Please note this is not a definitive guide for the unloading or loading of an ISO Tank Container. This is just an overview of the procedure and is provided purely for interest.
When loading or unloading an ISO tank container, the methods used will vary by type of cargo.
Overview of procedures
Loading noxious or cargoes that yield hazardous vapours
For noxious or cargoes that yield hazardous vapours, loading or unloading through the top or bottom outlet may be necessary. To prevent any vapours escaping, the process uses a ‘closed loop’ system whereby any gases or vapours are returned to the storage tank via a vapour return line that is fitted between the container’s airline connection and the storage tank.
Cargoes that cannot be contaminated by water vapour or oxygen
For cargoes that cannot be contaminated by water vapour or oxygen, these can be loaded through the top or bottom outlet. Prior to loading, all air within the container should be purged. Once filled, the cargo should then be carried under a blanket of an inert gas.
For cargoes that foam or are susceptible to oxidation
This type of cargo should be loaded through the bottom outlet. If not possible then, use the top outlet and siphon tube.
Measuring the quantity of cargo loaded can be done using a flow meter, by use of the dipping rod or via a weighbridge. Dip rods should never be used with hazardous cargoes and those loaded using the ‘closed loop’ system.
Types of loading
Product is loaded in to the ISO tank container from an overhead storage tank through the manlid. For a closed loop system using gravity, the container must be loaded through the top or bottom outlets with the vapours being returned to the supply tank via the airline connection.
Using this method, the cargo is pumped in to the tank through either the manlid, or top and bottom connection. If the cargo requires that closed loop system, vapours are vented back to the storage container via the airline.
In general, tanks must be filled to not less that 80% of their capacity so that any dangerous surge or swell during transport is avoided.
Also, tanks must not be filled to 100% of their capacity. There must be sufficient ullage space left and this must be determined based on the thermal expansion of the product being transported.
Some dangerous products can only be carried in tanks that have no openings below the surface level of the liquid with the product being discharged through the syphon pipe by either pressure of pumping.
General safety points
There is always a pressure difference between a closed tank and atmosphere so, all valves should be opened very carefully and pressure within the tank must always be relieved before opening the manlid. When using the bottom outlet, always open and close the foot valve first.
Before discharging or filling check all valves that aren’t being used are closed and if loading through the manlid, secure the hose as close as possible to the manlid to stop any possible hose whiplash and to stop the hose coming in to contact with the tank surface.
Always earth the container to a local earthing point before making any other connections.