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 a suitable material.
To prevent leakage due to fire, only steel piping and welded joints shall be used between the jacket
and the connection to the first closure of any outlet. The method of attaching the closure to this
connection shall be to the satisfaction of the competent authority or its authorized body. Elsewhere
pipe joints shall be welded when necessary.

 

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 the
tubing as may happen when cutting threads.

The materials of construction of valves and accessories shall have satisfactory properties at the lowest
operating temperature of the portable tank.

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).

Pressure-relief devices

Every shell shall be provided with not less than two independent spring-loaded pressure-relief devices.
The pressure-relief devices shall open automatically at a pressure not less than the MAWP and be
fully open at a pressure equal to 110% of the MAWP. These devices shall, after discharge, close at a
pressure not lower than 10% below the pressure at which discharge starts and shall remain closed at
all lower pressures. The pressure-relief devices shall be of the type that will resist dynamic forces
including surge.

Shells for non-flammable refrigerated liquefied gases and hydrogen may in addition have frangible
discs in parallel with the spring-loaded devices as specified in 6.7.4.7.2 and 6.7.4.7.3.

Pressure-relief devices shall be designed to prevent the entry of foreign matter, the leakage of gas and
the development of any dangerous excess pressure.

Pressure-relief devices shall be approved by the competent authority or its authorized body.

Capacity and setting of pressure-relief devices

In the case of the loss of vacuum in a vacuum-insulated tank or of loss of 20% of the insulation of a
tank insulated with solid materials, the combined capacity of all pressure-relief devices installed shall
be sufficient so that the pressure (including accumulation) inside the shell does not exceed 120% of
the MAWP.

For non-flammable refrigerated liquefied gases (except oxygen) and hydrogen, this capacity may be
achieved by the use of frangible discs in parallel with the required safety-relief devices. Frangible
discs shall rupture at nominal pressure equal to the test pressure of the shell.

Under the circumstances described in 6.7.4.7.1 and 6.7.4.7.2 together with complete fire engulfment
the combined capacity of all pressure-relief devices installed shall be sufficient to limit the pressure in
the shell to the test pressure.

The required capacity of the relief devices shall be calculated in accordance with a well-established
technical code recognized by the competent authority7.

Marking of pressure-relief devices

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