructive testing -- Radiographic inspection of corrosion and deposits in pipes by
X- and gamma rays - Part 2: Double wall radiographic inspection (ISO 20769-2:2018)
Zerstörungsfreie Prüfung - Durchstrahlungsprüfung auf Korrosion und Ablagerungen in
Rohren mit Röntgen - und Gammastrahlen - Teil 2: Doppelwand-Durchstrahlungsprüfung
(ISO 20769-2:2018)
Essais non destructifs - Examen radiographique de la corrosion et des dépôts dans les
canalisations, par rayons X et rayons gamma - Partie 2: Examen radiographique double
paroi (ISO 20769-2:2018)
Ta slovenski standard je istoveten z: EN ISO 20769-2:2018
ICS:
19.100 Neporušitveno preskušanje Non-destructive testing
23.040.01 Deli cevovodov in cevovodi Pipeline components and
na splošno pipelines in general
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 20769-2
EUROPEAN STANDARD
NORME EUROPÉENNE
October 2018
EUROPÄISCHE NORM
ICS 19.100 Supersedes EN 16407-2:2014
English Version
Non-destructive testing - Radiographic inspection of
corrosion and deposits in pipes by X- and gamma rays -
Part 2: Double wall radiographic inspection (ISO 20769-
2:2018)
Essais non destructifs - Examen radiographique de la Zerstörungsfreie Prüfung - Durchstrahlungsprüfung
corrosion et des dépôts dans les canalisations, par auf Korrosion und Ablagerungen in Rohren mit
rayons X et rayons gamma - Partie 2: Examen Röntgen - und Gammastrahlen - Teil 2: Doppelwand-
radiographique double paroi (ISO 20769-2:2018) Durchstrahlungsprüfung (ISO 20769-2:2018)
This European Standard was approved by CEN on 9 August 2018.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2018 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 20769-2:2018 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 20769-2:2018) has been prepared by Technical Committee ISO/TC 135 "Non-
destructive testing" in collaboration with Technical Committee CEN/TC 138 “Non-destructive testing”
the secretariat of which is held by AFNOR.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by April 2019, and conflicting national standards shall be
withdrawn at the latest by April 2019.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN 16407-2:2014.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,
Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.
Endorsement notice
The text of ISO 20769-2:2018 has been approved by CEN as EN ISO 20769-2:2018 without any
modification.
INTERNATIONAL ISO
STANDARD 20769-2
First edition
2018-09
Non-destructive testing —
Radiographic inspection of corrosion
and deposits in pipes by X- and
gamma rays —
Part 2:
Double wall radiographic inspection
Essais non destructifs — Examen radiographique de la corrosion et
des dépôts dans les canalisations, par rayons X et rayons gamma —
Partie 2: Examen radiographique double paroi
Reference number
ISO 20769-2:2018(E)
©
ISO 2018
ISO 20769-2:2018(E)
© ISO 2018
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
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Published in Switzerland
ii © ISO 2018 – All rights reserved

ISO 20769-2:2018(E)
Contents Page
Foreword .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Classification of radiographic techniques . 3
5 General . 3
5.1 Protection against ionizing radiation . 3
5.2 Personnel qualification . 4
5.3 Identification of radiographs . 4
5.4 Marking . 4
5.5 Overlap of films or digital images . 4
5.6 Types and positions of image quality indicators (IQI) . 4
5.6.1 Single wire IQI . 4
5.6.2 Duplex wire IQI (digital radiographs) . 5
6 Recommended techniques for making radiographs . 5
6.1 Test arrangements . 5
6.1.1 General. 5
6.1.2 Double wall single image (DWSI) . 5
6.1.3 Double wall double image (DWDI) . 7
6.1.4 Alignment of beam and film/detector . 9
6.2 Choice of radiation source . . 9
6.3 Film systems and screens .10
6.4 Screens and shielding for imaging plates (computed radiography only).11
6.5 Reduction of scattered radiation .13
6.5.1 Filters and collimators .13
6.5.2 Interception of back scattered radiation .13
6.6 Source-to-detector distance .13
6.6.1 Double wall single image .13
6.6.2 Double wall double image .14
6.7 Axial coverage and overlap .14
6.8 Circumference coverage .15
6.8.1 General.15
6.8.2 DWSI .16
6.8.3 DWDI .16
6.9 Selection of digital radiographic equipment .16
6.9.1 General.16
6.9.2 CR systems .17
6.9.3 DDA systems .17
7 Radiograph/digital image sensitivity, quality and evaluation.17
7.1 Minimum image quality values .17
7.1.1 Wire image quality indicators .17
7.1.2 Duplex wire IQIs (digital radiographs) .17
7.1.3 Minimum normalized signal to noise ratio (digital radiographs) .17
7.2 Density of film radiographs . .18
7.3 Film processing.18
7.4 Film viewing conditions .18
8 Measurement of differences in penetrated thickness .18
8.1 Principle of technique .18
8.2 Measurement of attenuation coefficient .19
8.3 Source and detector positioning .19
8.4 Image grey level profiles .19
8.5 Validation .19
ISO 20769-2:2018(E)
8.6 Key points .20
9 Digital image recording, storage, processing and viewing .20
9.1 Scan and read out of image .20
9.2 Calibration of DDAs .20
9.3 Bad pixel interpolation .20
9.4 Image processing .21
9.5 Digital image recording and storage .21
9.6 Monitor viewing conditions .21
10 Test report .21
Annex A (normative) Minimum image quality values .23
Annex B (normative) Penetrated thickness measurements from image grey levels .25
Annex C (normative) Determination of basic spatial resolution .27
Bibliography .30
iv © ISO 2018 – All rights reserved

ISO 20769-2:2018(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see www .iso
.org/iso/foreword .html.
This document was prepared by Technical Committee ISO/TC 135 Non-destructive testing, Subcommittee
SC 5 Radiographic testing.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/members .html.
A list of all parts in the ISO 20769 series can be found on the ISO website.
INTERNATIONAL STANDARD ISO 20769-2:2018(E)
Non-destructive testing — Radiographic inspection of
corrosion and deposits in pipes by X- and gamma rays —
Part 2:
Double wall radiographic inspection
1 Scope
This document specifies fundamental techniques of film and digital radiography with the object of
enabling satisfactory and repeatable results to be obtained economically. The techniques are based on
generally recognized practice and fundamental theory of the subject.
This document applies to the radiographic examination of pipes in metallic materials for service
induced flaws such as corrosion pitting, generalized corrosion and erosion. Besides its conventional
meaning, “pipe” as used in this document is understood to cover other cylindrical bodies such as tubes,
penstocks, boiler drums and pressure vessels.
Weld inspection for typical welding process induced flaws is not covered, but weld inspection is
included for corrosion/erosion type flaws.
The pipes can be insulated or not, and can be assessed where loss of material due, for example, to
corrosion or erosion is suspected either internally or externally.
This document covers double wall inspection techniques for detection of wall loss, including double
wall single image (DWSI) and double wall double image (DWDI).
Note that the DWDI technique described in this document is often combined with the tangential
technique covered in ISO 20769-1.
This document applies to in-service double wall radiographic inspection using industrial radiographic
film techniques, computed digital radiography (CR) and digital detector arrays (DDA).
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 11699-1, Non-destructive testing — Industrial radiographic film — Part 1: Classification of film
systems for industrial radiography
ISO 11699-2, Non-destructive testing — Industrial radiographic films — Part 2: Control of film processing
by means of reference values
ISO 17636-2, Non-destructive testing of welds — Radiographic testing — Part 2: X- and gamma-ray
techniques with digital detectors
ISO 19232-1, Non-destructive testing — Image quality of radiographs — Part 1: Determination of the
image quality value using wire-type image quality indicators
ISO 19232-5, Non-destructive testing — Image quality of radiographs — Part 5: Determination of the
image unsharpness value using duplex wire-type image quality indicators
ISO 20769-2:2018(E)
ISO 20769-1, Non-destructive testing of welds — Radiographic inspection of corrosion and deposits in pipes
by X- and gamma rays — Part 1: Tangential radiographic inspection
EN 14784-1, Non-destructive testing — Industrial computed radiography with storage phosphor imaging
plates — Part 1: Classification of systems
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 20769-1 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at http: //www .electropedia .org/
3.1
digital detector array system
DDA system
electronic device converting ionizing or penetrating radiation into a discrete array of analogue
signals which are subsequently digitized and transferred to a computer for display as a digital image
corresponding to the radiologic energy pattern imparted upon the input region of the device
3.2
double wall double image technique
DWDI
technique where the radiation source is located outside and away from the pipe, with the detector on
the opposite side of the pipe and where the radiograph shows details from both the pipe walls on the
detector and source sides of the pipe
Note 1 to entry: See Figure 3.
3.3
double wall single image technique
DWSI
technique where the radiation source is located outside the pipe and close to the pipe wall, with the
detector on the opposite side of the pipe and where the radiograph shows only detail from the pipe wall
on the detector side
Note 1 to entry: See Figure 1.
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 the basis of the nominal
thickness
Note 1 to entry: For double wall radiographic inspection of a pipe, the minimum value for w is twice the pipe wall
thickness. For multiple wall techniques (pipes in pipe or liners), the penetrated thickness is calculated from the
nominal wall thicknesses t.
2 © ISO 2018 – All rights reserved

ISO 20769-2:2018(E)
3.6
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
3.7
total effective penetrated thickness
w
tot
total equivalent thickness of metallic material in the direction of the radiation beam calculated on the
basis of the nominal thickness, with allowance for any liquid or other material present in the pipe and
any insulation
4 Classification of radiographic techniques
The double wall radiographic techniques are divided into two classes:
— basic techniques DWA;
— improved techniques DWB.
The basic techniques are intended for double wall radiography of generalized and localized wall loss.
For the basic techniques, DWA, when using Ir 192 sources for pipes with penetrated thicknesses
between 15 mm and 35 mm, the sensitivity for detection is high for imperfections, provided their
diameters are greater than or equal to 2 mm and the material loss is typically greater than or equal to
5 % of the pipe penetrated thickness, in the absence of liquid or other products in the pipe. When using
Se 75, the corresponding detection sensitivity is high for 2 mm diameter or larger imperfections with
material loss greater than or equal to 4 % of the pipe penetrated thickness. The detection sensitivity
is improved for flaws with larger diameters, whereas the presence of liquid or other products, and
external insulation, can reduce the sensitivity for material loss depending on their properties. Different
detection sensitivities may apply for penetrated thicknesses less than 15 mm and greater than 35 mm.
The presence of external corrosion product can reduce the techniques sensitivity to corrosion due to
the increased radiation attenuation in the product, which can even exceed the reduced attenuation
caused by the loss of steel. Build-up of internal solid material (e.g. scale) in pipes can similarly reduce
sensitivity to internal degradation.
These techniques can also be used for detection of deposits inside the pipe.
The improved techniques should be used where higher sensitivity is required such as for radiography
of fine, localized corrosion pitting.
Further improvements, beyond the improved techniques described herein, are possible and may be
agreed between the contracting parties by specification of all appropriate test parameters.
The choice of radiographic technique shall be agreed between the concerned parties.
5 General
5.1 Protection against ionizing radiation
WARNING — Exposure of any part of the human body to X-rays or gamma-rays can be highly
injurious to health. Wherever X-ray equipment or radioactive sources are in use, appropriate
measures shall be taken to ensure the safety and health of personnel.
ISO 20769-2:2018(E)
5.2 Personnel qualification
Testing shall be carried out by proficient, suitably trained and qualified personnel and, where
applicable, shall be supervised by competent personnel nominated by the employer or, by delegation of
the employer, the inspection company in charge of testing. To demonstrate appropriate qualification, it
is recommended that personnel be certified according to ISO 9712 or an equivalent formalized system.
Operating authorization for qualified persons shall be issued by the employer in accordance with a
written procedure.
NDT operations, unless otherwise agreed, shall be authorized by a competent and qualified NDT
supervisory individual (Level 3 or equivalent) approved by the employer.
The personnel shall prove additional training and qualification in digital industrial radiology if digital
detectors are used.
5.3 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
unambiguous identification of the section.
5.4 Marking
Permanent markings on the object to be examined should be made in order to accurately locate the
position of each radiograph.
Where the nature of the material and/or its service conditions do not permit permanent marking, the
location may be recorded by means of accurate sketches.
5.5 Overlap of films or digital images
When radiographing an area with two or more films or separate detectors, the films or detectors 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 which appears on each film or detector. If the
radiographs is taken sequentially, the high-density marker shall be visible on each of the radiographs.
5.6 Types and positions of image quality indicators (IQI)
5.6.1 Single wire IQI
The quality of image shall be verified by use of IQIs in accordance with ISO 19232-1.
For DWDI, the single wire IQI used shall be placed preferably on the source side of the test object at the
centre of the area of interest. The IQI shall be in close contact with the surface of the object. If the IQIs
cannot be placed in accordance with the above conditions (insulated pipes), they shall be placed on the
detector side. The image quality shall be determined at least once from a comparison exposure with
one IQI placed at the source side and one at the detector side under the same conditions.
For DWSI, the single wire IQI used shall be placed on the detector side of the test object at the centre of
the area of interest. If possible, the IQI shall be in close contact with the surface of the object. However,
if this is not possible due for example to the presence of insulation, the IQI shall be in contact with the
film/detector.
For both DWDI and DWSI, the wire IQIs shall be aligned across the pipe, with their long axis angled
at a few degrees (2° to 5°) to the orthogonal to the pipe axis. The IQI location should be in a section of
uniform thickness, near to the pipe centre line.
For DWDI, where the IQIs are placed at the detector side, the letter “F” shall be placed near the IQI and it
shall be noted in the test report.
4 © ISO 2018 – All rights reserved

ISO 20769-2:2018(E)
The extent of image quality verification for repeat exposures of closely similar objects under identical
conditions shall be subject to agreement between the contracting parties.
5.6.2 Duplex wire IQI (digital radiographs)
IQIs in accordance with ISO 19232-5 should be used for measurement of the basic spatial resolution
of the CR/DDA system in a reference radiograph (see 7.1.2 and Annex C). The duplex wire IQI shall be
placed on the source side of the imaging plate or detector array and positioned a few degrees tilted (2°
to 5°) to the digital rows or columns of the digital image.
6 Recommended techniques for making radiographs
6.1 Test arrangements
6.1.1 General
Normally, radiographic techniques in accordance with 6.1.2 and 6.1.3 shall be used.
The technique presented in 6.1.2 is normally used for larger diameter pipes. The technique presented in
6.1.3 is generally used for smaller diameter pipes (less than typically about 150 mm outside diameter).
For both techniques, the film or digital detector shall be placed as close to the pipe as possible.
6.1.2 Double wall single image (DWSI)
For this arrangement with curved detectors or film, the source is located near to the pipe and with the
film/detector on the opposite side, as shown in Figure 1 a) (without insulation) and Figure 1 b) (with
insulation). The relevant distances for determination of source to detector distance, SDD (see 6.6), are
also shown.
ISO 20769-2:2018(E)
a) Non-insulated pipe
b) Insulated pipe
Key
1 detector
Figure 1 — Test arrangement for double wall single image radiography (DWSI) using a curved
detector
Note that the wall loss can be located on either the inner diameter, outer diameter or both surfaces of
the pipe wall adjacent to the detector. Wall loss on the source side of the pipe is not imaged.
For rigid planar detectors, DWSI can also be applied as shown in Figure 2 a) and Figure 2 b). Although,
with this arrangement, a smaller fraction of the pipe circumference can be inspected at each position.
6 © ISO 2018 – All rights reserved

ISO 20769-2:2018(E)
a) Non-insulated pipe
b) Insulated pipe
Key
1 detector
Figure 2 — Test arrangement for double wall single image radiography (DWSI) using a planar
detector
6.1.3 Double wall double image (DWDI)
For this arrangement, the radiation source is located in front of the pipe and with the planar film/detector
at the opposite side, as shown in Figure 3 a) (non-insulated pipe) and Figure 3 b) (insulated pipe).
ISO 20769-2:2018(E)
a) Non-insulated pipe
b) Insulated pipe
Key
1 detector
Figure 3 — Test arrangement for double wall double image radiography (DWDI)
With DWDI, the wall loss can be located on either the inner diameter, outer diameter or both surfaces of
the pipe, and on either the source or detector side of the pipe.
If DWDI and tangential radiographic techniques are combined, the requirements of ISO 20769-1 shall
also be met.
8 © ISO 2018 – All rights reserved

ISO 20769-2:2018(E)
6.1.4 Alignment of beam and film/detector
The beam of radiation shall be directed at the centre of the area being examined and should be
perpendicular to the pipe axis.
For DWDI, the film or detector should be aligned to be orthogonal to the centre of the radiation beam.
Modifications to these alignments and the test arrangements given in 6.1.2 and 6.1.3 can be needed in
special cases, due for example to the presence of obstructions.
Other ways of radiographing may be agreed between contracting parties.
6.2 Choice of radiation source
Penetrated thickness ranges for X-ray and gamma ray sources are given in Table 1 and Figure 4. By
agreement between contracting parties, these ranges can be extended.
The maximum X-ray voltages shown in Figure 4 are best practice values for film radiography of welds.
If DDAs with accurate calibration are used, sufficient image quality can still be obtained using higher
X-ray voltages than those shown in Figure 4. For CR applications reduced X-ray voltages by at least 20 %
are recommended in comparison to Figure 4.
In cases where radiographs are produced using gamma rays, the total travel time to position and
rewind the source shall not exceed 10 % of the total exposure time.
By agreement between the contracting parties, the penetrated thickness minimum value for Ir 192 and
Se 75 may be reduced to 5 mm of steel.
Table 1 — Total effective penetrated thickness ranges for gamma-ray and high energy X-ray
sources for steel pipes
Total effective penetrated thickness, w
tot
Radiation source mm
basic technique, DWA improved technique, DWB
Yb 169 1 ≤ w ≤ 15
tot
a
Se 75 5 ≤ w ≤ 55 10 ≤ w ≤ 40
tot tot
Ir 192 10 ≤ w ≤ 100 20 ≤ w ≤ 90
tot tot
Co 60 40 ≤ w ≤ 200
tot
X-ray equipment with energy
30 ≤ w ≤ 200
tot
from 1 MeV to 4 MeV
X-ray equipment with energy
w ≥ 50
tot
from 4 MeV to 12 MeV
X-ray equipment with energy
w ≥ 80
tot
above 12 MeV
a
For aluminium and titanium, the penetrated material thickness is 35 mm ≤ w ≤ 120 mm for class DWA and DWB
tot
testing.
ISO 20769-2:2018(E)
Key
1 copper/nickel and alloys 4 aluminium and alloys
2 steel w penetrated thickness in mm
3 titanium and alloys U X-ray voltage in kV
Figure 4 — Maximum X-ray voltage, U, for X-ray devices up to 1 000 kV as a function of
penetrated thickness, w, and material
For product filled pipes, the additional radiation attenuation caused by the product shall be allowed
for in the selection of sources. For a water-filled pipe, the penetrated thickness, w, for steel tested with
Ir 192 shall be increased by approximately one-ninth of the path length in the water to calculate w .
tot
For an oil-filled pipe, w shall be increased by approximately one-eleventh of the path length in the oil to
calculate w .
tot
For insulated pipes, the additional radiation attenuation caused by the insulation shall be allowed for in
the selection of sources.
6.3 Film systems and screens
For radiographic examination, film system classes shall be used in accordance with ISO 11699-1.
The radiographic film system class and metal screens for different radiation sources are given in
Table 2.
When using metal screens, good contact between films and screens is required. This can be achieved
either by using vacuum-packed films or by applying pressure.
10 © ISO 2018 – All rights reserved

ISO 20769-2:2018(E)
Table 2 — Film system classes and metal screens for double wall radiography of steel, copper
and nickel based alloy pipes
a
Film system class
Radiation source Type and thickness of metal screens
Class DWA Class DWB
X-ray potentials 0,02 mm to 0,15 mm
C 5 C 4
≤ 250 kV front and back screens of lead
0,1 mm to 0,2 mm
b
front screens of lead
X-ray potentials
C 5 C 4
> 250 kV to 500 kV
0,02 mm to 0,2 mm
back screens of lead
X-ray potentials 0,25 mm to 0,7 mm front and
C 5 C 4
c
> 500 kV to 1 000 kV back screens of steel or copper
Se 75
0,02 mm to 0,2 mm front and
C 6 C 5
b
back screens of lead
Ir 192
0,25 mm to 0,7 mm front and
Co 60 C 6 C 5
c
back screens of steel or copper
X-ray equipment 0,25 mm to 0,7 mm front and
C 6 C 5
c
with energy from 1 MeV to 4 MeV back screens of steel or copper
Up to 1 mm front screen of copper,
d
steel or tantalum
X-ray equipment
C 6 C 5
with energy above 4 MeV
Back screen of copper or steel
d
up to 1 mm and tantalum up to 0,5 mm
a
Better film system classes may also be used.
b
Ready packed films with a front screen up to 0,03 mm may be used if an additional lead screen of 0,1 mm is placed
between the object and the film.
c
In class DWA, 0,5 mm to 2,0 mm screens of lead may also be used.
d
In class DWA, lead screens 0,5 mm to 1 mm may be used by agreement between the contracting parties.
Table 3 — Film system classes and metal screens for double wall radiography of aluminium and
titanium pipes
a
Film system class
Radiation source Type and thickness of intensifying screens
Class DWA Class DWB
X-ray potentials None or up to 0,03 mm front and
≤ 150 kV up to 0,15 mm back screens of lead
X-ray potentials 0,02 mm to 0,2 mm front and
C 5 C 4
b
>150 kV to 500 kV back screens of lead
Se 75 0,02 mm to 0,2 mm front and
c b
Ir 192 back screens of lead
a
Better film system classes may also be used.
b
Instead of one 0,2 mm lead screen, two 0,1 mm lead screens may be used.
c
Ir 192 may be applied by agreement of contracting parties.
Different film system classes may be used by agreement of the contracting parties, provided the
required optical densities defined in 7.2 and required minimum image quality values in Annex A are
achieved.
6.4 Screens and shielding for imaging plates (computed radiography only)
When using metal front screens, good contact between the sensitive detector layer and screens is
required. This can be achieved either by using vacuum-packed IPs or by applying pressure. Lead screens
ISO 20769-2:2018(E)
not in intimate contact with the IPs can contribute to image unsharpness. The intensification obtained
by use of lead screens in contact with imaging plates is significantly smaller than in film radiography.
Many IPs are very sensitive to low energy backscatter and X-ray fluorescence of back-shielding from
lead. This effect contributes significantly to edge unsharpness and reduced SNR, and should be
minimized. It is recommended that steel or copper shielding be used directly behind the IPs. A steel
or copper shielding between a backscatter lead plate and the IP can also improve the image quality.
Modern cassette and detector designs can consider this effect and can be constructed in a way such
that additional steel or copper shielding outside the cassette is not required.
NOTE Due to the protection layer between the lead and the sensitive layer of an IP, the effect of intensification
by electrons is considerably reduced and appears at higher energies. Depending on the radiation energy and
protection layer design, the effect of intensification amounts to between 20 % and 100 % only (compared to no
screen).
The small intensification effect generated by a lead screen in contact with an IP can be compensated
for by increased exposure time or milliampere minutes, if no lead screens are used. Since lead screens
in contact with IPs may generate scratches on IPs, if not carefully separated for the scan process,
lead screens should be used for intermediate filtering of scattered radiation outside of cassettes.
No intermediate filtering is recommended for inspecting steel specimens having a thickness less
than 12 mm.
Table 4 and Table 5 show the recommended screen materials and thicknesses for different radiation
sources. Other screen thicknesses may be also agreed between the contracting parties provided the
required image quality is achieved. The usage of metal screens is recommended in front of IPs, and they
may also reduce the influence of scattered radiation when used with DDAs.
Table 4 — Metal front screens for CR for double wall radiography for pipes of steel, copper and
nickel based alloys
Type and thickness of metal front screens
Radiation source
mm
a
X-ray potentials ≤ 250 kV 0 to 0,1 (lead)
a c
X-ray potentials > 250 kV to 1 000 kV 0 to 0,3 (lead)
c
Class DWA: 0 to 0,3 (lead)
a
Ir 192, Se 75
Class DWB: 0,3 to 0,8 (steel or c
...