Dangerous Goods by Road
The discharge pipes of tanks shall be capable of being closed by blank flanges or some other equally
reliable device. For tanks intended for the carriage of refrigerated liquefied gases, these blank flanges
or other equally reliable devices may be fitted with pressure-release openings of a maximum diameter
of 1.5 mm.
Shells intended for the carriage of liquefied gases may be provided with, in addition to the openings
prescribed in 6.8.2.2.2 and 6.8.2.2.4, openings for the fitting of gauges, thermometers, manometers
and with bleed holes, as required for their operation and safety.
The internal stop-valve of all filling and all discharge openings of tanks
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intended for the carriage of liquefied flammable or toxic gases shall be instant-closing and shall close
automatically in the event of an unintended movement of the tank or in the event of fire. It shall also
be possible to operate the internal stop-valve by remote control.
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However on tanks intended for the carriage of
liquefied non-toxic flammable gases, the
internal stop-valve with remote control may be
replaced by a non-return valve for filling
openings into the vapour phase of the tank
only. The non-return valve shall be positioned
internally in the tank, be spring loaded so that
the valve is closed if the pressure in the filling
line is equal to or lower than the pressure in
the tank and be equipped with appropriate
sealing15.
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All openings, other than those accommodating safety valves and closed bleed holes, of tanks intended
for the carriage of liquefied flammable and/or toxic gases shall, if their nominal diameter is more than
1.5 mm, shall be equipped with an internal shut-off device.
Notwithstanding the requirements of 6.8.2.2.2, 6.8.3.2.3 and 6.8.3.2.4, tanks intended for the carriage
of refrigerated liquefied gases may be equipped with external devices in place of internal devices if
the external devices afford protection against external damage at least equivalent to that afforded by
the wall of the shell.
If the tanks are equipped with gauges in direct contact with the substance carried, the gauges shall not
be made of a transparent material. If there are thermometers, they shall not project directly into the gas
or liquid through the shell.
14 For the definition of "demountable tank" see 1.2.1.
15 The use of metal to metal sealing is not permitted.
Filling and discharge openings situated in the upper part of tanks shall be equipped with, in addition to
what is prescribed in 6.8.3.2.3, a second, external, closing device. This device shall be capable of
being closed by a blank flange or some other equally reliable device.
Safety valves shall meet the requirements of 6.8.3.2.9 to 6.8.3.2.12 below:
Tanks intended for the carriage of compressed or liquefied gases or dissolved gases, may be fitted
with spring-loaded safety valves. These valves shall be capable of opening automatically under a
pressure between 0.9 and 1.0 times the test pressure of the tank to which they are fitted. They shall be
of such a type as to resist dynamic stresses, including liquid surge. The use of dead weight or counter
weight valves is prohibited. The required capacity of the safety valves shall be calculated in
accordance with the formula contained in 6.7.3.8.1.1.
Where tanks are intended for carriage by sea, the requirements of 6.8.3.2.9 shall not prohibit the
fitting of safety valves conforming to the IMDG Code.
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.
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The valves of demountable tanks that can be
rolled shall be provided with protective caps.
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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.