ISO 4706:2008

Gas cylinders - Refillable welded steel cylinders - Test pressure 60 bar and below

ISO 4706:2008 specifies the minimum requirements concerning material selection, design, construction and workmanship, procedure and test at manufacture of refillable welded-steel gas cylinders of a test pressure not greater than 60 bar, and of water capacities from 0,5 l up to and including 500 l exposed to extreme worldwide temperatures (-50 °C to +65 °C) used for compressed, liquefied or dissolved gases. Transportable large cylinders of water capacity above 150 l and up to 500 l may be manufactured and certified to ISO 4706 provided handling facilities are provided. ISO 4706 is primarily intended to be used for industrial gases other than Liquefied Petroleum Gas (LPG), but may also be applied for LPG. For specific LPG applications see ISO 22991.

Bouteilles à gaz — Bouteilles en acier soudées rechargeables — Pression d'essai de 60 bar et moins

General Information

• Status: Withdrawn
• Publication Date: 07-Apr-2008
• ICS: 23.020.30 - Pressure vessels, gas cylinders
• ICS: 23.020.35 - Gas cylinders
• Technical Committee: ISO/TC 58/SC 3 - Cylinder design
• Drafting Committee: ISO/TC 58/SC 3 - Cylinder design
• Current Stage: 9599 - Withdrawal of International Standard
• Start Date: 20-Sep-2023
• Completion Date: 13-Dec-2025
• Directive: TRRTP121 - Sklep o objavi prilog A in B k Evropskemu sporazumu o mednarodnem cestnem prevozu nevarnega blaga (ADR)

Relations

• Revised: ISO 4706:2023 - Gas cylinders - Refillable welded steel cylinders - Test pressure 60 bar and below
• Effective Date: 23-Apr-2020
• Revises: ISO 4706:1989 - Refillable welded steel gas cylinders
• Effective Date: 15-Apr-2008

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 4706
First edition
2008-04-15
Corrected version
2008-07-01
Gas cylinders — Refillable welded steel
cylinders — Test pressure 60 bar and
below
Bouteilles à gaz — Bouteilles en acier soudées rechargeables —
Pression d'essai de 60 bar et moins

Reference number
©
ISO 2008
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©  ISO 2008
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ii © ISO 2008 – All rights reserved

Contents Page
Foreword. iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and symbols. 2
4 Inspection and testing. 4
5 Materials . 4
6 Design . 5
7 Calculation of minimum wall thickness (sidewall and ends) . 6
8 Construction and workmanship. 11
9 Testing . 17
10 Acceptance criteria. 22
11 Technical requirements for new design type approval . 27
12 Markings . 28
13 Certificate . 28
Annex A (normative) Manufacturer's markings for LPG. 29
Annex B (informative) New design type approval certificate. 30
Annex C (informative) Acceptance certificate. 31
Bibliography . 33

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 4706 was prepared by Technical Committee ISO/TC 58, Gas cylinders, Subcommittee SC 3, Cylinder
design.
This second edition cancels and replaces the first edition (ISO 4706:1989), which has been technically revised.
ISO 4706 has been prepared to address the general requirements in Chapter 6.2 of the UN model regulations
for the transportation of dangerous goods ST/SG/AC.10/1Rev.15. 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
6.2.2.5 of ST/SG/AC.10/1/Rev.15.
This corrected version incorporates the following corrections:
⎯ following the cancellation of a proposed ISO 4706-2, the reference number has been changed from
ISO 4706-1 to ISO 4706, therefore
⎯ reference to individual parts of ISO 4706 has been removed from the foreword,
⎯ references to ISO 4706-1 have been replaced by ISO 4706, and
⎯ the page headers have been changed to read “ISO 4706:2008”;
⎯ the term “proof stress” has been replaced by the term “proof strength”;
⎯ Subclause 7.4, Design of openings, has been moved to Clause 6, Design, and renumbered 6.3;
⎯ the title of Figure 5 now relates to longitudinal welds, not circumferential welds;
⎯ the graphics in Figure 5 have been modified to depict a longitudinal weld.
iv © ISO 2008 – All rights reserved

Introduction
The purpose of this International Standard is to facilitate agreement on the design and manufacture of welded-
steel gas cylinders in all countries. The requirements are based on knowledge of, and experience with,
materials, design requirements, manufacturing processes and controls in common use for the manufacture of
gas cylinders.
With respect to those aspects concerning construction materials, approval of design rules and inspection
during manufacture, which are subject to national or international regulations, it is necessary for interested
parties to ensure that in the practical application of this International Standard, the requirements of the
relevant authority are also satisfied.

INTERNATIONAL STANDARD ISO 4706:2008(E)

Gas cylinders — Refillable welded steel cylinders — Test
pressure 60 bar and below
1 Scope
This International Standard specifies the minimum requirements concerning material selection, design,
construction and workmanship, procedure and test at manufacture of refillable welded-steel gas cylinders of a
1)
test pressure not greater than 60 bar , and of water capacities from 0,5 l up to and including 500 l exposed to
extreme worldwide temperatures (−50 °C to +65 °C) used for compressed, liquefied or dissolved gases.
Transportable large cylinders of water capacity above 150 l and up to 500 l may be manufactured and certified
to this International Standard provided handling facilities are provided (see 8.6.4).
This International Standard is primarily intended to be used for industrial gases other than Liquefied Petroleum
Gas (LPG), but may also be applied for LPG. For specific LPG applications see ISO 22991.
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 4136, Destructive tests on welds in metallic materials — Transverse tensile test
ISO 5817, Welding — Fusion-welded joints in steel, nickel, titanium and their alloys (beam welding
excluded) — Quality levels for imperfections
ISO 6892, Metallic materials — Tensile testing — Method of testing at ambient temperature
ISO 7438, Metallic materials — Bend test
ISO 9606-1, Qualification test of welders — Fusion welding — Part 1: Steels
ISO 10297:2006, Transportable gas cylinders — Cylinder valves — Specification and type testing
ISO 11117, Gas cylinders — Valve protection caps and valve guards — Design, construction and tests
ISO 13769, Gas Cylinders — Stamp marking
ISO 11622, Gas cylinders — Conditions for filling gas cylinders
ISO 15613, Specification and qualification of welding procedures for metallic materials — Qualification based
on pre-production welding test
ISO 15614-1, Specification and qualification of welding procedures for metallic materials — Welding
procedure test — Part 1: Arc and gas welding of steels and arc welding of nickel and nickel alloys

5 5 2
1) 1 bar = 10 Pa = 10 N/m .
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 17639, Destructive tests on welds in metallic materials — Macroscopic and microscopic examination of
welds
ISO 22991, Gas Cylinders — Transportable refillable welded steel cylinders for liquefied petroleum gas
(LPG) — Design and construction
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 strength
value corresponding to the upper yield strength, R , or, for steels when yielding does not occur at tensile
eH
testing, the 0,2 % proof strength (non-proportional elongation), R 2
p0,
3.1.2
normalizing
heat treatment in which a cylinder is heated to a uniform temperature above the upper critical point (Ac3) of
the steel to regenerate or homogenize the metallurgical structure of the steel, to a sufficient degree to achieve
the desired mechanical properties, and then cooled in a controlled or still air atmosphere
3.1.3
stress relieving
heat treatment given to the cylinder, the object of which is to reduce the residual stresses without altering the
metallurgical structure of the steel, by heating it to a uniform temperature below the lower critical point (Ac1) of
the steel, then cooling it in a controlled or still air atmosphere
3.1.4
stabilizing
heat treatment given to the cylinder, the object of which is to stabilize the structure of the steel by heating it to
a uniform temperature above the lower critical point (Ac1) of the steel and subsequently cooling it to obtain the
desired mechanical properties
3.1.5
batch
quantity of cylinders made consecutively by the same manufacturer using the same manufacturing techniques,
to the same design, size and material specifications using the same type of welding machines, welding
procedures and to the same heat treatment conditions
NOTE 1 In this context, “consecutively” need not apply to continuous production (start to finish).
NOTE 2 See 10.2 for specific batch quantities.
3.1.6
base materials
steel used to manufacture the cylinder including the pressure and non-pressure retaining materials of
construction
3.1.7
cylinder shell
cylinder after completion of all forming, welding and heat treatment operations
2 © ISO 2008 – All rights reserved

3.1.8
F Factor
design stress factor
3.1.9
parent material
all pressure retaining materials used in the fabrication of the cylinder
3.1.10
overlap
placement of steel on top of or below a weld joint for the purpose of joint alignment or added joint strength
3.2 Symbols
Symbol Definition Unit
a Calculated minimum thickness of the cylindrical shell mm
a Calculated minimum value of a used in the calculation of b (see 7.2.2) of the mm
cylinder head
a Minimum thickness of the cylindrical shell (including any corrosion allowance) mm
b
guaranteed by the manufacturer
A Percentage elongation after fracture %
Y Stabilized cylinder —
b Calculated minimum thickness of the end mm
C Shape factor —
D Outside diameter of the cylinder as given in the design drawing mm
D Outside diameter of a bend test former mm
f
F Design stress factor —
h Height of the cylindrical part of the end mm
H Outside height of the domed part of the end mm
J Stress reduction factor —
K Ellipsoidal Ratio —
L Length of the cylinder mm
L Original gauge length in accordance with ISO 6892 mm
n Ratio of diameter of bend test former to the thickness of the test piece —
N Normalized cylinder —
P Maximum pressure attained during the burst test bar
b
P Actual test pressure applied to the cylinder by the manufacturer bar
h
P Minimum test pressure (see ISO 11622) bar
tmin
r Inside knuckle radius of the end mm
R Inside dishing radius of the end mm

R Minimum value of yield strength (apparent) guaranteed by the cylinder N/mm
eH
manufacturer for the finished cylinder

R Guaranteed tensile strength by the manufacturer N/mm
g
R Actual value of tensile strength determined by the tensile test specified in 9.1.2.2 N/mm
m
R 0,2 % proof strength (see ISO 6892) N/mm
p0,2
S Stress relieved cylinder —
S Original cross-sectional area of tensile test piece in accordance with ISO 6892 mm
4 Inspection and testing
To ensure that the cylinders are in conformance with this International Standard, they shall be subject to
inspection and testing in accordance with Clauses 7, 8, 9 and 10.
Some countries of use may require that cylinders be inspected and tested by an authorized body. The
inspection body shall be recognized in the country of use and shall be competent for testing and inspecting
cylinders in accordance with this International Standard.
5 Materials
5.1 The material used for the fabrication of the gas cylinder shall be steel, other than rimming quality,
suitable for pressing or drawing and welding, and shall not deteriorate with time (i.e. non-ageing). The steel
grades used shall have specified, guaranteed, mechanical properties that are possible to achieve for the
finished cylinder after normalizing, stress relieving or stabilizing.
In cases where verification of the non-ageing property of the material is required, the criteria by which it is to
be specified should be agreed by the manufacturer and purchaser, and included in the order.
5.2 Materials for shells and end pressings, excluding bosses (see 5.3), shall conform to the requirements of
5.8 and 5.9.1.
5.3 Bosses shall be manufactured from compatible weldable materials with a maximum carbon content of
0,25 %(m/m).
5.4 All items welded to the cylinder (e.g. shrouds and footrings) shall be made of compatible weldable
material containing maximum values %(m/m) of:
a) carbon 0,250 %;
b) phosphorous 0,040 %;
c) sulphur 0,040 %.
5.5 The welding consumables shall be such that they are capable of giving consistent welds with a
minimum tensile strength at least equal to that specified for the parent materials in the finished cylinder.
5.6 The cylinder manufacturer shall have certificates of the ladle analysis and mechanical properties of the
steel supplied for the construction of the pressure retaining parts of the cylinder. The cylinder manufacturer
shall also have certificates of the ladle analysis for items welded to the cylinder (e.g. shrouds and footrings).
4 © ISO 2008 – All rights reserved

5.7 A system of identification shall be in place to determine the cast(s) of steel used for the construction of
the pressure retaining parts of the cylinder.
5.8 Grades of steel used for cylinder manufacture shall be compatible with the intended gas service (e.g.
corrosive or embrittling gases).
5.9 Chemical composition.
5.9.1 Materials used for the fabrication of gas cylinders shells and end pressings shall be of weldable
quality and values %(m/m) of:
a) carbon 0,25 %;
b) silicon 0,45 %;
c) manganese 1,60 %;
d) phosphorus 0,040 %;
e) sulphur 0,040 %;
shall not be exceeded in the cast analysis.
The use of micro-alloying elements such as niobium (columbium), titanium and vanadium shall not exceed:
a) niobium 0,05 %;
b) titanium 0,03 %;
c) vanadium 0,10 %;
d) niobium plus vanadium 0,12 %.
Where other micro-alloying elements are used, their presence and amounts shall be reported, together with
those already described in 5.9.1, in the steel manufacturer’s certificate.
5.9.2 When the country of use of the cylinder requires a check analysis on the steel, the analysis shall be
carried out either on specimens taken during manufacture from material in the form as supplied by the steel
maker to the cylinder manufacturer, or from the cylinder shell, or from finished cylinders. In any check analysis,
the maximum tolerance for cast analyses shall conform to the values specified in 5.9.1.
6 Design
6.1 General requirements
6.1.1 The calculation of the wall thickness of the pressure parts to resist the internal pressure in the gas
cylinders is related to the yield strength of the material for the finished cylinder.
6.1.2 For calculation purposes, the value of the yield strength i.e. R is limited to a maximum value of:
eH
a) 0,75 R for finished cylinders with a guaranteed tensile strength (R ) < 490 N/mm ;
g g
b) 0,85 R for finished cylinders with a guaranteed tensile strength (R ) W 490 N/mm .
g g
6.1.3 The internal pressure, on which the wall thickness calculation of the gas cylinder is based, shall be the
minimum test pressure P .
tmin
A minimum pressure of 30 bar shall be used in the design of LPG cylinders.
6.1.4 A fully dimensioned drawing including the specification of the material shall be produced.
6.2 Valve protection
The design of the cylinder shall provide protection for valves against damage in order to avoid release of
contents. When the requirements of 8.7 are not met then the cylinders shall be conveyed in crates or cradles
or shall be provided during transportation with some other effective valve protection, unless it can be
demonstrated that the valve can withstand damage without leakage of product.
6.3 Design of openings
6.3.1 The location of all openings shall be restricted to the ends of the cylinder.
6.3.2 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. Compliance shall be confirmed by calculation or performing a fatigue test in
accordance with the requirements of 9.6.
6.3.3 The welds of the openings shall be clear of circumferential and longitudinal joints.
6.3.4 If the leak-tightness between the valve and the cylinder is assured by a metallic seal (e.g. copper), a
suitable internal valve boss can be fitted to the cylinder by a method that need not independently assure leak-
tightness.
7 Calculation of minimum wall thickness (sidewall and ends)
7.1 Sidewall thickness
7.1.1 The wall thickness of the cylindrical shell shall not be less than that calculated using Equation (1).
⎛⎞
D 10 JF R − 3P
eH h
⎜⎟
a 1=−  (1)
21⎜⎟0 JF R
eH
⎝⎠
where
F = 0,77 for water capacities 0,5 l to 150 l;
F = 0,72 for water capacities 151 l to 250 l;
F = 0,68 for water capacities 251 l to 500 l;
and for longitudinal welds:
J = 1.0 for completely radiographed seams;
J = 0,9 for spot-radiographed seams;
J = 0,7 for seams that are not radiographed (carbon steels only);
J = 1,0 for cylinders without a longitudinal weld.
In no case shall the actual thickness be less than that specified in 7.3.
6 © ISO 2008 – All rights reserved

7.2 Design of ends concave to pressure
7.2.1 Unless otherwise specified in 7.4, the shape of ends of gas cylinders shall be such that:
a) for torispherical ends R u D; r W 0,1 D; h W 4b [see Figure 1 a)];
b) for semi-ellipsoidal ends H W 0,192 D; h W 4b [see Figure 1 b)].
7.2.2 The head thickness of all other end shapes shall be not less than that calculated using Equation (2).
ba= C (2)
where
a is the value of a calculated in accordance with 7.1.1 using J = 1,0;
C is a shape factor, the value of which depends on the ratio H/D.
The value of C shall be obtained from the graph shown in Figure 2 or 3, as applicable.
a)  Torispherical end b)  Semi-ellipsoidal end
NOTE a)  for torispherical ends:
⎡⎤DD⎡ ⎤
H=+Rb− Rb+ − × R+b+ − 2r+b
() () () ()
⎢⎥⎢ ⎥
⎣⎦⎣ ⎦
b)  for semi-ellipsoidal ends:
D
⎛⎞
⎜⎟
D+−22Kb b
()()( )()
2− b
⎝⎠
H= with K =
H
2()K ⎛⎞
⎜⎟
b
⎝⎠
Key
1 torispherical end
2 semi-ellipsoidal end
Figure 1 — Illustration of cylinder ends concave to pressure
8 © ISO 2008 – All rights reserved

Key
H/D, see 3.2
shape factor, C
Figure 2 — Values of shape factor C for H/D between 0,2 and 0,25
Key
H/D, see 3.2
shape factor, C
Figure 3 — Values of shape factor C for H/D between 0,25 and 0,5
10 © ISO 2008 – All rights reserved

7.2.3 Heads that do not contain markings may be 90 % of the minimum sidewall thickness as indicated
in 7.1.1 and 7.2.2.
Ends shaped other than those specified in 7.2 may be used provided that the adequacy of their design is
demonstrated by fatigue testing in accordance with the requirements of 9.6.
For heads convex to pressure, the minimum head thickness shall be a minimum of two times that specified
in 7.2.2.
7.3 Minimum wall thickness
7.3.1 The minimum wall thickness of the cylindrical shell a, and of the end, b, shall not be less than the
value derived from any of Equations (3), (4) and (5).
for D < 100 mm:
a = b = 1,1 mm (3)
min min
for 100 u D u 150 mm:
a = b = 1,1 + 0,008(D − 100) mm (4)
min min
for D > 150 mm:
a = b = (D/250) + 0,7 mm (with an absolute minimum of 2,0 mm) (5)
min min
For acetylene cylinders with D > 300 mm the minimum wall thickness shall be 3,0 mm.
7.3.2 Equation 1 (see 7.1.1) is not applicable where the length of the cylindrical portion of the cylinder,
measured between the beginning of the domed parts of the two ends, is not more than 2.bD In this case the
wall thickness shall be not less than that of the domed part (see 7.2.2).
8 Construction and workmanship
8.1 Quality conformance system
Each cylinder manufacturing facility should have a written quality system that meets the requirements of
ISO/TR 14600.
8.2 Welding qualification
8.2.1 General
a) before proceeding with the production of a given design, all welding operators and welding procedures
shall be approved by meeting the requirements of 8.2.2 to 8.2.9, ISO 9606-1, ISO 15613 or ISO 15614-1;
b) records of both qualifications shall be kept on file by the manufacturer;
c) weld approval tests shall be made in such a manner that the welds shall be representative of those made
in production;
d) welders shall have passed the approval tests for the specific type of work and procedure specification
concerned.
8.2.2 Base materials (pressure and non-pressure)
Base materials defined in the procedure specification shall be the same as the given design and those tested
by the welders.
8.2.3 Positions of welds
For welder qualification, the position of the part for welding shall be as specified in 8.2.1 c).
8.2.4 Welding materials
Weld consumables (see 5.5) shall be the same as those specified in the procedure specification, those tested
by the welders and those used for production.
8.2.5 Retesting
Where a welder fails to meet the requirements of a weld test:
a) an immediate retest may be made of two test welds of the type that failed, both of which shall meet all the
test requirements; or
b) a retest may be made provided there is evidence that the operator has had further training and practice in
the design and procedure specification.
8.2.6 Period of effectiveness
a) a welder shall be re-qualified if the design has not been produced by the welder for a period of three
months or more;
b) records of welder effectiveness shall be retained by the manufacturer.
8.2.7 Essential variables of the welding process
The procedure specification and welder qualification shall be set-up and tested when there is:
a) a change to the base materials used;
b) a change to the welding material used;
c) a change to the weld process;
d) a change to the weld position;
e) a decrease of 30 °C or more in the minimum specified preheating temperature;
f) a change from one heat treatment process to another (see 3.1.2, 3.1.3 and 3.1.4);
g) the omission or addition of a backing strip in single pass welds;
h) a change from multiple pass to single pass per side;
i) a change from a single arc to multi arc, or vice versa;
j) a change to the shielding gas or to the composition of the shielding gas (if there is a change greater than
15 % in the mixture).
12 © ISO 2008 – All rights reserved

8.2.8 Welder qualification tests
When required, the weldment shall, prior to radiography:
a) for longitudinal welds pass:
1) a bend test of the weld root;
2) a weld tensile test;
b) for circumferential welds pass:
1) a bend test of the weld root;
2) a weld tensile test;
c) for threaded connections to heads or bottoms pass macro tests, 180° apart;
d) for welded attachments, foot rings, collars or lugs, pass a macro test;
e) for fillet welds used for the attachment of bottom heads [see Figure 4 b)], pass macro tests, 180° apart.
8.2.9 Results
a) For radiography.
As specified in 9.4.1.
b) For bend tests.
Upon completion of the test, the test piece (weld metal and parent material) shall remain uncracked.
c) For tensile tests.
The tensile strength (R ) value obtained, shall not be less than that guaranteed by the cylinder
m
manufacturer (R ) regardless of the fracture location.
g
d) For macro tests.
The etched specimen shall be visually examined to determine adequate root penetration into both
members as to the established design.
8.3 Plates and pressed parts
Before assembly, the pressure parts of the cylinders shall be visually examined for cracks, seams, laminations,
galling and freedom from any defects that may ultimately affect cylinder integrity.
8.4 Welded joints
8.4.1 The welding of two-piece cylinder circumferential joints or three-piece cylinder longitudinal and
circumferential joints (pressure envelope) shall be by using a fully mechanized, semi-automatic or automatic
process to provide consistent and reproducible weld quality.
8.4.2 The longitudinal joint, of which there shall be no more than one, shall be of the butt-welded type.
8.4.3 Circumferential joints, of which there shall be no more than two, shall be butt welded, butt welded with
one member offset to form an integral backing strip {i.e. joggled [see Figure 4 a)]}, or fillet welded [see
Figure 4 b)] or lap welded [see Figure 4 c)].
Lap-welded joints shall have a minimum overlap of four times the minimum design thickness (a).
8.4.4 Before cylinders are closed, longitudinal welds shall be visually examined from both sides in
accordance with the requirements of ISO 17637.
Permanent backing strips shall not be used with longitudinal welds.
8.4.5 The fusion of the welded metal with the parent metal (pressure joint) for longitudinal seams,
circumferential seams and bosses shall be smooth and free from undercutting or abrupt irregularity. There
shall be no cracks, notching or porous patches in the welded surface and/or the surface adjacent to the weld.
The welded surface shall be regular and even, without concavity.
8.4.6 Butt welds shall have full penetration. The excess thickness shall be such that the weld integrity is not
compromised.
8.4.7 Joggled butt welds shall have adequate penetration verified by bend testing and tensile testing. If
adequate material is not available due to the cylinder geometry, the weld shall be verified by macro etch.
8.4.8 Lap welds shall have adequate penetration verified by macro etch and bend testing.
8.4.9 Fillet welds shall exhibit root penetration verified by macro etch.
8.4.10 The fusion of the welded metal with the non-pressure retaining attachments (e.g. shrouds and
footrings) shall be smooth and free from abrupt irregularity. There shall be no cracks, notching or porous
patches in the welded surface and/or the surface adjacent to the weld. The welded surface shall be regular
and even, without concavity.
Dimensions in millimetres
a)  Joggled butt joint
14 © ISO 2008 – All rights reserved

b)  Fillet weld
c)  Lap weld
Key
1 bevel (optional)
2 as desired
3 minimum overlap
4 inside of cylinder, avoid sharp break
e Thickness of metal which is offset.
e Thickness of metal which is not offset.
Figure 4 — Typical weld configurations
8.5 Tolerances
8.5.1 Out of roundness
The out of roundness of the cylindrical shell shall be limited so that the difference between the maximum and
the minimum outside diameters in the same cross section is not more than:
a) for two-piece cylinders, 1 % of the mean of the diameters; and
b) for three-piece cylinders 1,5 % of the mean of the diameters.
8.5.2 Straightness
Unless otherwise shown on the manufacturer’s drawing, the maximum deviation of the cylindrical part of the
shell from a straight line shall not exceed 0,3 % of the cylindrical length.
8.5.3 Verticality
When the cylinder is standing on its base, the deviation from vertical shall not exceed 1 % including the
shroud and footring.
8.6 Non-pressure-containing attachments
8.6.1 Where non-pressure-containing attachments are to be attached to the cylinder by welding, such
attachments shall be made of compatible weldable steel.
8.6.2 Attachments shall be designed to permit inspection of welds, which shall be clear of longitudinal and
circumferential joints, and so designed as to avoid trapping water.
8.6.3 Where a footring is fitted, it shall be of adequate strength to provide stability and be attached so that it
does not prevent inspection of any pressure-containing welds.
All footrings shall be designed to permit drainage and ventilation.
8.6.4 Depending on the geometry of the cylinder and the surrounding conditions, cylinders of water capacity
greater than 150 l shall require specific mechanical or other handling and transportation equipment (e.g. fork
lift truck).
The cylinder itself shall have a suitable provision for such a lift to be made (e.g. lugs welded onto the top
dome area of the cylinder and/or slots underneath the cylinder) where the forks of a fork lift truck can be
engaged.
8.7 Valve protection
Valves shall be protected from damage. This shall be accomplished by one of the following methods:
a) by a means that meets the requirements of ISO 11117 (e.g. a cap, guard or shroud);
b) valves that are not equipped with such a protective device shall have sufficient inherent strength to meet
the requirements of the impact test specified in ISO 10297:2006, Annex A.
If the above requirements are not met, cylinders shall be conveyed by a means providing effective protection
(e.g. crates, cradles or in an outer package).
8.8 Closure of openings
Apertures in finished cylinders shall be either
a) fitted with a plug of suitable non-absorbent material, or
b) fitted with the appropriate valve in the closed position or fitting to protect the thread from damage and to
prevent entry of moisture into the cylinder.
8.9 Heat treatment
8.9.1 Cylinders shall be delivered in the heat-treated condition as defined in 3.1.2, 3.1.3 or 3.1.4.
8.9.2 The cylinder manufacturer shall maintain records to indicate that the cylinders have been heat-treated
after completion of all welding and to indicate the adequacy of the heat-treatment process used.
8.9.3 Localized heat treatment shall not be used.
16 © ISO 2008 – All rights reserved

9 Testing
9.1 Mechanical testing
9.1.1 General requirements
9.1.1.1 Where not covered by the requirements of this clause, mechanical tests shall be carried out:
a) for the parent material in accordance with:
ISO 6892 for the tensile test;
ISO 7438 for the bend test, depending on whether the thickness of the test-piece is greater or less than
3 mm;
b) for welded test specimens, in accordance with 9.1.2.
9.1.1.2 All the mechanical tests for checking the properties of the parent metal and welds of the pressure
containing shells of the gas cylinder shall be on test specimens taken from heat-treated cylinders.
9.1.2 Types of test and evaluation of test results
9.1.2.1 Sample cylinder tests
a) for cylinders containing only circumferential welds (two-piece cylinders), on test specimens taken from the
locations shown in Figure 7 the following tests shall be carried out:
1) one tensile test (in accordance with the requirements of ISO 6892), parent metal parallel to the
circumferential seam or if it is not possible, in the longitudinal direction, or the centre of one dished
end;
2) one tensile test (in accordance with the requirements of ISO 4136), perpendicular to the
circumferential weld;
3) one root bend test (in accordance with the requirements of ISO 7438), of the circumferential weld;
b) for cylinders with longitudinal and circumferential welds (three piece cylinders), on test specimens taken
from the locations shown in Figure 8 the following tests shall be carried out:
1) one tensile test (in accordance with the requirements of ISO 6892), parent metal parallel to the
circumferential seam or if it is not possible, in the longitudinal direction, or the centre of one dished
end;
2) one tensile test (in accordance with the requirements of ISO 6892), parent metal from one dished
end, b);
3) one tensile test (in accordance with the requirements of ISO 4136), of longitudinal weld, c);
4) one root bend test (in accordance with the requirements of ISO 7438), of the longitudinal weld, d);
5) one tensile test (in accordance with the requirements of ISO 4136), of circumferential weld, e);
6) one root bend test (in accordance with the requirements of ISO 7438), of the circumferential weld, f).
9.1.2.2 Tensile test
9.1.2.2.1 Tensile test on parent metal
9.1.2.2.1.1 Tensile tests shall be carried out in accordance with the requirements of ISO 6892.
The two faces of the test specimen representing the inside and outside walls of the cylinder respectively shall
not be machined.
9.1.2.2.1.2 The values obtained for yield strength and tensile strength shall not be less than those
guaranteed by the cylinder manufacturer. Elongation (%) shall not be less than that specified in Table 1.
NOTE a u 3 for a 20 mm × 80 mm specimen.
a > 3, proportional L = 5.65 S specimen
o
o
Table 1 — Elongation requirements
Minimum elongation after fracture

A
Wall thickness of cylinder shell
2 2 2
a R u 410 N/mm R > 410 u 520 N/mm R > 520 N/mm
m m m
mm
a > 3 29 % 25 % 20 %
a u 3 22 % 19 % 15 %
9.1.2.2.2 Weld tensile tests
9.1.2.2.2.1 The tensile test perpendicular to the weld (see ISO 4136) shall be carried out on a test
specimen having a reduced cross section 25 mm in width for a length extending up to 15 mm beyond the
edges of the weld (see Figure 9). Beyond this central part the width of the test specimen shall increase
progressively.
9.1.2.2.2.2 The tensile strength value obtained, R , shall be not less than that guaranteed by the cylinder
m
manufacturer, R , irrespective of where the fracture occurs in the cross section of the central part of the test
g
specimen.
9.1.2.3 Bend test
9.1.2.3.1 The procedure for carrying out a bend test is given in ISO 7438. The bend test specimen shall be
25 mm in width. The mandrel shall be placed in the centre of the weld while the test is being performed and
remain in that position until the conclusion of the test (see Figure 10).
9.1.2.3.2 Cracks shall not appear in the test specimen when it is bent around a mandrel through 180° (see
Figure 11).
9.1.2.3.3 The ratio n between the diameter of the mandrel D and the thickness of the test specimen a shall
f
not exceed the values specified in Table 2.
18 © ISO 2008 – All rights reserved

Table 2 — Ratio of mandrel diameter and test piece thickness
Actual measured tensile strength
R n
m
N/mm
< 410 2
410 to 520 3
> 520 4
9.2 Burst test under hydraulic pressure
9.2.1 Test conditions
9.2.1.1 If it is proposed to apply markings (in accordance with Clause 12) on the section of the cylinder
subjected to pressure, then cylinders to be tested shall be similarly marked.
9.2.1.2 The burst test under hydraulic pressure shall be carried out with equipment that enables the
pressure to be increased gradually until the cylinder bursts. The pressure at which the cylinder bursts shall be
recorded. The rate of pumping shall not exceed five times the water capacity of the cylinder per hour.
9.2.2 Interpretation of test
The criteria adopted for the interpretation of the burst test are:
a) volumetric expansion of the cylinder that equals:
1) the volume of water used between the time when the pressure starts to rise and at the time of
bursting; or
2) the difference between the volume of the cylinder at the beginning and the end of the test (see
9.2.3.2);
b) examination of the tear and the shape of its edges shall be in accordance with 9.2.3.3.
9.2.3 Minimum test requirements
9.2.3.1 Bursting pressure
The measured bursting pressure, P , shall not under any circumstances be less than double the pressure
tmin
P and not less than 50 bar.
h
9.2.3.2 Volumetric expansion
The ratio of volumetric expansion of the cylinder at burst to its initial volume shall be greater than or equal to:
a) where the minimum value of R is u 410 N/mm :
g
1) 20 % if the length of the cylinder is greater than its diameter;
2) 14 % if the length of the cylinder is equal to or less than its diameter;
b) where the minimum value of R is > 410 N/mm2:
g
1) 15 % if the length of the cylinder is greater than its diameter;
2) 10 % if the length of the cylinder is equal to or less than its diameter.
9.2.3.3 Type of fracture
a) the burst test shall not cause any fragmentation of the cylinder;
b) the main fracture shall not show any brittleness (i.e. the edges of the fracture shall not be radial but shall
be at an angle to a diametrical plane and display a reduction of area throughout their thickness);
c) the fracture shall not reveal a visible defect in the metal;
d) the fracture shall not initiate in a weld;
e) the fracture shall not initiate in a marking area (see 12.4);
f) the fracture shall not initiate from a weld securing a footring or shroud.
9.3 Pressure test
9.3.1 The pressurization medium may be liquid or gas provided safety precautions have been taken.
9.3.2 The pressure indicating device(s) shall be certified to an accuracy of 0,5 % at cylinder test pressure
(P ).
h
9.3.3 The manufacturer shall employ manufacturing practices and techniques that will demonstrate that the
cylinders do not leak when subjected to the minimum test pressure (P ).
tmin
9.3.4 The minimum test pressure P to be applied shall be as specified in 6.1.3.
tmin
For butane only, the stress within the wall of the cylinder shall not exceed 90 % of the minimum yield strength
of the material i.e. R during the test.
eH
9.3.5 The pressure in the cylinder shall increase gradually until the test pressure is reached.
9.3.6 The cylinder shall remain at the test pressure for a period of time, at least 10 s for testing with
gaseous media and 30 s for liquid media, that will make it possible to establish that no leak in the cylinder or
welds can be observed.
9.3.7 After the test the cylinder shall show no signs of permanent deformation.
9.3.8 Where the manufacturer employs a gas as the pressurization medium for the pressure test, then no
leakage test shall be required. Otherwise, each cylinder shall be subjected to a leak test using a gaseous
media at the marked service pressure of the cylinder.
9.4 Radiographic and macro examination
9.4.1 Radiographic examination
9.4.1.1 General
The radiographic examination may be replaced by radioscopy or another suitable non-destructive testing
(NDT) method if the applied method is carried out in accordance with a process that provides the same level
of quality of examination as radiographic examination. Radiographic examination shall conform to the
techniques specified in 9.4.1.2 and 9.4.1.3.
9.4.1.2 Welds shall be radiographed in accordance with ISO 17636, Class B.
9.4.1.3 Cylinders shall not have any of the following imperfections as specified in ISO 5817:
a) cracks, inadequate welds, lack of penetration or lack of fusion of the weld;
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b) elongated inclusions or any group of rounded inclusions in a row where the length represented over a
weld length of 12a is greater than 6 mm;
c) any gas pores measuring more than (a/3) mm;
d) any gas pores measuring more than (a/4) mm, which is 25 mm or less from any other gas pore;
e) gas pores over any 100 mm length, where the total area, in mm , of all the figures is greater than 2a.
9.4.2 Macro examination
The macro examination, carried out in accordance with ISO 17639, of a full transverse section of the welds
shall show complete fusion and comp
...