ISO/FDIS 9809-4
(Main)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
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
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.
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
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.
General Information
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Standards Content (Sample)
FINAL DRAFT
International
Standard
ISO/TC 58/SC 3
Gas cylinders — Design,
Secretariat: BSI
construction and testing of
Voting begins on:
refillable seamless steel gas
2025-11-24
cylinders and tubes —
Voting terminates on:
2026-01-19
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 Rm
inférieure à 1 100 MPa
RECIPIENTS OF THIS DRAFT ARE INVITED TO SUBMIT,
WITH THEIR COMMENTS, NOTIFICATION OF ANY
RELEVANT PATENT RIGHTS OF WHICH THEY ARE AWARE
AND TO PROVIDE SUPPOR TING DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
ISO/CEN PARALLEL PROCESSING LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
Reference number
FINAL DRAFT
International
Standard
ISO/TC 58/SC 3
Gas cylinders — Design,
Secretariat: BSI
construction and testing of
Voting begins on:
refillable seamless steel gas
cylinders and tubes —
Voting terminates on:
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 Rm
inférieure à 1 100 MPa
RECIPIENTS OF THIS DRAFT ARE INVITED TO SUBMIT,
WITH THEIR COMMENTS, NOTIFICATION OF ANY
RELEVANT PATENT RIGHTS OF WHICH THEY ARE AWARE
AND TO PROVIDE SUPPOR TING DOCUMENTATION.
© ISO 2025
IN ADDITION TO THEIR EVALUATION AS
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BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
ISO/CEN PARALLEL PROCESSING
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
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ii
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 .5
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
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
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, 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
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
FINAL DRAFT International Standard ISO/FDIS 9809-4:2025(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 MPa
m
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 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
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
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).
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.
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
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
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
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.
a) b) c)
d) e) f)
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.
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 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 may be 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 shall be greater than 100 Nm.
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
adversely affect the safe working of the cylinder. Imperfections shall be evaluated as specified in Annex A.
8.4 Ultrasonic examination
8.4.1 After completion of the final heat treatment and cold working and after the final cylindrical wall
thickness has been achieved, each cylinder shall be ultrasonically examined for internal, external and sub-
surface imperfections in accordance with Annex B.
8.4.2 In addition to the ultrasonic examination as specified in 8.4.1, the cylindrical area to be closed (which
creates the shoulder and in case of cylinders made from tube, also the base) shall be ultrasonically examined
prior to the forming process to detect any defects that after closure could be positioned in the cylinder ends.
In case of cylinders produced from tubes (provided that the thickness of the tube is unaltered), this
additional test is not required if the tube is 100 % ultrasonic tested before closure of the ends in accordance
with Annex B.
The test shall be performed as close as possible to the open end of the shell.
The untested area shall extend to a length of not more than 40 mm from the open end of the shell.
In both 8.4.1 and 8.4.2, it is not required to perform the ultrasonic examination for small cylinders with a
cylindrical length of less than 200 mm or where p × V < 600 bar. l (for R ≥ 650 MPa) or p × V < 1 200 bar.
h ma h
l (for R < 650 MPa).
ma
8.5 Out-of-roundness
The out-of-roundness of the cylindrical shell, i.e. the difference between the maximum and minimum outside
diameters at the same cross-section, shall not exceed 2 % of the mean of these diameters.
For cold stretch and cryoformed cylinders, higher values are acceptable provided they are validated by the
pressure cycling test and the maximum shall be specified on the approved design drawing.
8.6 Mean diameter
The mean external diameter of the cylindrical part outside the transition zones on a cross-section shall not
deviate by more than ±1 % from the nominal design diameter.
For cold stretch and cryoformed cylinders, higher values are acceptable provided they are validated by the
pressure cycling test and the maximum shall be specified on the approved design drawing.
8.7 Straightness
The maximum deviation of the cylindrical part of the shell from a straight line
...
ISO/TC 58/SC 3
Secretariat: BSI
Date: 2025-07-2310-22
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 MPa
m
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 inférieure à 1 100 MPa
m
Partie 4: Bouteilles en acier inoxydable ayant une valeur de Rm inférieure à 1 100 MPa
FDIS stage
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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
Fax: + 41 22 749 09 47
E-mail: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
Contents
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ISO/DISFDIS 9809-4:2023(E2025(en)
Contents
Foreword . vi
Introduction . vii
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 . 5
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 . 10
7.5 Neck design . 11
7.6 Foot rings . 11
7.7 Neck rings . 12
7.8 Design drawing . 12
8 Construction and workmanship . 12
8.1 General . 12
8.2 Wall thickness . 12
8.3 Surface imperfections . 12
8.4 Ultrasonic examination . 12
8.5 Out-of-roundness . 13
8.6 Mean diameter . 13
8.7 Straightness . 13
8.8 Verticality and stability . 13
8.9 Neck threads . 15
9 Type approval procedure . 15
9.1 General requirements . 15
9.2 Prototype test . 16
9.3 Type approval certificate . 20
9.4 Specific type approval/production tests for cylinders ordered in quantities below 200 . 20
10 Batch tests . 20
10.1 General requirements . 20
10.2 Tensile test . 24
10.3 Impact test . 25
10.4 Hydraulic burst test . 29
10.5 Intergranular corrosion test . 34
11 Tests/examinations on every cylinder . 34
11.1 General . 34
11.2 Hydraulic test . 35
iv
11.3 Hardness test . 35
11.4 Leak test . 35
11.5 Water -capacity check . 36
12 Certification . 36
13 Marking . 36
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 . 37
Annex B (normative) Ultrasonic examination . 61
Annex C (informative) Example of type approval certificate . 71
Annex D (informative) Example of acceptance certificate . 73
Annex E (informative) Example of shear strength calculation for parallel threads . 76
Bibliography . 78
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ISO/DISFDIS 9809-4:2023(E2025(en)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types of
ISO documents should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
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, 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 Error! Reference source not found.3.8;;
— — modification of 0Formula 1 in 7.27.2;;
— — bend test and flattening test moved under 9Clause 9 (prototype tests);
— — clarification of shear stress calculation for parallel threads;
— — clarification of 9.49.4;;
— — 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.
vi
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.
[
This document has been written so that it is suitable to be referenced in the UN Model Regulations Error!
[1] ]
Reference source not found. . .
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DRAFT International Standard ISO/FDIS 9809-4:2025(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 MPa
m
Part 4:
Stainless steel cylinders with an R m value of less than 1 100 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/DISFDIS 9809-4:2023(E2025(en)
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 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 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 3.2
burst pressure
p
b
highest pressure reached in a cylinder during a burst test
3.3 3.3
cold working
process in which a cylinder is subjected to a pressure higher than the cylinder test pressure (Error! Reference
source not found.(3.11)) to increase the yield strength (Error! Reference source not found.(3.12)) of the
steel
3.4 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 3.5
design stress factor
F
ratio of the equivalent wall stress at test pressure, p , (Error! Reference source not found.(3.11)) to
h
guaranteed minimum yield strength, R
eg
3.6 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 3.7
reject
action to set aside a cylinder (level 2 or level 3) that is not allowed to go into service
3.8 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 3.9
repair
action to return a rejected cylinder to a level 1 condition
3.10 3.10
tempering
toughening heat treatment which follows quenching (Error! Reference source not found.(3.6),), in which
the cylinder is heated to a uniform temperature below the lower critical point (Ac ) of the steel
3.11 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 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 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 0Figure 2))
a guaranteed minimum thickness, in millimetres, at the centre of a concave base (see 0Figure 2))
b guaranteed minimum thickness, in millimetres, at the centre of a convex base (see 0Figure 1))
c maximum permissible deviation, in millimetres, of burst profile for quenched and tempered cylinders
(see 0Figure 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 0Figure 12))
D nominal outside diameter of the cylinder, in millimetres (see 0Figure 1))
D diameter, in millimetres, of former (see 0Figure 6))
f
F design stress factor (variable)
H outside height, in millimetres, of the domed part (convex head or base end) (see 0Figure 1))
h outside depth (concave base end), in millimetres (see 0Figure 2))
L original gauge length, in millimetres, as defined in ISO 6892-1 (see 0Figure 5))
o
l overall length of the cylinder, in millimetres (see 0Figure 3))
n ratio of the diameter of the bend test former to the actual thickness of test piece, t
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p measured burst pressure, in bar, above atmospheric pressure
b
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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
r inside knuckle radius, in millimetres (see 0Figures 1 and 02))
R actual value of the yield strength, in megapascals, as determined by the tensile test (see 10.210.2))
ea
R minimum guaranteed value of the yield strength (see 7.1.17.1.1),), in megapascals, for the finished
eg
cylinder
R actual value of the tensile strength, in megapascals, as determined by the tensile test (see 10.210.2))
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 0Figure 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 9Clauses 9, 10, 10 and 1111.
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 6.1.1 Materials for the manufacture of gas cylinders shall fall within one of the following categories:
a) a) internationally recognized cylinder steels;
b) b) nationally recognized cylinder steels;
c) c) new cylinder steels resulting from technical progress.
For all categories, the relevant conditions specified in 6.26.2 and 6.36.3 shall be satisfied.
6.1.2 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 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 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 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 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 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 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 6.3.1 The cylinder manufacturer shall certify the heat treatment process applied to the finished
cylinders.
6.3.2 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 6.46.4).).
6.3.3 6.3.3 For the ferritic and martensitic steels, the heat treatment process shall achieve the required
mechanical properties.
6.3.4 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.
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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) 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) b) If the test has been carried out in a satisfactory manner, the cause of test failure shall be
identified.
1) 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) 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 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 7.1.2 Cylinders shall be designed with one or two openings along the central cylinder axis only.
7.1.3 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 0Formulae (1) and 0(2),, and additionally, 0Formula (3) shall be satisfied.
(1)
𝐷 10𝐹𝑅 −√3𝑝
eg h
𝑎 = (1 − √ ) (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
eg
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
), in megapascals, for the finished cylinder;
p is the hydraulic test pressure, in bar, above atmospheric pressure.
h
0,65
where the value of F (design stress factor) is the lesser of or 0,85.
𝑅 ⁄𝑅
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
where R minimum guaranteed value of the tensile strength, in megapascals, for the finished cylinder.
mg
The wall thickness shall also satisfy 0Formula (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 0Formula (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 and
h
manufactured to conform with this document.
7.3 Design of convex ends (heads and bases)
7.3.1 7.3.1 When convex base ends (see 0Figure 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 0Figure 1.
Shape b) shall not be excluded from this requirement.
7.3.2 7.3.2 The cylinder manufacturer shall prove by the pressure cycling test detailed in 9.2.29.2.2 that
the design is satisfactory.
The shapes shown in 0Figure 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.
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a) b) c)
d) e) f)
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
1 cylindrical part
a′ guaranteed minimum thickness, in millimetres, of the cylindrical shell
MUST BE USED
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)
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r inside knuckle radius, in millimetres
Figure 1 — Typical convex ends
7.4 Design of the concave base ends
7.4.1 7.4.1 When concave base ends (see 0Figure 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 7.4.2 The cylinder manufacturer shall in any case prove by the application of the pressure cycling
test detailed in 9.2.29.2.2 that the design is satisfactory.
Key
a′ guaranteed minimum thickness, in millimetres, of the cylindrical shell
a1 guaranteed minimum thickness, in millimetres, of a concave base at the knuckle
a2 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
a′ guaranteed minimum thickness, in millimetres, of the cylindrical shell
a1 guaranteed minimum thickness, in millimetres, of a concave base at the knuckle
a2 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 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 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 may be 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 9.2.49.2.4 and 9.2.59.2.5).).
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.
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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 shall be greater than 100 Nm.
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) a) forging or drop forging from a solid ingot or billet;
b) b) manufacturing from seamless tube;
c) c) pressing from a flat plate;
d) 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
adversely affect the safe working of the cylinder. Imperfections shall be evaluated as specified in
Annex AAnnex A. .
8.4 Ultrasonic examination
8.4.1 8.4.1 After completion of the final heat treatment and cold working and after the final cylindrical
wall thickness has been achieved, each cylinder shall be ultrasonically examined for internal, external and sub-
surface imperfections in accordance with Annex BAnnex B.
8.4.2 8.4.2 In addition to the ultrasonic examination as specified in 8.4.18.4.1,, the cylindrical area to be
closed (which creates the shoulder and in case of cylinders made from tube, also the base) shall be
ultrasonically examined prior to the forming process to detect any defects that after closure could be
positioned in the cylinder ends.
In case of cylinders produced from tubes (provided that the thickness of the tube is unaltered), this additional
test is not required if the tube is 100 % ultrasonic tested before closure of the ends in accordance with
Annex BAnnex B.
The test shall be performed as close as possible to the open end of the shell.
The untested area shall extend to a length of not more than 40 mm from the open end of the shell.
In both 8.4.18.4.1 and 8.4.28.4.2,, it is not required to perform the ultrasonic examination for small cylinders
with a cylindrical length of less than 200 mm or where p × V < 600 bar. l (for R ≥ 650 MPa) or
h ma
p × V < 1 200 bar. l (for R < 650 MPa).
h ma
8.5 Out-of-roundness
The out-of-roundness of the cylindrical shell, i.e. the difference between the maximum and minimum outside
diameters at the same cross-section, shall not exceed 2 % of the mean of these diameters.
For cold stretch and cryoformed cylinders, higher values are acceptable provided they are validated by the
pressure cycling test and the maximum shall be specified on the approved design drawing.
8.6 Mean diameter
The mean external diameter of the cylindrical part outside the transition zones on a cross-section shall not
deviate by more than ±1 % from the nominal design diameter.
For cold stretch and cryoformed cylinders, higher values are acceptable provided they are validated by the
pressure cycling test and the maximum shall be specified on the approved design drawing.
8.7 Straightness
The maximum deviation of the cylindrical part of the shell from a straight line shall not exceed 3 mm per metre
in length (see footnote 'b' in 0Figure 3).).
For cold stretch and cryoformed cylinders, higher values can be used provided that they are acceptable for the
intended application.
8.8 Verticality and stability
For a cylinder designed to stand on its base, the deviation from vertical shall not exceed 10 mm per metre in
length (l ) (see footnote 'a' in 0Figure 3).). The outer diameter of the surface in contact with the ground is
recommended to be greater than 75 % of the nominal outside diameter.
For cold stretch and cryoformed cylinders, higher values for deviation from vertical can be used provided that
they are acceptable for the intended application.
MUST BE USED
FOR FINAL
DRAFT
ISO/DISFDIS 9809-4:2023(E2025(en)
a
≤ 0,01 × l2 (see 8.8).
b
≤ 0,003 × l (see 8.7
a
≤ 0,01 × l (see 8.8).
b
≤ 0,003 × l (see 8.7).
).
Figure 3 — Deviation of the cylindrical part of the shell from a straight line and from vertical
8.9 Neck threads
The internal neck threads shall conform to a recognized standard agreed between the parties to permit the
use of a corresponding valve thus minimizing neck stresses following the valve torqueing operation. Internal
neck threads shall be checked using gauges corresponding to the agreed neck thread or by an alternative
method agreed between the parties.
EXAMPLE Where the neck thread is specified to be in accordance with ISO 11363-1, the corresponding gauges are
specified in ISO 11363-2.
Particular care shall be taken to ensure that neck threads are accurately cut, are of full form and are free from
any sharp profiles, e.g. burrs.
9 Type approval procedure
9.1 General requirements
A technical specification of each new design of cylinder or cylinder family as specified in f), including design
drawing, design calculations, steel details, manufacturing process and heat treatment details, shall be
submitted by the manufacturer to the inspector. The type approval tests detailed in 9.29.2 shall be carried out
on each new design under the supervision of the inspector.
A cylinder shall be considered to be of a new design, compared with an existing approved design, when at least
one of the following applies:
a) a) it is manufactured in a different factory;
b) b) it is manufactured by a different process (see 8.18.1);); this includes the case when major
process changes are made during the production period, e.g. end forging to spinning, change in heat
treatment process;
c) c) it is manufactured from a steel of different specified chemical composition range from that
specified in 6.26.2;;
d) d) it is given a different heat treatment beyond the limits stipulated in 6.36.3 and 6.46.4;;
e) e) the base or the base profile has changed, e.g. concave, convex, hemispherical, or the base
thickness/cylinder diameter ratio has changed;
f) f) the overall length of the cylinder has increased by more than 50 % (cylinders with a
length/diameter ratio less than 3 shall not be used as reference cylinders for any new design with this
ratio greater than 3);
g) g) the nominal outside diameter has changed;
h) h) the guaranteed minimum thickness has changed;
i) i) the hydraulic test pressure, p , has been increased (where a cylinder is to be used for lower-
h
pressure duty than that for which design approval has been gi
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