SIST EN 17290:2021
(Main)Non-destructive testing - Ultrasonic testing - Examination for loss of thickness due to erosion and/or corrosion using the TOFD technique
Non-destructive testing - Ultrasonic testing - Examination for loss of thickness due to erosion and/or corrosion using the TOFD technique
This document specifies the application of the time-of-flight diffraction (TOFD) technique in testing of metals for quantifying loss of thickness due to erosion and/or corrosion.
This document applies to all types of corrosion or erosion damage, particularly those defined in ISO 16809.
This test applies to unalloyed or low-alloyed steel materials.
It applies to components with a nominal thickness ≥ 6 mm. For smaller thicknesses feasibility tests will be performed to validate the technique.
For other materials, feasibility tests are essential too.
The TOFD technique can be used here as a stand-alone technique or in combination with other non-destructive testing techniques, during manufacturing and for testing in-service, in order to detect material loss caused by erosion and/or corrosion.
This technique is based on analysis of TOFD images established using reflected and/or diffracted ultrasonic signals.
This document does not specify acceptance levels.
Zerstörungsfreie Prüfung - Ultraschallprüfung - Prüfung für den Verlust der Dicke aufgrund von Erosion und/oder Korrosion unter Anwendung der Beugungslaufzeittechnik (TOFD)
Dieses Dokument legt die Anwendung der Beugungslaufzeittechnik (en: time of flight diffraction, TOFD) bei der Prüfung von Metallen zur Quantifizierung von Dickenverlusten durch Erosion und/oder Korrosion fest.
Dieses Dokument gilt für alle Arten von Korrosions- oder Erosionsschäden, insbesondere für die in ISO 16809 festgelegten.
Diese Prüfung gilt für unlegierte oder niedrig legierte Stahlwerkstoffe.
Sie gilt für Bauteile mit einer Nenndicke von ≥ 6 mm. Für kleinere Dicken werden Machbarkeitsprüfungen durchgeführt, um die Technik zu bestätigen.
Auch für andere Werkstoffe sind Machbarkeitsprüfungen unerlässlich.
Die TOFD-Technik kann hier als eigenständige Technik oder in Kombination mit anderen zerstörungsfreien Prüftechniken verwendet werden, während der Herstellung oder für die betriebsbegleitende Prüfung, um durch Erosion und/oder Korrosion verursachten Werkstoffverlust festzustellen.
Diese Technik basiert auf der Auswertung von TOFD Bildern, die mit reflektierten und/oder gebeugten Ultraschallsignalen erstellt wurden.
Dieses Dokument legt keine Zulässigkeitsgrenzen fest.
Essais non destructifs - Contrôle par ultrasons - Examen de la perte d’épaisseur due à l’érosion et/ou à la corrosion par la technique TOFD
Le présent document spécifie l’application de la technique de diffraction du temps de vol (TOFD) pour le contrôle des métaux, afin de quantifier la perte d’épaisseur due à l’érosion et/ou à la corrosion.
Le présent document s’applique à tous les types d’endommagements par la corrosion ou par l’érosion, en particulier ceux définis dans l’ISO 16809.
Ce contrôle s’applique aux matériaux en acier non allié ou faiblement allié.
Il s’applique à tous les composants ayant une épaisseur nominale ≥ 6 mm. Pour les plus petites épaisseurs, des essais de faisabilité seront réalisés pour valider la technique.
Pour les autres matériaux, il est également indispensable de réaliser des essais de faisabilité.
La technique TOFD peut être utilisée ici de manière autonome ou en combinaison avec d’autres techniques d’essais non destructifs, lors de la fabrication et pour le contrôle en cours de service, afin de détecter la perte de matériau causée par l’érosion et/ou par la corrosion.
Cette technique repose sur l’analyse d’images TOFD établies à l’aide de signaux ultrasonores réfléchis et/ou diffractés.
Le présent document ne spécifie pas les niveaux d’acceptation.
Neporušitvene preiskave - Preskušanje z ultrazvokom - Preiskava za ugotavljanje izgube debeline zaradi erozije in/ali korozije z uporabo tehnike TOFD
General Information
Standards Content (Sample)
SLOVENSKI STANDARD
SIST EN 17290:2021
01-december-2021
Neporušitvene preiskave - Preskušanje z ultrazvokom - Preiskava za ugotavljanje
izgube debeline zaradi erozije in/ali korozije z uporabo tehnike TOFD
Non-destructive testing - Ultrasonic testing - Examination for loss of thickness due to
erosion and/or corrosion using the TOFD technique
Zerstörungsfreie Prüfung - Ultraschallprüfung - Prüfung für den Verlust der Dicke
aufgrund von Erosion und/oder Korrosion unter Anwendung der Beugungslaufzeittechnik
(TOFD)
Essais non destructifs - Contrôle par ultrasons - Examen de la perte d’épaisseur due à
l’érosion et/ou à la corrosion par la technique TOFD
Ta slovenski standard je istoveten z: EN 17290:2021
ICS:
19.100 Neporušitveno preskušanje Non-destructive testing
SIST EN 17290:2021 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST EN 17290:2021
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SIST EN 17290:2021
EN 17290
EUROPEAN STANDARD
NORME EUROPÉENNE
October 2021
EUROPÄISCHE NORM
ICS 19.100
English Version
Non-destructive testing - Ultrasonic testing - Examination
for loss of thickness due to erosion and/or corrosion using
the TOFD technique
Essais non destructifs - Contrôle par ultrasons - Zerstörungsfreie Prüfung - Ultraschallprüfung -
Examen de la perte d'épaisseur due à l'érosion et/ou à Prüfung für den Verlust der Dicke aufgrund von
la corrosion par la technique TOFD Erosion und/oder Korrosion unter Anwendung der
Beugungslaufzeittechnik (TOFD)
This European Standard was approved by CEN on 5 March 2021.
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, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, 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
© 2021 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 17290:2021 E
worldwide for CEN national Members.
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SIST EN 17290:2021
EN 17290:2021 (E)
Contents Page
European foreword . 3
1 Scope . 4
2 Normative references . 4
3 Terms and definitions . 5
4 General specifications . 5
4.1 General . 5
4.2 Limits of the test technique . 5
5 Qualification of personnel . 5
6 Test equipment . 5
6.1 Instrument . 5
6.2 Probes and TOFD set-up . 5
6.3 Encoder . 6
6.4 Combined equipment . 6
6.5 Reference blocks . 6
6.6 Couplant. 6
7 Application of the technique . 6
7.1 Surface condition . 6
7.2 Temperature . 6
7.3 Marking . 6
7.4 Selection of probes and PCS . 7
7.5 Instrument settings . 8
7.6 Testing . 9
8 Interpretation and analysis of TOFD images . 10
8.1 Validation of TOFD images . 10
8.2 Relevant indications . 10
8.3 Determination of dimensions and location . 11
9 Test report . 15
Annex A (informative) Example of a reference block . 17
Annex B (informative) Examples of typical TOFD images of loss of thickness due to erosion
and/or corrosion . 19
Bibliography . 22
2
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SIST EN 17290:2021
EN 17290:2021 (E)
European foreword
This document (EN 17290:2021) has been prepared by 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 2022, and conflicting national standards shall be
withdrawn at the latest by April 2022.
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.
Any feedback and questions on this document should be directed to the users’ national standards body.
A complete listing of these bodies can be found on the CEN website.
According to the CEN-CENELEC Internal Regulations, the national standards organisations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the
United Kingdom.
3
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SIST EN 17290:2021
EN 17290:2021 (E)
1 Scope
This document specifies the application of the time-of-flight diffraction (TOFD) technique in testing of
metals for quantifying loss of thickness due to erosion and/or corrosion.
This document applies to all types of corrosion and/or erosion damage, particularly those defined in
EN ISO 16809.
This document applies to unalloyed or low-alloyed steels.
It applies to components with a nominal thickness ≥ 6 mm. For smaller thicknesses, feasibility tests are
performed to validate the test technique.
For other materials, feasibility tests are essential, too.
The TOFD technique can be used as a stand-alone technique or in combination with other non-
destructive testing techniques, for in-service testing, in order to detect material loss caused by erosion
and/or corrosion.
This technique is based on analysis of TOFD images using reflected and/or diffracted ultrasonic signals.
This document does not specify acceptance levels.
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.
EN ISO 5577, Non-destructive testing — Ultrasonic testing — Vocabulary (ISO 5577)
EN ISO 9712, Non-destructive testing — Qualification and certification of NDT personnel (ISO 9712)
EN ISO 10863:2020, Non-destructive testing of welds — Ultrasonic testing — Use of time-of-flight
diffraction technique (TOFD) (ISO 10863:2020)
EN ISO 16828:2014, Non-destructive testing — Ultrasonic testing — Time-of-flight diffraction technique
as a method for detection and sizing of discontinuities (ISO 16828:2012)
EN ISO 17659, Welding — Multilingual terms for welded joints with illustrations (ISO 17659)
EN ISO 22232-1, Non-destructive testing — Characterization and verification of ultrasonic test equipment
— Part 1: Instruments (ISO 22232-1)
EN ISO 22232-2, Non-destructive testing — Characterization and verification of ultrasonic test equipment
— Part 2: Probes (ISO 22232-2)
EN ISO 22232-3, Non-destructive testing — Characterization and verification of ultrasonic test equipment
— Part 3: Combined equipment (ISO 22232-3)
4
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SIST EN 17290:2021
EN 17290:2021 (E)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in EN ISO 5577, EN ISO 10863 and
EN ISO 16828 apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at http://www.electropedia.org/
— ISO Online browsing platform: available at https://www.iso.org/obp
4 General specifications
4.1 General
The TOFD technique can be applied for thickness measurement on the body of components e.g. plates
and pipes, and on welded joints.
Testing and determination of thickness shall be carried out from the side opposite to the
eroded/corroded surface.
4.2 Limits of the test technique
For testing pipes and components in service, the limits described in EN ISO 16828 apply. The presence
of internal discontinuities can hamper the testing for loss of wall thickness.
When applied on welded joints, special precautions shall be taken for the following situations:
a) misalignment;
b) tapering; and
c) weld on permanent support.
Feasibility tests on representative welds are recommended before using the TOFD technique.
5 Qualification of personnel
The personnel performing the testing and interpreting the results shall have corresponding training
and experience in the field of ultrasonic testing. Additionally, the personnel shall be qualified to
properly perform TOFD UT in accordance with the requirements in EN ISO 9712 or equivalent.
6 Test equipment
6.1 Instrument
The ultrasonic instrument used for testing shall comply with the requirements of EN ISO 22232-1.
6.2 Probes and TOFD set-up
The ultrasonic probes used for the TOFD technique shall comply with the requirements of
EN ISO 22232-2.
The selection of probe characteristics is covered in 7.4.
The maximum diffraction efficiency occurs when the included angle is about 120°. The probes should be
arranged such that the beam axes intersect at about this angle in the depth region to be tested.
5
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SIST EN 17290:2021
EN 17290:2021 (E)
Deviations of more than –35° or +45° from this value may cause the diffracted echoes to be weak and
should not be used unless detection capabilities can be demonstrated.
The probe support mechanism shall ensure constant probe centre separation (PCS) within ± 1 mm and
constant alignment between the index points.
6.3 Encoder
Information on the position shall be provided by an encoding system.
The encoding system shall be compatible with the acceptance levels specified for the spatial resolution.
6.4 Combined equipment
Any combined equipment (instrument, probes and cables) that is used shall comply with the
requirements of EN ISO 16828 and EN ISO 22232-3.
6.5 Reference blocks
The use of one or more reference blocks is recommended.
The reference block(s) should be made of a material with acoustic properties equivalent to those of the
test object, at least with regard to sound velocity, surface condition, and geometry.
The thickness of reference blocks is recommended to be between 0,8 and 1,5 times the thickness of the
test object with a maximum difference in thickness of 20 mm compared to the test object.
The characteristics of the reference reflectors (type, size, geometry, dimensions, position, accuracy of
implementation) shall be in accordance with the expected erosion and/or corrosion. They may be flat-
bottomed holes, hemispherically-bottomed holes, side-drilled holes, EDM notches, or other shapes, if
applicable.
An example of a reference block is given in Annex A, Figures A.1, A.2, A.3 and A.4.
6.6 Couplant
The same couplant shall be used for the settings and for the testing.
7 Application of the technique
7.1 Surface condition
The test surface shall be free of loose scale, dried coupling medium and any other product or surface
irregularity that may interfere with the transmission of ultrasound into the test object, or that may
hinder free movement of the probes or probe holders. The surface roughness, R , shall not be greater
a
than 12,5 µm. The surface should be ground if needed.
It is possible to perform testing through adhered paint or coating, provided that the test performance is
checked.
7.2 Temperature
The surface temperature of the test object shall not exceed 50 °C, unless suitable probes and couplant
are used and a correction for the temperature is performed.
7.3 Marking
The tested zones shall be marked and the references used shall be documented to allow the zones to be
identified and any discontinuities to be located.
6
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SIST EN 17290:2021
EN 17290:2021 (E)
7.4 Selection of probes and PCS
The TOFD setup (transmitter probe, receiver probe and PCS) depends on the thickness of the zone to be
tested.
The thickness value to be considered for the probe selections and the settings can be determined by one
of the following cases:
1) Nominal thickness (specified by the client);
2) Reference thickness (determined by an earlier measurement);
3) Thickness measured next to the eroded and/or corroded zone, but not affected by corrosion and/or
erosion.
The value of the chosen thickness shall be reported together with the used case.
For welds joining two different thicknesses, the settings shall be based on the thinner of the two.
As a guideline, Table 1 provides recommended parameters for probe selection, when using longitudinal
waves.
Table 1 — Recommended TOFD probe parameters
Wall thickness T Centre frequency Nominal probe angle Transducer dimensions
(mm) (MHz) (°) (mm)
6 to 10 15 70 2 to 3
10 to 15 10 to 15 70 2 to 3
15 to 35 5 to 10 60 to 70 2 to 6
35 to 50 3 to 5 60 to 70 3 to 6
50 to 100 3 to 5 45 to 60 6 to 12
100 to 200 2 to 5 45 to 60 6 to 20
200 to 300 1 t
...
SLOVENSKI STANDARD
oSIST prEN 17290:2018
01-november-2018
Neporušitveno preskušanje - Preskušanje z ultrazvokom - Preiskava za
ugotavljanje izgube debeline zaradi erozije in/ali korozije z uporabo tehnike TOFD
Non-destructive testing - Ultrasonic testing - Examination for loss of thickness due to
erosion and/or corrosion using the TOFD technique
Zerstörungsfreie Prüfung - Ultraschallprüfung - Prüfung für den Verlust der Dicke
aufgrund von Erosion und/oder Korrosion unter Anwendung der Beugungslaufzeittechnik
(TOFD)
Essais non destructifs - Contrôle par ultrasons - Examen de la perte d’épaisseur due à
l’érosion et/ou à la corrosion par la technique TOFD
Ta slovenski standard je istoveten z: prEN 17290
ICS:
19.100 Neporušitveno preskušanje Non-destructive testing
oSIST prEN 17290:2018 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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oSIST prEN 17290:2018
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oSIST prEN 17290:2018
DRAFT
EUROPEAN STANDARD
prEN 17290
NORME EUROPÉENNE
EUROPÄISCHE NORM
September 2018
ICS 19.100
English Version
Non-destructive testing - Ultrasonic testing - Examination
for loss of thickness due to erosion and/or corrosion using
the TOFD technique
Essais non destructifs - Contrôle par ultrasons - Zerstörungsfreie Prüfung - Ultraschallprüfung -
Examen de la perte d'épaisseur due à l'érosion et/ou à Prüfung für den Verlust der Dicke aufgrund von
la corrosion par la technique TOFD Erosion und/oder Korrosion unter Anwendung der
Beugungslaufzeittechnik (TOFD)
This draft European Standard is submitted to CEN members for enquiry. It has been drawn up by the Technical Committee
CEN/TC 138.
If this draft becomes a European Standard, 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.
This draft European Standard was established by CEN 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.
Recipients of this draft are invited to submit, with their comments, notification of any relevant patent rights of which they are
aware and to provide supporting documentation.
Warning : This document is not a European Standard. It is distributed for review and comments. It is subject to change without
notice and shall not be referred to as a European Standard.
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. prEN 17290:2018 E
worldwide for CEN national Members.
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oSIST prEN 17290:2018
prEN 17290:2018 (E)
Contents Page
European foreword . 4
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 6
4 General specifications . 6
4.1 General . 6
4.2 Limits of the technique . 6
5 Test equipment . 6
5.1 Instrument . 6
5.2 Probes and TOFD set-up . 6
5.3 Encoder . 6
5.4 Combined equipment . 7
5.5 Reference blocks . 7
5.6 Couplant. 7
6 Application of the technique . 7
6.1 Surface condition . 7
6.2 Temperature . 7
6.3 Marking . 7
6.4 Selection of probes and PCS . 7
6.5 Instrument settings . 8
6.5.1 Time window . 8
6.5.2 Time-to-depth conversion . 9
6.5.3 Sensitivity setting . 9
6.5.4 Checking of the combined equipment . 9
6.6 Testing . 10
6.6.1 General . 10
6.6.2 Scan plan . 10
6.6.3 Complementary evaluation . 10
6.6.4 Scan increment . 10
6.6.5 Displacement speed . 10
7 Interpretation and analysis of TOFD images . 11
7.1 Validation of TOFD images . 11
7.2 Relevant indications . 11
7.3 Determination of dimensions and location . 11
7.3.1 General . 11
7.3.2 Discontinuity height . 15
7.3.3 Location of a discontinuity in the plane parallel to the scanning surface . 15
7.3.4 Length of discontinuity . 16
8 Qualification of personnel . 16
9 Test report . 16
Annex A (informative) Example of a reference block . 18
Annex B (informative) Examples of typical TOFD images of thickness loss due to
corrosion/erosion . 20
2
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oSIST prEN 17290:2018
prEN 17290:2018 (E)
Annex C (informative) Example of reference coordinates for the localization of thickness
loss . 23
Bibliography . 24
3
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oSIST prEN 17290:2018
prEN 17290:2018 (E)
European foreword
This document (prEN 17290:2018) has been prepared by Technical Committee CEN/TC 138 “Non-
destructive testing”, the secretariat of which is held by AFNOR.
This document is currently submitted to the CEN Enquiry.
4
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oSIST prEN 17290:2018
prEN 17290:2018 (E)
1 Scope
This document specifies the application of the time-of-flight diffraction (TOFD) technique in testing of
metals for quantifying loss of thickness due to erosion and/or corrosion.
This document applies to all types of corrosion or erosion damage, particularly those defined in
ISO 16809.
This test applies to unalloyed or low-alloyed steel materials.
It applies to components with a nominal thickness ≥ 6 mm. For smaller thicknesses feasibility tests will
be performed to validate the technique.
For other materials, feasibility tests are essential too.
The TOFD technique can be used here as a stand-alone technique or in combination with other non-
destructive testing techniques, during manufacturing and for testing in-service, in order to detect
material loss caused by erosion and/or corrosion.
This technique is based on analysis of TOFD images established using reflected and/or diffracted
ultrasonic signals.
This document does not specify acceptance levels.
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.
EN 12668-1, Non-destructive testing - Characterization and verification of ultrasonic examination
equipment – Part 1: Instruments
EN 12668-2, Non-destructive testing - Characterization and verification of ultrasonic examination
equipment – Part 2: Probes
EN 12668-3:2013, Non-destructive testing - Characterization and verification of ultrasonic examination
equipment – Part 3: Combined equipment
EN ISO 5577, Non-destructive testing - Ultrasonic testing - Vocabulary (ISO 5577)
EN ISO 9712, Non-destructive testing - Qualification and certification of NDT personnel (ISO 9712)
EN ISO 10863:2011, Non-destructive testing of welds - Ultrasonic testing - Use of time-of-flight diffraction
technique (TOFD) (ISO 10863:2011)
EN ISO 15626:2013, Non-destructive testing of welds - Time-of-flight diffraction technique (TOFD) -
Acceptance levels (ISO 15626:2011)
EN ISO 16828:2014, Non-destructive testing - Ultrasonic testing - Time-of-flight diffraction technique as a
method for detection and sizing of discontinuities (ISO 16828:2012)
EN ISO 17659, Welding - Multilingual terms for welded joints with illustrations (ISO 17659)
5
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oSIST prEN 17290:2018
prEN 17290:2018 (E)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in EN ISO 5577, EN ISO 16828 and
EN ISO 10863 apply.
4 General specifications
4.1 General
The TOFD technique can be applied for thickness measurement on the body of components, pipes and
along welded joints.
Testing and determination of thickness shall be carried out from the opposite side of the corroded
surface.
4.2 Limits of the technique
For pipes, components and instrument sleeves in service, the limits described in EN ISO 16828 apply.
The presence of internal discontinuities can hamper the testing for loss of wall thickness.
When applied on welded joints, special precautions for use shall be taken when discontinuities of the
following types are present:
a) separation;
b) misalignment;
c) tapering; and
d) weld on permanent support.
Feasibility tests on representative welds are recommended before using the TOFD technique.
5 Test equipment
5.1 Instrument
The ultrasonic instrument used for the examination complies with the requirements of EN 12668-1 and
EN ISO 16828.
5.2 Probes and TOFD set-up
The ultrasonic probes used for the TOFD technique shall comply with the requirements of EN 12668-2
and EN ISO 16828. The selection of probe characteristics is covered in 6.4.
The maximum diffraction efficiency occurs when the included angle is about 120°. The probes should be
arranged such that the beam axes intersect at about this angle in the depth region to be tested.
Deviations of more than – 35° or + 45° from this value may cause the diffracted echoes to be weak and
should not be used unless detection capabilities can be demonstrated.
The probe support mechanism shall ensure probe centre separation (PCS) within ± 1 mm and constant
alignment between the index points.
5.3 Encoder
Information on the position shall be provided by an encoding system.
The encoding system shall be compatible with the acceptance levels specified for the spatial resolution.
6
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oSIST prEN 17290:2018
prEN 17290:2018 (E)
5.4 Combined equipment
Any combined equipment (instrument, probes and cables) that is used shall comply with the
requirements of EN ISO 16828 and at least fulfil the checks specified in EN 12668-3:2013, 3.2.1, 3.2.2,
3.4.2, 3.4.3, 3.4.4, and 5.7.4 of this document.
5.5 Reference blocks
The use of one or more reference blocks is recommended.
The reference blocks should be made of a material with acoustic properties equivalent to those of the
test object, at least with regard to sound velocity, surface condition, and geometry.
When using the TOFD technique for thickness measurement of welded joints, at least one reference
block with a weld is recommended.
Thickness of reference blocks is recommended to be between 0,8 and 1,2 times the thickness of the test
object with a maximum difference in thickness of 20 mm compared to the test object.
The geometry of reference reflectors depends on the profile of corrosion to be covered by the test. They
may be flat-bottomed holes, hemispherically-bottomed holes, side-drilled holes, EDM notches.
The characteristics of the reference reflectors (type, size, geometry, dimensions, position, accuracy of
implementation) shall be in accordance with the expected performance levels.
An example of a reference block is given in Annex A.
5.6 Couplant
The same couplant shall be used for the settings and for the testing.
6 Application of the technique
6.1 Surface condition
The test surface being examined shall be free of paint, loose scale, dried coupling medium and any other
product or surface irregularity that may interfere with the transmission of ultrasound into the test
object, or that may hinder free movement of the probes or probe holders. The surface roughness, Ra,
shall not be greater than 12,5 µm. The surface should be ground if needed.
It is allowed to perform testing through the paint (adherent coating) on parts of piping, provided that
the test performance is checked.
6.2 Temperature
The surface temperature of the object shall not exceed 50 °C, unless suitable probes and couplant are
used and a correction for the temperature is performed.
6.3 Marking
The tested zones examined shall be marked and the references used shall be documented to allow the
zones to be identified and any discontinuities to be located.
6.4 Selection of probes and PCS
The TOFD set-up (transmitter probe, receiver probe and PCS) is defined by the thickness of th
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