oSIST prEN ISO 20601:2026

• Abstract:

  This document specifies the application of phased array technology for the semi- or fully automated ultrasonic testing of fusion-welded joints in steel parts with thickness values between 3,2 mm and 8,0 mm. This meets the typical range of tube wall thickness values in boilers, which is an important application of this testing technology. The minimum and maximum value of the wall thickness range can be exceeded, when testing level "D" of this document is applied. This document applies to full penetration welded joints of simple geometry in plates, tubes, pipes, and vessels, where both the weld and parent material are low-alloy and/or fine grained steel.; NOTE "Semi-automated testing" encompasses a controlled movement of one or more probes on the surface of a component along a fixture (guidance strip, ruler, etc.), whereby the probe position is unambiguously measured with a position sensor. The probe is moved manually. "Fully automated testing" includes mechanized propulsion in addition.; Where material-dependent ultrasonic parameters are specified in this document, they are based on steels having a sound velocity of (5 920 ± 50) m/s for longitudinal waves, and (3 255 ± 30) m/s for transverse waves. It is necessary to take this fact into account when testing materials with a different velocity.; This document provides guidance on the specific capabilities and limitations of phased array technology for the detection, location, sizing and characterization of discontinuities in fusion-welded joints. Ultrasonic phased array technology can be used as a stand-alone technique or in combination with other non-destructive testing (NDT) methods or techniques, during manufacturing and testing of new welds/repair welds (pre-service testing).; This document specifies two testing levels:; — level "C" for standard situations;; — level "D" for different situations/special applications.; This document describes assessment of discontinuities for acceptance purposes based on:; — height and length;; — amplitude (equivalent reflector size) and length;; — go/no-go decision.; This document does not include acceptance levels for discontinuities.

• Status: Not Published
• Public Enquiry End Date: 01-Nov-2026
• ICS: 25.160.40 - Welded joints and welds
• Technical Committee: VAR - Welding
• Current Stage: 4020 - Public enquire (PE) (Adopted Project)
• Start Date: 10-Sep-2026
• Due Date: 28-Jan-2027
• Ref Project: prEN ISO 20601 - Non-destructive testing of welds - Ultrasonic testing - Phased array technique for thin-walled steel components (ISO/DIS 20601:2026)

• Revises: SIST EN ISO 20601:2019 - Non-destructive testing of welds - Ultrasonic testing - Use of automated phased array technology for thin-walled steel components (ISO 20601:2018)
• Effective Date: 01-Oct-2026

Overview

oSIST prEN ISO 20601:2026 specifies the requirements and guidelines for the non-destructive testing (NDT) of fusion-welded joints in thin-walled steel components using the ultrasonic phased array technique. Developed by the Slovenian Institute for Standardization (SIST) and harmonized with international ISO and CEN requirements, this standard covers both semi-automated and fully automated ultrasonic testing for parts typically ranging from 3.2 mm to 8.0 mm in thickness. The standard is especially relevant for industries reliant on boiler tubes, pressure vessels, and steel pipes where weld integrity in thin-walled sections is critical to safety and performance.

Phased array ultrasonic testing (PAUT) enables the detection, sizing, and characterization of internal discontinuities in welded joints, providing a reliable, repeatable, and efficient solution for quality control during manufacturing and in-service assessments.

Key Topics

• Scope and Applicability

  • Applies to full penetration welded joints in low-alloy and/or fine-grained steel with simple geometry (plates, tubes, pipes, vessels).
  • Testing thickness range: 3.2 mm to 8.0 mm, with flexibility for other thicknesses under testing level "D".
  • Addresses testing of both weld and parent material.

• Testing Methods

  • Ultrasonic Phased Array Technique: Enables multi-angle monitoring and advanced flaw characterization.
  • Semi-automated Testing: Probe moved manually along a guided path with position sensors.
  • Fully Automated Testing: Mechanized propulsion and data acquisition for increased repeatability and efficiency.

• Testing Levels

  • Level "C": Standard approach for most thin-walled components, typically requiring testing from two sides or after cap removal.
  • Level "D": Special or challenging applications, including wall thicknesses outside standard range, complex geometries, or non-standard temperatures.

• Assessment Criteria

  • Detection and evaluation of discontinuities based on size (height, length), amplitude (equivalent reflector size), and go/no-go decisions.
  • No acceptance/rejection criteria are included, leaving such thresholds to complementary standards or project requirements.

• Personnel and Equipment

  • Personnel to be qualified according to ISO 9712 or equivalent.
  • Equipment and probes must comply with ISO 18563 series for phased array systems.

Applications

• Boiler and Pressure Vessel Manufacturing
  • Inspection of thin-walled welds in critical components, optimizing safety and quality in energy and process industries.
• Steel Pipe and Tube Fabrication
  • Ensuring weld integrity in pipes for oil and gas, chemical processing, and water supply systems.
• Maintenance and Repair
  • Pre-service or post-repair inspections, assisting in life cycle management of industrial infrastructure.
• Quality Assurance
  • Suitable for both production-line testing and in-field assessments, supporting compliance with regulatory and customer requirements.

Related Standards

The following standards complement or provide references used within oSIST prEN ISO 20601:2026:

• ISO 5577 - Non-destructive testing - Ultrasonic testing - Vocabulary
• ISO 9712 - Non-destructive testing - Qualification and certification of NDT personnel
• ISO 17640 - Non-destructive testing of welds - Ultrasonic testing - Techniques, testing levels, and assessment
• ISO 18563-1, 18563-2, 18563-3 - Phased array equipment characterization and verification
• ISO 23243 - Ultrasonic testing with arrays - Vocabulary

Practical Value

By implementing the guidelines of oSIST prEN ISO 20601:2026, organizations can:

• Achieve higher accuracy and reliability in the ultrasonically-based inspection of welded joints.
• Support regulatory compliance and customer acceptance in sectors such as energy, petrochemicals, water processing, and heavy industry.
• Reduce inspection time and increase data traceability with automated phased array solutions.
• Leverage advanced flaw detection and characterization methods, improving maintenance and risk management strategies.

Keywords: non-destructive testing, ultrasonic phased array, weld inspection, thin-walled steel, welded joints, pressure vessels, quality assurance, ISO 20601, oSIST prEN ISO 20601:2026, industrial standards

SLOVENSKI STANDARD
01-oktober-2026
Neporušitveno preskušanje zvarnih spojev - Ultrazvočno preskušanje -
Avtomatska tehnika s faznim krmiljenjem za tankostenske sestavne dele iz jekla
(ISO/DIS 20601:2026)
Non-destructive testing of welds - Ultrasonic testing - Phased array technique for thin-
walled steel components (ISO/DIS 20601:2026)
Zerstörungsfreie Prüfung von Schweißverbindungen - Ultraschallprüfung -
Phasengesteuerte Array-Technologie für dünnwandige Bauteile aus Stahl (ISO/DIS
20601:2026)
Essais non destructifs des assemblages soudés - Contrôle par ultrasons - Technique
multiélément automatisée pour les composants en acier de parois minces (ISO/DIS
20601:2026)
Ta slovenski standard je istoveten z: prEN ISO 20601
ICS:
25.160.40 Varjeni spoji in vari Welded joints and welds
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

DRAFT
International
Standard
ISO/DIS 20601
ISO/TC 44/SC 5
Non-destructive testing of welds —
Secretariat: AFNOR
Ultrasonic testing — Phased array
Voting begins on:
technique for thin-walled steel
2026-09-07
components
Voting terminates on:
2026-11-30
Essais non destructifs des assemblages soudés — Contrôle par
ultrasons — Technique multi-éléments pour les composants en
acier à paroi mince
ICS: 25.160.40
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
This document has not been edited by the ISO Central Secretariat.
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NOTIFICATION OF ANY RELEVANT PATENT
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PROVIDE SUPPORTING DOCUMENTATION.
Reference number
ISO/DIS 20601:2026(en)
DRAFT
ISO/DIS 20601:2026(en)
International
Standard
ISO/DIS 20601
ISO/TC 44/SC 5
Non-destructive testing of welds —
Secretariat: AFNOR
Ultrasonic testing — Phased array
Voting begins on:
technique for thin-walled steel
components
Voting terminates on:
Essais non destructifs des assemblages soudés — Contrôle par
ultrasons — Technique multi-éléments pour les composants en
acier à paroi mince
ICS: 25.160.40
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
This document has not been edited by the ISO Central Secretariat.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
© ISO 2026
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
STANDARDS MAY ON OCCASION HAVE TO
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BE CONSIDERED IN THE LIGHT OF THEIR
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RECIPIENTS OF THIS DRAFT ARE INVITED
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TO SUBMIT, WITH THEIR COMMENTS,
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NOTIFICATION OF ANY RELEVANT PATENT
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Published in Switzerland Reference number
ISO/DIS 20601:2026(en)
ii
ISO/DIS 20601:2026(en)
Contents Page
Foreword .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Testing levels . 2
5 Information required before testing . . 4
5.1 Items to be specified before procedure development .4
5.2 Specific information required by the operator before testing .4
5.3 Written test procedure .4
6 Requirements for test personnel and test equipment . 5
6.1 Qualification of test personnel .5
6.2 Test equipment .5
6.2.1 General .5
6.2.2 Instruments .5
6.2.3 Probes .5
6.2.4 Scanning mechanisms .6
7 Preparation for testing . 6
7.1 Volume to be tested .6
7.2 Verification of test setup .6
7.3 Scan increment setting .7
7.4 Geometry considerations .7
7.5 Preparation of scanning surfaces .7
7.6 Temperature .7
7.7 Couplant .7
8 Testing of parent material . 7
9 Range and sensitivity settings . 8
9.1 Settings . . .8
9.1.1 General .8
9.1.2 Pulse-echo time window .8
9.1.3 Pulse-echo sensitivity settings .8
9.2 Checking of the settings .9
9.3 Reference blocks .9
9.3.1 General .9
9.3.2 Material.9
9.3.3 Dimensions and shape .9
9.3.4 Reference reflectors .10
9.4 Test blocks for testing level D . .10
9.4.1 General .10
9.4.2 Material.10
9.4.3 Dimensions and shape .10
9.4.4 Reflectors in test blocks .11
10 Checks of test equipment .11
11 Verification of the test procedure .11
12 Weld testing.11
13 Data storage .12
14 Interpretation and analysis of phased array data .12
14.1 General . 12
14.2 Assessing the quality of the phased array data . 12
14.3 Identification of relevant indications . 13

iii
ISO/DIS 20601:2026(en)
14.4 Classification of relevant indications . 13
14.5 Determination of location and length . 13
14.5.1 Location . 13
14.5.2 Length . 13
14.6 Indication assessment . 13
14.6.1 General . 13
14.6.2 Assessment based on height and length.14
14.6.3 Assessment based on amplitude and length .14
14.6.4 Characterization of discontinuities .14
14.7 Evaluation against acceptance criteria .14
15 Test report . 14
Annex A (informative) Typical reference blocks .16
Bibliography .18

iv
ISO/DIS 20601:2026(en)
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 44, Welding and allied processes, Subcommittee
SC 5, Testing and inspection of welds.
This second edition cancels and replaces the first edition (ISO 20601:2018) which has been technically
revised.
Any feedback, question or request for official interpretation related to any aspect of this document should be
directed to the Secretariat of ISO/TC 44/SC 5 via your national standards body. A complete listing of these
bodies can be found at www.iso.org/members.html. Official interpretations, where they exist, are available
from this page: https://committee.iso.org/sites/tc44/home/interpretation.html.

v
DRAFT International Standard ISO/DIS 20601:2026(en)
Non-destructive testing of welds — Ultrasonic testing —
Phased array technique for thin-walled steel components
1 Scope
This document specifies the application of phased array technology for the semi- or fully automated
ultrasonic testing of fusion-welded joints in steel parts with thickness values between and including 3,2 mm
and 8,0 mm. This meets the typical range of tube wall thickness values in boilers, which is an important
application of this testing technology. The minimum and maximum value of the wall thickness range can
be exceeded, when testing level “D” of this document is applied. This document applies to full penetration
welded joints of simple geometry in plates, tubes, pipes, and vessels, where both the weld and parent
material are low-alloy and/or fine grained steel.
NOTE “Semi-automated testing” encompasses a controlled movement of one or more probes on the surface of a
component along a fixture (guidance strip, ruler, etc.), whereby the probe position is unambiguously measured with a
position sensor. The probe is moved manually. “Fully automated testing” includes mechanized propulsion in addition.
Where material-dependent ultrasonic parameters are specified in this document, they are based on steels
having a sound velocity of (5 920 ± 50) m/s for longitudinal waves, and (3 255 ± 30) m/s for transverse
waves. It is necessary to take this fact into account when testing materials with a different velocity.
This document provides guidance on the specific capabilities and limitations of phased array technology
for the detection, location, sizing and characterization of discontinuities in fusion-welded joints. Ultrasonic
phased array technology can be used as a stand-alone technique or in combination with other non-
destructive testing (NDT) methods or techniques, during manufacturing and testing of new welds/repair
welds (pre-service testing).
This document specifies two testing levels:
— level “C” for standard situations;
— level “D” for different situations/special applications.
This document describes assessment of discontinuities for acceptance purposes based on:
— height and length;
— amplitude (equivalent reflector size) and length;
— go/no-go decision.
This document does not include acceptance levels for discontinuities.
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 5577, Non-destructive testing — Ultrasonic testing — Vocabulary
ISO 9712, Non-destructive testing — Qualification and certification of NDT personnel
ISO 17640, Non-destructive testing of welds — Ultrasonic testing — Techniques, testing levels, and assessment

ISO/DIS 20601:2026(en)
ISO 18563-1, Non-destructive testing — Characterization and verification of ultrasonic phased array equipment
— Part 1: Instruments
ISO 18563-2, Non-destructive testing — Characterization and verification of ultrasonic phased array equipment
— Part 2: Array probes
ISO 18563-3, Non-destructive testing — Characterization and verification of ultrasonic phased array equipment
— Part 3: Complete systems
ISO 23243, Non-destructive testing — Ultrasonic testing with arrays — Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 5577 and ISO 23243and 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
indication, noun
phased array indication, noun
pattern or disturbance in the phased array image which may need further evaluation
3.2
phased array setup, noun
probe arrangement defined by probe characteristics (e.g. frequency, probe element size, beam angle, wave
mode), probe position, and the number of probes, adaptation to the curvature of the test object
[SOURCE: ISO 23243 , text added "adaptation to the curvature of the test object"]
4 Testing levels
Quality requirements for welded joints are mainly associated with the material, welding process and service
conditions. To comply with these requirements, this document specifies two testing levels “C” and “D”.
a) A written procedure is mandatory for both testing levels C and D.
b) Testing level C applies to the standardized approach for thin-walled components (see Table 1 and
Table 2), e.g. testing from two sides or testing from one side of the weld when the cap is removed.
c) Testing level D shall be agreed upon for special applications, e.g. tests on wall thickness below 3,2 mm,
varying thicknesses (counter bore) and tests at object temperatures outside the range specified in 7.6.
[1]
NOTE For larger wall thicknesses, ISO 13588 applies.
d) For testing level D, verification on test blocks is mandatory.
[2]
In general, the testing levels are related to quality levels (given in ISO 5817 , for example). The appropriate
[3]
testing level can be specified by standards for weld testing (e.g. ISO 17635 ), product standards or other
specifications.
[3]
e) When ISO 17635 is specified, the recommended testing levels are as given in Table 1.

ISO/DIS 20601:2026(en)
Table 1 — Recommended testing levels
[2]
Testing level Quality level in ISO 5817
C B, C, D
D Special applications
Table 2 shows the minimum requirements for the phased array modes for testing levels C and D.
f) The setup shall be verified with reference and/or test blocks; as described in 7.2.
g) In cases where scanning is performed from one scanning surface (e.g. the outer surface of a vessel), at
least half and full skip shall be used.
h) If scanning is performed from both scanning surfaces (e.g. top and bottom surfaces), testing at half skip
could be sufficient, depending on weld and probe dimensions.
i) If the evaluation of the indications is based on amplitude only, the deviation of the beam axis from the
normal to the weld bevel shall not exceed 6°.
j) In case it is not possible to stay within this 6° value, because of the geometry of the test object (e.g. weld
cap, narrow gap weld), the scan plan shall describe the corrective measures and explain how the areas
outside the 6° requirement are covered with sufficient sensitivity.
Table 2 — Description of test setup depending on testing levels
Test setup Testing levels
Examples
Phased array
Scanning C D
mode
line scanning (at
electronic linear
fixed distance to Two sides To be specified
scanning
weld)
electronic secto-
line scanning (at Two sides or two
rial scanning or
fixed distance to probe positions To be specified
combined elec-
weld) on the same side
tronic scanning
electronic sectori- area scanning One side, weld cap
To be specified
al scanning (raster, meander) removed
line scanning (at
a
Skewed scan fixed distance to Not applicable To be specified
weld)
a
If detection of transverse discontinuities is required by specification, a suitable additional test setup shall be applied. Skewed
probe or electronically skewed beam can be used.

ISO/DIS 20601:2026(en)
5 Information required before testing
5.1 Items to be specified before procedure development
Information on the following items is required:
a) purpose and extent of testing;
b) type(s) of parent material (i.e. cast, forged, rolled), grain size;
c) testing levels;
d) acceptance criteria;
e) specification of reference blocks;
f) manufacturing or operational stage at which the testing has to be carried out;
g) weld details and information on the size of the heat-affected zone;
h) requirements for access, surface conditions and temperature;
i) personnel qualifications;
j) reporting requirements.
5.2 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 specified
in 5.1, together with the following additional information:
a) written test procedure;
b) joint preparation and dimensions;
c) relevant information on the welding process;
d) time of inspection relative to any post-weld heat treatment.
5.3 Written test procedure
For all testing levels, a written test procedure is required.
The procedure shall include the following information as a minimum:
a) purpose and extent of testing;
b) testing techniques;
c) testing levels;
d) personnel qualification, training requirements;
e) test equipment to be used (including frequency, sampling rate, pitch between elements, element size);
f) reference and/or test blocks;
g) sensitivity and range setting of test equipment;
h) available access and surface conditions;
i) testing of parent material;
j) example of reference scan;
ISO/DIS 20601:2026(en)
k) evaluation of indications;
l) acceptance levels and/or recording levels;
m) scan plan showing probe placement, movement, and c
...