ISO/TS 16111:2006

TECHNICAL ISO/TS
SPECIFICATION 16111
First edition
2006-10-15
Transportable gas storage devices —
Hydrogen absorbed in reversible metal
hydride
Appareils de stockage de gaz transportables — Hydrogène absorbé
dans un hydrure métallique réversible

Reference number
©
ISO 2006
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©  ISO 2006
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ii © ISO 2006 – All rights reserved

Contents Page
Foreword. iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions. 2
4 Service conditions. 3
4.1 Pressures. 3
4.2 Rated capacity. 4
4.3 Temperature ranges . 4
4.4 Environmental conditions. 4
4.5 Service life . 4
4.6 Requalification procedures . 4
4.7 Hydrogen quality. 5
4.8 Special service conditions. 5
5 Design considerations . 5
5.1 Shell design. 5
5.2 Design strength. 5
5.3 Material selection. 6
5.4 Overpressure and fire protection. 7
5.5 Shut-off valves . 7
5.6 Actively cooled canisters. 7
5.7 Particulate containment . 7
6 Type/qualification tests. 8
6.1 General. 8
6.2 Fire test . 8
6.3 Drop test . 10
6.4 Leak test . 12
6.5 Hydrogen cycling and strain measurement test . 12
6.6 Shut-off valve impact test . 14
6.7 Type test reports. 15
7 Routine tests and inspections. 15
8 Marking, labelling, and documentation . 16
8.1 Marking . 16
8.2 Labelling . 16
9 Documentation accompanying the product . 16
9.1 Material safety data sheets . 16
9.2 Users or operating manual . 17
Annex A (informative) Material compatibility for hydrogen service . 18

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 normative 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 16111 was prepared by Technical Committee ISO/TC 197, Hydrogen technologies.

iv © ISO 2006 – All rights reserved

Introduction
As the utilization of gaseous hydrogen evolves from the chemical industry into a fuel for various emerging
applications, the importance of new and improved storage techniques has become essential. One of these
techniques employs the absorption of hydrogen into specially formulated alloys. The material can be stored
and transported in a solid form, and later released and used under specific thermodynamic conditions. This
Technical Specification describes the service conditions, design criteria, type tests and routine tests for these
canisters.
TECHNICAL SPECIFICATION ISO/TS 16111:2006(E)

Transportable gas storage devices — Hydrogen absorbed
in reversible metal hydride
1 Scope
This Technical Specification defines the requirements applicable to the safe design and use of transportable
hydrogen gas storage canisters, including all necessary shut-off valve, pressure-relief devices (PRD), and
appurtenances, intended for use with reversible metal hydride hydrogen storage systems. This Technical
Specification only applies to refillable storage canisters where hydrogen is the only transferred media. Storage
canisters intended to be used as fixed fuel storage onboard hydrogen fuelled vehicles are excluded.
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 7225, Gas cylinders — Precautionary labels
ISO 7866, Gas cylinders — Refillable seamless aluminium alloy gas cylinders — Design, construction and
testing
ISO 9809-1, 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 9809-3, Gas cylinders — Refillable seamless steel gas cylinders — Design, construction and testing —
Part 3: Normalized steel cylinders
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 11119-1, Gas cylinders of composite construction — Specification and test methods — Part 1: Hoop
wrapped composite gas cylinders
ISO 11119-2, Gas cylinders of composite construction — Specification and test methods — Part 2: Fully
wrapped fibre reinforced composite gas cylinders with load-sharing metal liners
ISO 14687, Hydrogen fuel — Product specification
1)
ISO 16528 (all parts) , Boilers and pressure vessels

1) To be published.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
absorbed
taken and held through the formation of bonding interactions within the bulk of the material
3.2
canister
single complete hydrogen storage system, including shell, metal hydride, PRD, shut-off valve and other
appurtenances (e.g. for heat exchange, to prevent excessive stress on the shell walls due to hydride
expansion, etc.)
NOTE The canister extends only to, and includes, the first shut-off valve.
3.3
design stress limit
total stress loading allowed on the shell wall, according to the standard to which the shell was designed
3.4
full flow capacity pressure
gas pressure at which the pressure relief device is fully open
3.5
hydrogen absorbing alloy
material capable of combining directly with hydrogen gas to form a reversible metal hydride
3.6
maximum developed pressure
MDP
highest gas gauge pressure for a canister at rated capacity and equilibrated at the maximum service
temperature
NOTE The MDP term was specifically selected for metal hydride systems to avoid confusion with the MAWP and the
service pressure used in other ISO International Standards. In metal hydride systems, the shell design takes to take into
account the gas pressure plus the pressure exerted by the hydrogen absorbing alloy expansion.
3.7
metal hydride
solid material formed by reaction between hydrogen and hydrogen absorbing alloy
3.8
normal operating conditions
range of conditions such as pressure, temperature, hydrogen flow rate, hydrogen impurities, etc. that the
product may be exposed to during all use and filling operations
3.9
normal service conditions
range of conditions, such as pressure, temperature, hydrogen flow rate, hydrogen impurities, etc. that the
product may be exposed to during normal operating, transportation and storage conditions
3.10
pressure relief device
PRD
basic safety device used to relieve excessive pressure within the canister before damage to the canister can
occur
2 © ISO 2006 – All rights reserved

NOTE A pressure relief device may be “pressure-activated”, set to activate at a certain pressure. Alternately, a
pressure relief device may be “thermally-activated”, set to activate at a certain temperature. A pressure relief device may
also be both “pressure-activated” and “thermally-activated”.
3.11
pressure relief valve
PRV
PRD that includes a valve that will open at a set pressure and reclose once the pressure drops below a set
pressure
NOTE Pressure relief valves are typically spring-loaded valves.
3.12
rated capacity
stated deliverable quantity of hydrogen specified by the manufacturer
3.13
rated charging pressure
RCP
maximum pressure allowed to be applied to the product for refilling
3.14
reversible metal hydride
metal hydride for which there exists an equilibrium condition where the hydrogen absorbing alloy, hydrogen
gas and the metal hydride co-exist
NOTE Changes in pressure or temperature will shift the equilibrium favouring the formation or decomposition of the
metal hydride with respect to the hydrogen absorbing alloy and hydrogen gas.
3.15
rupture
structural failure of a shell resulting in the rapid and violent release of the stored energy in such a manner that
it may pose a safety hazard to people or property
3.16
shell
enclosure designed to contain the hydrogen gas, metal hydride and other internal components of the canister
NOTE A shell may be a cylinder, a pressure vessel or other type of container.
3.17
stress level at MDP
sum of all the stresses on the shell wall caused by the metal hydride material at rated capacity, hydrogen gas
at MDP and any other applicable mechanical loadings
3.18
transportable
designed to be mobile and not intended to be used in a fixed, permanent installation
4 Service conditions
4.1 Pressures
4.1.1 Maximum developed pressure (MDP)
The MDP shall be determined by the manufacturer from the metal hydride's temperature-pressure
characteristics at the maximum service temperature.
4.1.2 Rated charging pressure (RCP)
The RCP shall be specified by the manufacturer in order to prevent charging at a pressure that could result in
the shell wall stress exceeding the design stress limit.
4.1.3 Stress level at MDP
The stress level at MDP shall be determined by the manufacturer from the hydrogen absorbing alloy's packing
and expansion properties, the MDP within the canister, and other applicable mechanical loadings.
4.1.4 PRD activation pressure
The pressure of actuation of pressure-activated PRD shall be specified by the manufacturer and shall be
greater than the MDP. For pressure-relief valves (PRV), the full flow capacity pressure shall also be specified.
4.2 Rated capacity
The manufacturer shall state the rated capacity of the canister by units of mass of hydrogen.
4.3 Temperature ranges
4.3.1 Operating temperature range
The minimum and maximum temperature for normal operating conditions to which the canister is rated shall
be specified by the manufacturer.
4.3.2 Service temperature range
The minimum and maximum temperature for normal service conditions to which the canister is rated shall be
specified by the manufacturer. At a minimum this range shall be of at least from –40 °C to +65 °C and shall
include the entire operating temperature range.
4.3.3 PRD activation temperature
The temperature at which any thermally actuated PRD is set to activate shall be specified by the manufacturer
and it shall be greater than the maximum service temperature. The PRD shall have a pressure rating of
greater than the MDP at all temperatures less than or equal to 10 °C above the maximum service temperature.
NOTE Exposure to higher temperatures may be expected in some geographical regions and should be considered.
4.4 Environmental conditions
The canisters are expected to be exposed to a number of environmental conditions over their service life,
such as vibration and shock, varying humidity levels, and corrosive environments. The manufacturer shall
specify the environmental conditions for which the canister was designed.
4.5 Service life
The service life for the canisters shall be specified by the manufacturer on the basis of use under service
conditions specified herein. The service life shall not exceed that specified by the standard to which the shell
is designed as per 5.1 and in no case shall exceed 20 years.
4.6 Requalification procedures
The canister may be requalified in accordance with the requirements of the standard to which the shell was
originally designed, or in accordance with a method acceptable to the authority having jurisdiction.
4 © ISO 2006 – All rights reserved

NOTE Caution should be taken, as certain procedures (e.g. hydrostatic testing) allowed for cylinder or pressure
vessel requalification may not be appropriate for metal hydride canisters. In such cases, an alternative method (e.g.
ultrasonic examination) may be applicable.
If requalification is authorized, the manufacturer shall specify the minimum requalification procedures.
4.7 Hydrogen quality
The quality of the hydrogen gas that shall be used to fill a canister shall be specified by the manufacturer
according to ISO 14687 or as appropriate.
NOTE If the quality of the hydrogen gas is considered a critical issue, the manufacturer may consider including the
information on the product label.
4.8 Special service conditions
Any additional service conditions that shall be met for the safe operation, handling and usage of the canister
shall be specified by the manufacturer.
5 Design considerations
5.1 Shell design
The canister shell shall be designed according to ISO 7866, ISO 9809-1, ISO 9809-3, ISO 11119-1,
ISO 11119-2 or standards registered in accordance with ISO 16528, as applicable, or as required by the
authority having jurisdiction. The shell shall not exceed 150 litres water capacity, and the MDP shall not
exceed 25 MPa. The stress level at MDP, including contributors listed in 5.2, shall be less than or equal to the
design stress limit allowed by the standard to which the shell is designed (e.g. the shell’s maximum allowable
working pressure or maximum permissible working pressure). The operating and service temperature ranges
for the canister shall be less than or equal to that of the standard to which the shell is designed.
Alternatively for canisters with an internal volume of less than 0,12 litres, the shell design shall be deemed to
be appropriate if the canister design meets all the other requirements of this Technical specification,
successfully passes all tests specified in Clause 6 and meets the following design criteria:
a) the pressure in the canister shall not exceed 5 MPa at 55 °C when the canister is filled to its rated
capacity; and
b) the canister design shall withstand, without leaking or bursting, a minimum shell burst pressure of 2 times
the pressure in the canister at 55 °C when filled to rated capacity, or 200 kPa more than the pressure in
the canister at 55 °C when filled to rated capacity, whichever is greater.
5.2 Design strength
The shell design shall take into account the stress level at MDP. Consideration of components contributing to
the stress level at MDP shall include but not be limited to:
⎯ the MDP;
⎯ thermal stress, including dissimilar rates of thermal expansion and contraction;
⎯ weight of internals in any possible canister orientation;
⎯ shock and vibration loading;
⎯ maximum stress due to hydrogen absorbing alloy expansion;
⎯ other mechanical loadings.
To verify that the design stress limit is not exceeded, the canister design shall be subjected to the hydrogen
cycling and strain measurement test described in 6.5.
NOTE The process of introducing and subsequently removing hydrogen in the hydrogen absorbing alloy causes it to
expand and contract. In turn, this can result in large stresses inside the alloy's particles that cause them to fragment into
smaller particles, a phenomenon known as decrepitation. After several charge/discharge cycles, the average particle size
may have significantly decreased. Stresses on the canister walls may be derived from expansion of the hydrogen
absorbing alloy during hydrogenation and from changes in the packing configuration due to decrepitation over the service
life of the canister. The magnitude of the expansion/contraction phenomena will vary greatly as a function of the hydrogen
absorbing alloy used.
5.3 Material selection
5.3.1 General
The canister components shall be made of materials that are suitable for the range of conditions expected
during normal service conditions over the service life of the canister. Components that are in contact with
gaseous hydrogen and/or metal hydride material shall be sufficiently resistant to their chemical and physical
action under normal service conditions to maintain operational and pressure containment integrity.
Metal hydride material that is capable of rapid disassociation or explosion when exposed to prolonged heating
shall not be used in a canister.
5.3.2 External surfaces
The canister shell, shut-off valve, PRDs and other appurtenances shall be resistant to the environmental
conditions specified in 4.4. Resistance to these environmental conditions may be provided by using materials
inherently resistant to the environment or by applying resistant coatings to the components. Exterior protection
may be provided by using a surface finish giving adequate corrosion protection (e.g. metal sprayed on
aluminium or anodizing); or a protective coating (e.g. organic coating or paint). If an exterior coating is part of
the design, the coating shall be evaluated using the test methods acceptable to the authority having
jurisdiction. Any coatings applied to canisters shall be such that the application process does not adversely
affect the mechanical properties of the shell or performance and operation of other components. The coatings
shall be designed to facilitate subsequent in-service inspection and the manufacturer shall provide guidance
on coating treatment during such inspections to ensure the continued integrity of the canister.
5.3.3 Compatibility
The compatibility of canister materials with process fluids and solids, specifically embrittlement due to the
exposure to hydrogen, shall be considered. Materials necessary for the pressure containment and structural
integrity of the canister and its internal and external appurtenances shall be resistant to hydrogen
embrittlement, hydrogen attack and reactivity with contained materials and maintain their required integrity for
the service life of the canister. Recognized test methods, such as those specified in ISO 11114-4, shall be
used to select metallic materials resistant to hydrogen embrittlement where required for pressure or structural
integrity. Consideration shall be given to the impact that temperature may have on hydrogen embrittlement.
Alternatively, materials known to be resistant to hydrogen embrittlement may be used.
If charged with gases or materials that are capable of combining chemically with each other or with the
canister material, the materials shall be selected so as the combination does not endanger the canister
integrity.
NOTE The susceptibility to hydrogen embrittlement of some commonly used metals is summarized in ISO/TR 15916.
Additional guidance regarding hydrogen compatibility is found in Annex A.
5.3.4 Temperature
The canister materials shall be suitable for the normal service temperature range of 4.3.2.
6 © ISO 2006 – All rights reserved

5.4 Overpressure and fire protection
The canister shall be protected with one or more PRD of the self-destructive type, such as fusible triggers,
rupture disks and diaphragms, or of the re-sealable type, such as spring-loaded PRV. The canister and any
added component (e.g. insulation or protective material) shall collectively pass the fire test specified in 6.2.
PRD shall be approved to a standard acceptable to the authority having jurisdiction.
For canisters with an internal volume of less than 0,12 litres and that meet the alternative shell requirements
of 5.1, another means may be used to protect from overpressurization, such as venting through a feature
integral to the shell. Canisters that use an alternative means of relieving pressure shall meet the acceptance
criteria of the fire test specified in 6.2.
5.5 Shut-off valves
5.5.1 General
The canister assembly shall incorporate a shut-off valve that shall close when the assembly is disconnected
from the refill or gas-consuming equipment. The shut-off valve shall be required to conform to an applicable
standard.
For canisters with an internal volume of less than 0,12 litres and that meet the alternative shell requirements
of 5.1, a valve design that does not conform to a standard may be used, if there is not an applicable valve
standard. Such canisters shall meet the acceptance criteria of all tests in Clause 6.
All canisters shall provide a means of valve protection.
NOTE Due to the temperature/pressure characteristics of metal hydrides, the development of sub-ambient pressures
are possible within canisters, therefore valve selection should include verification that valve seal is maintained with
vacuum conditions within the canister.
5.5.2 Integral valve protection
A canister design that uses an integral method of valve protection that is not meant to be removed for canister
operation, such as the use of a shroud, collar or recessing the valve in the canister assembly, shall meet the
requirements of the drop test in 6.3.
5.5.3 Removable valve protection
The canister designs that use a removable means of valve protection that is meant to be removed for canister
operation, such as a cover or cap, shall meet the requirements of the drop test in 6.3 with the protective
means in place and meet the requirements of the shut-off valve impact test in 6.6 without the protective
means in place.
5.6 Actively cooled canisters
Canisters that employ an active cooling system to control and/or affect system temperature shall be designed
to ensure that there will be no inadvertent leakage of fluid between the canister and the cooling system. The
cooling system shall be employed when performing the hydrogen cycling and strain measurement test in 6.5.
5.7 Particulate containment
Particulate matter shall not impede the functioning of the valves or PRDs. A means of particulate matter
containment may be used to achieve this purpose. The canisters shall meet the requirements of the hydrogen
cycling and strain measurement test of 6.5.
6 Type/qualification tests
6.1 General
The following type tests shall be performed to qualify a canister design. The canister used for the type tests
shall be representative of production canisters. The data for all type tests shall be acquired using calibrated
instruments.
Procedures shall be put in place to ensure the consistent loading of the hydrogen absorbing alloy in the
canister. Any change in shell design, hydrogen absorbing alloy, manufacturing process or installation
procedure shall require repeating the fire test of 6.2, the drop test of 6.3 and the hydrogen cycling and strain
measurement test of 6.5.
6.2 Fire test
6.2.1 General
The fire test shall be performed on all new canister designs to demonstrate that the fire protection system,
such as PRD and/or integral thermal insulation, will prevent the rupture of the canister under the specified fire
conditions. Any significant change to the design (for example changes in diameter or length, PRD, shell-type,
means of solid particulate containment or in the hydrogen absorbing alloy) shall necessitate repeating the fire
test.
As an exception, a manufacturer may use data and engineering calculations, based on previous fire test
results on existing designs, in cases involving design changes that are not considered significant (i.e.
reduction in shell diameter, reduction in shell length, or increase in PRD flow capacity), to show that a new
design does not require repeating the fire test.
Precautions shall be taken to ensure safety of personnel and property during the fire test in the event that a
canister rupture occurs.
6.2.2 Sample preparation
The canister shall be filled to rated capacity with hydrogen.
6.2.3 Data monitoring and recording
The temperature and pressure of the canister shall be monitored remotely and recorded at intervals of
15 seconds or less. A manual valve shall be installed to allow venting of the canister in the event of a
malfunction of the test equipment or system.
In addition to the temperature and pressure readings, the following information shall also be recorded for each
test:
⎯ canister manufacturer;
⎯ canister part or model number;
⎯ unique identifier;
⎯ PRD-type and rating;
⎯ PRD location and orientation;
⎯ date of test;
⎯ canister RCP;
⎯ number of charge/discharge cycles that the canister has undergone;
8 © ISO 2006 – All rights reserved

⎯ canister orientation (vertical, horizontal or inverted);
⎯ ambient temperature;
⎯ estimated wind condition/direction;
⎯ names of witnesses;
⎯ time of activation of PRD; and
⎯ elapsed time to completion of the test.
For canister designs that preclude monitoring pressure during the fire test, a statement of justification for not
monitoring the pressure during the fire test shall be provided, along with a description of the means for
determining activation of the PRD. Additional safety precautions may be required to safely carry out the fire
test.
6.2.4 Test set-up, fire source and test method
The fire tests shall be conducted on at least three canisters in each orientation of intended use and/or
transportation. For canister designs for which the orientation of use and transportation are not specified, at
least three canisters shall be fire tested in each of the vertical and horizontal orientation and any other
orientation due to asymmetry of the canister design, if applicable. The tests shall include at least one test with
the PRD oriented towards the fire source and at least one test with the PRD oriented 180 degrees away from
the fire source.
The canisters, over their entire width, shall be subjected to a fire source of a maximum length of 1,65 m. For
canisters less than 1,65 m in length, the fire source shall totally engulf the canister. Canisters longer than
1,65 m or equipped with multiple PRDs with a spacing greater than 1,65 m, shall be subjected to a partial
engulfment fire test in the horizontal orientation. If a canister is longer than 1,65 m and is fitted with a PRD at
one end, the opposite end of the canister shall be subjected to the fire source. If the canister is fitted with PRD
at both ends, or at more than one location along the length of the canister, the fire source shall be centred
midway between the PRD that are separated by the greatest horizontal distance.
For canisters less than 0,30 m in length, a temperature-indicating device shall be installed within 0,05 m of,
but not in contact with, the canister surface near each end. For canisters longer than 0,30 m, a temperature-
indicating device shall be installed at each end and one at the midpoint. Temperature-indicating devices may
be inserted into small metallic blocks (less than 0,025 m per side).
Canisters shall be subjected to a direct flame impingement test. Sufficient fuel shall be supplied to ensure a
burn time of at least 20 minutes. The canister shall be placed in the test orientation with the canister at least
0,1 m above the fuel or at a greater height to ensure total flame engulfment. The fire shall produce a flame
that totally engulfs the canister. Shielding shall be used to prevent direct flame impingement on tank shut-off
valve, fittings, and/or PRD(s). The shielding shall not be in direct contact with the specified fire protection
system.
Any fuel may be used for the fire source provided it supplies uniform heat sufficient to maintain the specified
test conditions for a minimum of 20 minutes. The selection of a fuel should take into consideration air pollution
concerns. The arrangement of the fire shall be recorded in detail to ensure that the rate of heat input to the
canister is reproducible.
NOTE Canisters that have been subjected to the cycling and strain measurement test of 6.5 may be used in this test.
6.2.5 Acceptance criteria
Any failure or inconsistency of the fire source during a test shall invalidate the result, and a re-test shall be
carried out. Any venting through or failure of the shell, a valve, fitting or tubing during the test that is not part of
the intended protection system, shall invalidate the result and a re-test shall be carried out.
The canister design shall be deemed to have passed the fire test if, for all valid tests, there is no generation of
projectiles and one of the following criteria is met:
⎯ the PRD of all canisters subjected to the fire test vent each canister to zero internal gauge pressure
without rupture of the canister; or
⎯ all canisters subjected to the fire test withstand the fire for a minimum of 20 minutes without rupture.
6.3 Drop test
6.3.1 General requirements
All canister designs shall meet the requirements of the drop test. Any significant change to the design, for
example changes in shell-type or means of solid particulate containment, shall necessitate repeating the drop
test.
The surface onto which the canisters are dropped shall be a smooth horizontal concrete pad or flooring. The
container shall be allowed to bounce on the concrete pad or flooring after the initial impact. No attempt shall
be made to prevent this secondary impact. A guide rail for posture maintenance may be used.
6.3.2 Sample preparation
The canisters used for these tests shall include their shut-off valve protection in accordance with 5.5. The
canisters shall have an equivalent weight (± 2 %), packing density and internal structure as production
canisters. Ballast material may be used in place of the hydrogen absorbing alloy. The canisters shall not be
pressurized.
6.3.3 Test procedure
Canisters shall be drop tested in accordance with the following conditions. One canister may be used for all
drop tests.
a) One canister shall be dropped vertically on the end containing the shut-off valve assembly. One canister
shall be dropped vertically on the end opposite the shut-off valve assembly. In both cases, the canister
shall be dropped from a height of not less than 1,8 m measured from the lower end of the canister.
b) One canister shall be dropped at a 45° angle on the end containing the shut-off valve assembly from a
height such that the centre of gravity is at a minimum height of 1,8 m. If the lower end of the canister is at
a height of less than 0,6 m, the drop angle shall be changed to maintain the lower end of the canister and
the centre of gravity at a minimum height of 0,6 m and 1,8 m respectively. When the shut-off valve, PRD
and other appurtenances are set on both ends of the canister, the canister shall be dropped at a 45°
angle on its weakest end.
c) One canister shall be dropped horizontally from a height of 1,8 m onto a steel apex as shown in Figure 1.
The canister shall be placed such that its centre of gravity is aligned with the rounded edge of the steel
apex as shown in Figure 1. In order to prevent movement of the steel apex by the collision of the canister,
the steel apex shall be fixed to the concrete pad or flooring. The canister shall strike the steel apex before
striking the concrete pad or flooring.
10 © ISO 2006 – All rights reserved

Centre of gravity
Steel apex
R= 5,0 mm ± 0,2 mm
Steel apex
Smooth horizontal concrete pad or flooring

Figure 1 — Canister drop test onto an apex
6.3.4 Acceptance criteria
The shut-off valve shall be intact and function properly after all drop tests.
All canisters that have undergone the drop tests shall be visually inspected and all apparent damage
recorded. All canisters shall be subjected to the leak test of 6.4 and then be hydrostatically pressurized to
destruction. The canisters shall meet the acceptance criteria of 6.4 and the recorded burst pressures shall
exceed 85 % of the minimum shell burst pressure specified by the standard to which the shell was designed
or in the case of canisters with an internal volume of less than 0,12 litres, 85 % of the minimum shell burst
pressure specified in 5.1.
38 mm
1,8 m
25 mm
6.4 Leak test
The canister shall be charged with hydrogen, helium or a blend of the two and monitored for leaks at the
conditions indicated in Table 1.
Table 1 — Temperature/pressure conditions for leak test
Temperature Pressure
Minimum service temperature RCP
15 °C ± 5 °C RCP
Maximum service temperature MDP
An acceptable result shall be a total hydrogen leak rate of less than 10 standard cm /h (standard conditions of
0 °C and 101,325 kPa absolute). If hydrogen gas is not used, the leak rate shall be converted into an
equivalent hydrogen leak rate.
NOTE Before placing the canister in an enclosed area to perform the leak test, it is recommended to test for the
presence of major leaks using a soap bubble solution, or by other adequate means, on all possible leak locations.
6.5 Hydrogen cycling and strain measurement test
6.5.1 General
The hydrogen cycling and strain measurement test shall be performed on all new canister designs to
demonstrate that the design stress limits of the shell are not exceeded during use. Any significant change to
the design (including, but not limited to changes to: the shell type, shell specifications, means of solid
particulate containment or hydrogen absorbing alloy) shall necessitate repeating the hydrogen cycling and
strain measurement test. Canisters that employ an active cooling system to control and/or affect system
temperature shall be subjected to the test with the cooling system in place.
Precautions shall be taken to ensure safety of personnel and property during testing in the event that a
canister failure or hydrogen release occurs.
6.5.2 Test set-up
Each canister shall be adequately instrumented with strain gauges to determine the maximum local strain that
the shell experiences during cycling. With metal hydride canisters, the strain may not be uniform throughout
the canister. The number and location of the strain gauges required to ensure that the highest strain
experienced by the shell may be determined from engineering models based on knowledge of the design,
including the internal configuration and geometry, hydrogen absorbing alloy distribution, etc. If engineering
models cannot accurately determine the points of expected highest strain, then the number and locations of
required strain gauges shall be empirically determined by extensively instrumenting at least two canisters with
strain gauges and performing the test. Based on the results, further testing may be performed using fewer
strain gauges that are strategically placed to measure the highest strain levels experienced by the shell.
As a minimum, the hoop strain shall be monitored on cylindrical and dome sections of canisters, bending
strain shall be monitored on flat sections of canisters and for strain concentration points (such as corners and
edges), the strain in areas around the concentration point shall be monitored, and a concentration factor shall
be used to estimate the strain at the concentration point.
The strain gauges shall be protected from damage during extended testing and exposure to the cycling
environment, for example by the use of a chemically resistant epoxy. Periodically during and, at least at the
start and end of cycling, the strain gauges shall be calibrated to ensure proper functioning. If any strain gauge
is found to not be properly functioning, it shall be replaced.
12 © ISO 2006 – All rights reserved

The strain at the design stress limit shall be determined either by engineering calculations based on the shell
design and material properties, or empirically by internally applying either a pneumatic or hydrostatic pressure
up to a pressure equivalent to the shell design stress limit and measuring the strain. For any canister where
the strain gauges are applied to an outer layer and not directly to the shell or liner in contact with the metal
hydride and hydrogen gas (such as type II, III and IV fibre-wrapped composite tanks) or for any shell th
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