Composites Alive And Well In Offshore Oil Applications
The petroleum industry is moving forward with many interesting projects that will increase composite demand.
By Sara Black, Technical Editor | March 2006
Dozens of potential apps will consume composites
Pipelines are not the only means of petroleum product transport under consideration. Trans Ocean Gas Inc. (St. Johns, Newfoundland, Canada) has a new concept — transporting compressed natural gas (CNG) by ship in large composite pressure bottles or tanks. A $1.5 million joint industry project (JIP) involving Trans Ocean Gas, Composites Atlantic Ltd. (Lunenberg, Nova Scotia, Canada), certification society Det Norske Veritas and several other parties are currently verifying the technology for certification. "About half of the world's discovered natural gas is considered 'stranded,' or beyond the economical limit of a pipeline, and most is located offshore," says Trans Ocean Gas president Steven Campbell. "CNG transport by ship will allow stranded gas to be economically gathered and delivered to market."
Source: Fiberspar
Manufacture of bonded composite spoolable pipe includes orbital filament winding.
While the company is mum on specific fabrication and material details, the concept involves filament winding large, cylindrical, fiberglass-reinforced pressure tanks as long as 12m/40 ft, with thermoplastic liners and stainless steel fittings on both ends. They will be placed upright in modular "cassettes" holding from 16 to 25 tanks, and connected to upper and lower piping manifolds for ease of filling and draining. Cassettes will be permanently installed and transported in container ship hull forms, says Campbell. Pressure will range between 10 Mpa and 25 MPa (1,450 psi and 3,600 psi) and temperature will be kept as low as possible, to maximize the amount of gas that can be transported. Says Campbell, "The density of our CNG is about 85 percent that of LNG without processing." Prototype bottles are being fabricated by Composites Atlantic and will be tested as part of the JIP.
"Composites are the preferred material over steel," notes Campbell, "because of lighter weight, corrosion resistance (thanks to the thermoplastic liner), cryogenic temperature resistance and crack and rupture resistance. Cost is also competitive with steel, given the proposed bottle size and relatively high steel prices."
While several presenters at CMOO-4 discussed composite riser projects in the works, their optimism was somewhat overshadowed by the industry's inability to get a number of composite riser joints installed on the ConocoPhillips' Magnolia tension leg platform (TLP) in the Gulf of Mexico. The CompRiser project, which was originated and championed by Conoco and Kvaerner in 1997, saw titanium-lined composite risers successfully tested on Statoil's Heidrun platform in the North Sea (see HPC July 2002, p. 40). The next-generation design has steel replacing the titanium as the liner material. A steel-lined riser design was successfully qualified for Magnolia, but field joints failed the factory acceptance pressure tests in late 2004. The cause of the failure appears to be a problem with welds in the steel liner, which allowed leakage, says Marc Leveque, principal engineer with ConocoPhillips. "For the Magnolia project, it's too late to get any risers in place now," states Leveque. "The problem was found at the very last moment and there wasn't time to continue — it's very painful, given the amount of money spent." ConocoPhillips terminated the CompRiser project and is no longer part of a riser JIP, but Leveque says that other JIP entities are likely to carry on. Shell Oil is pursuing a steel-lined riser project, working with Lincoln Composites (Lincoln, Neb.). Several European groups, including the Institut Francais du Petrole (Ruell-Malmaison Cedex, France), Vetco Gray (Stavanger, Norway) and Umoe Mandal (Mandal, Norway), also are developing riser concepts.
Other projects to watch for include a new flexible fiberglass pipe produced by Deepflex (Houston, Texas), which is similar to a steel-armored unbonded spoolable pipe but of all-composite construction. It's made with precured unidirectional laminate strips for pressure containment. Deepsea also is investigating a subsea buoyancy element. The hollow, thick-walled, cylindrical vessel is made with carbon fiber/epoxy sandwich construction to take the high compression loading of the deepwater environment. The element could be used for subsea separation, to house electronics or equipment on the seabed or for riser buoyancy.
"Deepwater development can be profitable and sustainable," sums up Shell's Hwang. "By working together with industry groups and contractors we can develop the best system solutions." Those solutions without a doubt will continue to include high-performance composite materials.
