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.

The heating system shall be designed or controlled so that a substance cannot reach a temperature at
which the pressure in the tank exceeds its MAWP or causes other hazards (e.g. dangerous thermal
decomposition).

The heating system shall be designed or controlled so that power for internal heating elements shall
not be available unless the heating elements are completely submerged. The temperature at the surface
of the heating elements for internal heating equipment, or the temperature at the shell for external
heating equipment shall, in no case, exceed 80% of the autoignition temperature (in °C) of the
substance carried.

If an electrical heating system is installed inside the tank, it shall be equipped with an earth leakage
circuit breaker with a releasing current of less than 100 mA.

Electrical switch cabinets mounted to tanks shall not have a direct connection to the tank interior and
shall provide protection of at least the equivalent of type IP56 according to IEC 144 or IEC 529.

Bottom openings

Certain substances shall not be carried in portable tanks with bottom openings. When the applicable
portable tank instruction identified in Column (10) of Table A of Chapter 3.2 and described
in 4.2.5.2.6 indicates that bottom openings are prohibited there shall be no openings below the liquid
level of the shell when it is filled to its maximum permissible filling limit. When an existing opening
is closed it shall be accomplished by internally and externally welding one plate to the shell.

Bottom discharge outlets for portable tanks carrying certain solid, crystallizable or highly viscous
substances shall be equipped with not less than two serially fitted and mutually independent shut-off
devices. The design of the equipment shall be to the satisfaction of the competent authority or its
authorized body and shall include:
(a) An external stop-valve, fitted as close to the shell as reasonably practicable, and so designed as
to prevent any unintended opening through impact or other inadvertent act; and
(b) A liquid tight closure at the end of the discharge pipe, which may be a bolted blank flange or a
screw cap.

Every bottom discharge outlet, except as provided in 6.7.2.6.2, shall be equipped with three serially
fitted and mutually independent shut-off devices. The design of the equipment shall be to the
satisfaction of the competent authority or its authorized body and include:
(a) A self-closing internal stop-valve, that is a stop-valve within the shell or within a welded flange
or its companion flange, such that:
(i) The control devices for the operation of the valve are designed so as to prevent any
unintended opening through impact or other inadvertent act;
(ii) The valve may be operable from above or below;
(iii) If possible, the setting of the valve (open or closed) shall be capable of being verified
from the ground;
(iv) Except for portable tanks having a capacity of not more than 1 000 litres, it shall be
possible to close the valve from an accessible position of the portable tank that is remote
from the valve itself; and
(v) The valve shall continue to be effective in the event of damage to the external device for
controlling the operation of the valve;
(b) An external stop-valve fitted as close to the shell as reasonably practicable; and
(c) A liquid tight closure at the end of the discharge pipe, which may be a bolted blank flange or a
screw cap.

For a lined shell, the internal stop-valve required by 6.7.2.6.3 (a) may be replaced by an additional
external stop-valve. The manufacturer shall satisfy the requirements of the competent authority or its
authorized body.

Safety-relief devices

All portable tanks shall be fitted with at least one pressure-relief device. All relief devices shall be
designed, constructed and marked to the satisfaction of the competent authority or its authorized body.

Pressure-relief devices

Every portable tank with a capacity not less than 1 900 litres and every independent compartment of a
portable tank with a similar capacity, shall be provided with one or more pressure-relief devices of the
spring-loaded type and may in addition have a frangible disc or fusible element in parallel with the
spring-loaded devices except when prohibited by reference to 6.7.2.8.3 in the applicable portable tank
instruction in 4.2.5.2.6. The pressure-relief devices shall have sufficient capacity to prevent rupture of
the shell due to over pressurization or vacuum resulting from filling, discharging, or from heating of
the contents.
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