independent safety valves capable of opening at the maximum working pressure indicated on the tank.
Two of these safety valves shall be individually sized to allow the gases formed by evaporation during
normal operation to escape from the tank in such a way that the pressure does not at any time exceed
by more than 10% the working pressure indicated on the tank.
One of the safety valves may be replaced by a bursting disc which shall be such as to burst at the test
pressure.
In the event of loss of the vacuum in a double-walled tank, or of destruction of 20% of the insulation
of a single-walled tank, the combination of the pressure relief devices shall permit an outflow such
that the pressure in the shell cannot exceed the test pressure. The provisions of 6.8.2.1.7 shall not
apply to vacuum-insulated tanks.

These pressure relief devices of tanks intended for the carriage of refrigerated liquefied gases shall be
so designed as to function faultlessly even at their lowest working temperature. The reliability of their
operation at that temperature shall be established and checked either by testing each device or by
testing a specimen device of each design-type.

The valves of demountable tanks that can be
rolled shall be provided with protective caps.
                                                                    

 

Thermal insulation

If tanks intended for the carriage of liquefied gases are equipped with thermal insulation, such
insulation shall consist of either:
- a sun shield covering not less than the upper third but not more than the upper half of the tank
surface and separated from the shell by an air space at least 4 cm across; or
- a complete cladding, of adequate thickness, of insulating materials.

Tanks intended for the carriage of refrigerated liquefied gases shall be thermally insulated. Thermal
insulation shall be ensured by means of a continuous sheathing. If the space between the shell and the
sheathing is under vacuum (vacuum insulation), the protective sheathing shall be so designed as to
withstand without deformation an external pressure of at least 100 kPa (1 bar) (gauge pressure). By
derogation from the definition of "calculation pressure" in 1.2.1, external and internal reinforcing
devices may be taken into account in the calculations. If the sheathing is so closed as to be gas-tight, a
device shall be provided to prevent any dangerous pressure from developing in the insulating layer in
the event of inadequate gas-tightness of the shell or of its items of equipment. The device shall prevent
the infiltration of moisture into the heat-insulating sheath. For type testing of the effectiveness of the
insulation system, see 6.8.3.4.11.

Tanks intended for the carriage of liquefied gases having a boiling point below -182° C at atmospheric
pressure shall not include any combustible material either in the thermal insulation or in the means of
attachment.
 
The means of attachment for vacuum insulated tanks may, with the approval of the competent
authority, contain plastics substances between the shell and the sheathing.

By derogation from the requirements of 6.8.2.2.4 shells intended for the carriage of refrigerated
liquefied gases need not have an inspection opening.

Items of equipment for battery-vehicles and MEGCs

Service and structural equipment shall be configured or designed to prevent damage that could result
in the release of the pressure receptacle contents during normal conditions of handling and carriage.
When the connection between the frame of the battery-vehicle or MEGC and the elements allows
relative movement between the sub-assemblies, the equipment shall be so fastened as to permit such
movement without damage to working parts. Manifold piping leading to shut-off valves shall be
sufficiently flexible to protect the valves and the piping from shearing, or releasing the pressure
receptacle contents. The filling and discharge devices (including flanges or threaded plugs) and any
protective caps shall be capable of being secured against unintended opening.

In order to avoid any loss of content in the event of damage, the manifolds, the discharge fittings (pipe
sockets, shut-off devices), and the stop-valves shall be protected or arranged from being wrenched off
by external forces or designed to withstand them.

The manifold shall be designed for service in a temperature range of -20° C to +50° C.
The manifold shall be designed, constructed and installed so as to avoid the risk of damage due to
thermal expansion and contraction, mechanical shock and vibration. All piping shall be of suitable
metallic material. Welded pipe joints shall be used wherever possible.
Joints in copper tubing shall be brazed or have an equally strong metal union. The melting point of
brazing materials shall be no lower than 525ºC. The joints shall not decrease the strength of tubing as
may happen when cutting threads.

Except for UN No.1001 acetylene, dissolved, the permissible maximum stress σ of the manifolding
arrangement at the test pressure of the receptacles shall not exceed 75% of the guaranteed yield
strength of the material.
The necessary wall thickness of the manifolding arrangement for the carriage of UN No.1001
acetylene, dissolved shall be calculated according to an approved code of practice.
NOTE: For the yield strength, see 6.8.2.1.11.
The basic requirements of this paragraph shall be deemed to have been complied with if the following
standards are applied: (Reserved).

By derogation from the requirements of 6.8.3.2.3, 6.8.3.2.4 and 6.8.3.2.7, for cylinders, tubes,
pressure drums and bundles of cylinders (frames) forming a battery-vehicle or MEGC, the required
closing devices may be provided for within the manifolding arrangement.

If one of the elements is equipped with a safety valve and shut-off devices are provided between the
elements, every element shall be so equipped.

The filling and discharge devices may be affixed to a manifold.

Each element, including each individual cylinder of a bundle, intended for the carriage of toxic gases,
shall be capable of being isolated by a shut-off valve.
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