All openings with a diameter of more than 1.5 mm in shells of portable tanks, except openings for
pressure-relief devices, inspection openings and closed bleed holes, shall be fitted with at least three
mutually independent shut-off devices in series, the first being an internal stop-valve, excess flow
valve or equivalent device, the second being an external stop-valve and the third being a blank flange
or equivalent device.

When a portable tank is fitted with an excess flow valve, the excess flow valve shall be so fitted that
its seating is inside the shell or inside a welded flange or, when fitted externally, its mountings shall be
designed so that in the event of impact its effectiveness shall be maintained. The excess flow valves
shall be selected and fitted so as to close automatically when the rated flow specified by the
manufacturer is reached. Connections and accessories leading to or from such a valve shall have a
capacity for a flow more than the rated flow of the excess flow valve.

For filling and discharge openings, the first shut-off device shall be an internal stop-valve and the
second shall be a stop-valve placed in an accessible position on each discharge and filling pipe.

For filling and discharge bottom openings of portable tanks intended for the carriage of flammable
and/or toxic non-refrigerated liquefied gases or chemicals under pressure the internal stop-valve shall
be a quick closing safety device which closes automatically in the event of unintended movement of
the portable tank during filling or discharge or fire engulfment. Except for portable tanks having a
capacity of not more than 1 000 litres, it shall be possible to operate this device by remote control.

In addition to filling, discharge and gas pressure equalizing orifices, shells may have openings in
which gauges, thermometers and manometers can be fitted. Connections for such instruments shall be
made by suitable welded nozzles or pockets and not be screwed connections through the shell.

All portable tanks shall be fitted with manholes or other inspection openings of suitable size to allow
for internal inspection and adequate access for maintenance and repair of the interior.

External fittings shall be grouped together so far as reasonably practicable.

Each connection on a portable tank shall be clearly marked to indicate its function.

Each stop-valve or other means of closure shall be designed and constructed to a rated pressure not
less than the MAWP of the shell taking into account the temperatures expected during carriage. All
stop-valves with a screwed spindle shall close by a clockwise motion of the handwheel.
For other stop-valves the position (open and closed) and direction of closure shall be clearly indicated.
All stop-valves shall be designed to prevent unintentional opening.

Piping 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 525 °C. The joints shall not decrease the strength of tubing as
may happen when cutting threads.

The burst pressure of all piping and pipe fittings shall be not less than the highest of four times the
MAWP of the shell or four times the pressure to which it may be subjected in service by the action of
a pump or other device (except pressure-relief devices).

Ductile metals shall be used in the construction of valves and accessories.

Bottom openings

Certain non-refrigerated liquefied gases shall not be carried in portable tanks with bottom openings
when portable tank instruction T50 in 4.2.5.2.6 indicates that bottom openings are not allowed. There
shall be no openings below the liquid level of the shell when it is filled to its maximum permissible
filling limit.
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