ISO 20703:2006
(Main)Gas cylinders — Refillable welded aluminium-alloy cylinders — Design, construction and testing
Gas cylinders — Refillable welded aluminium-alloy cylinders — Design, construction and testing
ISO 20703:2006 specifies minimum requirements for the material, design, construction and workmanship, manufacturing processes and tests at manufacture of refillable, transportable, welded aluminium-alloy gas cylinders of water capacities from 0,5 l up to and including 150 l, and of a test pressure not greater than 60 bar (6 MPa) for compressed, liquefied and dissolved gases. It includes requirements for spherical receptacles and cylinders made from seamless bodies with welded non-pressure-bearing attachments such as shrouds and foot-rings.
Bouteilles à gaz — Bouteilles rechargeables soudées en alliage d'aluminium — Conception, construction et essais
General Information
Standards Content (Sample)
INTERNATIONAL ISO
STANDARD 20703
First edition
2006-05-01
Gas cylinders — Refillable welded
aluminium-alloy cylinders — Design,
construction and testing
Bouteilles à gaz — Bouteilles rechargeables soudées en alliage
d'aluminium — Conception, construction et essais
Reference number
ISO 20703:2006(E)
©
ISO 2006
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ISO 20703:2006(E)
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ii © ISO 2006 – All rights reserved
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ISO 20703:2006(E)
Contents Page
Foreword. v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and symbols. 2
3.1 Terms and definitions. 2
3.2 Symbols . 2
4 Materials . 4
4.1 General provisions . 4
4.2 Heat treatment. 4
4.3 Gas/material compatibility . 5
5 Design . 5
5.1 General provisions . 5
5.2 Calculation of wall thickness. 7
5.3 Design of convex ends (heads and bases) . 8
5.4 Neck design. 12
5.5 Foot-rings . 12
5.6 Neck-rings . 12
5.7 Shroud . 12
5.8 Design drawing . 12
6 Construction and workmanship. 12
6.1 Seamless bodies. 12
6.2 Welding . 12
6.3 Non-destructive examination of welds. 13
6.4 Surface defects . 13
6.5 Neck threads . 13
6.6 Out-of-roundness. 14
6.7 Straightness . 14
6.8 Eccentricity. 14
6.9 Stability . 14
7 Tests and examinations . 14
7.1 General. 14
7.2 Mechanical tests . 14
7.3 Hydraulic burst test . 21
7.4 Pressure-cycling test. 23
7.5 Hydraulic test . 24
7.6 Check on the homogeneity of a batch. 24
7.7 Leakage test . 24
7.8 Capacity check. 24
7.9 Examination for neck folds. 24
8 Conformity evaluation. 25
9 Identification marks. 25
10 Records. 25
Annex A (normative) Corrosion tests . 26
Annex B (normative) New design type testing and production testing . 40
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ISO 20703:2006(E)
Annex C (normative) Description, evaluation of manufacturing defects and conditions for
rejection of welded aluminium-alloy gas cylinders at time of visual inspection . 44
Annex D (informative) Examples of new design type approval and production test certificates . 48
Bibliography . 54
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ISO 20703:2006(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
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 20703 was prepared by Technical Committee ISO/TC 58, Gas cylinders, Subcommittee SC 3, Cylinder
design.
This International Standard 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 6.2.2.5 of the above mentioned model regulations.
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ISO 20703:2006(E)
Introduction
The purpose of this International Standard is to provide a specification for the design, manufacture, inspection and
approval of refillable, transportable, welded aluminium-alloy gas cylinders. 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 in the countries of the participating members.
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INTERNATIONAL STANDARD ISO 20703:2006(E)
Gas cylinders — Refillable welded aluminium-alloy cylinders —
Design, construction and testing
1 Scope
This International Standard specifies minimum requirements for the material, design, construction and
workmanship, manufacturing processes and tests at manufacture of refillable, transportable, welded
aluminium-alloy gas cylinders of water capacities from 0,5 l up to and including 150 l, and of a test pressure
not greater than 60 bar (6 MPa) for compressed, liquefied and dissolved gases.
This International Standard includes requirements for spherical receptacles and cylinders made from
seamless bodies with welded non-pressure-bearing attachments such as shrouds and foot-rings.
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 2107, Aluminium and aluminium alloys — Wrought products — Temper designations
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 7866:1999, Gas cylinders — Refillable seamless aluminium alloy gas cylinders — Design, construction
and testing
ISO 9606-2, Qualification test of welders — Fusion welding — Part 2: Aluminium and aluminium alloys
ISO 10042:2005, Welding — Arc-welded joints in aluminium and its alloys — Quality levels for imperfections
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 for industrial and medical gas
cylinders — Design, construction and tests
ISO 13341, Transportable gas cylinders — Fitting of valves to gas cylinders
ISO 13769, Gas cylinders — Stamp marking
ISO 15614-2:2005, Specification and qualification of welding procedures for metallic materials — Welding
procedure test — Part 2: Arc welding of aluminium and its alloys
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ISO 20703:2006(E)
3 Terms, definitions and symbols
3.1 Terms and definitions
For the purposes of this document the following terms and definitions apply.
3.1.1
yield stress
value corresponding to the 0,2 % proof stress (non proportional elongation), R
p0,2
3.1.2
solution heat treatment
thermal treatment which consists of heating the products to a suitable temperature, holding at that
temperature long enough to allow constituents to enter into solid solution, and cooling rapidly enough to hold
the constituents in solution
3.1.3
quenching
controlled rapid cooling in a suitable medium to retain the solute phase in solid solution
3.1.4
artificial ageing
heat treatment process in which the solute phase is precipitated to give an increased yield stress and tensile
strength
3.1.5
batch
quantity of up to 250 cylinders, plus cylinders for destructive testing, of the same nominal diameter, thickness
and design, made successively from the same cast and subjected to the same heat treatment for the same
period of time; the lengths of the cylinders in the heat treatment batch may vary by up to ± 12 %
3.1.6
design stress factor
F
ratio of equivalent wall stress at test pressure (p ) to guaranteed minimum yield stress (R )
h e
3.1.7
non-destructive examination
examination or test that does not materially or adversely affect the item being examined
3.2 Symbols
A percentage elongation, determined by the tensile test 7.2.3
a calculated minimum thickness, in millimetres, of the cylindrical or spherical shell
a′ guaranteed minimum thickness, in millimetres, of the cylindrical or spherical shell
b guaranteed minimum thickness, in millimetres, at the centre of a convex base
D nominal outside diameter, in millimetres, of the cylinder, spherical cylinder or domed end (see Figure 2)
o
D nominal inside diameter, in millimetres, of the cylinder, spherical cylinder or domed end (see Figure 2)
i
d diameter of former, in millimetres (see Figure 4)
F design stress factor (variable) (see 3.1.6)
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ISO 20703:2006(E)
h internal height, in millimetres, of semi-ellipsoidal or torispherical domed end (convex head or base end)
i
(see Figure 2)
h variable used in the determination of shape factor, K (see 5.3.1)
e
h external height, in millimetres, of a semi-ellipsoidal or torispherical domed end (convex head or base
o
end) (see Figure 2)
K shape factor for a semi-ellipsoidal or torispherical domed end, obtained according to the values h /D
e o
and a/D , with interpolation where necessary (see Figure 1)
o
L original gauge length, in millimetres, according to ISO 6892
o
n ratio of the diameter of the bend test former to actual thickness of test piece (t)
1)
p measured burst pressure, in bar above atmospheric pressure
b
1)
p hydraulic test pressure, in bar above atmospheric pressure
h
1)
p lower cyclic pressure, in bar above atmospheric pressure
lc
1)
p observed yield pressure which produces a permanent volumetric expansion of 0,2 %, in bar above
y
atmospheric pressure
R minimum guaranteed value of yield stress (see 3.1.1), in megapascals, for the finished cylinder
e
R actual value of yield stress, in megapascals, determined by the tensile test 7.2.3.
ea
R minimum guaranteed value of tensile strength, in megapascals, for the finished cylinder
g
R actual value of tensile strength, in megapascals, determined by the tensile test 7.2.3
m
r internal knuckle radius, in millimetres, of torispherical end [see Figure 2c)]
i
r′ internal radius, in millimetres, of dishing of torispherical end [see Figure 2c)]
i
r external knuckle radius, in millimetres, of torispherical end [see Figure 2c)]
a
r′ external radius, in millimetres, of dishing of torispherical end [see Figure 2c)]
o
s straight flange length, in millimetres, for semi-ellipsoidal and torispherical domed ends [see Figure 2b)
f
and 2c)]
S original cross-sectional area of tensile test piece, in square millimetres, according to ISO 6892
o
t actual thickness of test specimen, in millimetres
t calculated minimum thickness, in millimetres, of a domed end
e
w width, in millimetres, of tensile test piece
V volumetric expansion attained at burst, expressed as a percentage of the initial volume (see 7.3)
exp
Z stress reduction factor (see 5.2.1)
5 5 2
1) 1 bar = 10 Pa = 10 N/m .
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ISO 20703:2006(E)
4 Materials
4.1 General provisions
4.1.1 Aluminium alloys may be used to produce gas cylinders provided that they satisfy the requirements of
the corrosion resistance tests defined in Annex A, and meet all other requirements of this International
Standard.
4.1.2 Examples of the alloys most commonly used for the fabrication of gas cylinders are given in Table 1.
4.1.3 After the completion of all welding (including that of the attachments) and before the hydraulic test,
each cylinder shall be heat treated if required to meet the design criteria.
4.2 Heat treatment
4.2.1 General
Any welding on the pressure-bearing part shall take place before any final heat treatment (see 6.2).
4.2.2 Heat-treatable alloys
The manufacturer shall specify on the new design type testing documentation, where required, the solution
heat treatment and artificial ageing temperatures and the times for which the cylinders have been held at
those temperatures. The medium used for quenching after solution heat treatment shall be identified.
Unless the alloy is subjected to a temperature in excess of 400 °C during the forming process, a stabilizing
treatment shall be carried out and the temperature, and time at temperature, shall be identified by the
manufacturer.
However, the stabilizing treatment is not necessary for a cylinder of which the wall thickness in 5.2 is
calculated with the minimum guaranteed yield stress value of the O-tempered alloy (or the alloy annealed for
complete re-crystallization before forming of cylinder, as defined in ISO 2107).
If the cylinder is intended for dissolved-gas service it shall only be used in the fully annealed condition, i.e. the
minimum guaranteed properties used for the material shall consider the heat treatment to be applied,
e.g. during the massing operation.
4.2.3 Non-heat-treatable alloys
The manufacturer shall specify on the new design type testing documentation, where required, the type of
metal forming operation carried out (extrusion, drawing, ironing, head forming, etc.). Unless the alloy is
subjected to a temperature in excess of 400 °C during the forming process, a stabilizing treatment shall be
carried out and the temperature, and time at temperature, shall be identified by the manufacturer.
4.2.4 Control of specified heat treatment
During the heat treatment, the manufacturer shall comply with the specified temperatures and durations,
within the following ranges:
a) Temperatures
Solution temperature: maximum range 20 °C
Artificial ageing temperature: maximum range 20 °C
Stabilizing temperature: maximum range 20 °C
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ISO 20703:2006(E)
b) Durations
Time cylinders actually spend at temperature during treatments:
All treatments: maximum range 20 %
4.3 Gas/material compatibility
Gas/material compatibility shall be verified as specified in ISO 11114-1.
5 Design
5.1 General provisions
5.1.1 The calculation of the wall thickness of the pressure-bearing parts shall be related to the yield stress
(R ) of the material to ensure elastic behaviour.
e
5.1.2 For calculation purposes, the value of the yield stress (R ) is limited to a maximum of 0,9 R for
e g
aluminium alloys.
5.1.3 The internal pressure upon which the calculation of wall thickness is based shall be hydraulic test
pressure (p ).
h
5.1.4 For dissolved gases, the manufacturing process of the porous mass can modify the characteristics of
the aluminium alloy used. This shall be considered when designing the shell.
5.1.5 Wherever any exposure to heat is necessary (e.g. for dissolved acetylene, where the manufacturing
process of the porous mass can modify the characteristics of the aluminium alloy used) this shall be
considered when designing the shell, i.e. the mechanical properties guaranteed by the shell manufacturer
shall be those resulting from any heating prior to final use.
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ISO 20703:2006(E)
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Table 1 — Chemical composition of aluminium alloys
b, c
Type of Chemical composition — weight %
Type
a
alloy AA
Si Fe Cu Mn Mg Cr Zn Ti Pb Bi Others Aluminium
registered
designation
Each Total
5052 A min. — — — — 2,2 0,15 — — — — — — Remainder
max. 0,25 0,40 0,10 0,10 2,8 0,35 0,10 — — — 0,05 0,15
5154 A min. — — — — 3,1 0,15 — — — — — — Remainder
max. 0,25 0,40 0,10 0,10 3,9 0,35 0,20 0,20 — — 0,05 0,15
5083A D min. — — — 0,40 4,0 0,05 — — — — — — Remainder
max. 0,40 0,40 0,10 1,0 4,9 0,25 0,25 0,15 — — 0,05 0,15
6061A D min. 0,40 — 0,15 — 0,8 0,04 — — — — — — Remainder
max. 0,8 0,7 0,40 0,15 1,2 0,35 0,25 0,15 0,0030 0,0030 0,05 0,15
6063 C min. 0,2 — — — 0,4 — — — — — — — Remainder
max. 0,7 0,5 0,1 0,3 0,9 0,1 0,2 0,2 0,0030 — 0,05 0,15
6082 D min. 0,7 — — 0,40 0,60 — — — — — — — Remainder
max. 1,3 0,50 0,10 1,0 1,2 0,25 0,20 0,10 0,0030 0,0030 0,05 0,15
6082 B min. 1,2 — — 0,8 1,0 — — — — — — — Remainder
max. 1,6 0,5 0,1 1,0 1,4 0,1 0,2 0,2 0,0030 0,0030 0,05 0,15
a
AA is the Aluminium Association Inc., 900 19th Street N.W., Washington D.C., 20006-2168, USA.
b
Type A and Type B may be used for the body and Type C for the non pressure bearing part.
c
Type D may be used for the body and the non-pressure-bearing part.
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ISO 20703:2006(E)
5.2 Calculation of wall thickness
5.2.1 Wall thickness of cylindrical shell
The guaranteed minimum thickness of the cylindrical shell (a′) shall not be less than the thickness calculated
using the equation
⎛⎞
DF10 ZR−⋅3p
oe h
⎜⎟
a=−1
⎜⎟
2 10 FZ R
e
⎝⎠
0,65
The value of F is the lesser of and 0,85; R /R shall be limited to 0,9.
e g
(/R R)
eg
The value of Z is dependent on the amount of non-destructive examination (NDE) and the type of cylinder; it
shall be as specified in Table 2. Z shall apply to external welds such as welding of shrouds and foot-rings.
The manufacturer may choose between 100 % NDE of welds or spot checks defined as follows:
⎯ for circumferential welds (including of bung or boss welds), 25 mm on each side of the weld overlap shall
be examined;
⎯ for longitudinal welds, 100 mm beyond the intersection of the circumferential/longitudinal weld and 25 mm
on each side of the circumferential weld shall be examined.
Table 2 — Stress reduction factor Z
Cylinder type Stress reduction factor
Z
100 % of welds NDE tested 1,00
Without longitudinal welds
Welds spot checked 0,95
100 % of welds NDE tested 0,95
With longitudinal welds
Welds spot checked 0,90
The calculated minimum thickness shall also satisfy the equation
D
o
aW +1,5 mm.
200
When choosing the guaranteed value of the wall thickness of the cylindrical shell (a′), the manufacturer shall
take into account all the test requirements for new design type and production testing, particularly the burst
test requirements of 7.3.2.2.
The burst ratio (p /p ) shall be determined by test and shall be > 2,0.
b h
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ISO 20703:2006(E)
5.2.2 Wall thickness of spherical cylinder
The thickness of the wall shall not be less than the values given by the following equations:
a = (p D )/(40FZR − 4,5p )
h i e h
a = (p D )/(40FZR − 2,5p )
h o e h
aD= 2,48 R
ig
The values of F and Z shall be as defined in 5.2.1.
5.3 Design of convex ends (heads and bases)
5.3.1 Thickness of domed ends
For cylinders made with a seamless body, the method of construction of ISO 7866:1999, 7.3.1, 7.3.2 and
7.3.3 shall be used. For cylinders made with a welded body, the minimum thickness of a hemispherical domed
end shall be equal to the minimum thickness of the cylindrical shell a.
The minimum thickness of a semi-ellipsoidal or torispherical domed end shall be the greater of
a) the thickness of the cylindrical wall, and
b) the value of t calculated from the equation
e
t = aK
e
where K shall be as determined from Figure 1.
For a semi-ellipsoidal end, h = h .
e o
2
D ⎛⎞D r
o oo
For a torispherical end, h is the lesser of h , and .
⎜⎟
e o
4r′ 2
o ⎝⎠
NOTE The external height of a torispherical domed end (h ), can be determined from
o
⎧⎫
⎪⎪⎛⎞DD⎛ ⎞
oo
hr=−′′r− ×r′+ − 2r
⎨⎬
oo⎜⎟o ⎜o o⎟
22
⎪⎪⎝⎠⎝ ⎠
⎩⎭
The wall thickness of the base shall not exceed 1,15 times the guaranteed minimum design thickness of the
base (b). The external surface of the base of the selected cylinders may be machined if necessary.
5.3.2 Limitations of shape (see Figure 2)
The shape of the ends shall be subject to the following limitations.
a) For a torispherical end, r′ shall be not greater than D .
i o
b) For a torispherical end, r shall be not less than 0,1D and not less than three times the actual thickness of
i i
the end as manufactured.
c) For a semi-ellipsoidal end, the ratio h /D shall be not less than 0,192.
o o
d) For a semi-ellipsoidal end and a torispherical end, s shall be not less than 0,3 D t .
()
f oe
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ISO 20703:2006(E)
a) Shape factor K
Figure 1 — Shape factor K plotted against h /D
e o
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ISO 20703:2006(E)
b) Shape factor K [enlargement of a)]
Figure 1 (continued)
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ISO 20703:2006(E)
a) Hemispherical
b) Semi-ellipsoidal
c) Torispherical
Figure 2 — Domed ends
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ISO 20703:2006(E)
5.4 Neck design
The external diameter and thickness of the formed neck end of the cylinder shall be designed for the torque
applied in fitting the valve to the cylinder. The torque may vary according to the diameter of thread, the form,
and the sealant used in the fitting of the valve. The torques specified in ISO 13341 shall not be exceeded,
since this could result in permanent damage to the cylinder. Where the cylinder manufacturer specifies a
lower maximum torque than that indicated in ISO 13341 (but within the range of ISO 13341), the manufacturer
shall notify any such requirements to the purchaser of aluminium-alloy cylinders.
5.5 Foot-rings
A foot-ring, if provided, shall be sufficiently strong and made of material compatible with that of the cylinder. In
addition, the shape should preferably be cylindrical and shall give the cylinder sufficient stability. The foot-ring
shall be secured to the cylinder, e.g. by welding. Water traps shall be sealed.
5.6 Neck-rings
When a neck-ring is provided, it shall be of material compatible with that of the cylinder, and shall be securely
attached. The manufacturer shall ensure that the axial load required to remove the neck-ring is greater than
10 times the weight of the empty cylinder and not less than 1 000 N, and that the minimum
...
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