ISO 22991:2004
(Main)Gas cylinders — Transportable refillable welded steel cylinders for liquefied petroleum gas (LPG) — Design and construction
Gas cylinders — Transportable refillable welded steel cylinders for liquefied petroleum gas (LPG) — Design and construction
ISO 22991:2004 specifies minimum requirements concerning material, design, construction and workmanship, procedure and test at manufacture of transportable refillable welded steel liquefied petroleum gas (LPG) cylinders of water capacity up to and including 150 l, exposed to ambient temperatures.
Bouteilles à gaz — Bouteilles en acier soudé transportables et rechargeables pour gaz de pétrole liquéfié (GPL) — Conception et fabrication
General Information
Standards Content (Sample)
INTERNATIONAL ISO
STANDARD 22991
First edition
2004-05-01
Gas cylinders — Transportable refillable
welded steel cylinders for liquefied
petroleum gas (LPG) — Design and
construction
Bouteilles à gaz — Bouteilles en acier soudé transportables et
rechargeables pour gaz de pétrole liquéfié (GPL) — Conception et
fabrication
Reference number
ISO 22991:2004(E)
©
ISO 2004
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ISO 22991:2004(E)
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ISO 22991:2004(E)
Contents Page
Foreword. iv
Introduction . v
1 Scope. 1
2 Normative references . 1
3 Terms and definitions. 2
4 Symbols . 3
5 Materials. 3
6 Design . 4
6.1 General requirements . 4
6.2 Calculation of cylindrical shell thickness. 5
6.3 Design of ends concave to pressure . 5
6.4 Ends of other shapes. 9
6.5 Minimum wall thickness. 9
6.6 Design of openings. 9
6.7 Valve protection . 9
7 Construction and workmanship . 10
7.1 Welding qualification . 10
7.2 Plates and pressed parts. 10
7.3 Welded joints. 10
7.4 Tolerances . 10
7.5 Non-pressure-containing attachments.11
7.6 Valve protection . 11
7.7 Closure of openings . 11
7.8 Heat treatment . 11
8 Testing. 12
8.1 Mechanical testing . 12
8.2 Burst test under hydraulic pressure . 17
8.3 Pressure test . 18
8.4 Radiographic and macro examination.18
8.5 Visual examination of the surface of the weld. 20
8.6 Pressure cycling (fatigue) test. 20
9 Acceptance procedure . 21
9.1 General. 21
9.2 Batch testing . 21
9.3 Failure to meet batch test requirements. 23
10 Technical requirements for type approval . 23
11 Marking. 24
12 Certification . 24
Annex A (normative) Manufacturer's marking . 25
Annex B (informative) Examples of type approval and production test certificates. 26
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ISO 22991:2004(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 22991 was prepared by Technical Committee ISO/TC 58, Gas cylinders, Subcommittee SC 3, Cylinder
design.
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ISO 22991:2004(E)
Introduction
This International Standard calls for the use of substances and procedures that may be injurious to health if
adequate precautions are not taken. It refers only to technical suitability and does not absolve the user from
legal obligations relating to health and safety at any stage. It has been assumed in the drafting of this
International Standard, that the execution of its provisions is entrusted to appropriately qualified and
experienced people.
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INTERNATIONAL STANDARD ISO 22991:2004(E)
Gas cylinders — Transportable refillable welded steel cylinders
for liquefied petroleum gas (LPG) — Design and construction
1 Scope
This International Standard specifies minimum requirements concerning material, design, construction and
workmanship, procedure and test at manufacture of transportable refillable welded steel liquefied petroleum
gas (LPG) cylinders of water capacity up to and including 150 l, exposed to ambient temperatures.
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 643, Steels — Micrographic determination of the apparent grain size
ISO 1106-1:1984, Recommended practice for radiographic examination of fusion welded joints — Part 1:
Fusion welded butt joints in steel plates up to 50 mm thick
ISO 1106-3:1984, Recommended practice for radiographic examination of fusion welded joints — Part 3:
Fusion welded circumferential joints in steel pipes of up to 50 mm wall thickness
ISO 2504:1973, Radiography of welds and viewing conditions for films — Utilization of the recommended
patterns of image quality indications (I.Q.I.)
ISO 4136, Destructive tests on welds in metallic materials — Transverse tensile test
ISO 4978, Flat rolled steel products for welded gas cylinders
ISO 5178, Destructive tests on welds in metallic materials — Longitudinal tensile test on weld metal in fusion
welded joints
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 at ambient temperature
ISO 7438, Metallic materials — Bend test
ISO 9606-1, Approval testing of welders — Fusion Welding — Part 1: Steels
ISO 9956-3, Specification and approval of welding procedures for metallic materials — Part 3: Welding
procedure tests for arc welding of steels
ISO 10920, Gas cylinders — 25E taper thread for connection of valves to gas cylinders — Specification
ISO 11116-1, Gas cylinders — 17E taper thread for connection of valves to gas cylinders — Part 1:
Specifications
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ISO 22991:2004(E)
ISO 13769, Gas cylinders — Stamp marking
ISO 14732, Welding personnel — Approval testing of welding operators for fusion welding and of resistance
weld setters for fully mechanized and automatic welding of metallic materials
ISO 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 and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
yield stress
upper yield strength, R , or, for steels that do not exhibit a defined yield, the 0,2 % proof stress (non-
eh
proportional elongation), R
p
[ISO 6892]
3.2
normalizing
heat treatment in which the cylinder is heated to a uniform temperature above the upper critical point (AC ) of
3
the steel and then cooled in a controlled atmosphere or still air
3.3
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 to a uniform temperature below the lower critical point (AC ) of
1
the steel and cooling in a controlled atmosphere or still air
3.4
competent body
person or corporate body who, by combination of appropriate qualifications, training, experience and
resources, is able to make objective judgements on the subject
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ISO 22991:2004(E)
4 Symbols
Table 1 — Symbols and their designations and units
Symbol Designation Unit
a calculated minimum thickness of the cylindrical shell mm
A percentage elongation after fracture %
b calculated minimum thickness of the end of the cylinder mm
C
shape factor (see Table 3 and Figure 2) 1
D outside diameter of the cylinder as given in the design drawing (see Figure 1) mm
D mm
outside diameter of a bend tests former (see Figure 10)
p
h height of the cylindrical part of the end (see Figure 1) mm
H outside height of the domed part of the end (see Figure 1) mm
J stress reduction factor 1
L
length of the cylinder mm
L mm
original gauge length of the test piece in accordance with ISO 6892
o
n ratio of diameter of bend test former to the thickness of the test piece (see Table 4) 1
calculation pressure used to calculate the minimum required thickness of the cylindrical shell and
P
bar
c
ends (see 6.1.3)
P bar
maximum pressure attained during the burst test
b
P bar
actual test pressure, applied to the cylinder by the manufacturer
t
P
bar
minimum permissible test pressure
tmin
r inside knuckle radius of the end mm
R inside dishing radius of the end mm
R MPa
minimum guaranteed tensile strength
g
R MPa
minimum value of yield stress guaranteed by the cylinder manufacturer for the finished cylinder
0
R
actual value of tensile strength determined by the tensile test specified in 8.1.2.2 MPa
m
2
NOTE 1 MPa = 1 N/mm = 10 bar.
5 Materials
5.1 Materials for shells and end pressings shall either conform to ISO 4978 or to another equivalent
material specification meeting the requirements of Table 2.
NOTE “Materials” refers to materials in the state before any specific transformation with regard to the manufacturing
process.
5.2 All parts welded to the cylinder shall be made of compatible material.
5.3 The welding consumables shall be such that they are capable of giving consistent welds with minimum
tensile strength at least equal to that specified for the parent materials in the finished cylinder.
5.4 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.
5.5 The manufacturer shall maintain a system of identification for the materials used in fabrication in order
that all materials for pressure parts in the completed cylinder be traceable to its origin.
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ISO 22991:2004(E)
Table 2 — Material requirements
Limits
Element
% max.
Materials, other than those given in ISO 4978, used for the fabrication
of gas cylinders, shall be of weldable quality and the following limits
shall not be exceeded in the cast analysis:
Carbon 0,22
Silicon 0,45
Manganese 1,60
Phosphorus 0,025
Sulfur 0,020
Phosphorus plus sulfur 0,040
Use of micro-alloying elements such as niobium, titanium and
vanadium shall be confined to the following contents:
Niobium 0,08
Titanium 0,20
Vanadium 0,20
Niobium plus vanadium 0,20
Where other micro-alloying elements are used, their presence and amounts shall be reported, together with
the above, in the steel manufacturer’s certificate.
Should check analyses be required, they 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 finished
cylinders.
6 Design
6.1 General requirements
6.1.1 The calculation of the wall thickness of the pressure parts intended to resist the internal pressure in
the gas cylinders shall be related to the yield stress of the material.
6.1.2 For calculation purposes, the value of the yield stress R is limited to a maximum of 0,85R .
0 g
6.1.3 The internal pressure upon which the calculation of the wall thickness of gas cylinders is based shall
be the calculation pressure P .
c
a) For cylinders for commercial butane service only P = P = 15 bar;
c tmin
b) For all other LPG cylinders P = P = 30 bar.
c tmin
6.1.4 A fully dimensional drawing including the specification of the material shall be produced.
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ISO 22991:2004(E)
6.2 Calculation of cylindrical shell thickness
The wall thickness of the cylindrical shell shall be not less than that calculated using the formula:
PD×
c
a =
20××RJ
o
+ P
c
4
3
for cylinders with a longitudinal weld: J = 0,9;
for cylinders without a longitudinal weld: J = 1,0.
In no case shall the actual thickness be less than that specified in 6.5.
6.3 Design of ends concave to pressure
6.3.1 Except as permitted by 6.4, the shape of ends of gas cylinders shall be such that the following
conditions are fulfilled:
for torispherical ends: R u D; r W 0,1 D; h W 4b [see Figure 1a)];
for semi-ellipsoidal ends: H W 0,2 D; h W 4b [see Figure 1b)].
6.3.2 The wall thickness of the ends of gas cylinders shall be not less than that calculated using the
formula:
PD××C
c
b =
20 × R
o
+ P
c
4
3
In this formula, C is a shape factor, the value of which depends on the ratio H/D.
The value of C shall be obtained from Table 3 and the graphs in Figure 2 and Figure 3.
The graph in Figure 2 details the value of C in relation to the ratio b/D.
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ISO 22991:2004(E)
Key
1 torispherical end
2 semi-ellipsoidal end
NOTE For torispherical ends:
DD
H=+ 2()R b− [(Rb+ ) − ]×[()Rb+ + − (r+b)]
22
Figure 1 — Illustration of cylinder ends concave to pressure
Table 3 — Relationship between H/D and shape factor C
H/D C H/D C
0,25 1,000 0,38 0,612
0,26 0,931 0,39 0,604
0,27 0,885 0,40 0,596
0,28 0,845 0,41 0,588
0,29 0,809 0,42 0,581
0,30 0,775 0,43 0,576
0,31 0,743 0,44 0,572
0,32 0,713 0,45 0,570
0,33 0,687 0,46 0,568
0,34 0,667 0,47 0,566
0,35 0,649 0,48 0,565
0,36 0,633 0,49 0,564
0,37 0,621 0,50 0,564
NOTE Intermediate values may be obtained by linear interpolation.
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ISO 22991:2004(E)
Key
X H/D ratio
Y shape factor C
Figure 2 — Values of shape factor C for H/D between 0,2 and 0,25
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ISO 22991:2004(E)
Key
X H/D ratio
Y shape factor C
Figure 3 — Values of shape factor C for H/D between 0,25 and 0,5
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ISO 22991:2004(E)
6.4 Ends of other shapes
Ends of shapes other than those covered by 6.3 may be used provided that the adequacy of their design is
demonstrated by fatigue testing in accordance with 8.6. For heads convex to pressure, the minimum head
thickness shall be a minimum of 2 times that specified in 6.2.
6.5 Minimum wall thickness
6.5.1 The minimum wall thickness of the cylindrical shell, a, and of the end, b, shall be not less than the
value derived from any of the following formulae:
for D < 100 mm:
a = b = 1,1 mm (1)
min min
for 100 mm u D u 150 mm:
a = b = 1,1 + 0,008(D − 100) mm (2)
min min
for D > 150 mm:
a = b = (D/250) + 0,7 mm (3)
min min
(with a minimum of 1,5 mm).
These formulae apply to cylindrical shells and ends irrespective of whether they are designed by calculation
as specified in 6.2 and 6.3 or by testing as specified in 6.4. Apart from the requirements of 6.3, 6.4 and 6.5,
any cylindrical part integral with an end shall, except as qualified by 6.5.2, also satisfy the requirements in 6.2
for the cylindrical shell.
6.5.2 The equation in 6.2 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 6.3.2).
6.6 Design of openings
6.6.1 The location of all openings shall be restricted to one dished end of the cylinder.
6.6.2 Each opening in the cylinder shall be reinforced, either by a valve boss or pad, of weldable and
compatible steel, securely attached by welding and so designed as to be of adequate strength and to result in
no harmful stress concentrations. This shall be confirmed by design calculations or a fatigue test in
accordance with 8.6.
6.6.3 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 which need not independently guarantee
leak-tightness.
6.6.4 Unless otherwise specified, valve threads shall conform to a recognized specification e.g. ISO 10920
for the 25E thread or ISO 11116-1 for the 17E thread.
6.7 Valve protection
The design of the cylinder shall provide protection for valves against damage in order to avoid release of
contents, unless otherwise protected for transportation, etc. in accordance with 7.6.
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ISO 22991:2004(E)
7 Construction and workmanship
7.1 Welding qualification
7.1.1 The manufacturer, with the agreement of a competent body, before proceeding with the production of
a given design of cylinder, shall approve the welding procedures to ISO 9956-3, welders to ISO 9606-1 and
welding operators to ISO 14732, for all welding associated with the pressure envelope including the non-
pressure-containing parts. Records of such approvals shall be retained by the manufacturer.
7.1.2 Welding procedure approval tests shall be made in such a manner that the welds shall be
representative of those made in production.
7.1.3 Welders shall have passed the approval tests for the specific type of work and procedure concerned.
7.2 Plates and pressed parts
Before assembly, the pressure parts of the cylinders shall be visually examined for uniform quality and
freedom from defects which may ultimately affect the cylinder integrity.
7.3 Welded joints
7.3.1 The welding of the longitudinal and circumferential joints shall be by a fully mechanized or semi-
automatic or fully automatic process to provide consistent and reproducible quality of welds.
7.3.2 The longitudinal joint, of which there shall be no more than one, shall be the butt welded type.
7.3.3 Circumferential joints, of which there shall be no more than two, shall be butt welded, or butt welded
with one member offset to form an integral backing strip, i.e. joggled (see Figure 4).
7.3.4 Before the cylinders are closed, longitudinal welds shall be visually examined from both sides in
accordance with ISO 17637. Permanent backing strips shall not be used with longitudinal welds.
7.3.5 The fusion of the welded metal with the parent metal shall be smooth and free from overlapping,
undercutting or abrupt irregularities. There shall be no cracks, notching or porous patches in the welded
surface and the surface adjacent to the weld. The welded surface shall be regular and even without concavity.
The excess thickness of the weld (bead height) shall not exceed one-fourth of the width of the weld.
7.3.6 Butt welds shall have full penetration.
7.3.7 Joggle butt welds shall have full root penetration verified by macro etch, bend testing and tensile
testing.
7.4 Tolerances
7.4.1 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 diameter in the same cross section is not more than 1 % of the mean of these diameters,
for two-piece cylinders, and 1,5 % for three-piece cylinders. The measurement shall not be taken over any of
the welds but shall be taken adjacent to the welds.
7.4.2 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.
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ISO 22991:2004(E)
Key
a d
Bevel optional. Inside of cylinder to avoid sharp break.
b
As desired. e Thickness of metal which is offset.
c
e Thickness of metal which is not offset.
Depth of offset = e .
1
1
Figure 4 — Illustration of a typical joggled butt joint
7.4.3 Verticality
When the cylinder is standing on its base, deviation from vertical shall not exceed 25 mm per metre of length.
7.5 Non-pressure-containing attachments
7.5.1 Where non-pressure-containing attachments are to be attached to the cylinder by welding, such
attachments shall be made of weldable and compatible steel (see 5.2).
7.5.2 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.
7.5.3 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. Any footring shall be suitably drained and the
space enclosed by the footring suitably ventilated, e.g., by means of openings.
7.6 Valve protection
When the requirements of 6.7 are not met, then the manufacturer shall specify that 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 product leakage.
7.7 Closure of openings
Where cylinders are supplied without the valve or safety device fitted, all openings shall be fitted with a plug of
non-absorbent material to protect the thread and prevent ingress of moisture.
7.8 Heat treatment
7.8.1 Except as permitted under 7.8.4, cylinders shall be delivered in the heat treated (normalized or stress
relieved) condition (see 3.2 and 3.3).
7.8.2 The cylinder manufacturer shall maintain records to indicate that the cylinders have been heat treated
(normalized or stress relieved) after completion of all welding and to indicate the adequacy of the process of
heat treatment.
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ISO 22991:2004(E)
7.8.3 Localized heat treatment shall not be permitted.
7.8.4 Cylinders may be delivered that have not been heat treated (normalized or stress relieved) where the
manufacturer complies with all the following requirements:
a) the cylinders shall be of three-piece construction;
b) ends shall be semi-ellipsoidal or torispherical in accordance with Figure 1, and pressing depth shall be
limited such that:
Hb−
u 0,26 (4)
D
and
hbu 8 (5)
c) the cylinders shall only be made from a fine grain steel with maximum grain size of 8, in the delivery
condition, when tested in accordance with ISO 643;
d) three samples of each type shall be subjected to fatigue testing in accordance with 8.6.
Any subsequent change in design, material thickness, material specification or weld procedure shall require
further fatigue testing.
8 Testing
8.1 Mechanical testing
8.1.1 General requirements
8.1.1.1 Where not covered by the requirements contained in this clause, the mechanical tests shall be
carried out in accordance with the following documents:
a) parent material:
ISO 6892 in the case of the tensile test;
ISO 7438, as appropriate, in the case of the bend test, according to whether the thickness of the test-
piece is 3 mm or above, or less than 3 mm;
b) welded test specimens tested in accordance with 8.1.2.
8.1.1.2 All the mechanical tests for checking the properties of the parent metal and welds of the pressure-
containing shells of the gas c
...
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