CEN ISO/TR 20491:2021

Fasteners - Fundamentals of hydrogen embrittlement in steel fasteners (ISO/TR 20491:2019)

This document presents the latest knowledge related to hydrogen embrittlement, translated into know-how in a manner that is complete yet simple, and directly applicable to steel fasteners.

Verbindungselemente - Grundlagen der Wasserstoffversprödung bei Verbindungselementen aus Stahl (ISO/TR 20491:2019)

Dieses Dokument enthält die neuesten Erkenntnisse über die Wasserstoffversprödung, die auf vollständige und dennoch einfache Weise in Fachwissen übertragen werden und unmittelbar auf Verbindungselemente aus Stahl anwendbar sind.

Fixations - Principes de la fragilisation par l'hydrogène pour les fixations en acier (ISO/TR 20491:2019)

Le présent document présente les connaissances les plus récentes relatives à la fragilisation par l'hydrogène sous forme de know-how, transcrite d'une façon complète, facilement accessible et directement applicable aux fixations en acier.

Vezni elementi - Osnove o vodikovi krhkosti v jeklenih pritrdilnih elementih (ISO/TR 20491:2019)

Ta dokument predstavlja najnovejša znanja o vodikovi krhkosti, prevedena na izčrpen, a preprost način v strokovno znanje in izkušnje, ter neposredno uporabna za jeklene pritrdilne elemente.

General Information

• Status: Published
• Publication Date: 07-Dec-2021
• ICS: 21.060.01 - Fasteners in general
• Technical Committee: CEN/TC 185 - Threaded and nonthreaded mechanical fasteners and accessories
• Drafting Committee: CEN/TC 185 - Threaded and nonthreaded mechanical fasteners and accessories
• Current Stage: 6060 - Definitive text made available (DAV) - Publishing
• Start Date: 08-Dec-2021
• Due Date: 07-Oct-2022
• Completion Date: 08-Dec-2021
• Ref Project: SIST-TP CEN ISO/TR 20491:2022 - Fasteners - Fundamentals of hydrogen embrittlement in steel fasteners (ISO/TR 20491:2019)

Standards Content (Sample)

SLOVENSKI STANDARD
01-februar-2022
Vezni elementi - Osnove o vodikovi krhkosti v jeklenih pritrdilnih elementih
(ISO/TR 20491:2019)
Fasteners - Fundamentals of hydrogen embrittlement in steel fasteners (ISO/TR
20491:2019)
Mechanische Verbindungselemente - Grundlagen der Wasserstoffversprödung in
Verbindungselementen aus Stahl (ISO/TR 20491:2019)
Fixations - Principes de la fragilisation par l'hydrogène pour les fixations en acier
(ISO/TR 20491:2019)
Ta slovenski standard je istoveten z: CEN ISO/TR 20491:2021
ICS:
21.060.01 Vezni elementi na splošno Fasteners in general
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

CEN ISO/TR 20491
TECHNICAL REPORT
RAPPORT TECHNIQUE
December 2021
TECHNISCHER BERICHT
ICS 21.060.01
English Version
Fasteners - Fundamentals of hydrogen embrittlement in
steel fasteners (ISO/TR 20491:2019)
Fixations - Principes de la fragilisation par l'hydrogène Mechanische Verbindungselemente - Grundlagen der
pour les fixations en acier (ISO/TR 20491:2019) Wasserstoffversprödung in Verbindungselementen aus
Stahl (ISO/TR 20491:2019)
This Technical Report was approved by CEN on 29 November 2021. It has been drawn up by the Technical Committee CEN/TC
185.
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. CEN ISO/TR 20491:2021 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
The text of ISO/TR 20491:2019 has been prepared by Technical Committee ISO/TC 2 "Fasteners” of the
International Organization for Standardization (ISO) and has been taken over as
held by BSI.
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.
Endorsement notice
The text of ISO/TR 20491:2019 has been approved by CEN as CEN ISO/TR 20491:2021 without any
modification.
TECHNICAL ISO/TR
REPORT 20491
First edition
2019-02
Fasteners — Fundamentals of
hydrogen embrittlement in steel
fasteners
Fixations — Principes de la fragilisation par l'hydrogène pour les
fixations en acier
Reference number
ISO/TR 20491:2019(E)
©
ISO 2019
ISO/TR 20491:2019(E)
© ISO 2019
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
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Phone: [phone]
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Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii © ISO 2019 – All rights reserved

ISO/TR 20491:2019(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms . 4
5 General description of hydrogen embrittlement . 4
6 Hydrogen damage mechanism . 4
7 Fracture morphology . 5
8 Conditions at the tip of a crack . 7
9 Conditions for hydrogen embrittlement failure . 7
9.1 Root cause and triggers for hydrogen embrittlement failure . 7
9.2 Material susceptibility . 8
9.2.1 General. 8
9.2.2 Defects and other conditions causing abnormal material susceptibility .10
9.2.3 Methodology for measuring HE threshold stress .10
9.3 Tensile stress .11
9.4 Atomic hydrogen .12
9.4.1 Sources of hydrogen . .12
9.4.2 Internal hydrogen .12
9.4.3 Environmental hydrogen .13
10 Case-hardened fasteners .13
11 Hot dip galvanizing and thermal up-quenching .15
12 Stress relief prior to electroplating .16
13 Fasteners thread rolled after heat treatment.16
14 Hydrogen embrittlement test methods .17
15 Baking .17
Bibliography .19
ISO/TR 20491:2019(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see www .iso
.org/iso/foreword .html.
This document was prepared by Technical Committee ISO/TC 2 Fasteners, Subcommittee SC 14, Surface
coatings.
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.
iv © ISO 2019 – All rights reserved

ISO/TR 20491:2019(E)
Introduction
High strength mechanical steel fasteners are broadly characterized by tensile strengths (R ) above
m
1 000 MPa and are often used in critical applications such as in bridges, engines, aircraft, where a
fastener failure can have catastrophic consequences. Preventing failures and managing the risk of
hydrogen embrittlement (HE) is a fundamental consideration implicating the entire fastener supply
chain, including: the steel mill, the fastener manufacturer, the coater, the application engineer, the joint
designer, all the way to the end user. Hydrogen embrittlement has been studied for decades, yet the
complex nature of HE phenomena and the many variables make the occurrence of fastener failures
unpredictable. Researches are typically conducted under simplified and/or idealized conditions that
cannot be effectively translated into know-how prescribed in fastener industry standards and practices.
Circumstances are further complicated by specifications or standards that are sometimes inadequate
and/or unnecessarily alarmist. Inconsistencies and even contradictions in fastener industry standards
have led to much confusion and many preventable fastener failures. The fact that HE is very often
mistakenly determined to be the root cause of failure as opposed to a mechanism of failure reflects the
confusion.
TECHNICAL REPORT ISO/TR 20491:2019(E)
Fasteners — Fundamentals of hydrogen embrittlement in
steel fasteners
1 Scope
This document presents the latest knowledge related to hydrogen embrittlement, translated into know-
how in a manner that is complete yet simple, and directly applicable to steel fasteners.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at http: //www .electropedia .org/
3.1
hardness
resistance of a metal to plastic deforma
...