EN ISO 9809-4:2022

Gas cylinders - Design, construction and testing of refillable seamless steel gas cylinders and tubes - Part 4: Stainless steel cylinders with an Rm value of less than 1 100 MPa (ISO 9809-4:2021)

This document specifies the minimum requirements for the materials, design, construction and workmanship, manufacturing processes, examinations and testing at time of manufacture for refillable, seamless, stainless steel gas cylinders with water capacities up to and including 150 l.
It is applicable to cylinders for compressed, liquefied and dissolved gases with a maximum actual tensile strength, Rma, of less than 1 100 MPa.
NOTE         If so desired, cylinders of water capacity between 150 l and 450 l can be manufactured to be in full conformance to this document.

Gasflaschen - Auslegung, Herstellung und Prüfung von wiederbefüllbaren nahtlosen Gasflaschen aus Stahl - Teil 4: Flaschen aus Edelstahl mit einem Rm-Wert von weniger als 1 100 MPa (ISO 9809-4:2021)

Dieses Dokument legt die Mindestanforderungen an die Werkstoffe, Auslegung, den Bau und die Ausführung, Herstellungsverfahren, Herstellungsuntersuchungen und  prüfungen für wiederbefüllbare nahtlose Gasfla¬schen aus nichtrostendem Stahl mit Fassungsräumen bis einschließlich 150 l (bezogen auf Wasser) fest.
Es ist anzuwenden für Flaschen für verdichtete, verflüssigte und gelöste Gase mit einer tatsächlichen Höchst Zugfestig¬keit Rma von weniger als 1 100 MPa.
ANMERKUNG   Falls gewünscht, können Gasflaschen mit einem Fassungsraum zwischen 150 l und 450 l hergestellt werden, die mit diesem Dokument vollständig übereinstimmen.

Bouteilles à gaz - Conception, construction et essais des bouteilles à gaz et des tubes rechargeables en acier sans soudure - Partie 4: Bouteilles en acier inoxydable ayant une valeur de Rm inférieure à 1 100 MPa (ISO 9809-4:2021)

Le présent document spécifie les exigences minimales concernant le matériau, la conception, la construction et la mise en œuvre, les procédés de fabrication, les examens et les essais au moment de la fabrication des bouteilles à gaz rechargeables en acier sans soudure d’une contenance en eau inférieure ou égale à 150 l.
Il s’applique aux bouteilles pour les gaz comprimés, liquéfiés et dissous ayant une résistance à la traction réelle, Rma, maximale inférieure à 1 100 MPa.
NOTE            Si cela est souhaité, les bouteilles d’une contenance en eau comprise entre 150 l et 450 l peuvent être fabriquées conformément au présent document.

Plinske jeklenke - Konstruiranje, izdelava in preskušanje ponovno polnljivih plinskih jeklenk in velikih jeklenk iz celega iz jekla - 4. del: Nerjavne jeklenke iz jekla z vrednostjo Rm, manjšo od 1100 MPa (ISO 9809-4:2021)

Ta dokument določa minimalne zahteve za materiale, konstruiranje, izdelavo in izvedbo, postopke izdelave, pregled in preskušanje ob času proizvodnje za ponovno polnljive nevarjene plinske jeklenke s prostornino vode do vključno 150 l.
Uporablja se za jeklenke za stisnjene, utekočinjene in raztopljene pline z največjo dejansko natezno trdnostjo Rma, manjšo od 1100 MPa.
OPOMBA:   Po želji je mogoče izdelati jeklenke s prostornino vode med 150 l in 450 l, ki so popolnoma skladne s tem dokumentom.

General Information

• Status: Published
• Publication Date: 13-Dec-2022
• ICS: 23.020.35 - Gas cylinders
• Technical Committee: CEN/TC 23 - Transportable gas cylinders
• Drafting Committee: CEN/TC 23/SC 1/WG 1 - Seamless steel cylinders
• Current Stage: 6060 - Definitive text made available (DAV) - Publishing
• Start Date: 14-Dec-2022
• Completion Date: 14-Dec-2022
• Directive: 2008/68/EC - Directve 2008/68/EC of the European Parliament and of the council of 24 September 2008 on the inland transport of the dangerous goods
• Mandate: M/TDG - Standards for referencing in the RID-ADR
• Ref Project: SIST EN ISO 9809-4:2023 - Gas cylinders - Design, construction and testing of refillable seamless steel gas cylinders and tubes - Part 4: Stainless steel cylinders with an Rm value of less than 1 100 MPa (ISO 9809-4:2021)

Relations

• Revised: FprEN ISO 9809-4 - Gas cylinders - Design, construction and testing of refillable seamless steel gas cylinders and tubes - Part 4: Stainless steel cylinders with an R m value of less than 1 100 MPa (ISO/FDIS 9809-4:2025)
• Effective Date: 11-Oct-2023

Overview - EN ISO 9809-4:2022 (Stainless steel gas cylinders)

EN ISO 9809-4:2022 adopts ISO 9809-4:2021 and specifies the minimum requirements for the design, construction and testing of refillable, seamless stainless steel gas cylinders (water capacity up to and including 150 L) with a maximum tensile strength (Rm) of less than 1 100 MPa. The standard applies to cylinders for compressed, liquefied and dissolved gases and may be used optionally for cylinders up to 450 L when full conformance is desired. As a CEN-adopted national standard, it supports regulatory compliance and safe manufacture in European markets.

Keywords: EN ISO 9809-4:2022, gas cylinders, stainless steel cylinders, refillable seamless steel gas cylinders, design construction testing

Key topics and technical requirements

The document structures the lifecycle requirements for stainless steel refillable cylinders. Major technical topics include:

• Materials: chemical composition controls, heat treatment, cold working/cryoforming and acceptance criteria for stainless steels with Rm < 1 100 MPa.
• Design: shell and head thickness calculation, convex/concave end design, neck and thread geometry, foot and neck rings, and required design drawings.
• Manufacturing and workmanship: wall thickness tolerances, surface imperfection limits, out-of-roundness, mean diameter, straightness, verticality and stability.
• Examination and non‑destructive testing: ultrasonic examination, leak testing and capacity checks.
• Type approval and certification: prototype tests, pressure cycling, base checks and type approval documentation.
• Batch and per‑cylinder tests:
  • Batch tests such as tensile, bend/flattening, impact, intergranular corrosion and hydraulic burst testing.
  • Tests on every cylinder including hydraulic proof/volumetric expansion, hardness, leak tests and capacity verification.
• Inspection procedures and documentation: traceability, test records and certification requirements.

Practical applications and users

This standard is essential for organizations involved in the production, certification and use of refillable stainless steel gas cylinders:

• Cylinder manufacturers and design engineers - to ensure compliant design and production processes.
• Testing laboratories and inspection bodies - for type approval, batch testing and routine inspections.
• Gas suppliers, distributors and industrial end-users - to verify cylinder safety, compatibility and regulatory compliance.
• Regulators and certification authorities - to reference for national adoption and conformity assessment.

Benefits include enhanced safety, consistent test methods, regulatory alignment and improved interchangeability of cylinders across markets.

Related standards

• Part of the ISO 9809 series (EN ISO 9809-4:2022 corresponds to ISO 9809-4:2021).
• Users should consider other parts of ISO 9809 (other materials or strength classes) and applicable national/regional transport and pressure-equipment regulations when implementing this standard.

Standards Content (Sample)

SLOVENSKI STANDARD
01-april-2023
Plinske jeklenke - Konstruiranje, izdelava in preskušanje ponovno polnljivih
plinskih jeklenk in velikih jeklenk iz celega iz jekla - 4. del: Nerjavne jeklenke iz
jekla z vrednostjo Rm, manjšo od 1100 MPa (ISO 9809-4:2021)
Gas cylinders - Design, construction and testing of refillable seamless steel gas cylinders
and tubes - Part 4: Stainless steel cylinders with an Rm value of less than 1 100 MPa
(ISO 9809-4:2021)
Gasflaschen - Auslegung, Herstellung und Prüfung von wiederbefüllbaren nahtlosen
Gasflaschen aus Stahl - Teil 4: Flaschen aus Edelstahl mit einem Rm-Wert von weniger
als 1 100 MPa (ISO 9809-4:2021)
Bouteilles à gaz - Conception, construction et essais des bouteilles à gaz et des tubes
rechargeables en acier sans soudure - Partie 4: Bouteilles en acier inoxydable avec une
valeur Rm inférieure à 1 100 MPa (ISO 9809-4:2021)
Ta slovenski standard je istoveten z: EN ISO 9809-4:2022
ICS:
23.020.35 Plinske jeklenke Gas cylinders
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 9809-4
EUROPEAN STANDARD
NORME EUROPÉENNE
December 2022
EUROPÄISCHE NORM
ICS 23.020.35
English Version
Gas cylinders - Design, construction and testing of
refillable seamless steel gas cylinders and tubes - Part 4:
Stainless steel cylinders with an Rm value of less than 1
100 MPa (ISO 9809-4:2021)
Bouteilles à gaz - Conception, construction et essais des Gasflaschen - Auslegung, Herstellung und Prüfung von
bouteilles à gaz et des tubes rechargeables en acier wiederbefüllbaren nahtlosen Gasflaschen aus Stahl -
sans soudure - Partie 4: Bouteilles en acier inoxydable Teil 4: Flaschen aus Edelstahl mit einem Rm-Wert von
ayant une valeur de Rm inférieure à 1 100 MPa (ISO weniger als 1 100 MPa (ISO 9809-4:2021)
9809-4:2021)
This European Standard was approved by CEN on 11 December 2022.

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, 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, Türkiye 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
© 2022 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 9809-4:2022 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
The text of ISO 9809-4:2021 has been prepared by Technical Committee ISO/TC 58 "Gas cylinders” of
the International Organization for Standardization (ISO) and has been taken over as EN ISO 9809-
4:2022 by 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 June 2023, and conflicting national standards shall be
withdrawn at the latest by June 2023.
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.
This document has been prepared under a Standardization Request given to CEN by the European
Commission and the European Free Trade Association.
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.
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, 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, Türkiye and the
United Kingdom.
Endorsement notice
The text of ISO 9809-4:2021 has been approved by CEN as EN ISO 9809-4:2022 without any
modification.
INTERNATIONAL ISO
STANDARD 9809-4
Second edition
2021-11
Gas cylinders — Design, construction
and testing of refillable seamless steel
gas cylinders and tubes —
Part 4:
Stainless steel cylinders with an R
m
value of less than 1 100 MPa
Bouteilles à gaz — Conception, construction et essais des bouteilles à
gaz et des tubes rechargeables en acier sans soudure —
Partie 4: Bouteilles en acier inoxydable avec une valeur R
m
inférieure à 1 100 MPa
Reference number
ISO 9809-4:2021(E)
ISO 9809-4:2021(E)
© ISO 2021
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
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
ISO 9809-4:2021(E)
Contents Page
Foreword .v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols . 3
5 Inspection and testing .4
6 Materials . 4
6.1 General requirements . 4
6.2 Controls on chemical composition . 5
6.3 Heat treatment. 5
6.4 Cold working or cryoforming . 5
6.5 Failure to meet test requirements . 6
7 Design . 6
7.1 General requirements . 6
7.2 Design of cylindrical shell thickness . 6
7.3 Design of convex ends (heads and bases) . 7
7.4 Design of the concave base ends . 8
7.5 Neck design . 9
7.6 Foot rings . . 9
7.7 Neck rings . 9
7.8 Design drawing . 10
8 Construction and workmanship .10
8.1 General . 10
8.2 Wall thickness . 10
8.3 Surface imperfections . 10
8.4 Ultrasonic examination . 10
8.5 Out-of-roundness . 11
8.6 Mean diameter . 11
8.7 Straightness . 11
8.8 Verticality and stability . 11
8.9 Neck threads .12
9 Type approval procedure .12
9.1 General requirements . 12
9.2 Prototype test . 13
9.2.1 General requirements . 13
9.2.2 Pressure cycling test . 14
9.2.3 Base check . 14
9.2.4 Torque test for taper thread only . 15
9.2.5 Shear stress calculation for parallel threads . 15
9.3 Type approval certificate .15
9.4 Specific type approval/production tests for cylinders ordered in small quantities . 16
10 Batch tests . .16
10.1 General requirements . 16
10.2 Tensile test . 18
10.3 Bend test and flattening test . 19
10.3.1 Bend test . 19
10.3.2 Flattening test . . 20
10.3.3 Ring flattening test. 20
10.4 Impact test . 20
iii
ISO 9809-4:2021(E)
10.5 Hydraulic burst test . 22
10.5.1 Test installation . .22
10.5.2 Test conditions . 23
10.5.3 Interpretation of test results . 24
10.6 Intergranular corrosion test .25
11 Tests/examinations on every cylinder .25
11.1 General . 25
11.2 Hydraulic test . 26
11.2.1 Proof pressure test .26
11.2.2 Volumetric expansion test . 26
11.3 Hardness test . 26
11.4 Leak test . 26
11.5 Capacity check . 27
12 Certification .27
13 Marking . .27
Annex A (normative) Description and evaluation of manufacturing imperfections and
conditions for rejection of seamless steel gas cylinders at the time of final
inspection by the manufacturer.28
Annex B (normative) Ultrasonic examination .43
Annex C (informative) Example of type approval certificate .49
Annex D (informative) Example of acceptance certificate .50
Annex E (informative) Example of shear strength calculation for parallel threads .52
Bibliography .54
iv
ISO 9809-4:2021(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 58, Gas cylinders, Subcommittee SC 3,
Cylinder design.
This second edition cancels and replaces the first edition (ISO 9809-4:2014), which has been technically
revised. The main changes compared with the previous edition are as follows:
— update of Clause 5;
— clarification of Figure 3;
— clarification of 8.9;
— modification of 9.1, 9.2, 9.2.4 and Annex A;
— new subclause 9.2.5 for parallel threads;
— new subclause 9.4 for cylinders ordered in small quantities.
A list of all parts in the ISO 9809 series can be found on the ISO website.
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.
v
ISO 9809-4:2021(E)
Introduction
This document provides a specification for the design, manufacture, inspection and testing of a
seamless stainless steel cylinder. The objective is to balance the design and economic efficiency against
international acceptance and universal utility.
ISO 9809 (all parts) aims to eliminate the concern about climate, duplicate inspections and restrictions
because of the lack of definitive International Standards.
[1]
This document has been written so that it is suitable to be referenced in the UN Model Regulations .
vi
INTERNATIONAL STANDARD ISO 9809-4:2021(E)
Gas cylinders — Design, construction and testing of
refillable seamless steel gas cylinders and tubes —
Part 4:
Stainless steel cylinders with an R value of less than 1 100
m
MPa
1 Scope
This document specifies the minimum requirements for the materials, design, construction and
workmanship, manufacturing processes, examinations and testing at time of manufacture for refillable,
seamless, stainless steel gas cylinders with water capacities up to and including 150 l.
It is applicable to cylinders for compressed, liquefied and dissolved gases with a maximum actual
tensile strength, R , of less than 1 100 MPa.
ma
NOTE If so desired, cylinders of water capacity between 150 l and 450 l can be manufactured to be in full
conformance to this document.
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 148-1, Metallic materials — Charpy pendulum impact test — Part 1: Test method
ISO 3651-2, Determination of resistance to intergranular corrosion of stainless steels — Part 2:
Ferritic,austenitic and ferritic-austenitic (duplex) stainless steels — Corrosion test in media containing
sulfuric acid
ISO 6506-1, Metallic materials — Brinell hardness test — Part 1: Test method
ISO 6508-1, Metallic materials — Rockwell hardness test — Part 1: Test method
ISO 6892-1, Metallic materials — Tensile testing — Part 1: Method of test at room temperature
ISO 9328-1, Steel flat products for pressure purposes — Technical delivery conditions — Part 1: General
requirements
ISO 9329-4, Seamless steel tubes for pressure purposes — Technical delivery conditions — Part 4: Austenitic
stainless steels
ISO 9712, Non-destructive testing — Qualification and certification of NDT personnel
ISO 10286, Gas cylinders — Vocabulary
ISO 13341, Gas cylinders — Fitting of valves to gas cylinders
ISO 13769, Gas cylinders — Stamp marking
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 10286 and the following apply.
ISO 9809-4:2021(E)
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
batch
quantity of up to 200 cylinders, plus cylinders for destructive testing of the same nominal diameter,
thickness, length and design made successively on the same equipment, from the same cast of steel, and
subjected to the same heat treatment for the same duration of time
3.2
burst pressure
p
b
highest pressure reached in a cylinder during a burst test
3.3
cold working
process in which a cylinder is subjected to a pressure higher than the cylinder test pressure (3.11) to
increase the yield strength (3.12) of the steel
3.4
cryoforming
process where the cylinder is subjected to a controlled low-temperature deformation treatment that
results in a permanent increase in strength
3.5
design stress factor
F
ratio of the equivalent wall stress at test pressure, p , (3.11) to guaranteed minimum yield strength, R
h eg
3.6
quenching
hardening heat treatment in which a cylinder, which has been heated to a uniform temperature above
the upper critical point, Ac , of the steel, is cooled rapidly on a suitable medium
3.7
reject
action to set aside a cylinder (Level 2 or Level 3) that is not allowed to go into service
3.8
rendered unserviceable
cylinder that has been treated in such a way as to render it impossible for use
Note 1 to entry: Examples for acceptable methods to render cylinders unserviceable can be found in ISO 18119.
Any actions on cylinders rendered unserviceable are outside the scope of this document.
3.9
repair
action to return a rejected cylinder to a Level 1 condition
3.10
tempering
toughening heat treatment which follows quenching (3.6), in which the cylinder is heated to a uniform
temperature below the critical point, Ac , of the steel
ISO 9809-4:2021(E)
3.11
test pressure
p
h
required pressure applied during a pressure test
Note 1 to entry: Test pressure is used for the cylinder wall thickness calculation.
3.12
yield strength
stress value corresponding to the 0,2 % proof stress or for austenitic steels in the solution-annealed
condition, 1 % proof stress
3.13
working pressure
settled pressure of a compressed gas at a uniform reference temperature of 15 °C in a full gas cylinder
4 Symbols
A percentage elongation after fracture
a calculated minimum thickness, in millimetres, of the cylindrical shell
a′ guaranteed minimum thickness, in millimetres, of the cylindrical shell
a guaranteed minimum thickness, in millimetres, of a concave base at the knuckle (see Figure 2)
a guaranteed minimum thickness, in millimetres, at the centre of a concave base (see Figure 2)
b guaranteed minimum thickness, in millimetres, at the centre of a convex base (see Figure 1)
c maximum permissible deviation, in millimetres, of burst profile for quenched and tempered
cylinders (see Figure 11)
c maximum permissible deviation, in millimetres, of the burst profile for cryoformed or solution-
annealed cylinders with less than 7,5 mm wall thickness (see Figure 12)
D nominal outside diameter of the cylinder, in millimetres (see Figure 1)
D diameter, in millimetres, of former (see Figure 6)
f
F design stress factor (variable)
H outside height, in millimetres, of the domed part (convex head or base end) (see Figure 1)
h outside depth (concave base end), in millimetres (see Figure 2)
L original gauge length, in millimetres, as defined in ISO 6892-1 (see Figure 5)
o
l overall length of the cylinder, in millimetres (see Figure 3)
n ratio of the diameter of the bend test former to the actual thickness of test piece, t
p measured burst pressure, in bar, above atmospheric pressure
b
NOTE 1 bar = 10 Pa = 0,1 MPa.
p hydraulic test pressure, in bar, above atmospheric pressure
h
p observed pressure when the cylinder starts yielding during the hydraulic burst test, in bar, above
y
atmospheric pressure
ISO 9809-4:2021(E)
r inside knuckle radius, in millimetres (see Figures 1 and 2)
R actual value of the yield strength, in megapascals, as determined by the tensile test (see 10.2)
ea
R minimum guaranteed value of the yield strength (see 7.1.1), in megapascals, for the finished cylinder
eg
R actual value of the tensile strength, in megapascals, as determined by the tensile test (see 10.2)
ma
R minimum guaranteed value of the tensile strength, in megapascals, for the finished cylinder
mg
S original cross-sectional area of the tensile test piece, in square millimetres, in accordance with
o
ISO 6892-1
t actual thickness of the test specimen, in millimetres
t average cylinder wall thickness at the position of testing during the flattening test, in millimetres
m
u ratio of the distance between the knife edges or platens in the flattening test to the average
cylinder wall thickness at the position of the test
V water capacity of the cylinder, in litres
w width, in millimetres, of the tensile test piece (see Figure 5)
5 Inspection and testing
Assessment of conformity to this document shall take into account the applicable regulations of the
countries of use.
To ensure that cylinders conform to this document, they shall be subject to inspection and testing in
accordance with Clauses 9, 10 and 11.
Tests and examinations performed to demonstrate compliance with this document shall be conducted
using instruments calibrated before being put into service and thereafter according to an established
programme.
6 Materials
6.1 General requirements
6.1.1 Materials for the manufacture of gas cylinders shall fall within one of the following categories:
a) internationally recognized cylinder steels;
b) nationally recognized cylinder steels;
c) new cylinder steels resulting from technical progress.
For all categories, the relevant conditions specified in 6.2 and 6.3 shall be satisfied.
6.1.2 There is a risk of intergranular corrosion in austenitic and duplex stainless steels resulting
from hot processing which can cause sensitization of the steel (e.g. chromium depletion in the grain
boundary). Intergranular corrosion testing shall be carried out for such materials in accordance with
10.6.
6.1.3 The cylinder manufacturer shall establish the means to identify the cylinders with the cast of
steel from which they are made.
ISO 9809-4:2021(E)
6.1.4 Grades of steel used for the cylinder manufacture shall be compatible with the intended gas
service, e.g. corrosive gases and embrittling gases (see ISO 11114-1).
6.1.5 Some grades of stainless steel can be susceptible to environmental stress corrosion cracking.
Special precautions shall be taken in such cases, such as appropriate coating.
6.1.6 Some grades of stainless steel can be susceptible to phase transformation at low temperatures
resulting in a brittle alloy. Special precautions shall be taken in such cases, i.e. not using the cylinder
below the minimum acceptable temperature.
6.2 Controls on chemical composition
6.2.1 The following are the four broad categories of stainless steels:
— ferritic;
— martensitic;
— austenitic;
— austenitic/ferritic (duplex).
Recognized steels are listed in ISO 15510. Other grades of stainless steel can also be used provided that
they fulfil all the requirements of this document.
6.2.2 The cylinder manufacturer shall obtain and make available certificates of cast (heat) analyses
of the steels supplied for the construction of gas cylinders.
Should check analyses be required, they shall be carried out either on the specimens taken during the
manufacture from the material in the form as supplied by the steel maker to the cylinder manufacturer,
or from finished cylinders. In any check analysis, the maximum permissible deviation from the limits
specified for the cast analyses shall conform to the values specified in ISO 9329-4.
6.3 Heat treatment
6.3.1 The cylinder manufacturer shall certify the heat treatment process applied to the finished
cylinders.
6.3.2 The finished cylinders made from the ferritic or martensitic steel categories shall be quenched
and tempered, except if they are cold worked (see 6.4).
6.3.3 For the ferritic and martensitic steels, the heat treatment process shall achieve the required
mechanical properties.
6.3.4 The actual temperature to which a type of steel is subjected to obtain a given tensile strength
shall not deviate by more than ±30 °C from the temperature specified by the cylinder manufacturer.
6.4 Cold working or cryoforming
Cold working or cryoforming is used to enhance the finished mechanical properties in certain stainless
steel materials.
For cylinders that are subjected to cold working or to the cryoforming process, all the heat treatment
requirements refer to the cylinder preform operations. Cold worked or cryoformed cylinders shall not
be subjected to any subsequent heat treatment.
ISO 9809-4:2021(E)
6.5 Failure to meet test requirements
In the event of failure to meet the test requirements, retesting or reheat treatment and retesting shall
be carried out as follows to the satisfaction of the inspector.
a) If there is evidence of a fault in carrying out a test, or an error of measurement, a further test shall
be performed. If the result of this test is satisfactory, the first test shall be ignored.
b) If the test has been carried out in a satisfactory manner, the cause of test failure shall be identified.
1) If the failure is considered to be due to the heat treatment applied, the manufacturer may
subject all the cylinders implicated by the failure to only one further heat treatment, e.g. if
the failure is in a test representing the prototype or batch cylinders. Test failure shall require
reheat treatment of all the represented cylinders prior to retesting. This reheat treatment
shall consist of either re-tempering or complete reheat treatment. Whenever the cylinders are
reheat-treated, the minimum guaranteed wall thickness shall be maintained. Only the relevant
prototype or batch tests needed to prove the acceptability of the new batch shall be performed
again. If one or more tests prove even partially unsatisfactory, all the cylinders of the batch
shall be rejected.
2) If the failure is due to a cause other than the heat treatment applied, all the cylinders with
imperfections shall be either rejected or repaired such that the repaired cylinders pass the
test(s) required for the repair. They shall then be reinstated as part of the original batch.
7 Design
7.1 General requirements
7.1.1 The calculation of the wall thickness of the pressure-containing parts shall be related to the
guaranteed minimum yield strength, R , of the material in the finished cylinder.
eg
7.1.2 Cylinders shall be designed with one or two openings along the central cylinder axis only.
7.1.3 The internal pressure upon which the calculation of wall thickness is based shall be the
hydraulic test pressure, p .
h
7.2 Design of cylindrical shell thickness
The guaranteed minimum thickness of the cylindrical shell, a′, shall not be less than the thickness
calculated using Formulae (1) and (2), and additionally, Formula (3) shall be satisfied.
 
10FR − 3p
D
eg h
 
a=−1 (1)
 
2 10FR
eg
 
where the value of F is equal to 0,77.
The wall thickness shall also satisfy Formula (2):
D
a≥+1 (2)
with an absolute minimum of a = 1,5 mm.
The burst ratio shall be satisfied by test as given in Formula (3).
p /p ≥ 1,6 (3)
b h
ISO 9809-4:2021(E)
NOTE It is generally assumed that p = 1,5 times working pressure for compressed gases for cylinders
h
designed and manufactured to conform with this document.
7.3 Design of convex ends (heads and bases)
7.3.1 When convex base ends (see Figure 1) are used, the thickness, b, at the centre of a convex end
shall be not less than that required by the following criteria: where the inside knuckle radius, r, is not
less than 0,075 D, then:
— b ≥ 1,5 a for 0,40 > H/D ≥ 0,20;
— b ≥ a for H/D ≥ 0,40.
To obtain a satisfactory stress distribution in the region where the end joins the shell, any thickening
of the end when required shall be gradual from the point of juncture, particularly at the base. For the
application of this rule, the point of juncture between the shell and the end is defined by the horizontal
lines indicating dimension H in Figure 1.
Shape b) shall not be excluded from this requirement.
7.3.2 The cylinder manufacturer shall prove by the pressure cycling test detailed in 9.2.2 that the
design is satisfactory.
The shapes shown in Figure 1 are typical of convex heads and base ends. Shapes a), b), d) and e) are
base ends, and shapes c) and f) are heads.
a) b) c)
ISO 9809-4:2021(E)
d) e) f)
Key
1 cylindrical part
Figure 1 — Typical convex ends
7.4 Design of the concave base ends
7.4.1 When concave base ends (see Figure 2) are used, the following design values are recommended:
— a ≥ 2 a;
— a ≥ 2 a;
— h ≥ 0,12 D;
— r ≥ 0,075 D.
The design drawing shall at least show values for a , a , h and r.
1 2
To obtain a satisfactory stress distribution, the thickness of the cylinder shall increase progressively in
the transition region between the cylindrical part and the base.
7.4.2 The cylinder manufacturer shall in any case prove by the application of the pressure cycling
test detailed in 9.2.2 that the design is satisfactory.

ISO 9809-4:2021(E)
Figure 2 — Concave base ends
7.5 Neck design
7.5.1 The external diameter and thickness of the formed neck end of the cylinder shall be adequate
for the torque applied in fitting the valve to the cylinder. The torque can vary according to the valve
type, diameter of the thread, the form of the thread and the sealant used in the fitting of the valve.
NOTE For information on torques, see ISO 13341.
7.5.2 In establishing the minimum thickness, the thickness of the wall in the cylinder neck shall
prevent permanent expansion of the neck during the initial and subsequent fittings of the valve into
the cylinder without support of an attachment. The external diameter and thickness of the formed neck
end of the cylinder shall not be damaged (no permanent expansion or crack) by the application of the
maximum torque required to fit the valve to the cylinder (see ISO 13341) and the stresses when the
cylinder is subjected to its test pressure. In specific cases (e.g. very thin-walled cylinders) where these
stresses cannot be supported by the neck itself, the neck maybe designed to require reinforcement,
such as a neck ring or shrunk on collar, provided the reinforcement material and dimensions are clearly
specified by the manufacturer and this configuration is part of the type approval procedure (see 9.2.4
and 9.2.5).
7.6 Foot rings
When a foot ring is provided, it shall be made of material compatible with that of the cylinder. The shape
should preferably be cylindrical and shall give the cylinder stability. The foot ring shall be secured to
the cylinder by a method other than welding, brazing or soldering. Any gaps which can form water
traps shall be sealed by a method other than welding, brazing or soldering.
7.7 Neck rings
When a neck ring is provided, it shall made of a material compatible with that of the cylinder and shall
be securely attached by a method other than welding, brazing or soldering.
The axial load to remove the neck ring shall be greater than 10 times the weight of the empty cylinder
but not less than 1 000 N, and that the torque to turn the neck ring is greater than 100 Nm.
ISO 9809-4:2021(E)
7.8 Design drawing
A fully dimensioned drawing shall be prepared which includes the specification of the material and
details relevant to the design of the permanent fittings. Dimensions of non-safety related fittings can be
agreed between the customer and manufacturer and need not be shown on the design drawing.
8 Construction and workmanship
8.1 General
The cylinder shall be produced by:
a) forging or drop forging from a solid ingot or billet;
b) manufacturing from seamless tube;
c) pressing from a flat plate;
d) cold working or cryoforming preform.
Metal shall not be added in the process of closure of the end. Manufacturing defects shall not be
corrected by plugging of bases (e.g. addition of metal by welding).
8.2 Wall thickness
During production, each cylinder or semi-finished shell shall be examined for thickness. The wall
thickness at any point shall be not less than the minimum thickness specified.
8.3 Surface imperfections
The internal and external surfaces of the finished cylinder shall be free from imperfections which could
adverse
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