Applications of Carbon fibers on Submarines, air cushion vehicle and oil exploration

Submarines: Two submarines capable of diving to a depth of 6000m were constructed using a sandwich construction of a special syntactic core and carbon fiber prepreg, to withstand the extreme pressures and were used to enable underwater shots when making the film Titanic.

Air cushion vehicle: Aker Finnyards oy used a foam sandwich structure, utilizing an epoxy resin infusion process with carbon fiber reinforcement to make the superstructure of a prototype air cushion vehicle.

Oil exploration: The US Department of the Interior has depicted the types of deepwater development systems basically into two categories:

  1. Bottom supported and vertically moored structures
  2. Floating production and subsea systems

A brief description of each type is given to better understand how cfrp can be used in their construction.

  1. Fixed platform- a jacket comprising a tall tubular steel vertical section supported by piles driven into the seabed, with the crew accommodated on a platform and operation capability at depths up to 460m.
  2. Compliant Tower- built to withstand large lateral forces and normally operates at 305-610m.
  3. Tension leg platform- a floating structure held in place by tensioned tendons securely fixed with templates to the seabed. As long as vertical motion is limited, it can operate up to 1220m.
  4. Mini-tension leg platform- a low cost mini-tension leg platform, it can also be used as a satellite for early deepwater production.
  5. SPAR platform- large diameter single vertical cylinder equipped with a deck, three types of riser and a hull moored with 6-20 taut catenary systems fixed to the seabed. It is presently used at 915 m but could be extended to 2285m.
  6. Floating Production System- a semi-submersible unit anchored with wire rope and chain. The surface deck receives oil from production risers designed to accommodate platform motion and used at a water depth of 185-2285m.
  7. Subsea system- sends oil to an FPS or TLP system and can be used in water depths greater than 1525m.
  8. Floating production, Storage and offloading system- a large tanker type vessel moored to the sea floor. Periodically, it offloads to a smaller shuttle tanker.

The oil industry is now showing great interest in deepwater production in areas like the Gulf of Guinea, Brazil and the Gulf of Mexico, where the most promising production is at a depth of 1220m. The deposits are vast and although initial investment is very large, the cost of the recovered oil is cheaper than shallow water operations. Petrobras/ RB Falcon has reached a depth of 2777m in the Brazil location and obviously, as depth increases, the risk factor becomes greater and the oil companies will require smart systems, which can be built into composite structures. As the water depth increases, cfrp risers, tendons and rig elements offer considerable savings over conventional materials. The standard platform installation is not suitable and would be extremely costly to modify. A tension leg platform, using carbon fiber composite cables at tethers, becomes cost competitive in water deeper than 1600m.

Automated Dynamics corporation have used PES and PEEK /carbon fiber thermoplatstic prepreg for the manufacture of high temperature pipe and down hole components.

Deepwater composites, a joint venture between Aker Knaerner and Conocophillips, produces comptether, carbon fiber reinforced 6mm diameter pultruded rods for use as tethers in part of the mooring system used for tension let platforms. About 781 rods bundled together into 13 strands of 85 or 31 rods were used. To facilitate spooling, the assembled tendon, strands and profiles are given a helical twist during the assembly process.

Spencer composites have used filament winding to fabricate drilling risers about 15m long and 560mm diameter, by overwinding carbon fiber and fiber glass onto Ti tubing, costing 40% less, weighing 20% less and with an expected fatigue life some three times that of the Ti tubing it is replacing.

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