Gas cylinders — Refillable welded stainless steel cylinders — Part 1: Test pressure 6 MPa and below
ISO 18172-1:2007 specifies minimum requirements concerning material, design, construction and workmanship, manufacturing processes and testing of refillable transportable welded stainless steel gas cylinders, of water capacities from 0,5 l up to and including 500 l, for compressed, liquefied and dissolved gases. ISO 18172-1:2007 is applicable only to cylinders manufactured from stainless steels with test pressures up to 6 MPa (60 bar). If required, transportable large cylinders of water capacity above 150 l and up to 500 l may be manufactured and certified to ISO 18172-1:2007, providing that handling facilities are provided.
Bouteilles à gaz — Bouteilles soudées en acier inoxydable rechargeables — Partie 1: Pression d'épreuve de 6 MPa et inférieure
Standards Content (Sample)
Gas cylinders — Refillable welded
stainless steel cylinders —
Test pressure 6 MPa and below
Bouteilles à gaz — Bouteilles soudées en acier inoxydable
Partie 1: Pression d'épreuve de 6 MPa et inférieure
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Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and symbols. 2
3.1 Terms and definitions. 2
3.2 Symbols . 3
4 Materials and heat treatment . 4
4.1 General. 4
4.2 Categories . 5
4.3 Heat treatment. 5
4.4 Test requirements. 5
5 Design . 5
5.1 General requirements. 5
5.2 Calculation of cylindrical shell wall thickness . 6
5.3 Design of convex ends. 6
5.4 Minimum wall thickness. 9
5.5 Ends of other shapes . 9
5.6 Design of openings. 9
6 Construction and workmanship. 9
6.1 General. 9
6.2 Welding procedures . 10
6.3 Cryoforming procedure. 10
6.4 Welded joints of pressure-containing parts . 10
6.5 Non-pressure-containing attachments.10
6.6 Valve protection. 11
6.7 Neck threads . 11
6.8 Visual examination . 11
7 New design tests. 12
7.1 General requirements. 12
7.2 Verifications and tests. 13
7.3 Descriptions of tests . 13
7.4 Design testing certificate . 14
8 Batch tests. 14
8.1 General. 14
8.2 Information . 15
8.3 Tensile test . 15
8.4 Bend test. 18
8.5 Macroscopic examination of weld cross-sections. 20
8.6 Checks and verifications . 20
9 Tests on every cylinder. 21
9.1 Pressure test . 21
9.2 Hardness test . 21
9.3 Leakage test . 21
10 Failure to meet test requirements. 21
11 Markings . 22
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12 Certificate. 22
Annex A (normative) Radiographic examination of welds. 23
Annex B (normative) Description and evaluation of manufacturing defects and conditions
for rejection of welded stainless steel gas cylinders at time of visual inspection . 25
Annex C (informative) Examples of design and batch testing certificates. 27
Annex D (normative) Manufacturer's markings for LPG . 32
Bibliography . 33
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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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
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.
ISO 18172-1 was prepared by Technical Committee ISO/TC 58, Gas cylinders, Subcommittee SC 3, Cylinder
ISO 18172 consists of the following parts, under the general title Gas cylinders — Refillable welded stainless
⎯ Part 1: Test pressure 6 MPa and below
⎯ Part 2: Test pressure greater than 6 MPa
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The purpose of this part of ISO 18172 is to provide a specification for the design, manufacture and testing of
refillable transportable welded stainless steel gas cylinders with a test pressure up to 6 MPa (60 bar).
The specifications given are based on knowledge of, and experience with, materials, design requirements,
manufacturing processes and control during manufacture of cylinders in common use.
ISO 18172 has been prepared to address the general requirements in Section 6.2.1 of the UN model
regulations for the transportation of dangerous goods ST/SG/AC.10/1/Rev.13. It is intended to be used under
a variety of regulatory regimes, but has been written so that it is suitable for use with the conformity
assessment system in paragraph 18.104.22.168 of the above-mentioned model regulations.
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INTERNATIONAL STANDARD ISO 18172-1:2007(E)
Gas cylinders — Refillable welded stainless steel cylinders —
Test pressure 6 MPa and below
This part of ISO 18172 specifies minimum requirements concerning material, design, construction and
workmanship, manufacturing processes and testing of refillable transportable welded stainless steel gas
cylinders, of water capacities from 0,5 l up to and including 500 l, for compressed, liquefied and dissolved
gases. This part of ISO 18172 is applicable only to cylinders manufactured from stainless steels with test
pressures up to 6 MPa (60 bar).
If required, transportable large cylinders of water capacity above 150 l and up to 500 l may be manufactured
and certified to this part of ISO 18172, providing that handling facilities are provided (see 6.5.5).
For acetylene service, additional requirements for the cylinder and the basic requirements for the porous mass
are given in ISO 3807-1 and ISO 3807-2.
2 Normative references
The following referenced documents are indispensable for the application 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 2504:1973, Radiography of welds and viewing conditions for films — Utilization of recommended patterns
of image quality indicators (I.Q.I.)
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 5817, Welding — Fusion-welded joints in steel, nickel, titanium and their alloys (beam welding
excluded) — Quality levels for imperfections
ISO 6506-1, Metallic materials — Brinell hardness test — Part 1: Test method
ISO 6892, Metallic materials — Tensile testing at ambient temperature
ISO 7438, Metallic materials — Bend test
ISO 9328-7:2004, Steel flat products for pressure purposes — Technical delivery conditions — Part 7:
ISO 9606-1, Approval testing of welders — Fusion welding — Part 1: Steels
ISO 9956-1, Specification and approval of welding procedures for metallic materials — Part 1: General rules
for fusion welding
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ISO 9956-3, Specification and approval of welding procedures for metallic materials — Part 3: Welding
procedure tests for arc welding of steels
ISO 11114-1, Transportable gas cylinders — Compatibility of cylinder and valve materials with gas
contents — Part 1: Metallic materials
ISO 11117, Gas cylinders — Valve protection caps and valve guards — Design, construction and tests
ISO 13769, Gas cylinders — Stamp marking
ISO 14732, Welding personnel — Approval testing of welding operators for fusion welding and of resistance
weld setters for fully mechanized and automatic welding of metallic materials
ISO 17636, Non-destructive testing of welds — Radiographic testing of fusion-welded joints
ISO 17637, Non-destructive testing of welds — Visual testing of fusion-welded joints
ISO 20807, Non-destructive testing — Qualification of personnel for limited application of non-destructive
3 Terms, definitions and symbols
For the purposes of this document, the following terms, definitions and symbols apply.
3.1 Terms and definitions
value corresponding to 0,2 % proof stress (R ) or, for austenitic steels in the solution annealed condition,
1 % proof stress (R )
softening heat treatment for austenitic steels in which a cylinder is heated to a uniform temperature above the
solid solution temperature, followed by rapid cooling
process where the cylinder is subjected to a controlled low temperature deformation treatment that results in a
permanent increase in strength
plastic deformation treatment given to sheet material at ambient temperature, with the aim of permanently
increasing the material strength
final deformation treatment at ambient temperature given to the prefabricated cylinder, known as the preform,
which results in a permanent increase in the material strength
quantity of cylinders made consecutively by the same manufacturer, using the same manufacturing
techniques, to the same design, size and material, from the same cast on the same type of welding machines
and welding procedures
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design stress factor
ratio of equivalent wall stress at test pressure (p ) to guaranteed minimum yield stress (R )
meta-stable austenitic steel
CrNi stainless steel, which is austenitic in the annealed state at room temperature, but is unstable regarding
transformation when plastically deformed at low temperatures
a calculated minimum thickness, in mm, of the cylindrical shell
a′ guaranteed minimum thickness, in mm, of the cylindrical shell, including any corrosion allowance
a calculated value of a used in the calculation of b (see 5.3.2)
a mean wall thickness, in mm, of the cylindrical shell of the cylinder preform
A percentage elongation after fracture
b calculated minimum thickness, in mm, of the cylinder end
b′ guaranteed minimum thickness, in mm, of the cylinder end (see 7.1.1)
C shape factor of dished ends
D outside diameter, in mm, of the cylinder (see Figure 1)
D diameter of former, in mm (see 8.4.3 and Figure 10)
D mean diameter of the cylindrical shell of a cylinder preform, in mm
F design stress factor (see 3.1.7)
f cryoforming factor established by the manufacturer for each batch of cylinders
h height, in mm, of the cylindrical part of the end (see Figure 1)
H outside height, in mm, of the domed part of the end (see Figure 1)
J stress reduction factor
L length, in mm, of the cylinder
n ratio of diameter of bend test former (D ) to the thickness of the test piece (t)
p measured burst pressure, in MPa (bar) , above atmospheric pressure, in the burst test
p cryoforming or cold forming pressure in MPa (bar), above atmospheric pressure
1) 0,1 MPa = 10 Pa = 1 bar
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p hydraulic test pressure, in MPa (bar), above atmospheric pressure
p observed yield pressure, in MPa (bar), above atmospheric pressure
r inside radius of the knuckle end, in mm (see Figure 1)
R inside radius of the dished end, in mm (see Figure 1)
R yield stress, in MPa, as defined in 3.1.1 and used for design calculation
R value of the actual yield stress, in MPa, determined by the tensile test
R minimum value of 0,2 % proof stress, in MPa, guaranteed by the cylinder manufacturer for the finished
cylinder, in accordance with ISO 6892 (see Note)
R minimum value of 1,0 % proof stress, in MPa, guaranteed by the cylinder manufacturer for the finished
cylinder, in accordance with ISO 6892 (see Note)
R minimum value of tensile strength, in MPa, guaranteed by the cylinder manufacturer for the finished
R actual value of tensile strength, in MPa, determined by a tensile test (see 8.3)
t actual thickness of the test specimen, in mm (see Figure 7)
NOTE For cryoformed and cold formed cylinders, the minimum value guaranteed by the manufacturer refers only to
the cylindrical part of the finished cylinder.
4 Materials and heat treatment
4.1.1 Materials of shells and end pressings shall be stainless steels in a condition suitable for pressing or
drawing and welding, and shall conform to ISO 9328-7.
4.1.2 Grades of steel used for the cylinder manufacture shall be compatible with the intended gas service
(e.g. corrosive gases, embrittling gases), in accordance with ISO 11114-1.
4.1.3 There is a risk of sensitization to intergranular corrosion resulting from the hot processing of austenitic
and duplex stainless steels. If any heat treatment was done during manufacturing, an intergranular corrosion
test in accordance with 7.3.3 shall be carried out.
4.1.4 The manufacturer shall be able to guarantee cylinder steel casting traceability for each pressure-
retaining part of the cylinder.
4.1.5 All parts welded to the cylinder shall be made of compatible material with respect to the weldability.
4.1.6 The cylinder manufacturer shall obtain and provide material certificates of the ladle analysis from the
steel manufacture of the steel supplied for the construction of the pressure-retaining parts of the cylinder and
for the welding consumables.
4.1.7 Some grades of stainless steel may be susceptible to environmental stress corrosion cracking (SCC).
A check shall be made of the material standard to ensure that the selection of material is compatible with the
intended service. Special precautions shall be taken, e.g. by carrying out a post-processing SCC test or by
using a grade of material more resistant to SCC. No special precautions shall compromise any other
requirements in this part of ISO 18172.
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4.1.8 The welding consumables shall be such that they are capable of giving consistent welds. The strength
characteristics of the welds shall not be less than those considered in the design and/or calculations.
4.1.9 Cylinders for acetylene service shall be manufactured with materials compatible with the
manufacturing process of the porous mass, or an internal coating shall be applied.
The following three broad categories of stainless steels are recognised:
⎯ ferritic/austenitic (duplex).
The steels used shall be in accordance with ISO 9328-7.
4.3 Heat treatment
4.3.1 For cylinders subjected to cold forming or cryoforming processes, heat treatment of the preform
component part is not required. Cryoformed cylinders shall not be subjected to any subsequent heat treatment
or to additional heat application, such as welding.
4.3.2 Raw materials used for the manufacture of pressure-retaining parts of the cylinders shall be annealed
for ferritic steels, or solution annealed for austenitic and duplex steels (see ISO 9328-7:2004, Annex C).
4.3.3 The cylinder manufacturer shall obtain and provide certificates for the heat treatment of all parts
covered by 4.3.2 that are used for the construction of the gas cylinders.
4.3.4 The cylinder manufacturer shall maintain records of any heat treatment carried out.
4.4 Test requirements
The material of the finished cylinders shall satisfy the requirements of Clause 7.
5.1 General requirements
5.1.1 The calculation of the wall thickness of the pressure containing parts shall be related to the yield
stress of the parent material.
5.1.2 For calculation purposes, the value of the yield stress R is limited to a maximum of 0,85 R .
5.1.3 The internal pressure upon which the calculation of gas cylinders is based shall be the test pressure
5.1.4 A fully dimensioned drawing of the material, including the specification, shall be produced.
5.1.5 Cylinders for acetylene service shall be designed to allow for a test pressure of 6 MPa (60 bar).
5.1.6 Cylinders for acetylene service shall be designed and manufactured to ensure that conditions are safe
for the eventual filling of the porous mass, e.g. ensuring that there are no sharp edges and voids.
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5.2 Calculation of cylindrical shell wall thickness
The wall thickness, a, of the cylindrical shell shall not be less than that calculated using the formula
10⋅⋅F JR⋅ − 3⋅p
F = 0,77
J = 1 for circumferential welds
J = 0,9 for longitudinal welds
The minimum wall thickness shall also satisfy the requirements of 5.4.
5.3 Design of convex ends
5.3.1 The shape of ends of gas cylinders shall be such that the following conditions are fulfilled:
⎯ for torispherical shaped ends [see Figure 1 a)]: R u D; r W 0,1 D; h W 4 b
⎯ for ellipsoidal shaped ends [see Figure 1 b)]: H W 0,192 D; h W 4 b
5.3.2 The wall thickness, b, of the ends of gas cylinders shall be not less than that calculated using the
b = a × C (2)
a is the value of a calculated in accordance with 5.2, using J = 1,0
C is a shape factor, whose value shall be obtained from the graph given in Figure 2 or Figure 3.
5.3.3 For cryoformed cylinders, convex ends shall be hemispherically shaped. The shape factor C shall be
equal to 1.
The minimum 1,0 % proof stress to be achieved in the hemispherical ends shall be equal to
R = R × (a ÷ 2b) (3)
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Outside Inside Outside Inside
a) Torispherical shaped end b) Ellipsoidal shaped end
NOTE For torispherical shaped ends, the height H can be calculated using
H=+(Rb)− [(Rb+ )− ]⋅[(Rb+ )+ − 2(r+b)] (4)
Figure 1 — Illustration of cylinder ends
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Figure 2 — Values of shape factor C for H/D between 0,2 and 0,25
Figure 3 — Values of shape factor C for H/D between 0,25 and 0,5
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5.4 Minimum wall thickness
5.4.1 The minimum wall thickness of the cylindrical shell a and of the end b shall be not less than the value
derived from the following formulae, as appropriate:
for D u 100 mm: a = b = 1,1 mm (5)
for 100 mm < D u 150 mm: a = b = 1,1 + 0,008 (D − 100) mm (6)
for D > 150 mm: a = b = + 0,7 mm, with an absolute minimum of 1,5 mm (7)
These formulae apply to cylindrical shells and ends irrespective of whether they are designed by calculation
under 5.2 and 5.3, or in accordance with 5.5.
5.4.2 Apart from the requirements of 5.3, 5.4 and 5.5, any cylindrical part integral with an end shall, except
as qualified by 5.4.3, also satisfy the requirements given in 5.2 for the cylindrical shell.
5.4.3 Where the length of the cylindrical portion of the gas cylinder, measured between the beginning of the
domed parts of the two ends, is not more than 2bD , the wall thickness shall be not less than that of the
domed part (see 5.3.2).
5.5 Ends of other shapes
Ends of shapes other than those covered by 5.3 may be used, provided that the adequacy of their design is
demonstrated by a pressure cycling test in accordance with 7.3.2, or by stress analysis.
5.6 Design of openings
5.6.1 The location of all openings shall be restricted to the end(s) of cylinders, except for certain LPG
cylinders, where openings may be in the cylinder sidewall.
5.6.2 Each opening in the cylinder shall be reinforced either by a valve boss or pad, of weldable and
compatible steel, securely attached by welding and so designed as to be of adequate strength and to result in
no harmful stress concentrations. This shall be confirmed by design calculations or a pressure cycling test in
accordance with 7.3.2.
5.6.3 The welds of the openings shall be separated from longitudinal and circumferential joints by a
distance not less than 3a.
6 Construction and workmanship
The cylinder or cylinder preform shall be produced by using one of the following:
⎯ seamless or longitudinally welded tube with forged or deep drawn ends circumferentially welded,
⎯ longitudinally welded tube with spun ends,
⎯ a seamless tube, followed by hot forming where the base is sealed with added weld metal,
⎯ cold worked tube or plate,
⎯ welded deep drawn parts,
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⎯ cold forming or cryoforming of welded cylinder preforms, or
⎯ plate material rolled and formed with longitudinal weld, with forged or deep drawn ends circumferentially
6.2 Welding procedures
Before proceeding with the production of a given design of cylinder, each manufacturer shall qualify all
welding procedures to ISO 9956-1 and ISO 9956-3, and welders to ISO 14732 and ISO 9606-1. Records of
such qualification shall be kept on file by the manufacturer.
6.3 Cryoforming procedure
6.3.1 Cryoforming, as defined in 3.1.3, is a method to increase the mechanical properties of especially
metastable austenitic steels by applying a high internal pressure to the vessel preform at cryogenic
The relevant process parameters are the cryoforming pressure p and the cryoforming temperature.
The design of the finished cylinder shall be in accordance with Clause 5.
6.3.2 The cryoforming operation shall be carried out at a cryoforming