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 126.96.36.199.8.2;
(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 188.8.131.52.
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
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.
Portable tanks and their fastenings under the maximum permissible load shall be capable of absorbing
the following separately applied static forces:
(a) In the direction of travel: twice the MPGM multiplied by the acceleration due to gravity (g) 1;
(b) Horizontally at right angles to the direction of travel: the MPGM (when the direction of travel
is not clearly determined, the forces shall be equal to twice the MPGM) multiplied by the
acceleration due to gravity (g) 1;
(c) Vertically upwards: the MPGM multiplied by the acceleration due to gravity (g) 1; and
(d) Vertically downwards: twice the MPGM (total loading including the effect of gravity)
multiplied by the acceleration due to gravity (g) 1.