Marking of pressure-relief devices

Every pressure-relief device shall be clearly and permanently marked with the following particulars:
(a) The pressure (in bar or kPa) or temperature (in °C) at which it is set to discharge;
(b) The allowable tolerance at the discharge pressure for spring-loaded devices;
(c) The reference temperature corresponding to the rated pressure for frangible discs;
(d) The allowable temperature tolerance for fusible elements; and
(e) The rated flow capacity of the spring-loaded pressure relief devices, frangible discs or fusible
elements in standard cubic metres of air per second (m3/s);
(f) The cross sectional flow areas of the spring loaded pressure-relief devices, frangible discs and
fusible elements in mm2.
When practicable, the following information shall also be shown:
(g) The manufacturer’s name and relevant catalogue number of the device.

The rated flow capacity marked on the spring-loaded pressure-relief devices shall be determined
according to ISO 4126-1:2004 and ISO 4126-7:2004.

Connections to pressure-relief devices

Connections to pressure-relief devices shall be of sufficient size to enable the required discharge to
pass unrestricted to the safety device. No stop-valve shall be installed between the shell and the
pressure-relief devices except where duplicate devices are provided for maintenance or other reasons
and the stop-valves serving the devices actually in use are locked open or the stop-valves are
interlocked so that at least one of the duplicate devices is always in use. There shall be no obstruction
in an opening leading to a vent or pressure-relief device which might restrict or cut-off the flow from
the shell to that device. Vents or pipes from the pressure-relief device outlets, when used, shall deliver
the relieved vapour or liquid to the atmosphere in conditions of minimum back-pressure on the
relieving devices.

Siting of pressure-relief devices

Each pressure-relief device inlet shall be situated on top of the shell in a position as near the
longitudinal and transverse centre of the shell as reasonably practicable. All pressure-relief device
inlets shall under maximum filling conditions be situated in the vapour space of the shell and the
devices shall be so arranged as to ensure the escaping vapour is discharged unrestrictedly. For
flammable substances, the escaping vapour shall be directed away from the shell in such a manner that
it cannot impinge upon the shell. Protective devices which deflect the flow of vapour are permissible
provided the required relief-device capacity is not reduced.

Arrangements shall be made to prevent access to the pressure-relief devices by unauthorized persons
and to protect the devices from damage caused by the portable tank overturning.

Gauging devices

Glass level-gauges and gauges made of other fragile material, which are in direct communication with
the contents of the tank shall not be used.

Portable tank supports, frameworks, lifting and tie-down attachments

Portable tanks shall be designed and constructed with a support structure to provide a secure base
during carriage. The forces specified in and the safety factor specified in shall be
considered in this aspect of the design. Skids, frameworks, cradles or other similar structures are

The combined stresses caused by portable tank mountings (e.g. cradles, framework, etc.) and portable
tank lifting and tie-down attachments shall not cause excessive stress in any portion of the shell.
Permanent lifting and tie-down attachments shall be fitted to all portable tanks. Preferably they shall
be fitted to the portable tank supports but may be secured to reinforcing plates located on the shell at
the points of support.

In the design of supports and frameworks the effects of environmental corrosion shall be taken into

Forklift pockets shall be capable of being closed off. The means of closing forklift pockets shall be a
permanent part of the framework or permanently attached to the framework. Single compartment
portable tanks with a length less than 3.65 m need not have closed off forklift pockets provided that:
(a) The shell including all the fittings are well protected from being hit by the forklift blades; and
(b) The distance between the centres of the forklift pockets is at least half of the maximum length
of the portable tank.
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