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.

Pressure-relief devices

Portable tanks shall be provided with one or more spring-loaded pressure-relief devices. The pressurerelief
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 a type that will resist dynamic forces including liquid
surge. Frangible discs not in series with a spring-loaded pressure-relief device are not permitted.

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.

Portable tanks intended for the carriage of certain non-refrigerated liquefied gases identified in
portable tank instruction T50 in 4.2.5.2.6 shall have a pressure-relief device approved by the
competent authority. Unless a portable tank in dedicated service is fitted with an approved relief
device constructed of materials compatible with the load, such device shall comprise a frangible disc
preceding a spring-loaded device. The space between the frangible disc and the device shall be
provided with a pressure gauge or a suitable tell-tale indicator. This arrangement permits the detection
of disc rupture, pinholing or leakage which could cause a malfunction of the pressure-relief device.
The frangible discs shall rupture at a nominal pressure 10% above the start-to-discharge pressure of
the relief device.

In the case of multi-purpose portable tanks, the pressure-relief devices shall open at a pressure
indicated in 6.7.3.7.1 for the gas having the highest maximum allowable pressure of the gases allowed
to be carried in the portable tank.

Capacity of relief devices

The combined delivery capacity of the relief devices shall be sufficient that, in the event of total fire
engulfment, the pressure (including accumulation) inside the shell does not exceed 120% of the
MAWP. Spring-loaded relief devices shall be used to achieve the full relief capacity prescribed. In the
case of multi-purpose tanks, the combined delivery capacity of the pressure-relief devices shall be
taken for the gas which requires the highest delivery capacity of the gases allowed to be carried in
portable tanks.

To determine the total required capacity of the relief devices, which shall be regarded as being the
sum of the individual capacities of the several devices, the following formula5 shall be used:

Insulation systems, used for the purpose of reducing the venting capacity, shall be approved by the
competent authority or its authorized body. In all cases, insulation systems approved for this purpose
shall:
(a) Remain effective at all temperatures up to 649 °C; and
(b) Be jacketed with a material having a melting point of 700 °C or greater.

Marking of pressure-relief devices

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