Benefits of intermodal transport
The use of tank containers for your bulk transportation needs offers many advantages. Tank containers are safe, durable and very cost-effective. They can be easily stored, in a loaded or empty condition, and they offer secure door-to-door transport. Tank containers can be used to transport all types of powders and non-hazardous or hazardous liquids including liquefied gases, flammables, corrosives, and toxics.
Tank containers have the added benefit of eliminating the risk associated with transferring a product from one vessel to another. They protect your product integrity from production phase to consumption phase.
Intermodal tanks, also referred to as ISO tanks, tank containers, or IMO portable tanks, are designed for international transportation by road, rail and ship. They are bulk containers for liquids and powders that can be lifted from one transportation mode to another. Intermodal tanks provide the flexibility of using various transportation modes such as truck, rail, and water. This modal flexibility provides for extremely safe and cost-effective transportation.
An intermodal portable tank consists of a single, cylindrical vessel (the tank body) within a rectangular steel framework. The frame is built according to International Standards Organisation (ISO) specifications.
The most common frame sizes range from 20ft to 30ft. The typical container height is 8 ft and 6 inches, and standard width is 8 ft. The frame design must meet strict standards, including stacking, longitudinal and lateral inertia.The tank design, which varies according to the commodity and customer’s specification, must also meet specified requirements. These standards are determined by a number of national and international government agencies. The weight of an empty tank container generally varies between 3000 and 5000 kg.
The tank body is usually built from stainless steel, carbon steel or aluminium and has one or more loading openings at the top (manholes), and usually one central discharge opening at the bottom. Safety valves avoid excessive pressure build up inside the tank shell, whilst triple closures (a combination of a foot valve, a product valve and a drip cap) avoid undesirable leakages of the loaded product during transit. Tank containers are usually discharged using ordinary air pressure (average pressure of 2 bar) to push out the loaded product. Products with high flashpoints are discharged using a pump, whilst vapour return lines are used to avoid any air contamination during the loading and discharge process. Many tanks are insulated by a variety of materials to maintain the temperature of the carried product.
More technical information can be found here.
International government agencies like Lloyds, Bureau Veritas, ABS London and Apragaz cover the manufacture, inspection and maintenance of tank containers, by specifying strict regulations. Tank containers are subjected to a number of tests relating to the structure and other elements.
Some examples of these tests are:
- Stacking test
- Lifting by the top and bottom corner fittings
- Impact test
- Pressure test
- Air test
- Water test
- Inspection of all welding
Each tank is initially tested immediately after construction. The tank is then supplied with an initial construction certificate and a printed calibration chart for the full contents of the tank. Official tests are repeated on a regular basis, depending on the type of tank and its length of service, to ensure maximum safety of the tank container. The air test for example, to see whether the tank is still completely airtight, is repeated every two and a half years. However, quality tank container operators, including Huktra, conduct these tests more regularly, to increase safety even further. After each test the construction certificate is renewed in the form of an approval certificate.
First signs of intermodal transport are generally traced back to experiments by Malcolm McLean (at that time working for the McLean trucking company and later SeaLand) in 1956. The first experiments involved loading some 35ft road trailers onto a vessel rather than unloading the contents of the trailer and loading these on the vessel by traditional cargo sling methods.
McLean’s experiment quickly showed that there was no need to take the wheels along and that more efficient stowage and handling methods were available if only the box part of the trailer was hauled aboard ship. This led to the separate container and chassis units, and to the standards for container size and handling equipment that remain in use to this day.