SIST EN ISO 9809-4:2026

SLOVENSKI STANDARD
01-maj-2026
Nadomešča:
SIST EN ISO 9809-4:2023
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 9809-4:2026)
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 9809-4:2026)
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 9809-4:2026)
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 9809-4:2026)
Ta slovenski standard je istoveten z: EN ISO 9809-4:2026
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
March 2026
EUROPÄISCHE NORM
ICS 23.020.35 Supersedes EN ISO 9809-4:2022
English Version
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 9809-4:2026)
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 9809-4:2026)
9809-4:2026)
This European Standard was approved by CEN on 20 February 2026.

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
© 2026 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 9809-4:2026 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 9809-4:2026) 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 September 2026, and conflicting national standards
shall be withdrawn at the latest by September 2026.
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 supersedes EN ISO 9809-4:2022.
This document has been prepared under a standardization request addressed to CEN by the European
Commission. The Standing Committee of the EFTA States subsequently approves these requests for its
Member States.
Any feedback and questions on this document should be directed to the users’ national standards
body/national committee. 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 9809-4:2026 has been approved by CEN as EN ISO 9809-4:2026 without any
modification.
International
Standard
ISO 9809-4
Third edition
Gas cylinders — Design,
2026-02
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 ayant une valeur de R
m
inférieure à 1 100 MPa
Reference number
ISO 9809-4:2026(en) © ISO 2026

ISO 9809-4:2026(en)
© ISO 2026
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: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
ISO 9809-4:2026(en)
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
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 .9
7.5 Neck design .10
7.6 Foot rings . .10
7.7 Neck rings .10
7.8 Design drawing .11
8 Construction and workmanship .11
8.1 General .11
8.2 Wall thickness .11
8.3 Surface imperfections .11
8.4 Ultrasonic examination .11
8.5 Out-of-roundness . 12
8.6 Mean diameter . 12
8.7 Straightness . 12
8.8 Verticality and stability . 12
8.9 Neck threads . 13
9 Type approval procedure .13
9.1 General requirements . 13
9.2 Prototype test .14
9.2.1 General requirements .14
9.2.2 Pressure cycling test .14
9.2.3 Base check . 15
9.2.4 Bend test and flattening test . 15
9.2.5 Torque test for taper thread only .16
9.2.6 Shear stress calculation for parallel threads .17
9.3 Type approval certificate .17
9.4 Specific type approval/production tests for cylinders ordered in quantities below 200 .17
10 Batch tests . .18
10.1 General requirements .18
10.2 Tensile test .19
10.3 Impact test . 20
10.4 Hydraulic burst test . 22
10.4.1 Test installation . . 22
10.4.2 Test conditions . 23
10.4.3 Interpretation of test results .24

iii
ISO 9809-4:2026(en)
10.5 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 Water -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 .42
Annex C (informative) Example of type approval certificate .48
Annex D (informative) Example of acceptance certificate .49
Annex E (informative) Example of shear strength calculation for parallel threads .51
Bibliography .53

iv
ISO 9809-4:2026(en)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document 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 not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
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, in collaboration with the European Committee for Standardization (CEN) Technical Committee CEN/
TC 23, Transportable gas cylinders, in accordance with the Agreement on technical cooperation between ISO
and CEN (Vienna Agreement).
This third edition cancels and replaces the second edition (ISO 9809-4:2021), which has been technically
revised.
The main changes are as follows:
— modification of definition in 3.8;
— modification of Formula 1 in 7.2;
— bend test and flattening test moved under Clause 9 (prototype tests);
— clarification of shear stress calculation for parallel threads;
— clarification of 9.4;
— update of Bibliography.
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 9809-4:2026(en)
Introduction
This document provides a specification for the design, construction, 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 9809-4:2026(en)
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

ISO 9809-4:2026(en)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 10286 and the following apply.
ISO and IEC maintain terminology 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 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
result of a treatment to a piece of equipment that renders it impossible to enter into service
Note 1 to entry: Examples for acceptable methods to render cylinders unserviceable can be found in ISO 18119.
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 lower critical point (Ac ) of the steel
ISO 9809-4:2026(en)
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 at-
y
mospheric pressure
ISO 9809-4:2026(en)
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 ISO 6892-1
o
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
For assessment of conformity to this document, users shall be aware of applicable country-specific
regulations.
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 means to identify the cylinders with the cast of steel from
which they are made.
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).

ISO 9809-4:2026(en)
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.
If check are 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 9809-4:2026(en)
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
 
a1 (1)
 
2 10FR
eg
 
where
a is the calculated minimum thickness, in millimetres, of the cylindrical shell;
D is the nominal outside diameter of the cylinder, in millimetres;
R is the minimum guaranteed value of the yield strength (see 7.1.1), in megapascals, for the
eg
finished cylinder;
p is the hydraulic test pressure, in bar, above atmospheric pressure.
h
06, 5
where the value of F (design stress factor) is the lesser of or 0,85.
RR
eg mg
R
eg
shall not exceed 0,90.
R
mg
where R minimum guaranteed value of the tensile strength, in megapascals, for the finished cylinder.
mg
ISO 9809-4:2026(en)
The wall thickness shall also satisfy Formula (2):
D
a1 (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
NOTE It is generally assumed that p = 1,5 times working pressure for compressed gases for cylinders designed
h
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 as follows: 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.

ISO 9809-4:2026(en)
a) b) c)
d) e) f)
ISO 9809-4:2026(en)
Key
1 cylindrical part
a′ guaranteed minimum thickness, in millimetres, of the cylindrical shell
b guaranteed minimum thickness, in millimetres, at the centre of a convex base
D nominal outside diameter of the cylinder, in millimetres
H outside height, in millimetres, of the domed part (convex head or base end)
r inside knuckle radius, in millimetres
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.
where
a is the calculated minimum thickness, in millimetres, of the cylindrical shell;
a guaranteed minimum thickness, in millimetres, of a concave base at the knuckle;
a guaranteed minimum thickness, in millimetres, at the centre of a concave base;
D is the nominal outside diameter of the cylinder, in millimetres;
h outside depth (concave base end), in millimetres;
r inside knuckle radius, in millimetres.
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 9809-4:2026(en)
Key
a′ guaranteed minimum thickness, in millimetres, of the cylindrical shell
a guaranteed minimum thickness, in millimetres, of a concave base at the knuckle
a guaranteed minimum thickness, in millimetres, at the centre of a concave base
D nominal outside diameter of the cylinder, in millimetres
r inside knuckle radius, in millimetres
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 th
...