SIST EN ISO 18491:2026

• Abstract:

  This document specifies methods for measuring the parameters needed to calculate arc energies for arc welding processes.

• Status: Not Published
• Public Enquiry End Date: 30-Jun-2025
• ICS: 25.160.01 - Welding, brazing and soldering in general
• ICS: 25.160.10 - Welding processes
• Technical Committee: VAR - Welding
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 23-Jul-2026
• Due Date: 27-Sep-2026
• Ref Project: EN ISO 18491:2026 - Welding and allied processes - Measurement of arc energies (ISO 18491:2026)

Overview

SIST EN ISO 18491:2026, titled Welding and allied processes - Measurement of arc energies (ISO/FDIS 18491:2026), is an international standard that specifies methods for measuring key parameters required to calculate arc energies in arc welding processes. This standard provides comprehensive guidance for accurate determination of arc energy, supports quality assurance in welding operations, and ensures compliance with industry best practices. Accurate measurement of arc energy is essential for maintaining weld quality, consistency, and safety, especially in environments where precise heat input control is critical.

Key Topics

• Arc Energy Calculation Methods
  The standard presents three recognized methods for determining arc energy:

  • Method A: Uses welding current, arc voltage, and welding speed.
  • Method B: Based on total instantaneous energy and length of the weld run.
  • Method C: Uses average instantaneous power and welding speed. For waveform-controlled welding, Methods B and C are recommended due to their higher accuracy for modern welding equipment.

• Measurement Parameters
  The document details procedures for measuring:

  • Arc voltage (with emphasis on minimizing errors from voltage drops in cables)
  • Welding current (accurate inclusion of all cables)
  • Welding speed and run length
  • Instantaneous energy and power (using compliant meters and sampling frequencies)

• Welding Equipment and Devices
  Guidance is provided for the selection and use of measuring devices such as clamp meters, voltmeters, wattmeters, and speed measurement tools, as well as their calibration and validation in line with ISO 17662.

• Calibration and Validation
  All measuring instruments are to be calibrated or validated to maintain accuracy and traceability of welding energy measurements.

• Adaptation to Modern Welding Technologies
  With advancements in waveform-controlled welding and complex power sources, the standard ensures measurement methods remain relevant and robust for contemporary and evolving welding processes.

Applications

ISO 18491:2026 finds wide application in various sectors:

• Production Welding: Supports manufacturers in ensuring weld consistency by verifying arc energy during production matches the Welding Procedure Specification (WPS).
• Procedure Qualification: Provides the basis for measuring and recording energy input during welding procedure specification qualification, as required by standards like ISO 15614.
• Inspection & Quality Assurance: Equips inspectors and quality managers with standardized methods for verifying energy compliance, minimizing inconsistency and improving safety and product quality.
• Welding Equipment Evaluation: Assists equipment manufacturers, purchasers, and users in validating and comparing the energy performance of welding systems, including those with complex waveform controls.
• Calibration Services: Offers instructions for calibration laboratories and service providers on proper verification of measurement tools used in welding.

By ensuring the correct measurement of arc energy, organizations can improve weld integrity, reduce the risk of non-conformance, and meet international regulatory and contractual requirements.

Related Standards

ISO 18491:2026 operates within a wider framework of welding standards, complementing and being referenced by several key documents:

• ISO 4063: Welding, brazing, soldering, and cutting – Nomenclature of processes and reference numbers
• ISO 17662: Welding – Calibration, verification, and validation of equipment used for welding, including ancillary activities
• ISO 15614: Specification and qualification of welding procedures for metallic materials
• IEC 60974-14: Arc welding equipment – Part 14: Calibration, validation, and consistency testing
• ISO/TR 17671: Recommendations for welding of metallic materials
• ISO/TR 25901 series: Welding and allied processes – Vocabulary

Organizations involved in welding and allied processes should integrate ISO 18491 with these related standards to establish robust measurement practices, comply with best practices, and optimize production quality.

Keywords: arc energy measurement, welding processes, heat input, waveform-controlled welding, welding quality assurance, welding procedure specification, calibration, ISO welding standards.

SLOVENSKI STANDARD
oSIST prEN ISO 18491:2025
01-junij-2025
Varjenje in sorodni postopki - Merjenje energije loka (ISO/DIS 18491:2025)
Welding and allied processes - Measurement of arc energies (ISO/DIS 18491:2025)
Schweißen und verwandte Verfahren - Messen der Schweißenergie (ISO/DIS
18491:2025)
Soudage et techniques connexes - Mesure des énergies de l'arc (ISO/DIS 18491:2025)
Ta slovenski standard je istoveten z: prEN ISO 18491
ICS:
25.160.01 Varjenje, trdo in mehko Welding, brazing and
spajkanje na splošno soldering in general
oSIST prEN ISO 18491:2025 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

oSIST prEN ISO 18491:2025
oSIST prEN ISO 18491:2025
DRAFT
International
Standard
ISO/DIS 18491
ISO/TC 44/SC 10
Welding and allied processes —
Secretariat: DIN
Measurement of arc energies
Voting begins on:
Soudage et techniques connexes — Mesure des énergies de l'arc
2025-04-09
Voting terminates on:
ICS: 25.160.01
2025-07-02
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 is circulated as received from the committee secretariat.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
STANDARDS MAY ON OCCASION HAVE TO
ISO/CEN PARALLEL PROCESSING
BE CONSIDERED IN THE LIGHT OF THEIR
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
NATIONAL REGULATIONS.
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.
Reference number
ISO/DIS 18491:2025(en)
oSIST prEN ISO 18491:2025
DRAFT
ISO/DIS 18491:2025(en)
International
Standard
ISO/DIS 18491
ISO/TC 44/SC 10
Welding and allied processes —
Secretariat: DIN
Measurement of arc energies
Voting begins on:
Soudage et techniques connexes — Mesure des énergies de l'arc
ICS: 25.160.01 Voting terminates on:
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 is circulated as received from the committee secretariat.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
© ISO 2025
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
ISO/CEN PARALLEL PROCESSING
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
BE CONSIDERED IN THE LIGHT OF THEIR
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
or ISO’s member body in the country of the requester.
NATIONAL REGULATIONS.
ISO copyright office
RECIPIENTS OF THIS DRAFT ARE INVITED
CP 401 • Ch. de Blandonnet 8
TO SUBMIT, WITH THEIR COMMENTS,
CH-1214 Vernier, Geneva
NOTIFICATION OF ANY RELEVANT PATENT
Phone: [phone]
RIGHTS OF WHICH THEY ARE AWARE AND TO
PROVIDE SUPPORTING DOCUMENTATION.
Email: [e-mail]
Website: www.iso.org
Published in Switzerland Reference number
ISO/DIS 18491:2025(en)
ii
oSIST prEN ISO 18491:2025
ISO/DIS 18491:2025(en)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 General . 2
5 Welding equipment and measuring devices . 3
6 Determination of arc energy . 3
7 Measurement parameters . 4
7.1 General .4
7.2 Arc voltage . .4
7.3 Welding current .4
7.4 Total instantaneous energy or average instantaneous power .4
7.5 Welding speed and length of the run .5
8 Calibration and validation of measuring instruments . 5
Annex A (informative) Range of power source types and measurement methods . 6
Annex B (informative) Conversion factors . 8
Bibliography . 9

iii
oSIST prEN ISO 18491:2025
ISO/DIS 18491:2025(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).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO [had/had not] received notice of
(a) patent(s) which may be required to implement this document. However, implementers are cautioned that
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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 10, Quality management in the field of welding.
This second edition cancels and replaces the first edition (ISO/TR 18491:2015), which has been technically
revised.
The main changes are as follows:
— update of normative references in Clause 2;
— update of vocabulary throughout this document in Clause 3 "Terms and defintions", Clause 4 "General",
Clause 5 "Welding equipment and measuring devices", Clause 6 "Determination of arc energy", Clause 7
"Measurement parameters", Clause 8 " Calibration and validation of measuring instruments" and in
Annex A "Range of power source types and measurement methods";
— addition of a new Annex B "Conversion factors";
— update of the Bibliography.
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. Official interpretations of ISO/TC 44 documents, where they exist, are
available from this page: https://committee.iso.org/sites/tc44/home/interpretation.html.

iv
oSIST prEN ISO 18491:2025
ISO/DIS 18491:2025(en)
Introduction
Welding “arc energy” or “heat input” are fundamental values used to manage the consistency of weld
metal and heat-affected zone properties. ISO 15614 requires the measurement of the welding energies
implemented during a welding procedure qualification, but it does not give details about the methods to be
used. Likewise, during the construction of a welded assembly, inspectors should make sure that the welding
energies comply with the Welding Procedure Specification (WPS). But again, the details of the methods
to be used are not specified. As a consequence, there may be a lack of consistency between the methods
used to measure the welding energies during welding of the test piece and the methods used during the
manufacturing process. This is a potential source of error which could have implications on the safety or
quality of a welded component or structure.
Moreover, the latest technological breakthroughs in microprocessors and electrical power manipulation
have yielded welding power sources and control systems that are capable of generating complex waveforms.
However, these control systems and waveforms increase the difficulties related to voltage and current
intensity measurements, as their values are manipulated at frequencies which can reach thousands of Hertz.
The measuring instruments generally used by inspectors, such as TRMS clamp meters, can no longer be
relied on to correctly measure the welding energy since differences exceeding 30 % with respect to the true
energy can sometimes be found.
This document provides guidance on how to accurately measure welding energy and calculate heat input,
both in the case of traditional welding systems and those that employ complex waveforms.

v
oSIST prEN ISO 18491:2025
oSIST prEN ISO 18491:2025
DRAFT International Standard ISO/DIS 18491:2025(en)
Welding and allied processes — Measurement of arc energies
1 Scope
This document specifies the measuring of parameters needed to calculate arc energies for arc welding
processes.
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 4063, Welding, brazing, soldering and cutting — Nomenclature of processes and reference numbers
ISO 17662, Welding — Calibration, verification and validation of equipment used for welding, including ancillary
activities
ISO/TR 17671 (all parts), Welding — Recommendations for welding of metallic materials
ISO/TR 25901-1, Welding and allied processes — Vocabulary — Part 1: General terms
ISO/TR 25901-3, Welding and allied processes — Vocabulary — Part 3: Welding processes
ISO/TR 25901-4, Welding and allied processes — Vocabulary — Part 4: Arc welding
IEC 60974-14, Arc welding equipment – Part 14: Calibration, validation and consistency testing
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO/TR 25901-1, ISO/TR 25901-3,
ISO/TR 25901-4 and ISO/TR 17671 (all parts) and the following apply.
ISO and IEC maintain terminology databases for
...