ISO/TS 15869:2009

TECHNICAL ISO/TS
SPECIFICATION 15869
First edition
2009-02-01
Gaseous hydrogen and hydrogen
blends — Land vehicle fuel tanks
Hydrogène gazeux et mélanges d'hydrogène gazeux — Réservoirs de
carburant pour véhicules terrestres

Reference number
©
ISO 2009
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©  ISO 2009
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ii © ISO 2009 – All rights reserved

Contents Page
Foreword. v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions. 2
4 Service conditions. 5
4.1 General. 5
4.2 Expected service. 5
4.3 Working pressure . 5
4.4 Maximum filling pressure . 5
4.5 Filling cycles . 5
4.6 Design temperature . 6
4.7 Gas composition. 6
4.8 External surfaces. 6
4.9 Fire effects. 6
5 Information to be recorded . 6
5.1 General. 6
5.2 Statement of service. 6
5.3 Design drawings and information. 7
5.4 Stress analysis report . 7
5.5 Material property data . 7
5.6 Fire protection. 8
5.7 Manufacturing data. 8
6 Materials . 8
6.1 Compatibility . 8
6.2 Steel. 8
6.3 Stainless steels . 8
6.4 Aluminium alloys . 8
6.5 Resins . 8
6.6 Fibres . 8
6.7 Plastic liners. 9
6.8 Metal end bosses. 9
7 Design requirements . 9
7.1 General. 9
7.2 Test pressure . 9
7.3 Burst pressure and fibre stress ratio. 9
7.4 Stress analysis. 10
7.5 Maximum defect size. 10
7.6 Fire protection. 11
8 Construction and workmanship. 11
8.1 Materials . 11
8.2 Type 3 metal liner. 11
8.3 Neck threads, neck ring, foot ring, attachment for support. 11
8.4 Forming. 12
8.5 Fibre winding. 12
8.6 Curing of thermosetting resins . 12
8.7 Auto-frettage . 13
8.8 Exterior environmental protection. 13
9 Type (qualification) tests. 13
9.1 Qualification of new designs . 13
9.2 Generic type tests . 13
9.3 Exemptions to generic type tests. 16
9.4 Qualification of design changes. 16
9.5 Alternative type tests. 19
10 Production and batch tests. 19
10.1 Production tests. 19
10.2 Batch tests. 20
10.3 Failure to meet batch and production test requirements . 22
11 Markings. 23
12 Preparation for dispatch. 24
Annex A (informative) Rationale for number of filling cycles . 25
Annex B (normative) Test methods and acceptance criteria. 28
Annex C (informative) Verification of stress ratios using strain gauges. 36
Annex D (informative) NDE defect size by flawed fuel tank cycling. 37
Annex E (normative) Alternative type tests . 38
Bibliography . 41

iv © ISO 2009 – All rights reserved

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.
In other circumstances, particularly when there is an urgent market requirement for such documents, a
technical committee may decide to publish other types of document:
⎯ an ISO Publicly Available Specification (ISO/PAS) represents an agreement between technical experts in
an ISO working group and is accepted for publication if it is approved by more than 50 % of the members
of the parent committee casting a vote;
⎯ an ISO Technical Specification (ISO/TS) represents an agreement between the members of a technical
committee and is accepted for publication if it is approved by 2/3 of the members of the committee casting
a vote.
An ISO/PAS or ISO/TS is reviewed after three years in order to decide whether it will be confirmed for a
further three years, revised to become an International Standard, or withdrawn. If the ISO/PAS or ISO/TS is
confirmed, it is reviewed again after a further three years, at which time it must either be transformed into an
International Standard or be withdrawn.
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/TS 15869 was prepared by Technical Committee ISO/TC 197, Hydrogen technologies, with collaboration
from Technical Committee ISO/TC 22, Road vehicles, and Technical Committee ISO/TC 58, Gas cylinders,
Subcommittee SC 3, Cylinder design.
Introduction
Fuel tanks for on-board storage of compressed gaseous hydrogen and hydrogen blends as fuels for land
vehicle service are required to maintain or improve the level of safety currently existing for land vehicle
applications. These requirements are achieved by:
a) specifying service conditions precisely and comprehensively as a firm basis for both fuel tank design and
use;
b) using an appropriate method to assess cyclic pressure fatigue life and to establish allowable defect sizes
in metal tanks or liners;
c) requiring design qualification tests;
d) requiring non-destructive testing and inspection of all production fuel tanks;
e) requiring destructive tests on fuel tanks and tank material taken from each batch of fuel tanks produced;
f) requiring manufacturers to specify the acceptable in-service damage levels for their design; and
g) requiring manufacturers to specify as part of their design, the safe service conditions for their fuel tanks.
Designs meeting the requirements of this International Standard:
a) will have a fatigue life that exceeds the expected service; and
b) will demonstrate appropriate strength and durability for expected service conditions.

vi © ISO 2009 – All rights reserved

TECHNICAL SPECIFICATION ISO/TS 15869:2009(E)

Gaseous hydrogen and hydrogen blends — Land vehicle fuel
tanks
1 Scope
This International Standard specifies the requirements for lightweight refillable fuel tanks intended for the on-
board storage of high-pressure compressed gaseous hydrogen or hydrogen blends on land vehicles.
This International Standard is not intended as a specification for fuel tanks used for solid, liquid hydrogen or
hybrid cryogenic high-pressure hydrogen storage applications.
This International Standard is applicable for fuel tanks of steel, stainless steel, aluminium or non-metallic
construction material, using any design or method of manufacture suitable for its specified service conditions.
This International Standard applies to the following types of fuel tank designs:
⎯ Type 1: metal fuel tanks;
⎯ Type 2: hoop-wrapped composite fuel tanks with a metal liner;
⎯ Type 3: fully wrapped composite fuel tanks with a metal liner;
⎯ Type 4: fully wrapped composite fuel tanks with no metal liner.
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 306, Plastics — Thermoplastic materials — Determination of Vicat softening temperature (VST)
ISO 527-2, Plastics — Determination of tensile properties — Part 2: Test conditions for moulding and
extrusion plastics
ISO 2808, Paints and varnishes — Determination of film thickness
ISO 4624, Paints and varnishes — Pull-off test for adhesion
ISO 6506-1, Metallic materials — Brinell hardness test — Part 1: Test method
ISO 7225, Gas cylinders — Precautionary labels
ISO 7866:1999, Gas cylinders — Refillable seamless aluminium alloy gas cylinders — Design, construction
and testing
ISO 9809-1:1999, Gas cylinders — Refillable seamless steel gas cylinders — Design, construction and
testing — Part 1: Quenched and tempered steel cylinders with tensile strength less than 1 100 MPa
ISO 9809-2:2000, Gas cylinders — Refillable seamless steel gas cylinders — Design, construction and
testing — Part 2: Quenched and tempered steel cylinders with tensile strength greater than or equal to
1 100 MPa
ISO 11114-4, Transportable gas cylinders — Compatibility of cylinder and valve materials with gas
contents — Part 4: Test methods for selecting metallic materials resistant to hydrogen embrittlement
ISO 11439, Gas cylinders — High pressure cylinders for the on-board storage of natural gas as a fuel for
automotive vehicles
ISO/TS 14687-2, Hydrogen fuel — Product specification — Part 2: Proton exchange membrane (PEM) fuel
cell applications for road vehicles
EN 1964-3:2000, Transportable gas cylinders — Specification for the design and construction of refillable
transportable seamless steel gas cylinders of water capacities from 0,5 litre up to and including 150 litres —
Part 3: Cylinders made of seamless stainless steel with an Rm value of less than 1 100 MPa
EN 12862:2000, Transportable gas cylinders — Specification for the design and construction of refillable
transportable welded aluminium alloy gas cylinders
EN 13322-2:2003/A1:2006, Transportable gas cylinders — Refillable welded steel gas cylinders — Design
and construction — Part 2: Stainless steel
ASTM B 117, Standard Practice for Operating Salt Spray (Fog) Apparatus
ASTM D 522, Standard Test Methods for Mandrel Bend Test of Attached Organic Coatings
ASTM D 1308, Standard Test Method for Effect of Household Chemicals on Clear and Pigmented Organic
Finishes
ASTM D 2344, Standard Test Method for Short-Beam Strength of Polymer Matrix Composite Materials and
Their Laminates
ASTM D 2794, Standard Test Method for Resistance of Organic Coatings to the Effects of Rapid Deformation
(Impact)
ASTM D 3170, Standard Test Method for Chipping Resistance of Coatings
ASTM D 3418, Standard Test Method for Transition Temperatures and Enthalpies of Fusion and
Crystallization of Polymers by Differential Scanning Calorimetry
ASTM G 154, Standard Practice for Operating Fluorescent Light Apparatus for UV Exposure of Nonmetallic
Materials
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
auto-frettage
pressure application procedure used in manufacturing composite fuel tanks with metal liners, which strains the
liner past its yield point
NOTE Auto-frettage results in the liner having compressive stresses and the fibres having tensile stresses at zero
internal pressure.
2 © ISO 2009 – All rights reserved

3.2
auto-frettage pressure
pressure within the over-wrapped composite fuel tank at which the required distribution of stresses between
the liner and the over-wrap is established
3.3
batch of composite fuel tanks
group of not more than 200 fuel tanks plus fuel tanks for destructive testing or, if greater, one shift of
successive production of fuel tanks, successively produced from qualified liners having the same size, design,
specified materials of construction and manufacturing process
3.4
batch of metal fuel tanks/liners
group of not more than 200 fuel tanks/liners plus fuel tanks/liners for destructive testing or, if greater, one shift
of successive production of metal fuel tanks/liners, successively produced having the same nominal diameter,
wall thickness, design, specified material of construction, manufacturing process, equipment for manufacturing
and heat treatment, and conditions of time, temperature and atmosphere during heat treatment
3.5
batch of non-metallic liners
group of not more than 200 liners plus liners for destructive testing or, if greater, one shift of successive
production of non-metallic liners, successively produced having the same nominal diameter, wall thickness,
design, specified material of construction and manufacturing process
3.6
burst pressure
pressure that causes the bursting of a pressure vessel subjected to a constant increase of pressure during a
destructive test
3.7
controlled tension winding
process used in manufacturing hoop-wrapped composite fuel tanks with metal liners by which compressive
stresses in the liner and tensile stresses in the over-wrap at zero internal pressure are obtained by winding the
reinforcing filaments under high tension
3.8
design change
change in the selection of structural materials or dimensional changes exceeding the tolerances as on the
design drawings
3.9
finished fuel tanks
fuel tanks that are ready for use, typical of normal production, complete with identification marks and external
coating including integral insulation specified by the manufacturer, but free from non-integral insulation or
protection
3.10
fully wrapped composite fuel tank
fuel tank with an over-wrap having a filament wound reinforcement both in the circumferential and axial
direction of the fuel tank
3.11
hoop-wrapped composite fuel tank
fuel tank with an over-wrap having a filament wound reinforcement in a substantially circumferential pattern
over the cylindrical portion of the liner such that the filament does not carry any significant load in a direction
parallel to the longitudinal axis of the fuel tank
3.12
hydrogen blend
mixture of natural gas and hydrogen
3.13
hydrogen storage system
system on a land vehicle comprised of the fuel tank and all closure devices (e.g. shut-off valves, check valves
and thermally activated pressure relief devices), as well as piping that contains hydrogen at the working
pressure
3.14
leakage
release of gas through a crack, pore, unbonded or similar defect
NOTE Permeation through the wall of a Type 4 fuel tank that is less than the rates described in B.16 is not
considered leakage.
3.15
liner
container that is used as an inner shell, on which reinforcing fibres are filament wound to achieve the
necessary strength
3.16
manufacturer
organization responsible for the design, manufacturing and testing of fuel tanks
3.17
over-wrap
reinforcement system of filament and resin applied over the liner
3.18
thermally activated pressure relief device
device that activates by temperature to release pressure and prevent a fuel tank from bursting due to fire
effects and that will activate regardless of fuel tank pressure
3.19
passenger vehicles
vehicles designed and constructed primarily for the carriage of persons (e.g. cars and buses)
3.20
pre-stress
process of applying auto-frettage or controlled tension winding
3.21
service conditions
conditions that the fuel tank will experience in service and that include on-road exposure to environmental
factors (road salt, acids, bases, temperature extremes) and expected usage (pressure cycles associated with
filling and discharge during service and driving, static pressure associated with vehicle parking, etc.)
3.22
settled pressure
gas pressure when a given settled temperature is reached
3.23
settled temperature
uniform gas temperature after any change in temperature caused by filling has dissipated
3.24
stress ratio
stress in fibre at specified minimum burst pressure divided by stress in fibre at working pressure
3.25
test pressure
required pressure applied during a pressure test
4 © ISO 2009 – All rights reserved

3.26
working pressure
nominal working pressure
settled pressure of compressed gas at a uniform temperature of 15 °C in a full fuel tank
4 Service conditions
4.1 General
The specified service conditions provide the basis for the design, manufacturing, inspection, and testing of fuel
tanks that are to be mounted on land vehicles and used to store compressed gaseous hydrogen or hydrogen
blends at ambient temperatures for use as a fuel on these vehicles.
The specified service conditions are also intended to provide information on how fuel tanks made in
accordance with this International Standard may safely be used, for
a) manufacturers of fuel tanks,
b) owners of fuel tanks,
c) designers or contractors responsible for the installation of fuel tanks,
d) designers or owners of equipment used to refuel land vehicle fuel tanks,
e) suppliers of gaseous hydrogen and hydrogen blends, and
f) regulatory authorities that have jurisdiction over fuel tank use.
The service conditions do not cover external loading that may arise from vehicle collisions, etc.
4.2 Expected service
The expected service for which fuel tanks are safe shall be specified by the fuel tank manufacturer.
4.3 Working pressure
The working pressure shall be specified by the fuel tank manufacturer for gaseous hydrogen and hydrogen
blends settled at a temperature of 15 °C.
4.4 Maximum filling pressure
Fuel tanks shall be designed to be filled up to a maximum pressure not exceeding 1,25 times the working
pressure, regardless of filling conditions or temperature, and which settles to a pressure of not greater than
the working pressure at the settled temperature of 15 °C.
4.5 Filling cycles
4.5.1 General
Except as permitted in 4.5.2, fuel tanks shall be designed for 11 250 fill cycles, representing a 15-year life of
use in commercial heavy-duty vehicles (see Annex A).
4.5.2 Reduced number of filling cycles
A reduced number of 5 500 filling cycles may be specified for the lifetime of the vehicle. Fuel tanks with the
reduced number of filling cycles may be qualified according to 9.2 or 9.5. In the case of fuel tanks with a
reduced number of filling cycles and qualified according to 9.2, these shall only be used in conjunction with a
tamper-proof counter system that records the number of fill cycles and terminates usage of the fuel tank
before the reduced number of fill cycles is exceeded.
4.6 Design temperature
Fuel tanks shall be designed to be suitable for use in the following material temperature range: −40 °C to
85 °C. Transient gas temperatures during filling and discharge may vary locally beyond these limits.
4.7 Gas composition
Fuel tanks shall be designed to be filled with compressed gaseous hydrogen and/or hydrogen blends
containing more than 2 % hydrogen by volume, combined with dry natural gas. The gas composition shall
comply with the following:
a) compressed hydrogen gas shall comply with the composition specified in ISO/TS 14687-2;
b) compressed natural gas (CNG) used in hydrogen blends may vary as stated in the dry gas composition
limits specified in ISO 11439.
4.8 External surfaces
Fuel tank external surfaces shall be designed to withstand mechanical and chemical exposure conditions as
reflected in the type tests specified in Clause 9.
4.9 Fire effects
Fuel tanks shall be protected from fire effects using non-reclosing thermally activated pressure relief devices.
Non-reclosing pressure-activated pressure relief devices can only be used in parallel with thermally activated
pressure relief devices. A thermally activated pressure relief device shall not under any circumstances require
the operation of the pressure-activated pressure relief device in order to function.
NOTE In the selection of thermally activated pressure relief devices, the requirements of the ANSI/IAS PRD 1-1998/
Addenda PRD 1a-1999 can be used as guidance until a standard on pressure relief devices for hydrogen service is
available.
The fire protection of fuel tanks may also be supplemented by the use of thermal insulation.
5 Information to be recorded
5.1 General
The fuel tank manufacturer shall keep on file the information specified herein. This information shall be
retained for the intended life of the fuel tank.
5.2 Statement of service
A statement of service shall be provided to the user. This statement of service shall include the following:
a) the name and address of the fuel tank manufacturer;
b) a description of the fuel tank design, including fuel tank identification, working pressure (MPa), fuel tank
type, diameter (mm), length (mm), internal volume (l), empty weight (kg) and valve thread type;
6 © ISO 2009 – All rights reserved

c) a statement that the fuel tank design is suitable for use in the service conditions provided in Clause 4;
d) a statement of the maximum service conditions for which the fuel tank was designed;
e) a statement of the maximum number of filling cycles for which the fuel tank was designed;
f) a statement of the working pressure for which the fuel tank was designed;
g) a specification for the fire protection system approved by the fuel tank manufacturer using non-reclosing
thermally activated pressure relief devices and, if used, thermal insulation;
h) a specification for the support methods, protective coatings and any other items required, but not
provided with the fuel tank;
i) any other information and instructions necessary to ensure the safe use and inspection of the fuel tank.
5.3 Design drawings and information
All fuel tank drawings and related technical data shall be kept on file by the fuel tank manufacturer and shall
show the following information:
a) title, reference number, date of issue and revision numbers with dates of issue, if applicable;
b) reference to a Type 1, Type 2, Type 3 or Type 4 design;
c) dimensions complete with tolerances, including details of end closure shapes with minimum thickness
and openings;
d) mass, complete with tolerance;
e) material specifications, complete with minimum mechanical and chemical properties and tolerance ranges
and, for metal fuel tanks or metal liners, the specified hardness range;
f) other data such as auto-frettage pressure range, minimum test pressure, details of the fire protection
system and of any exterior protective coating;
g) the gas that the fuel tank is designed to carry;
h) the working pressure of the design.
5.4 Stress analysis report
When a stress analysis is required to be carried out, the stress analysis report shall be kept on file and shall
include a table summarizing the calculated stresses.
NOTE Verification of the stress ratios may be performed using strain gauges or an equivalent method. An example of
an acceptable method is provided in Annex C.
5.5 Material property data
A detailed description of the materials and tolerances of the material properties used in the design shall be
kept on file. Test data shall also be presented characterizing the mechanical properties and the suitability of
the materials for service under the conditions specified in Clause 4.
5.6 Fire protection
The arrangement of the non-reclosing thermally activated pressure relief devices, and insulation if provided,
that will protect the fuel tank from sudden rupture when exposed to the fire conditions in B.9 shall be specified
by the fuel tank manufacturer.
5.7 Manufacturing data
Details of all fabrication processes, tolerances, non-destructive examinations, type tests, batch tests and
production tests shall be specified and kept on file by the fuel tank manufacturer. The manufacturer shall
specify the burst pressure range for the design. In no case shall the minimum specified burst pressure be less
than the minimum burst pressure specified in this International Standard.
Surface finish, thread details, acceptance criteria for ultrasonic scanning (or equivalent) and maximum lot
sizes for batch tests shall also be specified by the fuel tank manufacturer and kept on file.
6 Materials
6.1 Compatibility
Materials used shall be suitable for the service conditions specified in Clause 4. The design shall not have
incompatible materials in contact with each other. All metallic materials in contact with hydrogen and hydrogen
blends shall be compatible with hydrogen according to B.2.
NOTE Guidance on hydrogen compatibility can be found in the documents listed in the Bibliography.
6.2 Steel
Steels for fuel tanks and liners shall conform to the materials requirements of 6.1 to 6.4 of ISO 9809-1:1999,
or 6.1 to 6.3 of ISO 9809-2:2000, as appropriate.
6.3 Stainless steels
Stainless steels shall conform to the materials requirements of 4.1 to 4.4 of EN 1964-3:2000. Welded stainless
steels shall conform to the materials requirements of 4.1 to 4.3 of EN 13322-2:2003/A1:2006, as appropriate.
6.4 Aluminium alloys
Aluminium alloys shall conform to the materials requirements of 6.1 and 6.2 of ISO 7866:1999. Welded
aluminium alloys shall conform to the materials requirements of 4.2 and 4.3 of EN 12862:2000.
Aluminium alloys not covered by the materials requirements of ISO 7866:1999 may be used, provided that
hydrogen compatibility is demonstrated according to the method specified in B.2.
6.5 Resins
The material for impregnation may be thermosetting or thermoplastic resins. Examples of suitable matrix
materials are epoxy, modified epoxy, polyester and vinylester thermosetting plastics, as well as polyethylene
and polyamide thermoplastic.
6.6 Fibres
Structural reinforcing filament material types shall be glass fibre, aramid fibre or carbon fibre. If carbon fibre
reinforcement is used, the design shall incorporate means to prevent galvanic corrosion of metallic
components of the fuel tank.
8 © ISO 2009 – All rights reserved

The fuel tank manufacturer shall keep on file for the intended life of the fuel tank design the published
specifications for composite materials and the material manufacturer’s recommendations for storage
conditions and shelf life. The fuel tank manufacturer shall keep on file, for the intended life of each batch of
fuel tanks, the fibre manufacturer’s certification that each shipment conforms to the manufacturer’s
specifications for the product.
6.7 Plastic liners
The polymeric material used for plastic liners shall be compatible with the service conditions specified in
Clause 4.
6.8 Metal end bosses
The metal end bosses connected to a non-metallic liner shall be made of material compatible with the service
conditions specified in Clause 4.
7 Design requirements
7.1 General
This International Standard neither provides design formulae nor lists permissible stresses or strains, but
requires adequacy of design to be demonstrated by testing to show that the fuel tanks are capable of
consistently passing the material, type, production and batch tests that it specifies.
7.2 Test pressure
The minimum test pressure used during manufacturing shall be 1,5 times the working pressure.
7.3 Burst pressure and fibre stress ratio
7.3.1 Fuel tank
The minimum actual burst pressure of the fuel tank shall not be less than the values given in Table 1.
Composite reinforcement used on fuel tanks shall also meet the minimum stress ratio requirements of Table 1.
Verification of the stress ratios may be done by calculation. When the calculation method is used, the stress
ratio calculations shall include:
a) an analysis method with capability for non-linear materials, such as a special purpose computer program
or a finite element analysis program;
b) correct modelling of the elastic-plastic stress-strain curve for the liner material;
c) correct modelling of the mechanical properties of the composite materials;
d) calculations at auto-frettage pressure, zero pressure after auto-frettage, working pressure and minimum
burst pressure;
e) account for the pre-stresses from the winding tension;
f) minimum burst pressure, chosen such that the calculated stress at minimum burst pressure divided by
the calculated stress at the working pressure meets the stress ratio requirements for the fibre used;
g) when analyzing fuel tanks with hybrid reinforcement (two or more different fibres), consideration of the
load share between the different fibres based on the different elastic moduli of the fibres. The stress ratio
requirements for each individual fibre type shall be in accordance with the values given in Table 1.
Verification of the stress ratios may also be performed using strain gauges. An acceptable method is provided
in Annex C.
Table 1 — Minimum stress ratios and burst pressures
a
Construction Minimum stress ratio Minimum actual burst pressure
Type 2 Type 3 Type 4 Type 1 Type 2 Type 3 Type 4
All-metal  2,25
Glass 2,65 3,5 3,5 2,4 3,4 3,5
Aramid 2,25 3,0 3,0 2,25 2,9 3,0
Carbon (working pressures less than 2,25 2,25 2,25 2,25 2,25 2,25
35 MPa)
Carbon (working pressures greater 2,0 2,0 2,0 2,0 2,0 2,0
than or equal to 35 MPa)
b
Hybrid
a
Burst pressures are expressed as a factor of the working pressure.
b
Stress ratios and burst pressures shall be calculated in accordance with 7.3.1 g). The stress ratio requirements for each individual
fibre type shall be in accordance with the values given above.

7.3.2 Liner
For Type 2 designs, the un-reinforced metal liner shall have a minimum burst pressure of 1,25 times the
working pressure.
7.4 Stress analysis
A stress analysis shall be performed to justify the minimum design wall thickness. It shall include the
determination of the stresses in the liners and fibres of composite designs.
For Type 2 and Type 3 designs, the stresses in the composite and in the liner after pre-stress shall be
calculated at zero pressure, working pressure, test pressure and design burst pressure. The calculations shall
use suitable analysis techniques taking account of non-linear material behaviour of the liner to establish the
stress distributions.
For Type 2 and Type 3 designs using auto-frettage to provide pre-stress, the limits within which the auto-
frettage pressure shall fall shall be calculated and specified. For Type 2 and Type 3 designs using controlled
tension winding to provide pre-stress, the temperature at which it shall be performed, the tension required in
each layer of the composite and the consequent pre-stress in the liner shall be calculated.
For Type 4 designs, the stresses in the composite shall be calculated in the tangential and longitudinal
direction of the fuel tank. The pressures used for these calculations shall be zero pressure, working pressure,
test pressure and design burst pressure. The calculations shall use suitable analysis techniques to establish
the stress distribution throughout the fuel tank.
7.5 Maximum defect size
For Type 1, Type 2 and Type 3 designs, the maximum defect size for non-destructive examinations (NDE)
shall be established by a method suitable for the design. This method shall demonstrate that a fuel tank with
defects of the specified defect size will meet the ambient temperature pressure cycling requirements of B.7.
The NDE method shall be capable of detecting the maximum defect size allowed.
NOTE An example of a suitable method for establishing the maximum defect size is given in Annex D.
10 © ISO 2009 – All rights reserved

7.6 Fire protection
The fuel tank, its materials, non-reclosing thermally activated pressure relief devices and any added insulation
or protective material or non-reclosing pressure-activated pressure relief devices, shall be designed
collectively to ensure adequate safety during fire conditions of the test specified in B.9. In no case shall a
pressure relief device be composed of thermally activating and pressure-activating functions acting in series
such that both functions are required to activate to prevent a fuel tank from bursting due to fire effects.
Provided that the finished fuel tank with its fire protection system has passed the requirements of the bonfire
test in B.9, alternative installation configurations for the fire protection system can be used if it can be
demonstrated to provide the same or an improved level of safety. The final fire protection system used for
vehicle installations involving multiple fuel tanks may require a different arrangement or number of non-
reclosing thermally activated pressure relief devices.
If the configuration of fuel tanks results in the possibility of multiple fuel tanks having to vent through one
single pressure relief device (PRD), then the bonfire test shall flow that full amount of hydrogen through the
PRD associated with the fuel tank that is venting. It is not necessary to subject the extra fuel tank(s) that
contain this additional hydrogen to the bonfire, provided that a single fuel tank has already passed the bonfire
test with its own PRD.
NOTE 1 The non-reclosing thermally activated pressure relief device that is part of the fuel tank manufacturer specified
fire protection system is not necessarily provided with the fuel tank. It is, however, required that the effectiveness of this
fire protection system be demonstrated.
NOTE 2 It should not be possible to isolate the non-reclosing thermally activated pressure relief device from the fuel
tank by the normal operation or failure of another component.
8 Construction and workmanship
8.1 Materials
Type 1 designs and Type 2 liners shall be of seamless construction using steel or aluminium alloys that
comply with the materials requirements in 6.2 or 6.4, as appropriate. Type 3 liners shall be constructed from
steel, aluminium alloys, stainless steels, welded stainless steels or welded aluminium alloys that comply with
the materials requirements in 6.2, 6.3 or 6.4, as appropriate.
8.2 Type 3 metal liner
For Type 3 designs, the compressive stress in the liner at zero pressure and the design temperature range
shall not cause the liner to buckle or crease.
NOTE During pressurization, a Type 3 design has a behaviour in which the displacements of the composite over-
wrap and the metal liner are linearly superimposed. Due to different manufacturing techniques, this International Standard
does not give a definite method for design.
The welding of stainless steel liners shall conform to 6.1, 6.2 and 6.4 of EN 13322-2:2003/A1:2006, and the
welding of alumini
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