Safe Handling of Tank Containers - ITCO

ICHCA International Safety Panel Briefing Pamphlet No 30
6.2.4 Pressure Relief Valves
6.2.4.1 Pressure (or combined pressure / vacuum valves) provide safety against
over or under pressurisation conditions in the tank shells. Where the
container is carrying certain specified dangerous goods the pressure relief
valve is fitted with a secondary security feature, the frangible disc, which
prevents an accidental release of the cargo’s vapour.
6.2.4.2 The degree of filling requirements (see Annex 2 section A2.2) ensures that
there is always a vapour space at the top of the pressure vessel so that the
pressure relief valve is exposed to the vapour only.
6.2.4.3 The pressure relief valve is protected from swipe damage by the spill box
where fitted.
6.2.5 Airline Valves
6.2.5.1 When not in use airline valves are blanked or capped off to prevent
accidental operation of the valve.
6.2.5.2 The airline valve is protected from swipe damage by the spill box where
fitted.
6.2.6 Top Discharge Openings / Valves
6.2.6.1 When not in use top discharge openings and valves are blanked off to
prevent accidental operation of the valve.
6.2.6.2 The top discharge fittings are protected from swipe damage by the spill box
where fitted.
6.2.7 Bottom Discharge Valves
6.2.7.1 The bottom discharge valve comprises of two or more separate and serial
closure methods as described in section 5.4.1. All pressure vessels are
fitted with an internal foot valve that can retain the contents of the pressure
vessel without any additional closure. External valve devices, such as the
ball or butterfly valves which provide the secondary closure device, are
attached to the pressure vessel using fittings that are designed to fail without
damaging the pressure vessel.
6.2.7.2 It is of great importance that containers
carrying hazardous cargoes are fitted with
the correct bottom discharge valve
combinations. The internal foot valve must
be fitted and closed during transport
otherwise damage to the external valves
can result in the cargo being accidentally
discharged. Picture 44 shows an example
where the internal valve should retain the
cargo following the shear section breaking.
Picture 44
Note: Should a shear force be applied to the bottom discharge assembly
there is a risk that a small quantity of the cargo may be released.
Therefore when handling tank containers every effort should be
made to ensure that the tank container is landed on level surface
free from objects that are likely to damage the bottom valve
assembly.
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