ISO 4706:2023

INTERNATIONAL ISO
STANDARD 4706
Third edition
2023-09
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 2023
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Published in Switzerland
ii
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 . 3
4 Inspection and testing .4
5 Materials . 4
5.1 General . 4
5.2 Chemical composition . 5
6 Design . 5
6.1 General requirements . 5
6.2 Valve protection . 6
6.3 Design of openings . 6
7 Calculation of minimum wall thickness (sidewall and ends) . 6
7.1 Sidewall thickness . 6
7.2 Design of ends concave to pressure . 7
8 Construction and workmanship .10
8.1 Welding qualification . . 10
8.1.1 General . 10
8.1.2 Base materials (pressure and non-pressure) . 11
8.1.3 Positions of welds . 11
8.1.4 Welding materials . 11
8.1.5 Retesting . 11
8.1.6 Period of effectiveness . 11
8.1.7 Changes to welding process requiring recertification . 11
8.1.8 Welder qualification tests .12
8.1.9 Results of welder qualification .12
8.2 Plates and pressed parts . . 12
8.3 Welded joints .12
8.4 Tolerances . 14
8.4.1 Out of roundness . 14
8.4.2 Straightness . 14
8.4.3 Verticality .15
8.5 Non-pressure-containing attachments . 15
8.6 Valve protection . 15
8.7 Closure of openings . 15
8.8 Heat treatment. 15
9 Testing.16
9.1 Mechanical testing . 16
9.1.1 General requirements . 16
9.1.2 Types of test and evaluation of test results . 16
9.2 Burst test under hydraulic pressure . 20
9.2.1 Test conditions .20
9.2.2 Interpretation of test . 20
9.2.3 Volumetric expansion .20
9.3 Pressure test . . 21
9.4 Radiographic and macro examination . 21
9.4.1 Radiographic examination . 21
9.4.2 Macro examination . 22
iii
9.4.3 Examination of flange welding . 22
9.4.4 Examination of welding of non-pressure containing attachments .22
9.4.5 Unacceptable imperfections at radiographic or macro examination .22
9.5 Visual examination of the surface of the weld . 22
10 Acceptance criteria .23
11 Type approval . .24
12 Batch tests . .25
12.1 Inspection lots . 25
12.2 Rate of sampling . 25
12.3 Quantity ≤ 3 000 cylinders water capacity less than or equal to 35 l .26
12.4 Quantity over 3 001 cylinders water capacity greater than 35 l . 26
12.5 Failure to meet batch test requirements . 26
13 Test/examinations for all pressure cylinders .27
14 Markings .27
15 Certificate .27
Annex A (informative) New design type approval certificate .28
Annex B (informative) Acceptance certificate .30
Bibliography .32
iv
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO document should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use
of (a) patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed
patent rights in respect thereof. As of the date of publication of this document, ISO had not received
notice of (a) patent(s) which may be required to implement this document. However, implementers are
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database available at www.iso.org/patents. ISO shall not be held responsible for identifying any or all
such patent rights.
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expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 58, Gas cylinders, Subcommittee SC 3,
Cylinder design.
This third edition cancels and replaces the second edition (ISO 4706:2008), which has been technically
revised.
The main changes are as follows:
— references have been updated;
— X-ray is required on three-piece designs;
— X-ray frequency has been changed from 50 to 250;
— criteria for X-ray retesting requirements have been added.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
v
Introduction
The purpose of this document 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.
This document has been prepared to address the general requirements in chapter 6.2 of the UN model
[1]
regulations for the transportation of dangerous goods ST/SG/AC.10/1 Rev. 22.
vi
INTERNATIONAL STANDARD ISO 4706:2023(E)
Gas cylinders — Refillable welded steel cylinders — Test
pressure 60 bar and below
1 Scope
This document specifies the minimum requirements concerning material selection, design, construction
and workmanship, procedure, and test at manufacture of refillable welded-steel gas cylinders of water
capacities from 0,5 l up to and including 150 l and drums of water capacities of 150 l to 500 l of a test
1)
pressure not greater than 60 bar , exposed to extreme worldwide temperatures (−50 °C to +65 °C)
used for compressed, liquefied or dissolved gases.
NOTE Unless specified in the text, for the purpose of this document, the word “cylinder” includes “pressure
drums”.
This document is primarily intended to be used for industrial gases other than liquefied petroleum gas
(LPG), and is also applicable to LPG.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 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 6892-1, Metallic materials — Tensile testing — Part 1: Method of test at room temperature
ISO 7438, Metallic materials — Bend test
ISO 9606-1, Qualification testing of welders — Fusion welding — Part 1: Steels
ISO 10286, Gas cylinders — Vocabulary
ISO 11117, Gas cylinders — Valve protection caps and guards — Design, construction and tests
ISO 11363-1, Gas cylinders — 17E and 25E taper threads for connection of valves to gas cylinders — Part 1:
Specifications
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
ISO 14732, Welding personnel — Qualification testing of welding operators and weld setters for mechanized
and automatic welding of metallic materials
ISO 17636-1, Non-destructive testing of welds — Radiographic testing — Part 1: X- and gamma-ray
techniques with film
ISO 17636-2, Non-destructive testing of welds — Radiographic testing — Part 2: X- and gamma-ray
techniques with digital detectors
5 2
1) 1 bar = 0,1 MPa = 10 Pa; 1 MPa = 1 N/mm .
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
3 Terms, definitions and symbols
3.1 Terms and definitions
For the purposes of this document, the terms and definitions in ISO 10286 and the following apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1.1
yield strength
value corresponding to the upper yield strength, R , or, for steels when yielding does not occur at
eg
tensile testing, the 0,2 % proof strength (non-proportional elongation), R
po,2
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 to entry: In this context, “consecutively” need not apply to continuous production (start to finish).
Note 2 to entry: See 12.1 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
3.1.8
F factor (F)
design stress factor
3.1.9
parent material
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
3.1.11
embossed
carve, mould or stamp a design on a surface or object so that it stands out in relief
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 elongation after fracture %
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 mandrel diameter mm
p
e thickness of metal which is offset (see Figure 4) mm
e thickness of metal which is not offset (see Figure 4) mm
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 6892-1 mm
n ratio of diameter of bend test former to the thickness of the test piece —
N normalized cylinder —
P highest pressure reached in the cylinder during the burst test (see ISO 10286) bar
b
P actual test pressure applied to the cylinder by the manufacturer bar
h
r inside knuckle radius of the end mm
R inside dishing radius of the end mm
R actual value of yield strength determined by tensile test specified in 9.1.2.2.1.2 MPa
e
R minimum value of yield strength guaranteed by the cylinder manufacturer for the MPa
eg
finished cylinder
R actual value of tensile strength determined by the tensile test specified in MPa
m
9.1.2.2.1.2
R minimum value of tensile strength guaranteed by the cylinder manufacturer for MPa
mg
the finished cylinder
R 0,2 % proof strength (see ISO 6892-1) MPa
po,2
S original cross-sectional area of tensile test piece in accordance with ISO 6892-1 mm
4 Inspection and testing
To ensure that the cylinders conform to this document, they shall be subject to inspection and testing in
accordance with Clauses 7, 8, 9 and 10.
Tests and examinations performed to demonstrate conformity to this document shall be conducted
using instruments calibrated before being put into service and thereafter according to an established
programme.
5 Materials
5.1 General
5.1.1 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.
5.1.2 Materials for shells and end pressings, excluding bosses (see 5.1.3), shall conform to the
requirements of 5.1.8 and 5.2.1.
5.1.3 Bosses shall be manufactured from compatible weldable materials with a maximum carbon
content of mass fraction of 0,25 %.
5.1.4 All items welded to the cylinder (e.g. shrouds and footrings) shall be made of compatible
weldable material containing the maximum values in % (mass fraction) given in Table 3.
5.1.5 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.
5.1.6 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).
5.1.7 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.
5.1.8 Grades of steel used for cylinder manufacture shall be compatible with the intended gas service
(e.g. corrosive or embrittling gases).
5.2 Chemical composition
5.2.1 Materials used for the fabrication of gas cylinders shells and end pressings shall be of weldable
quality and contain the values in % (mass fraction) given in Table 1.
Table 1 — Cylinder shell and ends chemistry allowable limits
Element Maximum content
% (mass fraction)
Carbon 0,250
Silicon 0,450
Manganese 1,600
Phosphorus 0,040
Sulfur 0,040
The use of micro-alloying elements such as niobium, titanium and vanadium shall not exceed the values
given in Table 2.
Table 2 — Micro alloying chemistry allowable limits
Element Maximum content
% (mass fraction)
Niobium 0,05
Titanium 0,03
Vanadium 0,10
Niobium plus Vanadium 0,12
Table 3 — Attachments welded to the cylinder chemistry allowable limits
Element Maximum content
% (mass fraction)
Carbon 0,250
Phosphorus 0,040
Sulfur 0,040
Where other micro-alloying elements are used, their presence and amounts shall be reported, together
with those already described in 5.2.1, in the steel manufacturer’s certificate.
5.2.2 In any check analysis, the maximum permissible deviation from the limits specified for the cast
analyses shall conform to the values in 5.2.1.
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
eg
of:
a) 0,75 R for finished cylinders with a guaranteed tensile strength (R ) < 490 MPa;
mg mg
b) 0,85 R for finished cylinders with a guaranteed tensile strength (R ) ≥ 490 MPa.
mg mg
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 .
h
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 8.6 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. Conformity shall be confirmed by calculation or performing
a fatigue test in accordance with the requirements of 11.3.
6.3.3 The welds of the openings shall be separated from circumferential and longitudinal joints by a
distance not less than 3a.
6.3.4 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 (see ISO 11363-1).
6.3.5 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
The guaranteed minimum sidewall thickness of the cylindrical shell, a, shall not be less than the
thickness calculated using Formula (1):
 
10JF R − 3Ph
D
eg
 
a=−1 (1)
 
2 10JF R
eg
 
where
the value of F is the lesser of:
06, 5
or 0,85
RR/
eg mg
and for longitudinal welds:
J 1,0 for completely radiographed seams;
J 0,9 for spot-radiographed seams;
J 1,0 for cylinders without a longitudinal weld.
The value of J shall be selected in accordance with 9.4.
Formula (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 2bD . In this case, the wall
thickness shall be not less than that of the domed part (see 7.2.2).
The sidewall thickness shall also satisfy the following:
— for D ≤ 100 mm: a = 1,1 mm;
— for D > 100 and D ≤ 150 mm: a = 1,1 + 0,008(D − 100) mm;
— for D > 150 mm: a = (D/250) + 0,7 mm (with an absolute minimum of 2,0 mm);
For acetylene cylinders with D > 300 mm, the minimum wall thickness shall be 3,0 mm.
The burst pressure ratio shall be demonstrated as follows:
— P ≥ P × 2 and ≥ 50 bar.
b h
7.2 Design of ends concave to pressure
7.2.1 Unless otherwise specified in 6.3, the shape of ends of gas cylinders shall be such that:
a) for torispherical ends R ≤ D; r ≥ 0,1 D; h ≥ 4b [see Figure 1 a)];
b) for semi-ellipsoidal ends H ≥ 0,192 D; h ≥ 4b [see Figure 1 b)].
7.2.2 The head thickness of all other end shapes shall be not less than that calculated using
Formula (2).
ba= C (2)
where
a is the value of a calculated in accordance with 7.1 using J = 1,0;
C is a shape factor, the value of which depends on the ratio H/D, and shall be obtained from the graph
shown in Figure 2 or Figure 3, as applicable.
7.2.3 Heads that do not contain markings may be 90 % of the minimum sidewall thickness as
indicated in 7.1.
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 11.3.
For heads convex to pressure, the minimum head thickness shall be a minimum of two times that
specified in 7.2.2.
a) Torispherical end b) Semi-ellipsoidal end
Key
1 torispherical end
2 semi-ellipsoidal end
a) for torispherical ends:
D D
   
HR=+()bR−+()b − ×+()Rb +− 2()rb+
   
 22  
b) for semi-ellipsoidal ends:
D
 
 
()DK+22()()bb− ()
2−b
 
H = withK =
H
2()K
 
 
b
 
Figure 1 — Illustration of cylinder ends concave to pressure
Figure 2 — Values of shape factor C for H/D between 0,2 and 0,25
Figure 3 — Values of shape factor C for H/D between 0,25 and 0,5
8 Construction and workmanship
8.1 Welding qualification
8.1.1 General
The following requirements apply:
a) before proceeding with the production of a given design, all welding operators and welding
procedures shall be approved by meeting the requirements of 8.1.2 to 8.1.9, ISO 9606-1, ISO 15613,
ISO 15614-1 Level 1 or ISO 14732;
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.
8.1.2 Base materials (pressure and non-pressure)
Base materials defined in the procedure specification shall be of the same specification as the given
design and those tested by the welders.
8.1.3 Positions of welds
For welder qualification, the position of the part for welding shall be as specified in 8.1.1 c).
8.1.4 Welding materials
Weld consumables (see 5.1.5) shall be the same specification as those specified in the procedure
specification, those tested by the welders and those used for production.
8.1.5 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.
8.1.6 Period of effectiveness
The following requirements apply:
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.
8.1.7 Changes to welding process requiring recertification
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 (normalizing, stress relieving, stabilizing);
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).
8.1.8 Welder qualification tests
When required, the weldment shall, after 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.
8.1.9 Results of welder qualification
The following requirements apply:
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
m
the cylinder manufacturer (R ) regardless of the fracture location;
mg
d) for macro tests: the etched specimen shall be visually examined to determine adequate root
penetration into both members as to the established design.
8.2 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.
8.3 Welded joints
8.3.1 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.
8.3.2 The longitudinal joint, of which there shall be no more than one, shall be of the butt-welded
type.
8.3.3 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)];
— fillet welded [see Figure 4 b)];
— lap welded [see Figure 4 c)].
Lap-welded joints shall have a minimum overlap of four times the minimum design thickness (a).
8.3.4 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.
8.3.5 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.
8.3.6 Butt welds shall have full penetration. The excess thickness shall be such that the weld integrity
is not compromised.
8.3.7 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.
8.3.8 Lap welds shall have adequate penetration verified by macro etch and bend testing.
8.3.9 Fillet welds shall exhibit root penetration verified by macro etch.
8.3.10 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
b) Fillet weld
c) Lap weld
Key
1 bevel (optional) 5 ≥ a and ≤ 2,5 a
2 as desired 6 ≥ 1,5 a
3 minimum overlap 7 e (thickness of metal which is offset)
4 inside of cylinder, avoid sharp break 8 e (thickness of metal which is not offset)
W weld width
Figure 4 — Typical weld configurations
8.4 Tolerances
8.4.1 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;
b) for three-piece cylinders 1,5 % of the mean of the diameters.
8.4.2 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.
8.4.3 Verticality
When the cylinder is standing on its base, the deviation from vertical shall not exceed 1 % including the
shroud and footring.
8.5 Non-pressure-containing attachments
8.5.1 Where non-pressure-containing attachments are to be attached to the cylinder by welding,
such attachments shall be made of compatible weldable steel.
8.5.2 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.
8.5.3 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.
8.5.4 Depending on the geometry of the pressure drum and the surrounding conditions, a pressure
drum with a water capacity greater than 150 l shall require specific mechanical or other handling and
transportation equipment (e.g. a forklift 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 forklift truck can
be engaged.
8.6 Valve protection
If a shroud is used to protect the valve, the cylinder containing the shroud shall be drop tested at
ambient temperature in accordance with ISO 11117.
8.7 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.
8.8 Heat treatment
8.8.1 Cylinders shall be delivered in the heat-treated condition for normalizing, stress relieving and
stabilizing.
8.8.2 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.
8.8.3 Localized heat treatment shall not be used.
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 6892-1 for the tensile test;
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
Sample cylinder tests are be carried out as follows:
a) for cylinders containing only circumferential welds (two-piece cylinders), on test specimens taken
from the locations shown in Figure 5, the following tests shall be carried out:
1) one tensile test (in accordance with the requirements of ISO 6892-1),
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