SIST EN ISO 20769-1:2019

SLOVENSKI STANDARD
01-marec-2019
1DGRPHãþD
SIST EN 16407-1:2014
Neporušitvene preskave - Radiografski pregled korozije in nanosov v ceveh z
rentgenskimi žarki in žarki gama - 1. del: Tangencialni radiografski pregled (ISO
20769-1:2018)
Non-destructive testing - Radiographic inspection of corrosion and deposits in pipes by X
- and gamma rays - Part 1: Tangential radiographic inspection (ISO 20769-1:2018)
Zerstörungsfreie Prüfung - Durchstrahlungsprüfung auf Korrosion und Ablagerungen in
Rohren mit Röntgen- und Gammastrahlen - Teil 1: Tangentiale Durchstrahlungsprüfung
(ISO 20769-1:2018)
Essais non destructifs - Examen radiographique de la corrosion et des dépôts dans les
canalisations, par rayons X et rayons gamma - Partie 1: Examen radiographique
tangentiel (ISO 20769-1:2018)
Ta slovenski standard je istoveten z: EN ISO 20769-1:2018
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 20769-1
EUROPEAN STANDARD
NORME EUROPÉENNE
October 2018
EUROPÄISCHE NORM
ICS 19.100 Supersedes EN 16407-1:2014
English Version
Non-destructive testing - Radiographic inspection of
corrosion and deposits in pipes by X - and gamma rays -
Part 1: Tangential radiographic inspection (ISO 20769-
1:2018)
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 1: Examen Röntgen- und Gammastrahlen - Teil 1: Tangentiale
radiographique tangentiel (ISO 20769-1:2018) Durchstrahlungsprüfung (ISO 20769-1:2018)
This European Standard was approved by CEN on 5 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 20769-1:2018 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 20769-1:2018) 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 16407-1:2014.
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 20769-1:2018 has been approved by CEN as EN ISO 20769-1:2018 without any
modification.
INTERNATIONAL ISO
STANDARD 20769-1
First edition
2018-09
Non-destructive testing —
Radiographic inspection of corrosion
and deposits in pipes by X- and
gamma rays —
Part 1:
Tangential radiographic inspection
Essais non destructifs — Examen radiographique de la corrosion et
des dépôts dans les canalisations, par rayons X et rayons gamma —
Partie 1: Examen radiographique tangentiel
Reference number
ISO 20769-1:2018(E)
©
ISO 2018
ISO 20769-1:2018(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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below or ISO’s member body in the country of the requester.
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Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2018 – All rights reserved

ISO 20769-1:2018(E)
Contents Page
Foreword .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Classification of radiographic techniques . 4
5 General . 5
5.1 Protection against ionizing radiation . 5
5.2 Personnel qualification . 5
5.3 Identification of radiographs . 5
5.4 Marking . 5
5.5 Overlap of films or digital images . 5
5.6 Types and positions of image quality indicators (IQI) . 5
5.6.1 Single wire or step hole IQIs . 5
5.6.2 Duplex wire IQI (digital radiographs) . 5
6 Recommended techniques for making radiographs . 6
6.1 Test arrangements . 6
6.1.1 General. 6
6.1.2 Radiation source located on the pipe centre line . 6
6.1.3 Radiation source located offset from the pipe centre line . 7
6.1.4 Alignment of beam and film/detector . 9
6.2 Choice of radiation source . . 9
6.3 Film systems and metal screens .10
6.4 Screens and shielding for imaging plates (computed radiography only).11
6.5 Reduction of scattered radiation .12
6.5.1 Filters and collimators .12
6.5.2 Interception of back scattered radiation .13
6.6 Source-to-detector distance .13
6.7 Axial coverage and overlap .14
6.8 Dimensional comparators .15
6.9 Image saturation and use of lead strips to avoid burn-off .16
6.10 Selection of digital radiographic equipment .16
6.10.1 General.16
6.10.2 CR systems .17
6.10.3 DDA systems .17
7 Radiograph/digital image sensitivity, quality and evaluation.17
7.1 Evaluation of image quality .17
7.1.1 General.17
7.1.2 Maximum grey level in free beam (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
7.5 Dimensional calibration of radiographs or digital images .19
7.5.1 General.19
7.5.2 Measurement of distances in radiographic setup .19
7.5.3 Measurement of pipe outside diameter .20
7.5.4 Dimensional comparator .20
7.6 Wall thickness measurements for film radiographs .20
7.7 Wall thickness measurements for digital radiographs .21
7.7.1 Interactive on-screen measurements .21
7.7.2 Grey-level profile analysis methods .21
7.8 Remaining thickness measurements for degradation .22
ISO 20769-1:2018(E)
7.8.1 Measurements for internal degradation .22
7.8.2 Measurements for external degradation .24
8 Digital image recording, storage, processing and viewing .26
8.1 Scan and read out of image .26
8.2 Multi radiograph technique .26
8.3 Calibration of DDAs .26
8.4 Bad pixel interpolation .26
8.5 Image processing .26
8.6 Digital image recording and storage .26
8.7 Monitor viewing conditions .27
9 Test report .27
Annex A (informative) Choice of radiation source for different pipes .29
Annex B (informative) Remaining thickness measurements for internal degradation .30
Annex C (informative) Remaining thickness measurements for external degradation .33
Bibliography .37
iv © ISO 2018 – All rights reserved

ISO 20769-1:2018(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 20769-1:2018(E)
Non-destructive testing — Radiographic inspection of
corrosion and deposits in pipes by X- and gamma rays —
Part 1:
Tangential 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 steel pipes 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 the tangential inspection technique for detection and through-wall sizing of wall
loss, including with the source:
a) on the pipe centre line; and
b) offset from pipe centre line by the pipe radius.
ISO 20769-2 covers double wall radiography, and note that the double wall double image technique is
often combined with tangential radiography with the source on the pipe centre line.
This document applies to tangential radiographic inspection using industrial radiographic film
techniques, computed 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 9712, Non-destructive testing — Qualification and certification of NDT personnel
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 16371-1, Non-destructive testing — Industrial computed radiography with storage phosphor imaging
plates — Part 1: Classification of systems
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 20769-1:2018(E)
3 Terms and definitions
For the purposes of this document, the following terms and definitions 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
actual wall thickness
t
act
real thickness of the pipe wall which can differ from the nominal thickness
3.2
axial coverage
L
d
total axial extent of the evaluated section of the pipe radiograph measured on the
detector (3.8)
3.3
axial coverage
L
p
total axial extent of the evaluated section of the pipe radiograph measured
along the central axis of the pipe
3.4
basic spatial resolution
detector
SR
b
smallest geometrical detail, which can be resolved in a digital image at a magnification
equal to 1; corresponds to half of the measured image unsharpness in a digital image; corresponds to
the effective pixel size (3.19) of the magnified image; and is determined from the smallest number of the
duplex wire pair, which is not separable by visual inspection or from the smallest number of the duplex
wire pair with less than 20 % modulation depth in a linearized profile
Note 1 to entry: For this measurement, the duplex wire IQI is placed directly on the digital detector (3.8) array or
imaging plate.
detector
Note 2 to entry: The measurements of SR and unsharpness are described in ISO 19232-5. and
b
[17]
ASTM E2002 .
3.5
basic spatial resolution
image
SR
b
smallest geometrical detail, which can be resolved in a digital image at a magnification
>1; corresponds to half of the measured image unsharpness in a digital image; corresponds to the
effective pixel size (3.19) of the magnified image; and is determined from the smallest number of the
duplex wire pair, which is not separable by visual inspection or from the smallest number of the duplex
wire pair with less than 20 % modulation depth in a linearized profile
image
Note 1 to entry: The measurements of SR and unsharpness are described in ISO 19232-5. and
b
[17]
ASTM E2002 .
3.6
comparator
C
reference object of defined dimension c and material for dimensional calibration of a radiographic image
2 © ISO 2018 – All rights reserved

ISO 20769-1:2018(E)
3.7
computed radiography
CR
complete system comprising a storage phosphor imaging plate (IP) (3.23) and a corresponding read-
out unit (scanner or reader), which converts the information from the IP into a digital image and the
control software of the read-out unit
3.8
detector
D
detection device, consisting of a NDT film system (see ISO 11699-1) or a digital radiography system
using a CR system or a DDA system
Note 1 to entry: Film systems and IPs can be used as flexible and curved detectors or in planar cassettes.
3.9
digital detector array
DDA
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 and the
control software
3.10
imaged comparator dimension
c′
dimension of the comparator (3.6) measured on the detector (3.8)
3.11
imaged outside diameter
D ′
e
nominal outside diameter of the pipe measured on the detector
3.12
maximum penetrated thickness
w
max
maximum thickness of material for a pipe which occurs for a tangent to the inner pipe surface
3.13
measured wall thickness
t
meas
thickness of the pipe wall as measured on the radiograph or digital image
3.14
nominal wall thickness
t
thickness of the pipe wall as given by the manufacturer, neglecting the manufacturing tolerances
3.15
normalized signal-to-noise ratio
SNR
N
image
ratio of signal-to-noise, normalized by the basic spatial resolution, SR , (3.5) as measured directly
b
in the digital image and/or calculated from the measured SNR , by:
measured
88,6 μm
SNRS= NR
Nmeasured
SR
b
SR image SR detector
Note 1 to entry: can be substituted by (3.4) at magnification equal to 1.
b b
ISO 20769-1:2018(E)
3.16
outside diameter
D
e
nominal outer diameter of the pipe as given by the manufacturer, neglecting the manufacturing
tolerances
3.17
pipe centre to detector distance
PDD
distance between the pipe centre and the detector (3.8)
3.18
pixel size
geometrical centre-to-centre distance between adjacent pixels in a row (horizontal pitch) or column
(vertical pitch) of the scanned image
[SOURCE: ISO 14096-2:2005, 3.2]
3.19
signal-to-noise ratio
SNR
ratio of mean value of the linearized grey values to the standard deviation of the linearized grey values
(noise) in a given region of interest in a digital image
3.20
source size
d
size of the radiation source
[SOURCE: ISO 16371-2:2017, 3.15]
3.21
source-to-detector distance
SDD
distance between the source of radiation and the detector (3.8) measured in the direction of the beam
3.22
source-to-pipe centre distance
SPD
distance between the source of radiation and the pipe centre (pipe axis) measured in the direction of
the beam
3.23
storage phosphor imaging plate
IP
photostimulable luminescent material capable of storing a latent radiographic image of a material being
examined and which, upon stimulation by a source of red light of appropriate wavelength, generates
luminescence proportional to radiation absorbed
4 Classification of radiographic techniques
The tangential radiographic techniques are divided into two classes:
— class TA, basic techniques;
— class TB, improved techniques.
The basic techniques, class TA, are intended for tangential radiography of generalized wall loss, such as
that due to erosion or large-scale corrosion.
4 © ISO 2018 – All rights reserved

ISO 20769-1:2018(E)
The improved techniques, class TB, should be used for the more demanding tangential radiography of
localized corrosion pitting flaws, which require higher sensitivity for detection and sizing.
Further technique improvements beyond TB 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.
5.2 Personnel qualification
Personnel performing non-destructive examination in accordance with this document shall be qualified
in accordance with ISO 9712 or equivalent to an appropriate level in the relevant industrial sector.
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 should be made on the object to be examined 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 will appear on each film or detector. If the
radiographs are 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 or step hole IQIs
For tangential radiography, single wire or step hole IQIs are not applicable.
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 7.1.3 and Annex A). The duplex wire IQI shall be
placed adjacent to 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.
ISO 20769-1:2018(E)
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. For both techniques,
the film or digital detector shall be placed as close to the pipe as possible.
6.1.2 Radiation source located on the pipe centre line
For this arrangement, the source is located in front of the pipe and with the film/detector at the opposite
side, as shown in Figure 1. The pipe can be non-insulated [Figure 1 a)] or insulated [Figure 1 b)].
a) Non-insulated pipe
6 © ISO 2018 – All rights reserved

ISO 20769-1:2018(E)
b) Insulated pipe
Key
1 detector, D
Figure 1 — Test arrangement and distances for tangential radiography with the source on the
pipe centre line
Note that the wall loss can be located on either the inner diameter, outer diameter or both surfaces of
the pipe.
6.1.3 Radiation source located offset from the pipe centre line
For this arrangement, the radiation source is located in front of the pipe and with the film/detector at
the opposite side, as shown in Figure 2 a) (non-insulated pipe) and Figure 2 b) (insulated pipe).
ISO 20769-1:2018(E)
a) Non-insulated pipe
b) Insulated pipe
Key
1 detector, D
Figure 2 — Test arrangement and distances for tangential radiography with the source offset
from the pipe centre line
8 © ISO 2018 – All rights reserved

ISO 20769-1:2018(E)
In this test arrangement, the source is offset from the pipe centre line, and is aligned with the centre of
the pipe wall, as shown in Figure 2. Note that the wall loss can be located on either the inner diameter,
outer diameter or both surfaces of the pipe.
6.1.4 Alignment of beam and film/detector
The beam of radiation shall be directed at the centre of the area being examined.
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
For tangential radiography, the choice of radiation source should be determined by the maximum
penetrated thickness of the pipe, w , which occurs for the path forming a tangent to the pipe inner
max
diameter, as shown in Figure 3.
Key
1 detector, D
Figure 3 — Maximum penetrated thickness, w , for the tangential technique
max
The maximum penetrated thickness, w , is given by Formula (1):
max
wt=−2 Dt (1)
()
maxe
where
t is the nominal thickness of the pipe;
D is the outside diameter of the pipe.
e
Table 1 gives recommended limits on the maximum penetrated thickness for different radiation
sources.
ISO 20769-1:2018(E)
Some forms of insulation (e.g. highly absorbing) can lead to a reduction in the limits on maximum
penetrated thickness, w , given in Table 1.
max
By agreement between the contracting parties, these values may vary provided the position of the inner
diameter edge can be measured with acceptable accuracy on the resulting radiograph/digital image
using the methods described in 7.6 or 7.7.
Table 1 — Maximum penetrated thickness range for different radiation sources for steel
Limits on maximum penetrated thickness, w
max
Radiation source
mm
Basic Improved
(for generalized wall loss) (for pitting flaws)
X-ray (100 kV) ≤10 ≤7
X-ray (200 kV) ≤30 ≤20
X-ray (300 kV) ≤40 ≤30
X-ray (400 kV) ≤50 ≤35
Se 75 ≤55 ≤40
Ir 192 ≤80 ≤60
Co 60 ≤120 ≤85
For digital radiographs, somewhat higher values for the limits on maximum penetrated thickness than
those given in Table 1 may be used.
To determine the appropriate source(s) for a particular pipe, the maximum penetrated thickness, w ,
max
should be determined using Formula (1) and compared with the values given in Table 1. A graphical
illustration of this procedure is given in Annex B.
To avoid motion unsharpness, in cases where radiographs are produced using gamma rays, the total travel
time of the source to the exposure position and rewind shall not exceed 10 % of the total exposure time.
6.3 Film systems and metal screens
For radiographic examination, film system classes shall be used in accordance with ISO 11699-1.
The radiographic film system class and metal screens to use with films for different radiation sources
are given in Tables 2 and 3. See also ISO 17636-1:2013, Tables 2 and 3.
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 20769-1:2018(E)
Table 2 — Film system classes and metal screens for tangential radiography of steel, copper
and nickel based alloy pipes
a
Film system class
Radiation source Type and thickness of metal screens
Class TA Class TB
X-ray potentials
C 5 C 4 0,02 mm to 0,15 mm front and back screens of lead
≤250 kV
b
0,1 mm to 0,2 mm 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 back
C 5 C 4
c
>500 kV to 1 000 kV screens of steel or copper
Se 75
b
C 6 C 5 0,02 mm to 0,2 mm front and back screens of lead
Ir 192
0,25 mm to 0,7 mm front and back screens
Co 60 C 6 C 5
c
of steel or copper
X-ray equipment with
0,25 mm to 0,7 mm front and back screens
energy from C 6 C 5
c
of steel or copper
1 MeV to 4 MeV
d
Up to 1 mm front screen of copper, steel or tantalum
X-ray equipment with
C 6 C 5
Back screen of copper or steel up to 1 mm and
energy above 4 MeV
d
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 TA, 0,5 mm to 2,0 mm screens of lead may also be used.
d
In class TA, 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 tangential radiography of aluminium and
titanium pipes
a
Film system class
Radiation source Type and thickness of metal screens
Class TA Class TB
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
b
0,02 mm to 0,2 mm front and back screens of lead
C 6 C 5
>150 kV to 500 kV
Se 75
b
0,02 mm to 0,2 mm front and back screens of lead
Ir 192
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.
Different film systems may be used by agreement of the contracting parties, provided the required
optical densities defined in 7.2 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
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
ISO 20769-1:2018(E)
minimized. It is recommended that steel or copper shielding be used directly behind the IPs. Also, a
steel or copper shielding between a backscatter lead plate and the IP can 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 can 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.
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. The usage
of metal screens is recommended in front of IPs, and they can also reduce the influence of scattered
radiation when used with DDAs.
Table 4 — Metal front screens for CR for tangential radiography of steels, copper and nickel
based alloys
Type and thickness of metal front screens
Radiation source
mm
b
X-ray potentials ≤250 kV 0 to 0,1 (lead)
b
X-ray potentials >250 kV to 1 000 kV 0 to 0,3 (lead)
Class TA: 0 to 0,3 (lead)
b
Ir 192, Se 75
Class TB: 0,3 to 0,8 (steel or copper)
a
Co 60 0,3 to 0,8 (steel or copper) + 0,6 to 2,0 (lead)
a
X-ray potentials >1 MV 0,3 to 0,8 (steel or copper) + 0,6 to 2,0 (lead)
a
In the case of multiple screens (steel + lead), the steel screen shall be located between the IP and the lead screen.
Instead of steel or steel and lead screens, those composed of copper, tantalum or tungsten may be used if the image quality
can be proven.
b
Pb screens may be replaced completely or partially by Fe or Cu screens. The equivalent thickness for Fe or Cu is three
times the Pb thickness.
Table 5 — Metal front screens for CR for the digital tangential radiography of aluminium and
titanium
Type and thickness of metal front screens
Radiation source
mm
a,b
X-ray potentials <500 kV ≤0,2 (lead)
Se 75
a,b
≤0,3 (lead)
Ir 192
a
E.g. instead of 0,2 mm lead, a 0,1 mm screen with an additional filter of 0,1 mm may be used outside of the cassette.
b
Pb screens may be replaced completely or partially by Fe or Cu screens. The equivalent thickness for Fe or Cu is three
times the Pb thickness.
6.5 Reduction of scattered radiation
6.5.1 Filters and collimators
In order to reduce the effect of back scattered radiation, direct radiation shall be collimated as much as
possible to the section under examination.
12 © ISO 2018 – All rights reserved

ISO 20769-1:2018(E)
For computed radiography and radiography with DDAs, with Ir 192, Co 60 and other MeV radiation
sources, or in the case of edge scatter, an additional sheet of lead can be used as a filter of low energy
scattered radiation between the pipe and the DDA or CR cassette. The thickness of this sheet is 0,5 mm
to 2,0 mm in accordance with the penetrated thickness.
Materials other than lead such as tin, copper, tungsten, tantalum or steel can be used as a filter. It is
recommended that in the case of a lead, tungsten or tantalum filter an additional steel or copper filter is
used between the lead and the detector
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