Transportable gas cylinders - Compatibility of cylinder and valve materials with gas contents - Part 4: Test methods for selecting steels resistant to hydrogen embrittlement (ISO 11114-4:2017)

ISO 11114-4: 2017 specifies test methods and the evaluation of results from these tests in order to qualify steels suitable for use in the manufacture of gas cylinders (up to 3 000 l) for hydrogen and hydrogen bearing embrittling gases.
This document only applies to seamless steel gas cylinders.
The requirements of this document are not applicable if at least one of the following conditions for the intended gas service is fulfilled:
-      the working pressure of the filled embrittling gas is less than 20 % of the test pressure of the cylinder;
-      the partial pressure of the filled embrittling gas of a gas mixture is less than 5 MPa (50 bar) in the case of hydrogen and other embrittling gases, with the exception of hydrogen sulphide and methyl mercaptan; in such cases, the partial pressure shall not exceed 0,25 MPa (2,5 bar).
NOTE       In such cases, it is possible to design the cylinder as for ordinary (non-embrittling) gases.

Ortsbewegliche Gasflaschen - Verträglichkeit von Werkstoffen für Gasflaschen und Ventile mit den in Berührung kommenden Gasen - Teil 4: Prüfverfahren zur Auswahl von Stählen, die gegen Wasserstoffversprödung unempfindlich sind (ISO 11114-4:2017)

Dieses Dokument legt Prüfverfahren und die Beurteilung von Ergebnissen dieser Qualifikations¬prüfungen von Stählen, die für die Herstellung von Gasflaschen (bis 3 000 l Fassungsraum) für Wasserstoff und wasserstoffhaltige versprödende Gase geeignet sind, fest.
Dieses Dokument gilt ausschließlich für nahtlose Gasflaschen aus Stahl.
Die Anforderungen dieses Dokuments sind nicht anwendbar, wenn mindestens eine der folgenden Bedingungen für den vorgesehenen Gasbetrieb erfüllt ist:
   der Betriebsdruck des für die Füllung vorgesehenen versprödenden Gases beträgt weniger als 20 % des Prüfdrucks der Flasche;
   der Partialdruck des für die Füllung vorgesehenen versprödenden Gases aus einem Gasgemisch im Falle von Wasserstoff und anderen versprödenden Gasen beträgt weniger als 5 MPa (50 bar), mit Ausnahme von Schwefelwasserstoff und Methylmercaptan: bei welchen in diesem Falle der Partialdruck 0,25 MPa (2,5 bar) nicht überschreiten darf.
ANMERKUNG   In derartigen Fällen ist es möglich, die Gasflaschen so auszulegen, wie für gewöhnliche (nicht versprödende) Gase.

Bouteilles à gaz transportables - Compatibilité des matériaux et des robinets avec les contenus gazeux - Partie 4: Méthodes d'essai pour le choix des aciers résistants à la fragilisation par l'hydrogène (ISO 11114-4:2017)

ISO 11114-4:2017 spécifie des méthodes d'essai et l'évaluation des résultats de ces essais permettant de qualifier les aciers pouvant être utilisés pour fabriquer des bouteilles à gaz (jusqu'à 3 000 l) pour l'hydrogène et les gaz hydrogénés fragilisants.
Le présent document s'applique uniquement aux bouteilles à gaz en acier sans soudure.
Les exigences du présent document ne s'appliquent pas si au moins l'une des conditions suivantes concernant l'utilisation avec le gaz prévu, est remplie:
-      la pression d'utilisation du gaz fragilisant dans la bouteille représente moins de 20 % de la pression d'épreuve de la bouteille;
-      la pression partielle du gaz fragilisant du mélange gazeux contenu dans la bouteille représente moins de 5 MPa (50 bar) dans le cas de l'hydrogène et d'autres gaz fragilisants, sauf pour le sulfure d'hydrogène et le méthyle de mercaptan; dans de tels cas, la pression partielle ne doit pas dépasser 0,25 MPa (2,5 bar).
NOTE          Dans de tels cas, il est possible de concevoir les bouteilles comme pour des gaz ordinaires (non fragilisants).

Premične plinske jeklenke - Združljivost materialov za ventil in jeklenko s plinom - 4. del: Preskusne metode za izbiro jekel, odpornih proti vodikovi krhkosti (ISO 11114-4:2017)

Ta dokument določa preskusne metode in oceno rezultatov teh preskusov za kvalificiranje jekel, primernih za uporabo pri izdelavi plinskih jeklenk (do 3000 l) za vodik in pline z vodikovo krhkostjo.
Ta dokument se uporablja samo za nevarjene plinske jeklenke iz jekla.
Zahteve tega dokumenta ne veljajo, če je izpolnjen vsaj eden od naslednjih pogojev za predviden plin:
– delovni tlak napolnjenega krhkega plina znaša manj kot 20 % preskusnega tlaka v jeklenki;
– delni tlak napolnjenega krhkega plina ali plinske mešanice znaša manj kot 5 MPa (50 barov) v primeru vodika in drugih krhkih plinov, z izjemo vodikovega sulfida in metil merkaptana; v takšnih primerih delni tlak ne sme preseči 0,25 MPa (2,5 bara).
OPOMBA: V takšnih primerih se lahko jeklenko konstruira kot za običajne (nekrhke) pline.

General Information

Status
Published
Publication Date
25-Apr-2017
Current Stage
6060 - Definitive text made available (DAV) - Publishing
Due Date
26-Apr-2017
Completion Date
26-Apr-2017

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SLOVENSKI STANDARD
SIST EN ISO 11114-4:2017
01-julij-2017
1DGRPHãþD
SIST EN ISO 11114-4:2005

3UHPLþQHSOLQVNHMHNOHQNH=GUXåOMLYRVWPDWHULDORY]DYHQWLOLQMHNOHQNRVSOLQRP

GHO3UHVNXVQHPHWRGH]DL]ELURMHNHORGSRUQLKSURWLYRGLNRYLNUKNRVWL ,62


Transportable gas cylinders - Compatibility of cylinder and valve materials with gas

contents - Part 4: Test methods for selecting steels resistant to hydrogen embrittlement

(ISO 11114-4:2017)
Ortsbewegliche Gasflaschen - Verträglichkeit von Werkstoffen für Gasflaschen und

Ventile mit den in Berührung kommenden Gasen - Teil 4: Prüfverfahren zur Auswahl von

Stählen, die gegen Wasserstoffversprödung unempfindlich sind (ISO 11114-4:2017)

Bouteilles à gaz transportables - Compatibilité des matériaux et des robinets avec les

contenus gazeux - Partie 4: Méthodes d'essai pour le choix des aciers résistants à la

fragilisation par l'hydrogène (ISO 11114-4:2017)
Ta slovenski standard je istoveten z: EN ISO 11114-4:2017
ICS:
23.020.35 Plinske jeklenke Gas cylinders
23.060.40 7ODþQLUHJXODWRUML Pressure regulators
SIST EN ISO 11114-4:2017 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------
SIST EN ISO 11114-4:2017
---------------------- Page: 2 ----------------------
SIST EN ISO 11114-4:2017
EN ISO 11114-4
EUROPEAN STANDARD
NORME EUROPÉENNE
April 2017
EUROPÄISCHE NORM
ICS 23.020.35 Supersedes EN ISO 11114-4:2005
English Version
Transportable gas cylinders - Compatibility of cylinder and
valve materials with gas contents - Part 4: Test methods
for selecting steels resistant to hydrogen embrittlement
(ISO 11114-4:2017)

Bouteilles à gaz transportables - Compatibilité des Ortsbewegliche Gasflaschen - Verträglichkeit von

matériaux et des robinets avec les contenus gazeux - Werkstoffen für Gasflaschen und Ventile mit den in

Partie 4: Méthodes d'essai pour le choix des aciers Berührung kommenden Gasen - Teil 4: Prüfverfahren

résistants à la fragilisation par l'hydrogène (ISO zur Auswahl von Stählen, die gegen

11114-4:2017) Wasserstoffversprödung unempfindlich sind (ISO
11114-4:2017)
This European Standard was approved by CEN on 8 December 2016.

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, 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.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels

© 2017 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 11114-4:2017 E

worldwide for CEN national Members.
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SIST EN ISO 11114-4:2017
EN ISO 11114-4:2017 (E)
Contents Page

European foreword ....................................................................................................................................................... 3

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SIST EN ISO 11114-4:2017
EN ISO 11114-4:2017 (E)
European foreword

This document (EN ISO 11114-4:2017) has been prepared by Technical Committee ISO/TC 58 “Gas

cylinders” in collaboration with Technical Committee CEN/TC 23 “Transportable gas cylinders” the

secretariat of which is held by BSI.

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 October 2017, and conflicting national standards shall

be withdrawn at the latest by October 2017.

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent

rights.
This document supersedes EN ISO 11114-4:2005.

This document has been prepared under a mandate given to CEN by the European Commission and the

European Free Trade Association.

According to the CEN-CENELEC Internal Regulations, the national standards organizations of the

following countries are bound to implement this European Standard: 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 the United Kingdom.
Endorsement notice

The text of ISO 11114-4:2017 has been approved by CEN as EN ISO 11114-4:2017 without any

modification.
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SIST EN ISO 11114-4:2017
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SIST EN ISO 11114-4:2017
INTERNATIONAL ISO
STANDARD 11114-4
Second edition
2017-04
Transportable gas cylinders —
Compatibility of cylinder and valve
materials with gas contents —
Part 4:
Test methods for selecting steels
resistant to hydrogen embrittlement
Bouteilles à gaz transportables — Compatibilité des matériaux et des
robinets avec les contenus gazeux —
Partie 4: Méthodes d’essai pour le choix des aciers résistants à la
fragilisation par l’hydrogène
Reference number
ISO 11114-4:2017(E)
ISO 2017
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SIST EN ISO 11114-4:2017
ISO 11114-4:2017(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2017, Published in Switzerland

All rights reserved. Unless otherwise specified, 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
Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel. +41 22 749 01 11
Fax +41 22 749 09 47
copyright@iso.org
www.iso.org
ii © ISO 2017 – All rights reserved
---------------------- Page: 8 ----------------------
SIST EN ISO 11114-4:2017
ISO 11114-4:2017(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction ..................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms, definitions, symbols and abbreviated terms ....................................................................................................... 2

3.1 Terms and definitions ....................................................................................................................................................................... 2

3.2 Symbols and abbreviated terms............................................................................................................................................... 3

4 General requirements ..................................................................................................................................................................................... 3

5 Test methods ............................................................................................................................................................................................................. 4

5.1 Disc test (method A) ........................................................................................................................................................................... 4

5.1.1 Principle of test ................................................................................................................................................................. 4

5.1.2 Test conditions and procedure ............................................................................................................................ 4

5.1.3 Treatment and interpretation of test results ........................................................................................... 6

5.1.4 Failure in conducting test ......................................................................................................................................... 7

5.1.5 Test report ............................................................................................................................................................................. 7

5.2 Fracture mechanics test (method B) .................................................................................................................................10

5.2.1 Principle of the test method ................................................................................................................................10

5.2.2 Test procedure ................................................................................................................................................................10

5.2.3 Test results .........................................................................................................................................................................14

5.3 Test method to determine the resistance to hydrogen assisted cracking of steel

cylinders (method C) ......................................................................................................................................................................14

5.3.1 General...................................................................................................................................................................................14

5.3.2 Specimen configurations and numbers of tests .................................................................................15

5.3.3 Fatigue precracking ....................................................................................................................................................15

5.3.4 Specimen testing procedure ...............................................................................................................................15

5.3.5 Test procedure ................................................................................................................................................................16

5.3.6 Crack growth examination ...................................................................................................................................16

5.3.7 Cylinder material qualification .........................................................................................................................17

5.3.8 Failure in conducting test ......................................................................................................................................17

5.3.9 Test report ..........................................................................................................................................................................17

5.4 Tensile tests ............................................................................................................................................................................................17

Bibliography .............................................................................................................................................................................................................................18

© ISO 2017 – All rights reserved iii
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SIST EN ISO 11114-4:2017
ISO 11114-4:2017(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 on 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 the following URL: www . i so .org/ iso/ foreword .html.

The committee responsible for this document is ISO/TC 58, Gas cylinders.

This second edition cancels and replaces the first edition (ISO 11114-4:2005), which has been

technically revised with the following changes:

— improvement of the procedure corresponding to Method C and adjustment of acceptance criteria;

— light modifications on procedures corresponding to Method A and Method B.
A list of parts in the ISO 11114 series can be found on the ISO website.
iv © ISO 2017 – All rights reserved
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SIST EN ISO 11114-4:2017
ISO 11114-4:2017(E)
Introduction

It is widely recognized that compressed hydrogen and some hydrogen bearing gases can have an

embrittling effect on steels. This embrittling effect has resulted in the failure of hydrogen gas cylinders

(including some bursts) that has led gas cylinder users and manufacturers to adopt specific measures.

The adoption of these measures has eliminated all known failures of hydrogen cylinders from this

embrittlement phenomenon as far has been reported.

The basic recommendation is to limit the tensile strength of the steels (see ISO 11114-1) and eliminate

manufacturing defects.

This tensile strength limit of 950 MPa was developed for quenched and tempered gas cylinders of

34 Cr Mo 4 type steels using steelmaking practices, chemistry and manufacturing techniques typical

of those used during the early 1980’s and successfully used for filling pressures up to 300 bar. This

practice has been in widescale use up to the current time. Other higher pressures, although at lower

tensile strength limits, have also been used.

In recent years, improvements in steelmaking, e.g. by reducing the sulphur and phosphorus contents,

have indicated the possibility of increasing the tensile strength limit of 950 MPa for embrittling gas

service. Experimental work has shown that the relevant parameters affecting hydrogen embrittlement

are the following:

a) microstructure resulting from the combination of the chemistry and the heat treatment;

b) mechanical properties of the material;
c) applied stress;
d) internal surface imperfections resulting in local stress concentrations;
e) characteristics of the gas contained (composition, quality, pressure, etc.).

When developing this document, only the material aspects, a) and b) and the characteristics of the

gas e) above, were considered. Other essential features, c) and d), are covered by the relevant parts of

ISO 9809.

Some low alloy steels other than 34 Cr Mo 4 may require tensile strength to be lower than 950 MPa, or

may be permitted to be higher than 950 MPa, to be suitable for the manufacture of gas cylinders for

embrittling gas service.

This document specifies test methods to identify steels which, when combined with the cylinder

manufacturing requirements specified in ISO 9809 (all parts), will result in cylinders suitable for use in

embrittling gas service.

These tests have been developed following an extensive world-wide programme which incorporated

laboratory and full scale tests. See also AFNOR FD E29-753.
© ISO 2017 – All rights reserved v
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SIST EN ISO 11114-4:2017
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SIST EN ISO 11114-4:2017
INTERNATIONAL STANDARD ISO 11114-4:2017(E)
Transportable gas cylinders — Compatibility of cylinder
and valve materials with gas contents —
Part 4:
Test methods for selecting steels resistant to hydrogen
embrittlement
1 Scope

This document specifies test methods and the evaluation of results from these tests in order to qualify

steels suitable for use in the manufacture of gas cylinders (up to 3 000 l) for hydrogen and hydrogen

bearing embrittling gases.
This document only applies to seamless steel gas cylinders.

The requirements of this document are not applicable if at least one of the following conditions for the

intended gas service is fulfilled:

— the working pressure of the filled embrittling gas is less than 20 % of the test pressure of the

cylinder;

— the partial pressure of the filled embrittling gas of a gas mixture is less than 5 MPa (50 bar) in the

case of hydrogen and other embrittling gases, with the exception of hydrogen sulphide and methyl

mercaptan; in such cases, the partial pressure shall not exceed 0,25 MPa (2,5 bar).

NOTE In such cases, it is possible to design the cylinder as for ordinary (non-embrittling) gases.

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 7539-1, Corrosion of metals and alloys — Stress corrosion testing — Part 1: General guidance on testing

procedures

ISO 7539-6:2011, Corrosion of metals and alloys — Stress corrosion testing — Part 6: Preparation and use

of precracked specimens for tests under constant load or constant displacement

ISO 9809-1, Gas cylinders — Refillable seamless steel gas cylinders — Design, construction and testing —

Part 1: Quenched and tempered steel cylinders with tensile strength less than 1 100 MPa

ISO 9809-2, Gas cylinders — Refillable seamless steel gas cylinders — Design, construction and testing —

Part 2: Quenched and tempered steel cylinders with tensile strength greater than or equal to 1 100 MPa

ISO 11114-1:2012, Gas cylinders — Compatibility of cylinder and valve materials with gas contents —

Part 1: Metallic materials

ISO 11120, Gas cylinders — Refillable seamless steel tubes of water capacity between 150 l and 3000 l —

Design, construction and testing
© ISO 2017 – All rights reserved 1
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SIST EN ISO 11114-4:2017
ISO 11114-4:2017(E)
3 Terms, definitions, symbols and abbreviated terms
3.1 Terms and definitions

For the purposes of this document, the following terms and definitions apply. Some of the definitions

used are based upon those in ISO 7539-1 and ISO 7539-6.

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 http:// www .iso .org/ obp
3.1.1
embrittling gases

gases which can cause cracking of metal due to the combined action of stress and hydrogen atoms

Note 1 to entry: Embrittling gases are listed as groups 2 and 11 in ISO 11114-1:2012, A.4.

3.1.2
hydrogen rupture pressure
maximum pressure recorded during the hydrogen rupture pressure test
3.1.3
helium rupture pressure
maximum pressure recorded during the helium rupture pressure test
3.1.4
hydrogen embrittlement index
maximum value of the ratio P /P as a function of the pressure rise rate
He H2
3.1.5
environmentally-assisted cracking

synergistic effect on a metal caused by the simultaneous action of a particular environment and a

nominally static tensile stress, which results in the formation of cracking
3.1.6
threshold stress

stress above which a crack will initiate and grow, for the specified test conditions

3.1.7
plane strain stress intensity factor

function of applied load, crack length and specimen geometry having dimensions of stress × length

which uniquely define the elastic-stress field intensification at the tip of a crack subjected to opening

mode displacements (mode I)

Note 1 to entry: K uniquely defines the elastic stress field intensification at the tip of a crack subjected to opening

mode displacements.
3.1.8

threshold stress intensity factor for susceptibility to environmentally-assisted cracking

stress intensity factor above which an environmentally-assisted crack will initiate and grow, for

the specified test conditions under conditions of high constraint to plastic deformation, i.e. under

essentially plane strain conditions
2 © ISO 2017 – All rights reserved
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SIST EN ISO 11114-4:2017
ISO 11114-4:2017(E)
3.2 Symbols and abbreviated terms
a effective crack length measured from the crack tip to the loading plane
a average value of a
B specimen thickness
e mean disc thickness
E modulus of elasticity
K applied elastic stress-intensity factor
IAPP
K threshold stress intensity factor
m elastic displacement per unit load
P applied load
P actual rupture pressure
P ′ corrected rupture pressure
P ′ corrected hydrogen rupture pressure
r H2

P ′ theoretical helium rupture pressure corresponding to the same pressure rise rate as for the

r He

hydrogen test, calculated by regression from the corrected helium rupture pressure

R actual value of tensile strength

V crack-mouth opening displacement (CMOD) defined as the mode 1 (also called opening-mode)

component of crack displacement due to elastic and plastic deformation, measured at the

location on a crack surface that has the greatest elastic displacement per unit load, m

W effective width of a compact specimen, measured from the back face to the loading plane

Y stress intensity factor coefficient derived from the stress analysis for a particular specimen

geometry, which relates the stress intensity factor for a given crack length to the load and

specimen dimensions
HAC hydrogen assisted cracking
4 General requirements

The test methods as described in Clause 5 are valid for all designed working pressures. The test shall

be performed at room temperature at not less than the designed working pressure. All tests shall be

conducted to evaluate the hydrogen embrittlement taking into account conditions that will be found in

the intended application. The composition of the tested gas shall have a concentration of embrittling gas

not less than the maximum concentration in the intended application. The tests shall be performed for

selecting steels for hydrogen/embrittling gases and mixtures cylinders. Chromium-molybdenum steels,

quenched and tempered with a guaranteed maximum actual ultimate tensile strength of 950 MPa,

do not need to be tested and can safely be used for the construction of hydrogen/embrittling gases

cylinders; however, H S mixtures at more than 100 bar working pressure need to be tested. For carbon-

manganese steels, different limits on ultimate tensile strength apply (as described in ISO 9809-1).

The tests described in Clause 5 are “qualification tests” for a given steel composition and heat treatment.

This means that the tests need not be repeated for each type, as defined in ISO 9809 (all parts), of

cylinder once a steel has been qualified for a specific design strength level.
© ISO 2017 – All rights reserved 3
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SIST EN ISO 11114-4:2017
ISO 11114-4:2017(E)

The test samples shall be taken from a representative cylinder or from a piece of tube (for long

cylinders, according to ISO 11120), representative of the relevant manufacturing process including heat

treatment.

The test samples shall have a mechanical strength not lower than the maximum intended tensile

strength to be used for the cylinders to be manufactured. If it is intended later to increase the maximum

strength of the steel, a new qualification test shall be performed.

With respect to the possible variation of the chemical composition, the chemistry of the steel tested shall

be recorded in the qualification test report and the difference in chemistry for the steels actually used

for the cylinders shall not exceed the “permissible difference” according to ISO 9809-2. In addition, for

sulphur and phosphorus, these permissible differences are limited to 0,005 % and 0,010 %, respectively.

In no case shall the phosphorus content of either the qualification or the production cylinders exceed

0,015 %.

With respect to the heat treatment, the manufacturer shall specify the relevant temperatures and

times, and the quenching conditions (if relevant). Any modification to the heat treatment needing a new

type approval according to ISO 9809-2 requires a new qualification test.

For the qualification of a given steel for the manufacturing of gas cylinders, method A, B, or C can be

used (see 5.1, 5.2 and 5.3, respectively). Additionally, tensile tests shall be carried out (see 5.4).

5 Test methods
5.1 Disc test (method A)
5.1.1 Principle of test

A mounted test piece in the shape of a disc is subjected to an increasing gas pressure at constant rate

to burst or to crack. The embrittling effect of hydrogen (or other embrittling gas) is evidenced by

comparing the hydrogen rupture pressures, P , with the helium rupture pressures, P , helium being

H2 He
chosen as a reference gas.
The ratio P /P shall be determined.
He H2

The lower the ratio, the less susceptible the steel will be to embrittlement. This ratio is dependent on

the pressure rise rate, which shall remain constant during the whole test.

NOTE Hydrogen/embrittling gases rupture pressures also depend on the hydrogen purity. Oxygen or traces

of water vapour can partially inhibit the hydrogen embrittlement effect.
5.1.2 Test conditions and procedure
5.1.2.1 Sample disc

The sample disc shall be flat and ground (or machined to an equivalent surface finish), and shall have

the following characteristics.
Dimensions:
— diameter: 58 mm;
−0,05
— thickness: 0,75 mm ± 0,01 mm;
— flatness: less than 1/10 mm deflection.

NOTE 1 The hydrogen rupture pressures are in the range of 300 bar. If it is intended to evaluate the steel for

higher working pressure, thickness higher than 0,75 mm can be used.
4 © ISO 2017 – All rights reserved
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SIST EN ISO 11114-4:2017
ISO 11114-4:2017(E)

NOTE 2 For gases intended to be used at maximum working pressure less than 100 bar, the test results could

be conservative. In such case, the test could be repeated with disk at thickness such that the failure pressure is

no more than service pressure.
Surface condition (both sides):

— roughness: Ra value (see ISO 4287) less than 0,001 mm; the roughness of the samples used for both

H and He tests shall be equivalent;
— no visible oxides.
The following operations shall be performed to verify the sample quality.

— Immediately after the final preparation and prior to the testing, store the samples in a dry

atmosphere, i.e. a desiccator.

— Degrease the sample and check thickness at 4 points taken 90° apart to define a mean thickness.

— Determine the disc’s hardness (e.g. Vickers) over its outer circumference (outside the O-ring zone)

to verify that machining has not altered the original material properties.
5.1.2.2 Cell and other apparatus
The cell (see Figure 2) is compos
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