Containerization

Maximum Gross Weight (MGW)

Container Safety Convention (CSC)

When released for world-wide use, CTU's that conform to the relevant standards are certified and carry a Container Safety Convention Plate. The essential part is shown here, other information might include ownership, a complete list of all loading tests undergone and timber treatment for their wooden floors. What is significant is the Maximum Gross Weight (MGW). When loaded, and presented for lifting, it is best to assume that it is fully laden up to the MGW rating.

An up to date Safety Approval Plate is essential for containers used in international trade and identification plate must be displayed in a prominant place, safe from being damaged. It acts as an international passport, guaranteeing the security of their contents besides being fit for purpose.Information appertaining to strength capacity of the container presented on the plate is covered in great detail in Amendments to the International Convention for Safe Containers of 2 December 1972
Perhaps the most comprehensive source of information for both Cargo Transport Units and CSC plating is available on the GDV link below. Over 17 million containers have accumulated around the world since their introduction, many of which may not be up to date nor even standard, but they may need shifting and when called upon to handle them and there are problems with identification, it would be wise to consult the

Main Transport Unit Types

Standard Series1 Containers

These are by far the most common type of CTU's in use and were the first units to be standardized under the Freight Container Certification Scheme introduced by Lloyd's Register of Shipping in 1968. These are referred to as General Cargo Dry Containers and originally had an 8ft square section so they could pass through railway tunnels and came in lengths of 10ft increments up to a maximum of 40ft.
Gauge Standard Applies to the space envelope defined by the Standard Series1 Container volumes and any cargo that extends beyond their limits is classified as Out of Gauge (OOG).
Nowadays the height is more usually 8ft6in but universally 8ft wide. A variant known as European overland container has an internal width of 8ft making the external width 8ft 6in. Non standard corner fittings are used that allow the the base and top pickup points to correspond to standard ISO dimensions for handling and securing purposes, but standard lifting lugs CANNOT be used in bottom corner fitting apertures with overhanging top flange.

Platforms

This may be carried by various freight units but generally by open topped containers, platforms or flat racks. Depending on the nature of this cargo it is subclassified as Standard OOG where cargo does not extend beyond the space envelopes of the equivalent container type, usually 20ft and 40ft lengths, and Non Standard OOG where it does. Cargo that could be contained but is deemed unsuitable for being enclosed eg fertilizers and uncured animal hides is often carried on platforms as OOG deck cargo.
The example opposite of an OOG lift shows a uniformly distributed loaded 40ft platform with both corner and inboard lifting points (corner castings). The inboard points have 30ft centres, resulting with greater lifting angles and, therefore, lower sling forces. These particular early platforms were very flexible and when fully laden this lifting arrangement, using inboard points rather than the corners, was widely practiced. Modern 40 ft types use end lifting points only on account of their increased rigidity.

Standard Platforms

These come in two standard lengths of 20ft and 40ft and are mainly for OOG cargo. There may be height restrictions on platforms when stowed as deck cargo. Ratings vary from one manufacturer to another but for general use are taken as 25 ton for 20ft unit and 40 ton for 40ft platform. What is paramount for this type of freight conveyor is that loading is central, and any eccentricity of load is not permitted.

Flat Racks

Like platforms these come in two standard lengths of 20ft and 40ft and are also for OOG cargo. These units have evolved to cater for ever increasing cargo profiles but basically have either fixed or collapsable ends. The fixed end types range from rigid corner pillars, topped with top corner fittings, to substantial end panels again with top corner fittings. These flat racks can be lifted by their ends with standard container gantry cranes using twistlocks that couple with top horizontal apperture of corner fittings for vertical lifting only. The collapsable type make it easier to transport because they can be stacked when empty. Their total MGW must obviously be within limits hence need for tare weight to be clearly marked. With both types their top end apertures are blanked of to prevent hooks being used for lifting. In any case they should never be lifted by the top end corner fittings using side lifting lugs but only from the very bottom corners and with slings fitted with spreaders to prevent contact with cargo. The same MGW and loading limitations for platforms also apply to flat racks.

Tank Containers.

These are generally 20ft long, and can be used to carry liquid, gases, dry powder or granules and are usually rated in Litres. When filled with liquids or solids, tanks may present problems when being lifted because of their mobile centre of gravity. There are three types:-
Beam Tank having 27,000 litres capacity for gases only, where the tank acts as a monocoque structure with corner fitting attachments welded to it resulting with low tare weight but limited strength.
Generic Tank. This is by far the most common type where a self contained tank is built into ISO dimensioned rigid frame for maximum protection. Capacity ranges from 17,000 Litres to a maximum of 26,000 Litres but when carrying dry materials Maximum Gross Weight is limited to 33.5ton.
Swap Tanks have an increased capacity of 35,000 Litres and are made for ease of intermodal transfer but being non standard they don't have the same degree of protection as the Generic Tank.

Non-standard Specialised Containment Units.

Not all freight units are ISO Standard Containers, variants have evolved to satisfy the ever changing demands in this industry and many now carry specialised equipment other than freight.