Safe Handling of Tank Containers - ITCO

ICHCA International Safety Panel Briefing Pamphlet No 30
5.3.1.6 The number of swing bolts or flange bolts varies from type to type and the
pressure rating of the tank. However when they are fully tightened they
should form a pressure tight seal that will contain a pressure greater than
the test pressure of the tank.
5.3.1.7 Where bolts are used in place of studs and nuts to secure the bolted
manway lid care needs to be taken at the time of manufacture, maintenance
and periodic testing to ensure that the bolts used are of the correct length so
that they may be fully tightened.
Note 1: See Annex 6 for more information on manway lid operation
Note 2: Once the container has been filled, opening the manway hatch / lid
is generally not required until the tank container arrives at its
destination.
Note 3: Many tanks have vacuum relief valves that are not sized to allow
tanks to be discharged without opening the manway or other
fittings. If a tank container needs to be opened, this must be carried
out by a suitably qualified person.
5.3.2 Pressure Relief Valves
5.3.2.1 In general all tank containers whether
they are designed for dangerous or non
regulated goods are fitted with one or
more spring loaded pressure relief
valves which comply with the
recommendations for their design, set
pressures and venting capacity set forth
in the United Nations
Recommendations on the Transport of
Picture 19
Dangerous Goods - Model Regulations
(Orange Book). The pressure relief valves (see Picture 19) are fitted in the
top space of the shell as close to the longitudinal and lateral centre so that
they always remain in contact with the gas or vapour even during the
extremes of bad weather.
5.3.2.2 Pressure relief valves can come in two forms:
5.3.2.2.1 Valves may be high pressure only to prevent a build up of pressure that
may result in the tank exploding, or,
5.3.2.2.2 Valves may be “twin acting” in that they are designed to relieve both
excess pressure and to provide vacuum-relief in case partial vacuum
conditions arise in the shell. The vacuum relief ensures that the tanks will
not implode due to low pressure.
5.3.2.3 Vacuum relief valves are also fitted on tanks that normally operate at
atmospheric pressure to protect the tank against, for example, the effect of
low ambient temperature that may cause a reduced internal pressure.
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