prEN ISO 20421-1

SLOVENSKI STANDARD
01-marec-2025
Kriogene posode - Velike premične, vakuumsko izolirane posode - 1. del:
Konstrukcija, izdelava, kontrola in preskus (ISO/DIS 20421-1:2025)
Cryogenic vessels - Large transportable vacuum-insulated vessels - Part 1: Design,
fabrication, inspection and testing (ISO/DIS 20421-1:2025)
Kryo-Behälter - Große ortsbewegliche vakuum-isolierte Behälter - Teil1: Gestaltung,
Herstellung, Inspektion und Prüfung (ISO/DIS 20421-1:2025)
Récipients cryogéniques - Grands récipients transportables isolés sous vide - Partie 1:
Conception, fabrication, inspection et essais
Ta slovenski standard je istoveten z: prEN ISO 20421-1
ICS:
23.020.40 Proti mrazu odporne posode Cryogenic vessels
(kriogenske posode)
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

DRAFT
International
Standard
ISO/DIS 20421-1
ISO/TC 220
Cryogenic vessels — Large
Secretariat: AFNOR
transportable vacuum-insulated
Voting begins on:
vessels —
2025-01-27
Part 1:
Voting terminates on:
2025-04-21
Design, fabrication, inspection and
testing
Récipients cryogéniques — Récipients transportables isolés sous
vide de grande contenance —
Partie 1: Conception, fabrication, inspection et essais
ICS: 23.020.40
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
This document is circulated as received from the committee secretariat.
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Reference number
ISO/DIS 20421-1:2025(en)
DRAFT
ISO/DIS 20421-1:2025(en)
International
Standard
ISO/DIS 20421-1
ISO/TC 220
Cryogenic vessels — Large
Secretariat: AFNOR
transportable vacuum-insulated
Voting begins on:
vessels —
Part 1:
Voting terminates on:
Design, fabrication, inspection
and testing
Récipients cryogéniques — Récipients transportables isolés sous
vide de grande contenance —
Partie 1: Conception, fabrication, inspection et essais
ICS: 23.020.40
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
This document is circulated as received from the committee secretariat.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
© ISO 2025
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
STANDARDS MAY ON OCCASION HAVE TO
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Published in Switzerland Reference number
ISO/DIS 20421-1:2025(en)
ii
ISO/DIS 20421-1:2025(en)
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Symbols . 5
5 General requirements . 6
6 Mechanical loads. 6
6.1 General .6
6.2 Load during the pressure test.7
7 Chemical effects . 7
8 Thermal conditions . 7
9 Materials . 7
9.1 Selection of materials .7
9.2 Inspection documentation .8
10 Design . 8
10.1 Design options .8
10.1.1 General .8
10.1.2 Design by calculation .8
10.1.3 Design by calculation and pressure strengthening .8
10.1.4 Design of components by calculation supplemented with experimental methods .8
10.2 Common design requirements .8
10.2.1 General .8
10.2.2 Design specification .9
10.2.3 Design loads .10
10.2.4 Fatigue .14
10.2.5 Corrosion allowance . 15
10.2.6 Inspection openings . 15
10.2.7 Pressure relief . 15
10.2.8 Valves .16
10.2.9 Insulation .16
10.2.10 Degree of filling .16
10.2.11 Electrical continuity .16
10.3 Design by calculation .16
10.3.1 General .16
10.3.2 Inner vessel .16
10.3.3 Outer jacket .19
10.3.4 Attachments . 20
10.3.5 Piping and accessories . 20
10.3.6 Calculation formula. 20
10.3.7 Calculations for operating loads . 44
11 Fabrication .45
11.1 General .45
11.2 Cutting . .45
11.3 Cold forming .45
11.3.1 Austenitic stainless steel .45
11.3.2 Ferritic steel . 46
11.3.3 Aluminium or aluminium alloy .47
11.4 Hot forming.47
11.4.1 General .47

iii
ISO/DIS 20421-1:2025(en)
11.4.2 Austenitic stainless steel .47
11.4.3 Ferritic steel .47
11.4.4 Aluminium or aluminium alloy .47
11.5 Manufacturing tolerances .47
11.5.1 General .47
11.5.2 Plate alignment . 48
11.5.3 Thickness . 49
11.5.4 Dished ends . 49
11.5.5 Cylinders . 49
11.6 Welding . .52
11.6.1 General .52
11.6.2 Qualification .52
11.6.3 Temporary attachments .52
11.6.4 Welded joints .52
11.7 Non-welded joints . 53
12 Inspection and testing .53
12.1 Quality plan . 53
12.1.1 General . 53
12.1.2 Inspection stages during manufacture of an inner vessel . 53
12.1.3 Additional inspection stages during manufacture of a large transportable
cryogenic vessel . 54
12.2 Production control test plates . 54
12.2.1 Requirements . 54
12.2.2 Extent of testing . 54
12.3 Non-destructive testing . 55
12.3.1 General . 55
12.3.2 Extent of examination for surface imperfections . 55
12.3.3 Extent of examination for inner-vessel weld seams . 56
12.3.4 Acceptance criteria for surface and volumetric imperfections as classified in
ISO 6520-1 . 56
12.4 Rectification .57
12.5 Pressure testing .57
13 Marking and labelling .58
14 Final acceptance test .58
15 Periodic inspection .58
16 Documentation .58
Annex A (informative) Examples of tank plates .60
Annex B (informative) Elastic stress analysis .63
Annex C (normative) Additional requirements for 9 % Ni steel .72
Annex D (normative) Pressure strengthening of vessels from austenitic stainless steels . 74
Annex E (informative) Specific weld details .88
Annex F (normative) Outer-jacket relief devices .92
Annex G (informative) Base materials .93
Annex H (informative) Components subject to external pressure (pressure on the convex
surface) — Calculation.101
Annex I (informative) Design of openings in cylinders, spheres and cones — Calculation .111
Annex J (normative) Reference material & equivalent thickness .120
Annex K (normative) Refrigerated liquefied gases .122
Bibliography .123

iv
ISO/DIS 20421-1:2025(en)
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 documents 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).
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. Details of any patent
rights identified during the development of the document will be in the Introduction and/or on the ISO list of
patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and 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 220, Cryogenic vessels.
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.
This third edition cancels and replaces the second edition (ISO 20421-1:2019), which has been technically
revised. It also incorporates ISO 20421-1:2006/Cor 1:2007. The main changes compared to the previous
edition are as follows:
— Subclause 12.3 has been revised;
— Subclause 10.2.3.1.4 Correction Load factors for normal operation for fatigue analysis in specified
transportation modes Table 2 —Load factors for normal operation for fatigue analysis in specified
transportation modes;
— Subclause 10.2.3.11 Loads for Piping and valves divided for Road/water and Rail condition;
— Subclause 10.3.2.1 Correction of Table 3;
— Subclause 10.3.2.3.1 Correction of used Material property K for the calculations under consideration of
ADR/RID/IMDG-Code/49CFR;
— Subclause D.3.1 Material Table D1 splitting in European Material D.1.1 and Non-European Material D.1.2;
— Subclause D.3 Correction of Requirements for Testing plates under consideration of cold strengthening
Table D.2 — Testing of pre-stretched welded test plates;
— Subclause J.3 Correction of Table J.1 Minimum wall thicknesses under consideration of ADR/RID/IMDG-
Code/49CFR.
A list of all parts in the ISO 20421 series can be found on the ISO website.

v
ISO/DIS 20421-1:2025(en)
Introduction
[1]
This document has been written so that it is suitable to be referenced in the UN Model Regulations .
This document does not include the general vehicle requirements, e.g. running gear, brakes, lighting, etc., for
which the relevant standards/regulations apply.

vi
DRAFT International Standard ISO/DIS 20421-1:2025(en)
Cryogenic vessels — Large transportable vacuum-insulated
vessels —
Part 1:
Design, fabrication, inspection and testing
1 Scope
This document 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 document 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 document does not include the general vehicle requirements, e.g. running gear, brakes, lighting, etc.
NOTE 1 This document 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.
NOTE 2 This document does not cover specific requirements for refillable liquid hydrogen and LNG tanks that are
primarily dedicated as fuel tanks in vehicles. For fuel tanks used in vehicles, see ISO 13985.
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 3834-2, Quality requirements for fusion welding of metallic materials — Part 2: Comprehensive quality
requirements
ISO 4126-2, Safety devices for protection against excessive pressure — Part 2: Bursting disc safety devices
ISO 5817, Welding — Fusion-welded joints in steel, nickel, titanium and their alloys (beam welding excluded) —
Quality levels for imperfections
ISO 9606-1, Qualification 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 NDT personnel
ISO 10042, Welding — Arc-welded joints in aluminium and its alloys — Quality levels for imperfections
ISO 10474:2013, Steel and steel products — Inspection documents
ISO 10675-1, Non-destructive testing of welds — Acceptance levels for radiographic testing — Part 1: Steel,
nickel, titanium and their alloys
ISO 14732, Welding personnel — Qualification testing of welding operators and weld setters for mechanized and
automatic welding of metallic materials

ISO/DIS 20421-1:2025(en)
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 15614-2, Specification and qualification of welding procedures for metallic materials — Welding procedure
test — Part 2: Arc welding of aluminium and its alloys
ISO 17635, Non-destructive testing of welds — General rules for metallic materials
ISO 17637, Non-destructive testing of welds — Visual 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 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 21013-3, Cryogenic vessels — Pressure-relief accessories for cryogenic service — Part 3: Sizing and capacity
determination
ISO 23208, Cryogenic vessels — Cleanliness for cryogenic service
ASME VIII-2, Rules for construction of pressure vessels, Division 2, Alternative Rules
EN 13445-3, Unfired pressure vessels — Part 3: Design
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological 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
cryogenic fluid
refrigerated liquefied gas
gas which is partially liquid because of its low temperature (see Table K.1)
Note 1 to entry: This includes totally evaporated liquids and supercritical fluids.
Note 2 to entry: In the context of this document, the refrigerated but non-toxic gases and gas mixtures given in
Table K.1 are referred to as cryogenic fluids.
3.2
large transportable cryogenic vessel
tank
thermally insulated vessel of more than 450 l intended for the transport of one or more cryogenic fluids (3.1),
consisting of an inner vessel (3.4), an outer jacket (3.5), all of the valves and service equipment (3.9) together
with the structural parts
Note 1 to entry: The large transportable cryogenic vessel comprises a complete assembly that is ready for service.

ISO/DIS 20421-1:2025(en)
3.3
insulation
vacuum interspace between the inner vessel (3.4) and the outer jacket (3.5)
Note 1 to entry: 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 (3.16) vessel intended to contain the cryogenic fluid (3.1) to be transported
3.5
outer jacket
gas-tight enclosure which contains the inner vessel (3.4) and enables the vacuum to be established
3.6
normal operation
intended operation of the vessel at a pressure (3.16) not greater than the maximum allowable working
pressure including the handling loads (3.7)
3.7
handling load
load exerted on the transportable cryogenic vessel in all normal conditions of transport including loading,
unloading, moving and lifting
3.8
piping system
all pipes, tubes and associated components which can come in contact with cryogenic fluids (3.1) including
valves, fittings, pressure-relief devices and their supports
3.9
service equipment
measuring instruments and filling, discharge, venting, safety, heating, cooling and insulating devices
including any equipment for storing cooling fluids
3.10
manufacturer
company that carries out the final assembly, including the final
acceptance test, of the large transportable cryogenic vessel (3.2)
3.11
gross volume
internal volume of the inner vessel (3.4), excluding nozzles, pipes, etc., determined at
minimum design temperature and atmospheric pressure (3.16)
3.12
tare mass
mass of the empty large transportable cryogenic vessel (3.2)
3.13
net volume
volume of the inner vessel (3.4), below the inlet to the relief devices, excluding nozzles, pipes, etc., determined
at minimum design temperature and atmospheric pressure (3.16)
3.14
net mass
maximum allowable mass of the cryogenic fluid (3.1) which may be filled
Note 1 to entry: The maximum allowable mass is equal to the mass of the cryogenic liquid occupying 98 % of the net
volume (3.13)of the inner vessel (3.4) 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.

ISO/DIS 20421-1:2025(en)
Note 2 to entry: Cryogenic liquid helium can occupy 100 % of the volume of the inner vessel at any pressure (3.16).
3.15
gross mass
sum of tare mass (3.12) plus net mass (3.14)
3.16
pressure
gauge pressure
pressure relative to atmospheric pressure
3.17
fixed tank
tank vehicle
large transportable vessel permanently attached to a vehicle or to units of running gear
3.18
demountable tank
large transportable vessel non-permanently attached to a vehicle
Note 1 to entry: 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.
3.19
portable tank
a thermally insulated tank having a capacity of more than 450 litres fitted with service equipment (3.9) and
structural equipment necessary for the transport of refrigerated liquefied gases
Note 1 to entry: It can be lifted full and loaded and discharged without removal of structural element.
Note 2 to entry: The list of the refrigerated liquefied gases is available in Annex K.
3.20
maximum allowable working pressure
ps
maximum gauge pressure (3.16) permissible at the top of the vessel in its normal operating position
3.21
relief plate
relief plug
plate or plug retained by atmospheric pressure (3.16) which allows relief of excess internal pressure,
generally from the vacuum jacket
3.22
bursting disc device
non-reclosing pressure-relief device ruptured by differential pressure (3.16)
Note 1 to entry: It is the complete assembly of installed components including the bursting disc holder, where
appropriate.
3.23
pressure-strengthened vessel
pressure (3.16) 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 1 to entry: Pressure (3.16) vessels made from solution heat-treated material are subject to a controlled plastic
deformation during the strengthening operation as its yield point is raised. Pressure vessels made from work-hardened
material are subject to little or no plastic deformation.
3.24
residual elongation
original elongation of the steel minus the elongation created by the cold-forming deformation

ISO/DIS 20421-1:2025(en)
3.25
leakproofness test
test using gas subjecting the shell and its service equipment (3.9), to an effective internal pressure (3.16) not
less than 90 % of the MAWP but not greater than the design pressure
4 Symbols
Symbol Definition Unit
b width of pad, ring or shell reinforcement mm
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
h thickness of pad reinforcement mm
l cone length between effective stiffenings (see Figure 5) mm
c
l ligament (web) between two nozzles mm
l l′ buckling length mm
b, b
l length of nozzle reinforcement outstanding mm
s
n number of lobes —
p design pressure as defined in 10.3.2.2 —
p calculation pressure as defined in 10.2.3.2.1 a) bar (or MPa)
c
p allowable external pressure limited by elastic buckling bar (or MPa)
e
p strengthening pressure bar (or MPa)
k
p liquid pressure bar (or MPa)
L
p allowable external pressure limited by plastic deformation bar (or MPa)
p
p maximum allowable gauge pressure bar (or MPa)
s
p test pressure (see 6.2) bar (or MPa)
T
r radius, e.g. inside knuckle radius of dished end and cones mm
s minimum thickness mm
s required wall thickness at opening edge mm
A
s actual wall thickness mm
e
s required wall thickness outside corner area mm
g
s thickness of nozzle reinforcement in stand mm
n
s wall thickness of nozzle mm
S
s required wall thickness within corner area mm
t in this context, centre-to-centre distance between two nozzles mm
x (decay-length zone) distance over which governing stress is assumed to act mm
x characteristic lengths (i = 1,2,3) to define corner area [Figure 7 a) and mm
i
Figure 7 b) and 10.3.6.5.4]
η factor indicative of the utilization of the permissible design stress in joints or —
factor allowing for weakenings
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 outside diameter of connected cylinder (see Figure 7) mm
a1
D outside diameter at effective stiffening (see Figure 9) mm
a2
D internal diameter, e.g. of a cylindrical shell mm
i
ISO/DIS 20421-1:2025(en)
Symbol Definition Unit
D design diameter (see Figure 7) mm
k
D shell diameter at nozzle (see Figure 8) mm
s
E Young’s modulus N/mm
I moment of inertia of reinforcing element mm
R minimum guaranteed yield stress or 0,2 % proof stress at 20 °C (1 % proof N/mm
e
stress for austenitic steel)
R minimum guaranteed tensile strength at 20 °C N/mm
m
K material property used for design (see 10.3.2.3) N/mm
K material property at temperature T in °C (e.g. K for material property at 20 °C N/mm
T 20
(see 10.3.2.3.2)
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 11.5.5.2) —
φ cone angle °
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 Clause 16, and all supporting
documentation (including that from his subcontractors, if any), for a required period (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 document.
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 can affect safety and which can lead to leakage. This requirement can be validated by:
— the calculation;
— the calculation and pressure-strengthening method, if allowed;
— the calculation and experimental method.

ISO/DIS 20421-1:2025(en)
6.2 Load during the pressure test
The load exerted during the pressure test shall be calculated with Formula (1):
pp≥+13,b1 ar or pp≥+1,30,1 MPa (1)
() []()
TS TS
where
p is the test pressure (in bar);
T
p is the maximum allowable pressure (in bar);
S
+1 is the allowance for external vacuum (in bar).
+0,1 is the allowance for external vacuum (in MPa).
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.
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
...