Section: 11 CARGO OPERATIONS - Univan

Univan Ship Management Limited Issue 1 REV 0 Page
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FLEET OPERATION MANUAL Date 01.01.2005
CONTAINER TYPES AND ASSOCIATED PROBLEMS
11.7.9 Tank Containers.
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SECTION 11.7
The tank container is a pressure vessel mounted in a frame, the latter of which determines
compatibility with standard dimensions. Tanks are cylindrical, but materials, linings and fittings
vary. The specifications of the shell and fittings determine the class of the tank and thus the type
of product it can carry. The frame is designed to support the tank when fully loaded, and there are
two different designs. The Frame Tank is a full frame with side rails connecting between end
frames, and the Beam Tank has only end frames. The latter has a lower tare weight and thus
higher payload capacity. Capacities generally range from 15,000 to 27,000 litres. A filling
port/manhole is positioned on the top of the tank, and a dip rod with calibration scale is provided.
Other fittings include a pressure/relief valve to protect the tank against over pressure or a
pressure valve to protect against excess external pressure, airline connections for pressuring the
tank during discharge/testing or vapour recovery, and a discharge pipe, valve and cap at the
bottom rear end. Loading and discharge may be via a top outlet valve connected to a vertical
siphon pipe.
Heating systems, either steam or electric, can be fitted, and are commonly capable of maintaining
temperatures up to 110°C. Insulation is usually in the form of expanded polyurethane. Tanks
capable of carrying dangerous cargoes conform to IMO requirements and are classed according
to how hazardous the cargo is and whether it is a liquid or gas. Food grade tanks are commonly
referred to as "Type O" tanks, which are suitable for the carriage of food stuffs intended for
human consumption (some alcohol/spirits may fall within IMO dangerous goods requirements).
These tanks and their fittings are usually constructed with stainless steel, and have highly
polished smooth interiors to avoid crevasse collection of contaminants.
Problems peculiar to this type of container include cargo contamination. Most tanks, particularly
food grade ones, are used for a single product, and some shippers even have their own
dedicated tanks for certain grades. Where this is not the case, there are particular risks of
contamination from previous cargoes and this usually arises where tanks are not cleaned
properly or their interior surfaces have deteriorated. Contamination can also result where
incorrect cleaning agents are used. Particularly with regard to food, it is important that the tank is
certified by a qualified surveyor as fit with regard to bacteria levels, odour, cleanliness and
sterilisation, etc. Fittings are another source of contamination, like for instance hoses and
connections, as is the air used in loading, discharging or blanketing operations. Whilst spillage is
not very common, it can and does occur, mostly via leaky valves and fittings. In order to guard
against this, valid pressure test certificates should be sighted. Leakage may also come about by
inadvertent valve operation and in order to guard against this seals should be fitted and the tank
clearly marked "loaded". Improper carriage on forklift trucks can result in accidents, the surge of
the cargo within the tank leading to toppling, most commonly when the tank is being transported
too fast and/or too far above the ground. Stability problems can also be encountered on other
vehicles, particularly when excessive cargo surge results from large ullages.
11.7.10 Open-sided containers.
Another variation on the standard general purpose container design is the open-sided container,
which as the name implies has no sides, only a base, roof and ends. The sides can be closed by
full height gates and/or curtains (usually nylon-reinforced PVC).
A common problem with this type of containers is the loss of cargo through shifting. The gates are
not usually designed to IMO transverse strength requirements, and accordingly, care