Liquid Cargo Vessels The Types and Methods Of Transportation

Liquid Cargo Vessels: The Types & Methods Of Transportation

by Manish Singh
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The means to transport liquid cargo vary. In ship chartering, it is important to find the right vessel.

Liquid cargo vessels are generally called tankers. In the mid-nineteenth century tankers were first developed. Like bulk carriers, the size of tankers has grown over the years. Now the largest deadweight or carrying capacity is more than 400,000 tons.

Tankers have a variety of tanks combined as one. Liquid cargo is pumped using a set pipeline system. Larger modern tankers have segregated ballast tanks. These enable them to stay low in the water even when the tankers are empty on their return journey. This improves overall stability. Some tankers have systems where the tanks are filled with inert gas. This reduces the risk of explosion or fire.

Types of liquid cargo vessels

Large crude oil tankers are divided into the following types:

Aframax

An Aframax is a medium-sized crude tanker. They have a range of 80,000 to 120,000 deadweight tonnage. The vessel got its name from AFRA ((Average Freight Rate Assessment), created by Shell Oil in 1954 to standardise contract terms. Compared to other cargo vessels like VLCC and ULCC, Aframax is relatively smaller and can carry cargo between 70,000 to 100,000 metric tonnes. Aframax tankers are capable of serving more ports because of their smaller size. They are suitable for places where there are no large ports or oil terminals offshore. Aframax tankers are an effective solution for transporting crude oil in small quantities.

Countries with lower crude oil production, such as Non-OPEC countries may choose Aframax tankers. This is because these countries don’t have canals and large harbours to accommodate ULCC and VLCC tankers. Some of such main areas of operations are North African exports to Southern Europe via the Mediterranean, South American oil cargo exports to the Gulf region of the US via the Caribbean and South East Asian exports to the Far East.

Suezmax

The Suezmax is named after the Suez Canal. They are typically medium to large-sized vessels. They have a deadweight tonnage of around 120,000 to 200,000. They can pass through the Suez Canal when laden. Before 1967, there was an 80,000 DWTrestriction on the size of the vessel that could pass through the canal. Later in 1975, this was increased to 150,000 DWT. A Suezmax of 200,000 DWT or more can now pass through the canal if its depth is between 18m to 20.1m. In the coming years, the size of Suezmax vessels may change as there are future plans to deepen the draft of the canal.

Very Large Crude Carrier (VLCC)

The Very Large Crude Carrier or VLCC is a large carrier with a deadweight tonnage of 180,000 to 320,000. They are built to smoothly pass through the Suez Canal. For the same reason they are used frequently around the Mediterranean, North Sea and West Africa. These ships can operate at ports that have low depth. They have the flexibility of using different terminals. These ships are larger in size with a length of around 470m, a width of 60m and a draught of around 20m.

Ultra Large Crude Carrier (ULCC)

Ultra Large Crude Carriers or ULCC are the largest shipping vessels in the world. They come in different sizes right from the deadweight tonnage of 320,000 to 500,000 and need to have custom terminals built due to their larger sizes. ULCCs can only enter the limited number of ports that have the necessary facilities to accommodate them. They are typically used for long-distance transportation of crude oil from the Gulf of Persia to Asia, Europe and North America. These are the largest vessels and have a length of 415 meters, a width of 63 meters and a draught of 35 meters.

Different Ways to transport liquid cargo

ISO tank

ISO tanks are best for transporting large volumes of liquid cargo. ISO tanks are available in the size of 20’ and 23’. The former can carry 5,300 – 6,900 gal., or 20,000 – 26,000 litres of materials and the latter can carry 8,700 gal., or 33,000 litres. An ISO tank can ship and carry a wide variety of liquid cargo and non-hazardous and hazardous materials in liquid, powder or gas form. This is possible with an ISO tank as it is made up of anti-corrosive materials or strong steel which protects the liquid throughout the transport.

The tank must be filled to a maximum of 80% – 95% of its capacity. If it is filled to more than 95% there will be no scope for achieving thermal expansion ( “ullage”). Conversely, if the tank is kept below 80% of its capacity during transit it may surge in a dangerous manner.

Pros

  • It is reusable
  • Can be used to ship hazardous and non-hazardous materials
  • Can be used for ocean, rail and road transport
  • Has a large capacity

Cons

  • Higher costs
  • High dependency on the return of cargo
  • Repositioning of costs

Intermediate bulk containers

Intermediate Bulk Containers are industrial containers in reusable form that are used for transporting bulk granular and liquid substances like food ingredients, chemicals, pharmaceuticals and solvents. These containers are easy to mount on pallets and to be stacked. This means they can be easily moved using a pallet jack or forklift.

These containers can hold around 200 – 1250 litres of cargo. The capacity of these containers is between drums and tanks, and so are deemed as “Intermediate”. There is no need to transfer cargo from a container to another storage tank as it comes with loading and discharging points on top and side.

Pros

  • Can be easily moved
  • Handling and storage space costs are lower.
  • Containers & liners can be Food Contact and FDA approved

Cons

  • Time-consuming refilling process
  • Working cost may be high
  • Logistics space can be difficult to manage.

Barrels / drums

Barrels and drums are available in different types. They may be steel, fibre or plastic. Each will need coating or lining for food hygiene safety and strapping and pallet for safety. Drums are available in different volumes from 20 to 250 litres. This may be a good option for shipping lower volumes of liquid. These ships can be UN Certified and so can be used to ship hazardous materials. However, drums can be tough to handle in terms of storage, safety, and movement.

Pros

  • Can be easily transported
  • Drums can be stacked on pallets easily because of their standard size.
  • Can be used for moving hazardous materials

Cons

  • Refilling is a time-consuming process
  • Packing and working costs are high
  • It is important to have enough space to store drums even when they are empty.

Flexitank

Flexitanks are developed from a special plastic material with a capacity of 25,000 litres. These tanks are placed inside containers of standard size 20’. Just like the ISO tank, the flexitank must be filled up to 24-25 tonnes to keep it within its maximum allowed pressure limits. The walls may rupture if overloaded. Conversely, if underloaded, there are chances of leakages. Weighing jacks can optimise the weight of the flexitank.

Flexitanks can only be used to transport non-hazardous materials. They may be used for moisture and oxygen, sensitive products like flat beer, wine and chemicals.

Pros

  • Faster loading and unloading
  • Empty tanks face low storage costs.
  • No cargo contamination
  • The low weight of equipment enables maximized payload
  • Packing methods are less expensive.

Cons

  • Cannot be reused
  • Cannot be used for hazardous materials
  • Cannot be used for transportation through railways.
  • Must be insured for specific purpose

Summary

Transportation of liquid cargo is always a challenge. The right cargo container solution must be used to transport cargo from a location to another.