ISO 20421-1:2006

INTERNATIONAL ISO
STANDARD 20421-1
First edition
2006-04-15

Cryogenic vessels — Large transportable
vacuum-insulated vessels —
Part 1:
Design, fabrication, inspection and
testing
Récipients cryogéniques — Récipients transportables isolés sous vide
de grande contenance —
Partie 1: Conception, fabrication, inspection et essais




Reference number
ISO 20421-1:2006(E)
©
ISO 2006

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ISO 20421-1:2006(E)
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ISO 20421-1:2006(E)
Contents Page
Foreword. v
1 Scope .1
2 Normative references .1
3 Terms and definitions .3
4 Symbols .6
5 General requirements.8
6 Mechanical loads .8
6.1 General.8
6.2 Load during the pressure test.8
7 Chemical effects .8
8 Thermal conditions.9
9 Materials .9
9.1 Selection of materials.9
9.2 Inspection certificates.9
10 Design .10
10.1 Design options.10
10.2 Common design requirements.10
10.3 Design by calculation.18
11 Fabrication.47
11.1 General.47
11.2 Cutting .47
11.3 Cold forming.47
11.4 Hot forming.49
11.5 Manufacturing tolerances .49
11.6 Welding .54
11.7 Non-welded joints.55
12 Inspection and testing.55
12.1 Quality plan .55
12.2 Production control test plates.56
12.3 Non-destructive testing.58
12.4 Rectification .60
12.5 Pressure testing.60
13 Marking and labelling .61
14 Final acceptance test .61
15 Periodic inspection.61
Annex A (informative) Examples of tank plates .62
Annex B (normative) Elastic stress analysis .65
Annex C (normative) Additional requirements for 9 % Ni steel .74
Annex D (informative) Pressure strengthening of vessels from austenitic stainless steels .76
Annex E (informative) Specific weld details .87
Annex F (informative) Outer-jacket relief devices.91
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ISO 20421-1:2006(E)
Annex G (informative) Base materials. 93
Annex H (normative) Components subject to external pressure (pressure on the convex surface)
— Calculation . 102
Annex I (normative) Design of openings in cylinders, spheres and cones — Calculation . 113

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ISO 20421-1:2006(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 20421-1 was prepared by Technical Committee ISO/TC 220, Cryogenic vessels.
ISO 20421 consists of the following parts, under the general title Cryogenic vessels — Large transportable
vacuum-insulated vessels:
⎯ Part 1: Design, fabrication, inspection and testing
⎯ Part 2: Operational requirements
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INTERNATIONAL STANDARD ISO 20421-1:2006(E)

Cryogenic vessels — Large transportable vacuum-insulated
vessels —
Part 1:
Design, fabrication, inspection and testing
1 Scope
This part of ISO 20421 specifies requirements for the design, fabrication, inspection and testing of large
transportable vacuum-insulated cryogenic vessels of more than 450 l volume, which are permanently (fixed
tanks) or not permanently (demountable tanks and portable tanks) attached to a means of transport, for one or
more modes of transport.
This part of ISO 20421 applies to large transportable vacuum-insulated cryogenic vessels for fluids specified
in 3.1 and does not apply to vessels designed for toxic fluids.
This part of ISO 20421 does not include the general vehicle requirements, e.g. running gear, brakes, lighting,
etc., which are in accordance with the relevant standards/regulations.
This International Standard does not cover specific requirements for refillable liquid-hydrogen tanks that are
primarily dedicated as fuel tanks in vehicles. For fuel tanks used in land vehicles, see ISO 13985.
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 4126-2, Safety devices for protection against excessive pressure — Part 2: Bursting disc safety devices
ISO 4136, Destructive tests on welds in metallic materials — Transverse tensile test
ISO 5173, Destructive tests on welds in metallic materials — Bend tests
ISO 9016, Destructive tests on welds in metallic materials — Impact tests — Test specimen location, notch
orientation and examination
ISO 9606-1, Approval testing of welders — Fusion welding — Part 1: Steels
ISO 9606-2, Qualification test of welders — Fusion welding — Part 2: Aluminium and aluminium alloys
ISO 9712, Non-destructive testing — Qualification and certification of personnel
ISO 10474, Steel and steel products — Inspection documents
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
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ISO 20421-1:2006(E)
ISO 15607, Specification and qualification of welding procedures for metallic materials — General rules
ISO 15613, Specification and approval 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 — Part 1: Welding
procedure tests for the arc welding of steels
ISO 15614-2, Specification and approval of welding procedures for metallic materials — Part 2: Welding
procedure tests for the arc welding of aluminium and its alloys
ISO 15614-3, Specification and approval of welding procedures for metallic materials — Part 3: Welding
procedure tests for the arc welding of aluminium and its alloys
ISO 17636, Non-destructive examination of welds — Radiographic testing of fusion-welded joints
ISO 20421-2, Cryogenic vessels — Large transportable vacuum-insulated vessels — Part 2: Operational
requirements
ISO 21010, Cryogenic vessels — Gas/material compatibility
ISO 21011, Cryogenic vessels — Valves for cryogenic service
ISO 21013-1, Cryogenic vessels — Safety devices for protection against excessive pressure —
Part 1: Reclosable pressure-relief valves
ISO 21028-1, Cryogenic vessels — Toughness requirements for materials at cryogenic temperature — Part 1:
Temperatures below −80 degrees C
ISO 21028-2, Cryogenic vessels — Toughness requirements for materials at cryogenic temperature — Part 2:
Temperatures between −80 degrees C and −20 degrees C
ISO 23208, Cryogenic vessels — Cleanliness for cryogenic service
ASME VIII-2
EN 1708-1, Welding — Basic weld joint details in steel — Part 1: Pressurized components
EN 10028-4, Flat products made of steels for pressure purposes — Part 4: Nickel alloy steels with specified
low temperature properties
EN 10028-7, Flat products made of steels for pressure purposes — Part 7: Stainless Steels
EN 12300, Cryogenic vessels — Cleanliness for cryogenic service
EN 13068-3, Non-destructive testing — Radioscopic testing — Part 3: General principles of radioscopic
testing of metallic materials by X- and gamma rays
EN 13445-3, Unfired pressure vessels — Part 3: Design
EN 13445-4, Unfired pressure vessels — Part 4: Fabrication
UN Recommendations on the transport of dangerous goods — Model regulations (12th revised edition)
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ISO 20421-1:2006(E)
3 Terms and definitions
For the purposes of this part of ISO 20421, the following terms and definitions apply.
3.1
cryogenic fluid
refrigerated liquefied gas
gas which is partially liquid because of its low temperature
NOTE 1 This includes totally evaporated liquids and supercritical fluids.
NOTE 2 In the context of this part of ISO 20421, the refrigerated but non-toxic gases and gas mixtures given in Table 1
are referred to as cryogenic fluids.
Table 1 — Refrigerated but non-toxic gases
Classification
a
Identification number, name and description
code
Asphyxiant gases
1913 Neon, refrigerated liquid
1951 Argon, refrigerated liquid
1963 Helium, refrigerated liquid
1970 Krypton, refrigerated liquid
3 °A
1977 Nitrogen, refrigerated liquid
2187 Carbon dioxide, refrigerated liquid
2591 Xenon, refrigerated liquid
3136 Trifluoromethane refrigerated liquid

3158 Gas, refrigerated liquid, N.O.S. (not otherwise specified)
Oxidizing gases
1003 Air, refrigerated liquid
3 °O 1073 Oxygen, refrigerated liquid
2201 Nitrous oxide, refrigerated liquid, oxidizing
3311 Gas, refrigerated liquid, oxidizing, N.O.S.
Flammable gases
1038 Ethylene, refrigerated liquid
1961 Ethane, refrigerated liquid
1966 Hydrogen, refrigerated liquid
3 °F
1972 Methane, refrigerated liquid or natural gas, refrigerated liquid, with high methane
content
3138 Ethylene, acetylene and propylene mixture, refrigerated liquid, containing at least
71,5 % ethylene with not more than 22,5 % acetylene and not more than 6 % propylene
3312 Gas, refrigerated liquid, flammable, N.O.S.
a
Classification codes, identification number, name and description according to the United Nations.
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ISO 20421-1:2006(E)
3.2
large transportable cryogenic vessels
tank
thermally insulated vessel of more than 450 l intended for the transport of one or more cryogenic fluids,
consisting of an inner vessel, an outer jacket, all of the valves and service equipment together with the
structural parts
NOTE The large transportable cryogenic vessel comprises a complete assembly that is ready for service
3.3
thermal insulation
vacuum interspace between the inner vessel and the outer jacket
NOTE The space may or may not be filled with material to reduce the heat transfer between the inner vessel and the
outer jacket.
3.4
inner vessel
pressure vessel intended to contain the cryogenic fluid to be transported
3.5
outer jacket
gas-tight enclosure which contains the inner vessel and enables the vacuum to be established
3.6
normal operation
the intended operation of the vessel at a pressure not greater than the maximum allowable working pressure
including the handling loads
3.7
handling loads
loads exerted on the transportable cryogenic vessel in all normal conditions of transport including loading,
unloading, moving and lifting
3.8
documentation
technical documents delivered by the manufacturer to the owner consisting of:
⎯ all certificates establishing the conformity with this part of ISO 20421 (e.g. material, pressure test,
cleanliness, safety devices);
⎯ a short description of the vessel (including characteristic data, etc.);
⎯ a list of fluids and their net mass for which the cryogenic vessel is designed;
⎯ an operating manual (for the user) which consists of:
⎯ a short description of the vessel (including characteristic data, etc.);
⎯ a statement that the vessel is in conformity with this part of ISO 20421;
⎯ the instructions for normal operation.
3.9
piping system
all pipes, tubes and associated components which can come in contact with cryogenic fluids including valves,
fittings, pressure-relief devices and their supports
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ISO 20421-1:2006(E)
3.10
service equipment
measuring instruments and filling, discharge, venting, safety, heating, cooling and insulating devices
3.11
manufacturer of the large transportable cryogenic vessel
company that carries out the final assembly, including the final acceptance test, of the large transportable
cryogenic vessel
3.12
gross volume of the inner vessel
internal volume of the inner vessel, excluding nozzles, pipes, etc., determined at minimum design temperature
and atmospheric pressure
3.13
tare mass
mass of the empty large transportable cryogenic vessel
3.14
net volume of the inner vessel
volume of the inner vessel, below the inlet to the relief devices, excluding nozzles, pipes, etc., determined at
minimum design temperature and atmospheric pressure
3.15
net mass
maximum allowable mass of the cryogenic fluid which may be filled
NOTE 1 The maximum allowable mass is equal to the mass of the cryogenic liquid occupying 98 % of the net volume
of the inner vessel under conditions of incipient opening of the relief device with the vessel in a level attitude and the mass
of the gas at the same conditions in the remaining volume of the inner vessel.
NOTE 2 Cryogenic liquid helium can occupy 100 % of the volume of the inner vessel at any pressure.
3.16
gross mass
sum of tare mass plus net mass
3.17
pressure
pressure relative to atmospheric pressure, i.e. gauge pressure
3.18
fixed tank
tank vehicle
large transportable vessel permanently attached to a vehicle or to units of running gear
3.19
demountable tank
large transportable vessel non-permanently attached to a vehicle
NOTE When attached to the carrier vehicle, the demountable tank meets the requirements prescribed for a fixed
tank. It is designed to be lifted only when empty.
3.20
portable tank
large transportable vessel designed primarily to be loaded onto a transport vehicle or ship
NOTE It can be lifted full and loaded and discharged without removal of structural element.
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ISO 20421-1:2006(E)
3.21
maximum allowable pressure
p
s
maximum pressure permissible at the top of the vessel in its normal operating position
3.22
relief plate/plug
plate or plug retained by atmospheric pressure which allows relief of excess internal pressure, generally from
the vacuum jacket
3.23
bursting disc device
a non-reclosing pressure-relief device ruptured by differential pressure
NOTE It is the complete assembly of installed components including where appropriate the bursting disc holder.
3.24
pressure-strengthened vessel
pressure vessel which has been subjected to a calculated and controlled internal pressure (strengthening
pressure) after completion, the wall thickness of which is calculated on the basis of the stress at the
strengthening pressure and not on the basis of the conventional design stress value of the material used
NOTE Pressure vessels made from solution heat-treated material will be subject to a controlled plastic deformation
during the strengthening operation as its yield point is raised. Pressure vessels made from work-hardened material will be
subject to little or no plastic deformation.
4 Symbols
For the purposes of this part of ISO 20421, the following symbols apply (units of measurement are in the
column at right):
c allowance for corrosion mm
d diameter of opening mm
i
d outside diameter of tube or nozzle mm
a
f narrow side of rectangular or elliptical plate mm
l l′ buckling length mm
b, b
n number of lobes —
p design pressure as defined in 10.3.2.2 bar
p calculation pressure bar

p allowable external pressure limited by elastic buckling bar
e
p strengthening pressure bar
k
p allowable external pressure limited by plastic deformation bar
p
p maximum allowable pressure bar
s
p pressure test (see 6.2) bar
T
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ISO 20421-1:2006(E)
r radius, e.g. inside knuckle radius of dished end and cones mm
s minimum thickness mm
s actual wall thickness mm
e
v factor indicative of the utilization of the permissible design stress in
joints or factor allowing for weakenings —
x (decay-length zone) distance over which governing stress is
assumed to act mm
2
A cross-sectional area of reinforcing element mm
C, β design factors —
D shell diameter mm
D outside diameter, e.g. of a cylindrical shell mm
a
D internal diameter, e.g. of a cylindrical shell mm
i
2
E Young’s modulus N/mm
4
I moment of inertia of reinforcing element mm
R minimum guaranteed yield stress or 0,2 % proof stress at 20 °C
e
2
(1 % proof stress for austenitic steel) N/mm
2
R minimum guaranteed tensile strength at 20 °C N/mm
m
2
K material property used for design (see 10.3.2.3) N/mm
K material property at temperature T in °C
T
2
(e.g. K for material property at 20 °C (see 10.3.2.3.2) N/mm
20
R radius of curvature, e.g. inside crown radius of dished end mm
S safety factor at design pressure, in relation with R —
e
S safety factor against elastic buckling at design pressure —
k
S safety factor against plastic deformation —
p
Z auxiliary value —
v Poisson’s ratio —
u out of roundness (see 11.5.4.2) —
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ISO 20421-1:2006(E)
5 General requirements
5.1 The large transportable cryogenic vessel shall safely withstand the mechanical and thermal loads and
the chemical effects encountered during pressure test and normal operation. These requirements are deemed
to be satisfied if Clauses 6 to 12 are fulfilled. The vessel shall be marked in accordance with Clause 13, tested
in accordance with Clause 14 and operated in accordance with ISO 20421-2.
5.2 Large transportable cryogenic vessels shall be equipped with valves, pressure-relief devices, etc.,
configured and installed in such a way that the vessel can be operated safely. The number of openings in the
inner vessel for this equipment shall be kept to a minimum.
5.3 The large transportable cryogenic vessel shall be clean for the intended service in accordance with
ISO 23208.
5.4 The manufacturer shall retain the documents referred to in 3.8, and all supporting documentation
(including that from his subcontractors, if any), for a period required by regulation(s) (e.g. product liability). In
addition, the manufacturer shall retain all supporting and background documentation (including that from his
subcontractors, if any) which establishes that the vessel conforms to this part of ISO 20421.
6 Mechanical loads
6.1 General
The large transportable cryogenic vessel shall resist the mechanical loads mentioned in 10.2.3 without such
deformation which could affect safety and which could lead to leakage. This requirement can be validated by:
⎯ the calculation;
⎯ the calculation and pressure-strengthening method, if allowed;
⎯ the calculation and experimental method.
6.2 Load during the pressure test
The load exerted during the pressure test shall be:
p W 1,3(p + 1)
T s
where
p = test pressure (in bar);
T
p = maximum allowable pressure (in bar);
s
+ 1 = allowance for external vacuum (in bar).
7 Chemical effects
Due to operating temperatures and the materials of construction, the possibility of chemical action on the inner
surfaces in contact with the cryogenic fluids can be neglected.
Due to the fact that the inner vessel is inside an evacuated outer jacket, neither external corrosion of the inner
vessel, nor corrosion on the inner surfaces of the outer jacket will occur. Therefore, inspection openings are
not required in the inner vessel or the outer jacket.
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ISO 20421-1:2006(E)
Corrosion allowance is also not required on surfaces in contact with the operating fluid or exposed to the
vacuum interspace between the inner vessel and the outer jacket.
The material and the protection for the surfaces exposed to the atmosphere shall be suitable for intended use
(e.g. resistant to industrial and marine atmospheres).
8 Thermal conditions
The following thermal conditions shall be taken into account:
For the inner vessel and its associated equipment the full range of temperature expected.
For the outer jacket and equipment thereof (other than equipment covered in the previous paragraph):
⎯ a minimum working temperature of −20 °C;
⎯ a maximum working temperature of 50 °C.
NOTE This does not apply if the jacket is designed for a lower temperature to be marked on the nameplate.
9 Materials
For the materials used to manufacture the transportable cryogenic vessels, the requirements defined in 9.1 to
9.3 shall be met.
9.1 Selection of materials
9.1.1 Materials which are or might be in contact with cryogenic fluids shall be in accordance with
ISO 21010.
9.1.2 Materials used at low temperatures shall follow the requirements of the relevant parts of ISO 21028-1
and ISO 21028-2; for non-metallic materials. low-temperature suitability shall be validated by an experimental
method, taking into account operating temperatures.
9.1.3 The base materials, listed in Annex G, subject to meeting the extra requirements given in the main
body of this part of ISO 20421, are suitable for and may be employed in the manufacture of the cryogenic
vessels, in conformance with ISO 20421-1.
9.2 Inspection certificates
9.2.1 The material according to ISO 21028-1 and ISO 21028-2 shall be declared by an inspection certificate
3.1b in accordance with ISO 10474.
9.2.2 The material manufactured to a recognized International Standard shall meet the testing requirements
of ISO 21028-1 and ISO 21028-2 and shall be declared by an inspection certificate 3.1b in accordance with
ISO 10474.
9.2.3 The delivery of material which is not manufactured to a recognized International Standard shall be
guaranteed by an inspection certificate 3.1a in accordance with ISO 10474 confirming that the material fulfils
9.1 of this part of ISO 20421-1. The material manufacturer shall follow a recognized International Standard for
processing and establishing the guaranteed material properties.
9.2.4 The outer jacket and the equipment not subjected to low temperature shall be manufactured from
material suitable for the intended service.
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ISO 20421-1:2006(E)
10 Design
10.1 Desi
...