Definitions

For the purposes of this section:
Alternative arrangement means an approval granted by the competent authority for a portable tank or
MEGC that has been designed, constructed or tested to technical requirements or testing methods
other than those specified in this Chapter;
Portable tank means a thermally insulated multimodal tank having a capacity of more than 450 litres
fitted with service equipment and structural equipment necessary for the carriage of refrigerated
liquefied gases. The portable tank shall be capable of being filled and discharged without the removal
of its structural equipment. It shall possess stabilizing members external to the tank, and shall be
capable of being lifted when full. It shall be designed primarily to be loaded onto a vehicle, wagon or
sea-going or inland navigation vessel and shall be equipped with skids, mountings or accessories to
facilitate mechanical handling. Tank-vehicles, tank-wagons, non-metallic tanks, intermediate bulk
containers (IBCs), gas cylinders and large receptacles are not considered to fall within the definition
for portable tanks;
Tank means a construction which normally consists of either :
(a) A jacket and one or more inner shells where the space between the shell(s) and the jacket is
exhausted of air (vacuum insulation) and may incorporate a thermal insulation system; or
(b) A jacket and an inner shell with an intermediate layer of solid thermally insulating material
(e.g. solid foam);
Shell means the part of the portable tank which retains the refrigerated liquefied gas intended for
carriage, including openings and their closures, but does not include service equipment or external
structural equipment;
Jacket means the outer insulation cover or cladding which may be part of the insulation system;
Service equipment means measuring instruments and filling, discharge, venting, safety, pressurizing,
cooling and thermal insulation devices;
Structural equipment means the reinforcing, fastening, protective and stabilizing members external to
the shell;
Maximum allowable working pressure (MAWP) means the maximum effective gauge pressure
permissible at the top of the shell of a loaded portable tank in its operating position including the
highest effective pressure during filling and discharge;
Test pressure means the maximum gauge pressure at the top of the shell during the pressure test;
Leakproofness test means a test using gas subjecting the shell and its service equipment, to an
effective internal pressure not less than 90% of the MAWP;
Maximum permissible gross mass (MPGM) means the sum of the tare mass of the portable tank and
the heaviest load authorized for carriage;
Holding time means the time that will elapse from the establishment of the initial filling condition
until the pressure has risen due to heat influx to the lowest set pressure of the pressure limiting
device(s);
Reference steel means a steel with a tensile strength of 370 N/mm2 and an elongation at fracture
of 27%;
Minimum design temperature means the temperature which is used for the design and construction of
the shell not higher than the lowest (coldest) temperature (service temperature) of the contents during
normal conditions of filling, discharge and carriage.

General design and construction requirements

Shells shall be designed and constructed in accordance with the requirements of a pressure vessel code
recognized by the competent authority. Shells and jackets shall be made of metallic materials suitable
for forming. Jackets shall be made of steel. Non-metallic materials may be used for the attachments
and supports between the shell and jacket, provided their material properties at the minimum design
temperature are proven to be sufficient. The materials shall in principle conform to national or
international material standards. For welded shells and jackets only materials whose weldability has
been fully demonstrated shall be used. Welds shall be skilfully made and afford complete safety.
When the manufacturing process or the materials make it necessary, the shell shall be suitably heat
treated to guarantee adequate toughness in the weld and in the heat affected zones. In choosing the
material, the minimum design temperature shall be taken into account with respect to risk of brittle
fracture, to hydrogen embrittlement, to stress corrosion cracking and to resistance to impact. When
fine grain steel is used, the guaranteed value of the yield strength shall be not more than 460 N/mm2
and the guaranteed value of the upper limit of the tensile strength shall be not more than 725 N/mm2
in accordance with the material specifications. Portable tank materials shall be suitable for the external
environment in which they may be carried.

Any part of a portable tank, including fittings, gaskets and pipe-work, which can be expected normally
to come into contact with the refrigerated liquefied gas carried shall be compatible with that
refrigerated liquefied gas.

Contact between dissimilar metals which could result in damage by galvanic action shall be avoided.

The thermal insulation system shall include a complete covering of the shell(s) with effective
insulating materials. External insulation shall be protected by a jacket so as to prevent the ingress of
moisture and other damage under normal carriage conditions.

When a jacket is so closed as to be gas-tight, a device shall be provided to prevent any dangerous
pressure from developing in the insulation space.

Portable tanks intended for the carriage of refrigerated liquefied gases having a boiling point below
minus (-) 182 °C at atmospheric pressure shall not include materials which may react with oxygen or
oxygen enriched atmospheres in a dangerous manner, when located in parts of the thermal insulation
when there is a risk of contact with oxygen or with oxygen enriched fluid.

Insulating materials shall not deteriorate unduly in service.

A reference holding time shall be determined for each refrigerated liquefied gas intended for carriage
in a portable tank.

The reference holding time shall be determined by a method recognized by the competent authority on
the basis of the following:
(a) The effectiveness of the insulation system, determined in accordance with 6.7.4.2.8.2;
(b) The lowest set pressure of the pressure limiting device(s);
(c) The initial filling conditions;
(d) An assumed ambient temperature of 30 °C;
(e) The physical properties of the individual refrigerated liquefied gas intended to be carried.

The effectiveness of the insulation system (heat influx in watts) shall be determined by type testing the
portable tank in accordance with a procedure recognized by the competent authority. This test shall
consist of either:
(a) A constant pressure test (for example at atmospheric pressure) when the loss of refrigerated
liquefied gas is measured over a period of time; or
(b) A closed system test when the rise in pressure in the shell is measured over a period of time.
When performing the constant pressure test, variations in atmospheric pressure shall be taken into
account. When performing either tests corrections shall be made for any variation of the ambient
temperature from the assumed ambient temperature reference value of 30 °C.
NOTE: For the determination of the actual holding time before each journey, refer to 4.2.3.7.

 

The jacket of a vacuum-insulated double-wall tank shall have either an external design pressure not
less than 100 kPa (1 bar) (gauge pressure) calculated in accordance with a recognized technical code
or a calculated critical collapsing pressure of not less than 200 kPa (2 bar) (gauge pressure). Internal
and external reinforcements may be included in calculating the ability of the jacket to resist the
external pressure.

Portable tanks shall be designed and constructed with supports to provide a secure base during
carriage and with suitable lifting and tie-down attachments.

Portable tanks shall be designed to withstand, without loss of contents, at least the internal pressure
due to the contents, and the static, dynamic and thermal loads during normal conditions of handling
and carriage. The design shall demonstrate that the effects of fatigue, caused by repeated application
of these loads through the expected life of the portable tank, have been taken into account.
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