Minimum shell thickness
The minimum shell thickness shall be the greater thickness based on:
(a) The minimum thickness determined in accordance with the requirements in 126.96.36.199; and
(b) The minimum thickness determined in accordance with the recognized pressure vessel code
including the requirements in 188.8.131.52.
The cylindrical portions, ends (heads) and manhole covers of shells of not more than 1.80 m in
diameter shall be not less than 5 mm thick in the reference steel or of equivalent thickness in the steel
to be used. Shells of more than 1.80 m in diameter shall be not less than 6 mm thick in the reference
steel or of equivalent thickness in the steel to be used.
The cylindrical portions, ends (heads) and manhole covers of all shells shall be not less than 4 mm
thick regardless of the material of construction.
The equivalent thickness of a steel other than the thickness prescribed for the reference steel
in 184.108.40.206.2 shall be determined using the following formula:
In no case shall the wall thickness be less than that prescribed in 220.127.116.11.1 to 18.104.22.168.3. All parts of the
shell shall have a minimum thickness as determined by 22.214.171.124.1 to 126.96.36.199.3. This thickness shall be
exclusive of any corrosion allowance.
When mild steel is used (see 188.8.131.52), calculation using the formula in 184.108.40.206.4 is not required.
There shall be no sudden change of plate thickness at the attachment of the ends (heads) to the
cylindrical portion of the shell.
Service equipment shall be so arranged as to be protected against the risk of being wrenched off or
damaged during handling and carriage. When the connection between the frame and the shell allows
relative movement between the sub-assemblies, the equipment shall be so fastened as to permit such
movement without risk of damage to working parts. The external discharge fittings (pipe sockets,
shut-off devices), the internal stop-valve and its seating shall be protected against the danger of being
wrenched off by external forces (for example using shear sections). The filling and discharge devices
(including flanges or threaded plugs) and any protective caps shall be capable of being secured against
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.