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ICHCA International <strong>Safe</strong>ty Panel Briefing Pamphlet No 30<br />
purpose <strong>of</strong> cooling the pumps down and for diverting the liquefied gas flow<br />
through the pump itself.<br />
5.6.5 Pressure Bleed Valves<br />
5.6.5.1 <strong>Tank</strong> containers are built to a given pressure rating which is linked to its<br />
“holding time” (see Annex 1 Definitions). Although every precaution possible<br />
is taken to reduce the ingress <strong>of</strong> ambient heat into the tank shell, some<br />
heating from ambient sources will occur leading to boiling <strong>of</strong> a small amount<br />
<strong>of</strong> the liquid and consequential pressure rise (which should be well within the<br />
capacity <strong>of</strong> the shell to withstand). Most T75 tank containers are fitted with<br />
a special automatic bleed valve to allow this low level pressure to drain<br />
away during transport. It may be switched on and <strong>of</strong>f manually. When<br />
switched <strong>of</strong>f, this minor rise in pressure is not automatically drained <strong>of</strong>f.<br />
The latest edition <strong>of</strong> the IMDG Code in force at the time <strong>of</strong> preparation <strong>of</strong> this<br />
pamphlet does not contain any restriction concerning leaving the valve in an<br />
operational condition though it is possible to interpret paragraph 7.1.8.1.3 <strong>of</strong><br />
the IMDG Code to mean that this valve should be closed when T75 tank<br />
containers are carried on board sea-going vessels.<br />
5.6.6 Vacuum Connection<br />
5.6.6.1 There will be a connection on the outer surface <strong>of</strong> the vacuum jacket to<br />
which gauges may be temporarily attached to measure the vacuum level<br />
and/or to attach a pump to draw a near perfect vacuum between the jacket<br />
and the shell. The location <strong>of</strong> this connection will varies from design to<br />
design.<br />
5.6.7 Formation <strong>of</strong> Ice on Fittings and Pipework<br />
5.6.7.1 It is possible for ice to form on fittings and pipework on T75 tank containers<br />
even in the hottest and most arid <strong>of</strong> conditions. The formation <strong>of</strong> ice in this<br />
way is not necessarily an indication that the tank container is leaking. The<br />
ice is formed from water vapour in the air condensing on the pipework, etc.<br />
5.7 Fixtures<br />
5.7.1 Walkways<br />
5.7.1.1 A light weight walkway usually constructed <strong>of</strong> perforated aluminium plate is<br />
<strong>of</strong>ten fitted on top <strong>of</strong> tank containers. It can be held in place by connections<br />
to one or both <strong>of</strong> the top side rails or to brackets attached to the end frame<br />
and pressure vessel.<br />
5.7.1.2 Where the tank container is fitted with a walkway or access platform on top<br />
<strong>of</strong> the tank container. It should be <strong>of</strong> adequate dimensions in a single plane<br />
and with no tripping hazards and constructed <strong>of</strong> a non slip surface material<br />
allowing suitable drainage.<br />
5.7.1.3 <strong>ITCO</strong> recommends that it should be at least 460mm wide with slope less<br />
than 10° and be positioned to give safe access to the manway lid and<br />
sampling areas. Those tank containers that have a small diameter shell and<br />
require step down to access such areas should also have adequate flooring<br />
at the lower level.<br />
Note: The walkway and supporting structure, including top side rails, are<br />
lightweight and only designed to support two persons. Over<br />
crowding the walkway or excessive loading can result in it failing<br />
with a severe risk <strong>of</strong> personnel falling.<br />
Page 20 ©ICHCA International Limited
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