SIST-TS CEN/TS 14751:2005

Welding - Use of time-of-flight diffraction technique (TOFD) for examination of welds

This document specifies the application of the time-of-flight diffraction (TOFD) technique for the semi-, or fully- automated ultrasonic testing of fusion welded joints in metallic materials equal to and above 6 mm thickness. It is primarily intended for use on full penetration welded joints of simple geometry in plates, pipes, and vessels, where both the weld and parent material are low alloyed carbon steel. Where specified and appropriate, TOFD may also be used on other types of materials that exhibit low ultrasonic attenuation (especially that due to scatter).
Where material dependent ultrasonic parameters are specified in this document, they are based on steels having a sound velocity of (5920 ± 50) m/s for longitudinal waves, and (3255 ± 30) m/s for transverse waves. This has to be taken into account when examining materials with a different velocity.
This document makes reference to the basic pre-standard ENV 583 6 and provides guidance on the specific capabilities and limitations of TOFD for the detection, location, sizing and characterisation of discontinuities in fusion welded joints. TOFD may be used as a stand-alone method or in combination with other NDT methods or techniques, both for manufacturing inspection (pre-service) and for in-service inspection.
This document specifies four examination levels (A, B, C, D) corresponding to an increasing level of inspection reliability. Guidance on the selection of examination levels is provided.
This document permits assessment of indications for acceptance purposes. This assessment is based on the evaluation of transmitted, reflected and diffracted ultrasonic signals within a generated TOFD image.
This document does not include acceptance levels for discontinuities.

Schweißverbindungen - Anwendung der Beugungslaufzeittechnik (TOFD) für die Prüfung von Schweißverbindungen

Diese Technische Spezifikation legt die Anwendung der Beugungslaufzeit- (TOFD-)Technik bei der halb- oder vollautomatischen Ultraschallprüfung von Schmelzschweißverbindungen in metallischen Werkstoffen mit einer Dicke von mindestens 6 mm fest. Sie ist insbesondere für die Anwendung an durchgeschweißten Verbindungen einfacher Geometrie in Platten, Rohren und Behältern vorgesehen, bei denen Schweißnaht und Grundwerkstoff aus niedriglegiertem Kohlenstoffstahl bestehen. Sofern festgelegt und sinnvoll, darf die TOFD-Technik auch auf andere Werkstoffarten angewendet werden, die eine geringe Ultraschallschwächung aufweisen (dies gilt insbesondere für die durch Streuung verursachte Ultraschallschwächung).
Sofern in dieser Technischen Spezifikation werkstoffabhängige Ultraschallparameter festgelegt sind, beruhen diese auf Stählen mit einer Schallgeschwindigkeit von (5 920 ± 50) m/s für Longitudinalwellen und (3 255 ± 30) m/s für Transversalwellen. Dies ist bei der Prüfung von Werkstoffen mit anderer Schallgeschwin-digkeit zu berücksichtigen.
Die vorliegende Technische Spezifikation nimmt Bezug auf die Vornorm ENV 583-6 und liefert einen Leitfaden hinsichtlich der besonderen Fähigkeiten und Einschränkungen der TOFD-Technik beim Auffinden, der Ortung, dem Ausmessen und der Charakterisierung von Inhomogenitäten in Schmelzschweißverbindungen. Die TOFD-Technik darf selbständig oder in Verbindung mit weiteren Verfahren oder Techniken der zerstörungsfreien Prüfung sowohl für die Prüfung während der Herstellung (vor der Inbetriebnahme) als auch für die Prüfung während des Betriebes angewendet werden.
Diese Technische Spezifikation legt vier Prüfklassen (A, B, C, D) fest, die einem zunehmenden Grad der Zuverlässigkeit der Prüfung entsprechen. Ein Leitfaden für die Auswahl der Prüfklassen wird angeführt.
Die vorliegende Technische Spezifikation erlaubt die Beurteilung von Anzeigen zum Zwecke der Bestimmung der Zulässigkeit. Diese Beurteilung beruht auf der Bewertung übertragener,

Soudage - Utilisation de la technique de diffraction des temps de vol (méthode TOFD) pour le contrôle des soudures

Le présent document spécifie l?application de la technique de diffraction des temps de vol (méthode TOFD)
pour le contrôle par ultrasons semi-automatique ou entierement automatique des assemblages soudés par
fusion de matériaux métalliques d?épaisseur égale ou supérieure a 6 mm. Cette technique est essentiellement
destinée a etre utilisée sur des joints soudés a pleine pénétration de géométrie simple sur plaques, tubes et
récipients dans lesquels le métal de base et le métal fondu sont tous les deux constitués d?acier au carbone
faiblement allié. Dans le cas ou son utilisation est spécifiée et qu?elle s?avere appropriée, la méthode TOFD
peut également etre utilisée sur d?autres types de matériaux qui présentent une atténuation ultrasonore faible
(spécialement celle due a la dispersion).
Lorsque les parametres ultrasonores dépendant du matériau sont spécifiés dans le présent document, ils sont
basés sur les aciers qui présentent une vitesse de propagation sonore de (5920 ± 50) m/s pour les ondes
longitudinales et (3 255 ± 30) m/s pour les ondes transversales. Cette condition doit etre prise en compte lors
de l?examen de matériaux ayant des vitesses de propagation différentes.
Le présent document fait référence a la pré-norme de base ENV 583-6 et fournit des lignes directrices sur les
possibilités et les limitations spécifiques de la méthode TOFD pour la détection, la localisation, le
dimensionnement et la caractérisation des discontinuités dans les joints soudés par fusion. La méthode TOFD
peut etre utilisée de maniere autonome ou en combinaison avec d?autres méthodes ou techniques de contrôle
non-destructif, aussi bien pour le contrôle de fabrication (avant service) que pour le contrôle en cours de
service.

Varjenje – Uporaba tehnike zvočne poti (TOFD) za preiskavo zvarov

General Information

• Status: Withdrawn
• Publication Date: 31-Dec-2004
• Withdrawal Date: 13-Sep-2011
• ICS: 25.160.40 - Welded joints and welds
• Technical Committee: VAR - Welding
• Current Stage: 9900 - Withdrawal (Adopted Project)
• Start Date: 13-Sep-2011
• Due Date: 06-Oct-2011
• Completion Date: 14-Sep-2011
• Ref Project: CEN/TS 14751:2004 - Welding - Use of time-of-flight diffraction technique (TOFD) for examination of welds

Relations

• Replaced By: SIST EN ISO 10863:2011 - Non-destructive testing of welds - Ultrasonic testing - Use of time-of-flight diffraction technique (TOFD) (ISO 10863:2011)
• Effective Date: 01-Nov-2011

Standards Content (Sample)

SLOVENSKI STANDARD
SIST-TS CEN/TS 14751:2005
01-januar-2005
9DUMHQMH±8SRUDEDWHKQLNH]YRþQHSRWL72)']DSUHLVNDYR]YDURY
Welding - Use of time-of-flight diffraction technique (TOFD) for examination of welds
Schweißverbindungen - Anwendung der Beugungslaufzeittechnik (TOFD) für die Prüfung
von Schweißverbindungen
Soudage - Utilisation de la technique de diffraction des temps de vol (méthode TOFD)
pour le contrôle des soudures
Ta slovenski standard je istoveten z: CEN/TS 14751:2004
ICS:
25.160.40 Varjeni spoji in vari Welded joints
SIST-TS CEN/TS 14751:2005 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST-TS CEN/TS 14751:2005

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SIST-TS CEN/TS 14751:2005
TECHNICAL SPECIFICATION
CEN/TS 14751
SPÉCIFICATION TECHNIQUE
TECHNISCHE SPEZIFIKATION
November 2004
ICS 25.160.40
English version
Welding - Use of time-of-flight diffraction technique (TOFD) for
examination of welds
Soudage - Utilisation de la technique de diffraction des Schweißverbindungen - Anwendung der
temps de vol (méthode TOFD) pour le contrôle des Beugungslaufzeittechnik (TOFD) für die Prüfung von
soudures Schweißverbindungen
This Technical Specification (CEN/TS) was approved by CEN on 11 July 2004 for provisional application.
The period of validity of this CEN/TS is limited initially to three years. After two years the members of CEN will be requested to submit their
comments, particularly on the question whether the CEN/TS can be converted into a European Standard.
CEN members are required to announce the existence of this CEN/TS in the same way as for an EN and to make the CEN/TS available
promptly at national level in an appropriate form. It is permissible to keep conflicting national standards in force (in parallel to the CEN/TS)
until the final decision about the possible conversion of the CEN/TS into an EN is reached.
CEN members are the national standards bodies of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France,
Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia,
Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36  B-1050 Brussels
© 2004 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN/TS 14751:2004: E
worldwide for CEN national Members.

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SIST-TS CEN/TS 14751:2005
CEN/TS 14751:2004 (E)
Contents Page
Foreword.4
1 Scope .5
2 Normative references .5
3 Terms and definitions .6
4 General remarks on the capabilities of the technique.6
5 Examination levels.7
6 Information required prior to testing .7
6.1 Items to be defined by specification.7
6.2 Specific information required by the operator before testing .8
6.3 Written test instruction .8
7 Requirements for personnel and equipment .8
7.1 Personnel qualifications .8
7.2 Equipment .8
7.2.1 Ultrasonic equipment and display .8
7.2.2 Ultrasonic probes .9
7.2.3 Scanning mechanisms.9
8 Preparation for testing .9
8.1 Volume to be inspected .9
8.2 Set up of probes.9
8.3 Scan increment setting .10
8.4 Geometry considerations .10
8.5 Preparation of scanning surfaces.11
8.6 Temperature .11
8.7 Couplant .11
8.8 Provision of datum points .11
9 Testing of base material.11
10 Range and sensitivity settings.11
10.1 Settings.11
10.1.1 General.11
10.1.2 Time window .11
10.1.3 Time-to-depth conversion.12
10.1.4 Sensitivity settings .12
10.2 Checking of the settings .12
10.3 Reference blocks .13
10.3.1 General.13
10.3.2 Material .13
10.3.3 Dimensions and shape.13
10.3.4 Reference reflectors .13
11 Weld testing.14
12 Interpretation and analysis of TOFD images .14
12.1 General.14
12.2 Assessing the quality of the TOFD image.14
12.3 Identification of relevant indications .15
12.4 Classification of relevant indications .15
12.4.1 General.15
12.4.2 Indications from surface breaking discontinuities .15
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12.4.3 Indications from embedded discontinuities.16
12.4.4 Unclassified indications .16
12.5 Determination of location and size.16
12.5.1 Location.16
12.5.2 Sizing .16
12.6 Evaluation against acceptance criteria.16
13 Test report.17
13.1 General .17
13.2 Information relating to object under test .17
13.3 Information relating to equipment .17
13.4 Information relating to test technique.17
13.5 Information relating to test results .17
Annex A (informative) Reference blocks .18
A.1 Thickness requirements .18
A.1.1 Maximum thickness .18
A.1.2 Minimum thickness .18
A.2 Reference reflectors.19
A.3 Typical reference blocks.21
Annex B (informative) Examples of typical scans .23
B.1 Satisfactory and unsatisfactory TOFD-images .23
B.2 Typical TOFD-images of discontinuities in fusion welded joints.28
B.3 TOFD-images of geometrical features .32
Bibliography.35

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SIST-TS CEN/TS 14751:2005
CEN/TS 14751:2004 (E)
Foreword
This document (CEN/TS 14751:2004) has been prepared by Technical Committee CEN/TC 121 “Welding”,
the secretariat of which is held by DIN.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following
countries are bound to announce this Technical Specification: Austria, Belgium, Czech Republic, Denmark,
Finland, France, Germany, Greece, Hungary Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway,
Portugal, Slovakia, Spain, Sweden, Switzerland and the United Kingdom.
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SIST-TS CEN/TS 14751:2005
CEN/TS 14751:2004 (E)
1 Scope
This document specifies the application of the time-of-flight diffraction (TOFD) technique for the semi-, or fully-
automated ultrasonic testing of fusion welded joints in metallic materials equal to and above 6 mm thickness.
It is primarily intended for use on full penetration welded joints of simple geometry in plates, pipes, and
vessels, where both the weld and parent material are low alloyed carbon steel. Where specified and
appropriate, TOFD may also be used on other types of materials that exhibit low ultrasonic attenuation
(especially that due to scatter).
Where material dependent ultrasonic parameters are specified in this document, they are based on steels
having a sound velocity of (5920 ± 50) m/s for longitudinal waves, and (3255 ± 30) m/s for transverse waves.
This has to be taken into account when examining materials with a different velocity.
This document makes reference to the basic pre-standard ENV 583-6 and provides guidance on the specific
capabilities and limitations of TOFD for the detection, location, sizing and characterisation of discontinuities in
fusion welded joints. TOFD may be used as a stand-alone method or in combination with other NDT methods
or techniques, both for manufacturing inspection (pre-service) and for in-service inspection.
This document specifies four examination levels (A, B, C, D) corresponding to an increasing level of
inspection reliability. Guidance on the selection of examination levels is provided.
This document permits assessment of indications for acceptance purposes. This assessment is based on the
evaluation of transmitted, reflected and diffracted ultrasonic signals within a generated TOFD image.
This document does not include acceptance levels for discontinuities.
2 Normative references
The following referenced documents are indispensable for the application 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 473, Non destructive testing — Qualification and certification of NDT personnel — General principles.
EN 583-1, Non-destructive testing — Ultrasonic examination — Part 1: General principles.
ENV 583-6, Non-destructive testing — Ultrasonic examination — Part 6: Time-of-flight diffraction technique as
a method for detection and sizing of discontinuities.
EN 1330-4:2000, Non-destructive testing — Terminology — Part 4: Terms used in ultrasonic testing.
EN 1714, Non destructive examination of welds — Ultrasonic examination of welded joints.
EN 12062, Non destructive examination of welds — General rules for metallic materials.
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, Non-destructive testing — Characterization and verification of ultrasonic examination
equipment —Part 3: Combined equipment.
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3 Terms and definitions
For the purposes of this document, the terms and definitions given in EN 1330-4:2000 and the following apply:
3.1
TOFD set-up
probe arrangement defined by probe characteristics (e.g. frequency, probe element-size, beam-angle, wave
mode) and probe centre separation (PCS)
3.2
probe centre separation (PCS)
distance between the index-points of the two probes. For curved surfaces it is the shortest distance between
the index-points
3.3
beam intersection point
point of intersection of the two main beam-axes
3.4
indication
pattern or disturbance, in the TOFD image which may need further evaluation
3.5
TOFD image
two-dimensional image, constructed by collecting adjacent A-scans while moving the TOFD set-up. The
signal-amplitude of the A-scans is typically represented by grey-scale values
3.6
offset-scan
scan parallel to the weld-axis, where the beam intersection point is not on the centre-line of the weld
4 General remarks on the capabilities of the technique
General principles of the TOFD-technique are described in ENV 583-6. For the testing of fusion welded joints
some specific capabilities and limitations of the technique have to be considered.
The TOFD technique is an ultrasonic image-generating technique, which offers the capability of detection,
location and sizing. To a certain extent characterisation of discontinuities in the weld material as well as in the
adjacent parent material is also possible.
Compared with purely reflection-based techniques, the TOFD technique, which is based upon diffraction as
well as reflection, is less sensitive to the orientation of the discontinuity. Discontinuities oriented perpendicular
to the surface, and at intermediate angles of tilt, are detectable as well as discontinuities in the weld fusion
faces.
In certain circumstances (thickness, weld preparation, scope of testing etc) more than one single TOFD set-up
is required.
A typical TOFD image is linear in time (vertical axis) and probe movement (horizontal axis). Because of the V-
geometry of the ultrasound paths, the location of a possible discontinuity is then non-linear. Similar to the
generation of radiographic images, a TOFD testing has to be carried out in a correct and consistent way, such
that valid images are generated which can be evaluated correctly. For example coupling losses and data
acquisition errors have to be avoided, see 12.2.
The interpretation of TOFD-images requires skilled and experienced operators. Some typical TOFD-images of
discontinuities in fusion welded joints are provided in Annex B.
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There is a reduced capability for the detection of discontinuities close to or connected with the scanning
surface or with the opposite surface. This has to be considered especially for crack-sensitive steels or at in-
service inspections. In cases where full coverage of these zones is required, additional measures shall be
taken. By example, TOFD can be accompanied by other NDT-methods or -techniques, e.g. conventional
pulse-echo testing, see EN 1714.
Diffracted signals from weld-discontinuities have small amplitudes comparable to grain-scatter signals from
coarse-grained materials which may hinder the detection and evaluation of discontinuities.
5 Examination levels
This document specifies four examination levels (A, B, C and D). From examination level A to examination
level C an increasing reliability will be achieved.
Table 1 — Examination levels
examination TOFD set-up reference block for reference block for offset-scan Written
level set-up verification sensitivity settings test
(see 8.2) (see 10.1.4) instruction
A acc. to Table 2 no No no this TS
B acc. to Table 2 no Yes no this TS
a
C acc. to Table 2 yes Yes yes
a
D as specified yes Yes yes
a
the necessity, number of and position of offset scans has to be determined

For pre-service inspections (see also EN 12062) all examination levels are applicable. Level A is only
applicable for wall-thickness up to 50 mm. For in-service inspections only examination level D shall be applied.
If the specified acceptance criteria require detection of a certain size of discontinuities at both or one surface
of the weld (see Clause 4) this may necessitate the use of techniques or methods outside the scope of this
document.
6 Information required prior to testing
6.1 Items to be defined by specification
Information on the following items is required:
a) purpose and extent of TOFD testing (see Clauses 5 and 8);
b) examination levels (see Clause 5), e.g.
 whether or not a written test instruction is required;
 whether or not reference blocks are required;
c) specification of reference blocks, if required (see 10.3);
d) manufacturing or operation stage at which the testing is to be carried out;
e) requirements for access and surface conditions (see Clause 8) and temperature;
f) reporting requirements (see Clause 13);
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g) acceptance criteria;
h) personnel qualifications (see 7.1).
6.2 Specific information required by the operator before testing
Before any testing of a welded joint can begin, the operator shall have access to all the information as
specified in Clause 6.1 together with the following additional information:
a) written test instruction (see 6.3), if required;
b) type(s) of parent material and product form (i.e. cast, forged, rolled);
c) joint preparation and dimensions;
d) welding instruction or relevant information on the welding process;
e) time of inspection relative to any post-weld heat treatment;
f) result of any parent metal testing carried out prior to and/or after welding.
6.3 Written test instruction
For examination levels A and B, this document satisfies the need for a written test instruction.
Where this is not the case, or where the techniques described in this document are not applicable to the
welded joint to be tested, specific written test instructions shall be used.
7 Requirements for personnel and equipment
7.1 Personnel qualifications
In addition to a general knowledge of ultrasonic weld inspection, all personnel shall be competent in TOFD
inspections. Documented evidence of their competence (training, experience) is required.
Preparation of written test instruction, final off-line analysis of data, and acceptance of the report shall be
performed by personnel certified as a minimum to level 2 in accordance with EN 473 or equivalent in
ultrasonic testing in the relevant industrial sector.
Equipment set-up, data acquisition, data storage, and report preparation shall be performed by personnel
certified as a minimum to level 1 in accordance with EN 473 or equivalent in ultrasonic testing in the relevant
industrial sector.
For data acquisition the level-1 person may be supported by an assistant technician.
In cases where the above minimum qualifications are not considered adequate, job-specific training shall be
carried out.
7.2 Equipment
7.2.1 Ultrasonic equipment and display
Ultrasonic equipment used for the TOFD technique shall, where applicable, comply with the requirements of
EN 12668-1, EN 12668-2 and EN 12668-3.
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In addition, the requirements of ENV 583-6 shall apply taking into account the following:
 The equipment shall be able to select an appropriate portion of the time base within which A-scans are
digitised;
 It is recommended to use a sampling rate of the A-scan of at least 6 times the nominal probe frequency.
7.2.2 Ultrasonic probes
Ultrasonic probes used for the TOFD technique on welds shall comply with ENV 583-6.
Adaptation of probes to curved scanning surfaces shall comply with EN 1714.
A recommendation for the selection of probes is given in Table 2.
7.2.3 Scanning mechanisms
The requirements of ENV 583-6 shall apply. To achieve consistency of the images (collected data), guiding
mechanisms may be used.
8 Preparation for testing
8.1 Volume to be inspected
Testing shall be performed in accordance with ENV 583-6. The purpose of the testing shall be defined by
specification. Based on this the volume to be inspected shall be determined.
The volume to be inspected is located between the probes. For examination levels A and B the probes shall
be placed symmetrically to the weld centre line. For examination levels C and D additional offset-scans may
be required.
For manufacturing examinations (pre-service inspection) the examination volume is defined as the zone which
includes weld and parent material for at least 10 mm on each side of the weld, or the width of the heat
affected zone, whichever is greater. In all cases the whole examination volume shall be covered.
Normally these examinations are carried out according to recognised standards applying acceptance levels
for quality assurance. If fitness-for-purpose methods are applied, then corresponding acceptance criteria shall
be specified.
For in-service inspections, the examination volume may be targeted to specify areas of interest, e.g. the inner
1/3 of the weld body. The acceptance criteria and minimum size discontinuity to be detected in the area of
interest shall be specified.
8.2 Set up of probes
The probes shall be set up to ensure adequate coverage and optimum conditions for the initiation and
detection of diffracted signals in the area of interest. For butt welds of simple geometry and with narrow weld
crowns at the opposite surface the testing shall be performed in one or more set-ups (scans) dependent upon
the wall thickness (see Table 2). For other configurations, e.g. X-shaped welds, different base metal thickness
at either side of the weld, or tapering, Table 2 may be used as guidance. In this case, effectiveness and
coverage shall be verified by the use of reference blocks.
Selection of probes for full coverage of the complete weld thickness (typically pre-service inspection) should
follow Table 2. Care should be taken to choose appropriate combinations of parameters. For example, in the
thickness range 15 mm to 35 mm a frequency of 10 MHz, a beam-angle of 70° and an element-size of 3 mm
may be appropriate for a thickness of 16 mm but not for 32 mm.
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If set-up parameters are not in accordance with Table 2, the capability shall be verified by the use of reference
blocks.
For examination levels C and D, all the set-ups chosen for the test object shall be verified by use of reference
blocks.
For in-service inspection the intersection point of the beam centre lines should be optimised for the specified
examination volume.
Table 2 — Recommended TOFD set-ups for simple butt-welds dependent on wall-thickness
Number of Centre- Beam-angle
Thickness Depth-range Element – Beam
TOFD frequency αααα / °
size / mm intersection
t / mm ∆∆∆∆t / mm
set-ups f / MHz
(long.-waves)
6-10 1 0-t 15 70 2-3 2/3 of t
10-15 1 0-t 15-10 70 2-3 2/3 of t
15-35 1 0-t 10-5 70-60 2-6 2/3 of t
0-t 2/3 of t
35-50 1 5-3 70-60 3-6
50-100 2 0-t/2 5-3 70-60 3-6 1/3 of t
t/2-t 5-3 60-45 6-12 5/6 of t;
or t for α ≤ 45°
100-200 3 0-t/3 5-3 70-60 3-6 2/9 of t
t/3-2t/3 5-3 60-45 6-12 5/9 of t
2/3t-t 5-2 60-45 6-20 8/9 of t; or t for
α ≤ 45°
200-300 4 0-t/4 5-3 70-60 3-6 1/12 of t
t/4-t/2 5-3 60-45 6-12 5/12 of t
t/2-3t/4 5-2 60-45 6-20 8/12 of t
3t/4-t 11/12 of t; or t
3-1 50-40 10-20
for α ≤ 45°

8.3 Scan increment setting
The scan increment setting is dependent upon the wall thickness to be examined. For thickness up to 10 mm
the scan increment shall be no more than 0,5 mm. For thickness between 10 mm and 150 mm the scan
increment shall be no more than 1 mm. Above 150 mm a scan increment of 2 mm can be used.
8.4 Geometry considerations
Care should be taken when examining welds of complex geometry, e.g. welds joining materials of unequal
thickness, materials that are joined at an angle, or nozzles. As TOFD is based upon the measurement of time
intervals of sound waves taking the shortest path between the point of emission and the point of reception via
points of reflection or diffraction, some areas of interest may be obscured. Additional scans may in many
cases overcome this problem. Planning examinations of complex geometries requires in depth knowledge of
sound propagation, representative reference blocks and sophisticated software and is beyond the scope of
this document.
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