ISO 20703:2006

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 2006
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©  ISO 2006
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ii © ISO 2006 – All rights reserved

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
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

iv © ISO 2006 – All rights reserved

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.
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.
vi © ISO 2006 – All rights reserved

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
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)
2 © ISO 2006 – All rights reserved

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 .
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
4 © ISO 2006 – All rights reserved

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.
6 © ISO 2006 – All rights reserved

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.

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.
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
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
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⎟
⎪⎪⎝⎠⎝ ⎠
⎩⎭
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
8 © ISO 2006 – All rights reserved

a)  Shape factor K
Figure 1 — Shape factor K plotted against h /D
e o
b)  Shape factor K [enlargement of a)]
Figure 1 (continued)
10 © ISO 2006 – All rights reserved

a)  Hemispherical
b)  Semi-ellipsoidal
c)  Torispherical
Figure 2 — Domed ends
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 torque to turn the
neck-ring is greater than 100 N⋅m. The valve protection requirements specified in ISO 11117 apply.
5.7 Shroud
When a shroud for valve protection is provided, it shall be secured to the cylinder, e.g. by welding. Design
consideration shall be given to avoid water traps in contact with the pressure-bearing part.
5.8 Design drawing
A fully dimensioned drawing shall be supplied which includes the specification of the material and makes
reference to this International Standard.
6 Construction and workmanship
6.1 Seamless bodies
For cylinders made with a seamless body, the method of construction of ISO 7866 shall be used.
6.2 Welding
Prior to welding, the components shall be prepared and inspected according to approved procedures. These
procedures shall be laid down in a welding procedure document to be supplied for new design type testing.
Welding shall be according to the approved welding procedures, which shall be in accordance with
ISO 15614-2. Test pieces and acceptance criteria shall be in accordance with ISO 15614-2:2005, Clause 7.
The number of test pieces shall be in accordance with ISO 15614-2:2005, Table 1.
If welding is carried out manually, the welders shall be approved in accordance with ISO 9606-2.
Before the cylinders are closed, longitudinal welds shall be visually examined from both sides.
Parts such as neck-rings, foot-rings, shrouds, handles or bosses may be attached to the cylinder by welding,
provided that the cylinder is not adversely affected by welding and any welding is performed prior to any heat
treatment.
Neck-rings may be attached to the cylinder by welding, screwing, shrinking, etc.
The longitudinal joint, of which there shall be no more than one, shall be butt-welded and shall have 100 %
penetration.
12 © ISO 2006 – All rights reserved

6.3 Non-destructive examination of welds
6.3.1 NDE shall be carried out in accordance with the design basis selected in 5.2 (i.e. 100 % NDE or spot
checks). The examination shall be performed by an X-ray inspection. The X-ray apparatus shall have a
minimum sensitivity capable of revealing defects having a size equal to 4 % of the combined thickness of the
weld and the backing material (if used).
6.3.2 The circumferential and longitudinal welds and the bung or boss butt-welds shall be radiographed in
order to establish satisfactory machine settings. This shall be carried out on the introduction, or reintroduction
after a period exceeding three days, of a new design of cylinder (see Annex A) to a production line, for the first
cylinder welded, or more at the discretion of the inspector. The radiographs shall be assessed in accordance
with ISO 10042 and bulk production shall not commence unless they are found to be satisfactory.
6.3.3 Thereafter during production of that design of cylinder, in order to demonstrate that satisfactory welds
are being produced consistently, one cylinder shall be selected at random at the beginning and end of each
working shift’s production or at intervals not exceeding 12 h, whichever is the shorter, and radiographed as
above.
6.3.4 Defect acceptance criteria shall be in accordance with ISO 10042:2005 quality level C. If the
radiographs show no unacceptable defects, the whole of the production of the relevant working shift shall be
accepted subject to further tests as specified in B.2.
6.3.5 Should any of the radiographs show an unacceptable defect, production shall be stopped and the
whole of the relevant shift’s production shall be quarantined until it is demonstrated that the cylinders are
satisfactory, either by radiography or by other appropriate means approved by the inspector.
6.3.6 Production shall not be restarted until the cause of the defect has been established and rectified, and
the starting up test procedure, as specified above, has been repeated.
6.3.7 Any weld repairs shall be according to an approved welding procedure. All weld repairs should be
radiographed and rewelded. After rewelding and, where necessary, re-radiography, all cylinders shall be
re-heat treated as part of a new batch or production run in accordance with B.3, and shall be retested
accordingly. Acceptance criteria shall be in accordance with Annex C.
6.4 Surface defects
The internal and external surfaces of the finished cylinder shall be free from defects that would adversely
affect the safe working of the cylinder. Such defects shall be removed by local dressing in a manner that does
not introduce stress risers. The wall thickness of any dressed area shall not be less than the minimum
thickness specified.
6.5 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 torquing 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 1 Where the neck thread is specified to be in accordance with ISO 10920:1997, the corresponding gauges
are specified in ISO 11191:1997.
EXAMPLE 2 Where the neck thread is specified to be in accordance with ISO 11116-1:1999, the corresponding
gauges are specified in ISO 11116-2:1999.
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.
6.6 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 two diameters.
6.7 Straightness
The maximum deviation of the cylindrical part of the shell from a straight line shall not exceed 10 mm per
metre length.
6.8 Eccentricity
When measured on the same cross-section of a cylinder, the minimum and maximum wall thicknesses of the
shell shall not deviate by more than 10 % from the average of these two thicknesses. However, for cylinders
with a wall thickness of less than 4 mm, the difference between the minimum and maximum wall thicknesses
of the shell measured on the same cross-section shall be less than or equal to 0,8 mm.
6.9 Stability
For a cylinder designed to stand on its base, the deviation from vertical shall be less than 1 % of its height,
and the outer diameter of the surface in contact with the ground shall be greater than 75 % of the nominal
outside diameter (D ).
o
7 Tests and examinations
7.1 General
Every cylinder submitted to any test shall be identifiable to the batch, and either to the welder and welding
machine, or in the case of an automatic machine to the welding machine.
7.2 Mechanical tests
7.2.1 General requirements
All mechanical tests for checking the quality of the metal used for gas cylinders shall be carried out on
material taken from cylinders on which all operations affecting mechanical properties have been completed.
They do not need to have been pressure tested.
The mechanical tests shall be carried out in accordance with 7.2.2 to 7.2.8, ISO 6892 and ISO 6506-1.
7.2.2 Types of test and evaluation of test results
The number, the localization and type of test specimens shall be taken as shown in Figure 3 and the tests
shall be performed as specified in 7.2.3 to 7.2.8. If the cylinder is a sphere or has a design where a dome
and/or a base does not exist, specimens shall be taken according to the requirements for the cylinder sidewall.
7.2.3 Tensile test on parent material
7.2.3.1 The test piece on which the tensile test is carried out shall conform to the provisions of ISO 6892.
The two faces of the test piece corresponding to the internal and external walls of the cylinder shall not be
machined.
7.2.3.2 The elongation after fracture shall not be less than 12 %.
7.2.3.3 The value obtained for tensile strength shall not be less than R . The value obtained for the yield
g
stress (R ), as defined in 3.1.1, during the tensile test shall not be less than R .
ea e
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7.2.4 Tensile test in the pressure-bearing welds
The test specimens T3 and T4 (see Figure 3) shall be cut transversely to the weld and shall be the full
thickness of the material at the welded joint. The shape and dimension of the test specimen shall be as shown
in ISO 15614-2.
In preparing the test specimens, the face and back shall not be machined except to remove the backing strip
or the tongue of a joggle joint. The face and back of the test piece shall each represent the surface of the
parent material and the weld.
The ends of the test specimens may be carefully straightened cold as necessary in order to place them in the
testing machine.
The tensile strength shall be not less than that specified for the parent material.

Where the samples can be procured, the weld should be
perpendicular to the longitudinal axis of the sample.
a)  Cylinders with circumferential seams only b)  Cylinders with a boss/bung weld only
Key
1 weld B4 bend test on weld, outer surface in tension
T1 tensile test on parent material B6 bend test on weld, inner surface in tension
T4 tensile test on welded joint NB2 nick-break test on weld
B1 bend test on parent material NB3 nick-break test on weld
NB4 nick-break test on weld
NOTE The location of specimens around the circumference of the cylinder is not specified.
Figure 3 — Location of test specimens in a cylinder
c)  Cylinders with circumferential seams only: alternative positions for T1 and B1
Figure 3 (continued)
16 © ISO 2006 – All rights reserved

d)  Cylinders with longitudinal and circumferential seams
Key
1 weld B3 bend test on weld, outer surface in tension
T1 tensile test on parent material B4 bend test on weld, outer surface in tension
T2 tensile test on parent material B5 bend test on weld, inner surface in tension
T3 tensile test on weld B6 bend test on weld, inner surface in tension
T4 tensile test on weld NB1 nick-break test on weld
B1 bend test on parent material NB2 nick-break test on weld
B2 bend test on parent material NB4 nick-break test on weld
For positions of specimens across circumferential welds, alternate on successive cylinders between the positions
indicated by full lines and those indicated by dash-dotted lines.
Figure 3 (continued)
e)  Cylinders with seamless bodies with a welded shroud and foot-ring
Key
1 weld
T1 tensile test on parent material
B1 bend test on parent material
HT1 and HT2 hardness test specimens
Figure 3 (continued)
7.2.5 Bend test on parent material
7.2.5.1 The bend tests shall be carried out on two test pieces obtained by cutting a ring of width 25 mm
or, if greater, 3a′ (± 1 mm) into equal parts. Each ring may be machined only on the edges. These edges may
be rounded to a radius of no more than one tenth of the thickness of the test pieces or chamfered at an angle
of 45° and a width of less than one tenth of the thickness of the test pieces.
7.2.5.2 The bend tests shall be carried out using a former of diameter d and two rollers separated by a
distance of d + 3a′. During the test the inside face of the ring shall remain in contact with the former. Several
test pieces can be tested at the same time on the same test machine.
7.2.5.3 The test piece shall not crack when bent inwards around the former until the inside edges are not
further apart than the diameter of the former (see Figure 4).
7.2.5.4 The ratio (n) between the diameter of the former and the thickness of the test piece shall not
exceed the values given in Table 3.
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Table 3 — Bend test requirements
Actual tensile strength, R Value of n
m
MPa
R u 220 5
m
220 < R u 330 6
m
330 < R u 440 7
m
R > 440 8
m
Figure 4 — Illustration of bend test on parent metal
7.2.6 Bend test across the welds
The width of the test specimen shall be in accordance with ISO 7438 and the length shall be such that it will
satisfy the requirements of this test. In preparing the test specimen the corners shall be rounded off and in
addition the backing strip or the tongue of a joggle joint, all excess weld metal and any weld reinforcement
shall be machined off. This test shall be carried out in accordance with ISO 6892 (see Figure 5).
The former diameter (d) shall be 10 times the specimen thickness.
Test specimens B3 and B4 (see Figure 3) shall be bent with the outer surface of the weld in tension and test
specimens B5 and B6 (see Figure 3) with the inner surface of the weld in tension. The inner and outer
surfaces shall be ground flush. With reference to Figure 5, an angle α of 75° is required in addition to any
pre-existing curvature (e.g. the curvature on samples taken from the boss/bung region).
For cylinders of outside diameter less than 120 mm, the bend test may be replaced by a nick-break test on the
welds as shown in Figure 6. For cylinders designed as shown in Figure 3 c), the bend test may be replaced by
a nick-break test on the welds if the diameter of the boss/bung weld is less than 120 mm.
After bending, the inner and outer surfaces and the sides of the test specimen shall be examined and shall be
free from cracks.
Dimensions in millimetres
Key
L distance from centre of roller to the weld prior to forming
f
0,7d < L < 0,9d
f
Figure 5 — Illustration of bend test across the welds
7.2.7 Nick-break test on the pressure-bearing welds
Nick-break tests shall be carried out on test specimens NB1, NB2, NB3 and NB4 (see Figure 3), which shall
be prepared in the same way as those required for the bend tests (see 7.2.6) except that a slot shall be cut
along the weld on each side at the centre line. The slot shall be of a form shown in Figure 6 except that for the
test specimens NB3 and NB4 the dimensions and the form shall be modified as necessary to suit the design
of the cylinder. The specimens shall then be broken cold in the weld and the fracture shall reveal a sound,
homogeneous weld with complete penetration, free from oxide or other inclusions or excessive porosity.
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