Requirement for the application of composites (fibre reinforced plastic) in ship building:

Composites are the materials of future. They are being widely used in the shipping industry because of their advantageous properties. This article gives the requirement for the replacement of traditional materials with FRP (composites) in ship building.

From a pure manufacturing point of view, steel is the most economical material for the construction of a ship. But considering the life cycle of a ship, the steel structures have to be replaced with new one as they undergo corrosion resulting in weakening its properties. Although its initial installation cost is less compared to FRP (Fibre reinforced Plastic) but steel structures (especially pipelines, ladders, catwalks etc.) will continue to cause costs for operations and maintenance during its usage. 
Moreover, steel structures have to be painted for protecting it from corrosion while the FRP structures do not corrode. But the FRP has its own disadvantages compared to steel. The advantages and disadvantages regarding the physical and chemical properties of FRP compared to steel are discussed later. The reasons that made us to think of switching over to FRP from conventional steel structures are discussed below.

Shipping is the primary mode for international movements of goods, but more than that it is an international business. The ultimate aim of any business is to make profit. We cannot make profit just by increasing the freight rate or decreasing the salary of the workers. It will affect the business. So in shipping the main ways of making profit is to reduce the operational and maintenance cost of the ship and is to reduce the weight of the ship by using composite structures which allows a greater payload for a given size or weight of vessel. They also allow reduced fuel consumption and can achieve higher speeds. Shipping is not a one-time business. The profit is normally calculated based on the life time of the ship. So the calculations shown in this paper are done considering the life cycle of a ship.

Weight Reduction:

The major achieved advantage when changing a traditional steel design in to a composite design is the remarkable reduction of structural weight. The density of FRP is about 1600 kg/m3 while that of steel is about 7800 kg/m3. A feasibility study was done on a large military patrol ship for the Danish Navy with a water line length of 105 m, where one version was designed by using traditional steel and other version was designed as a FRP sandwich design entirely built in carbon fibre according to same principle. When the two different hull concepts were compared it was found that the CFRP-sandwich version gave about 60% weight saving compared to the steel version.

If there is a weight reduction then it leads to reduced power requirement, reduced fuel consumption and thus reduced NOx , SOx and CO2 emissions. So if we can achieve a weight reduction in a cargo ship, then it will allow a greater payload for a given size or weight of vessel.

Patch Repair:

For a merchant ship with steel pipelines and other steel structures, the repair is normally carried out by welding and it is carried out when ship is in harbor or during dry-docking. However in case repairs have to be carried out on pipelines made out of steel on a floating offshore unit (FOUs), it have to be carried out in the field itself and for safety reasons running parts of the vessel would have to be shut down because welding involves hot work. If any system is shutting down then it is a loss of money. Just consider 50 USD per barrel and a FPSO producing 100000 barrels per day. Then shutting down of the vessel for welding work for one day will create a loss of 5 million USD, which is a huge loss.

But in case of a composite, bonded repair can be done. FRP materials use an adhesive joining process which requires no torch or arc welding equipment. The danger from fire or explosion is reduced. Composite material patches are bonded over the defect portion and the integrity of the structure is restored. The patch repair technology can also be utilized to provide upgrades, such as life extensions and higher design requirements.

Indirect Savings:

Indirect savings from FRP structures are more beneficial comparing with the above examples. Earlier the cost of FRP was more than two times than that of steel. But now the competition taken place in industries made its availability at a lower price (.9 to 1.75 times that of steel) and it depends on the quality of the material. 


Even though the cost price is higher, then also savings are made from -

• installation cost (working hour and man power required is less), 
• joining of pipes (no welding works required), 
• corrosion and chemical resistant and paint works are not required. 
• The reduction in weight that allows less fuel consumption and thus less emission to environment. 
• FRP pipelines that have less head loss compared with conventional steel pipelines which in turn allows less consumption of power.

Better Stability:

For ships with many decks (such as cruise vessels) the use of lightweight solutions in the upper decks helps to lower the centre of gravity, thus improving stability and permitting larger height/breadth ratios.

Scrapping:

Disposal of large composite structures used to be a very complex process in earlier times. Its main steps are dismantling, cutting and crushing. However the scrapping of a large composite ship was relatively easy. This can be verified by a scrapping of one of the Danish Standard Flex 300 ships. "The complete scrapping was done in an environmental friendly way in a floating dock and the complete scrapping was made in seven days. The total amount of composite scrap was 150 tons and the metal scrap was 50 tons. The composite scrap, which has high content of energy, was disposed by incineration."

To learn more:

Composites; the new innovation in material science (marine application)

Advantages and disadvantages of FRP in ship building
Properties of FRP (fibre reinforced plastic) composite suitable for marine application
Fibre reinforeced plastic (FRP) pipelines

Source: IndiaStudyChannel.com. Author: Nibil Ibrahim. 10 Mar 2011

http://www.indiastudychannel.com/resources/137545-Requirement-for-Application-Composites-Fibre.aspx