As the supply of fossil fuels diminish, there is a need to progress further into the outer reaches of the planet in search of oil and gas reservoirs. Deepwater oceanic reserves are a promising source for these natural fuels that serve as the world’s primary energy source. As oil companies progress into waters in excess of 1,000 feet, tension leg platforms (TLP) are used to increase the economic feasibility of drilling.
The basic construction of a TLP, consists of a hull that supports the rig and production facilities and is connected to the seafloor by means of tendons and risers. As offshore drilling proceeds into waters 5,000-10,000 feet deep, weight minimization becomes a critical design criteria, limiting the operating depth of the TLP. Alternative materials, therefore, are being considered to replace steel to provide for lighter components of the TLP. Composite tubes provide a realistic alternative to metals in many offshore applications, offering high stiffness to weight and strength to weight ratios as well as increased corrosion resistance and flexibility when compared to standard materials. This increased flexibility permits the tubes to be coiled onto spools, to allow for ease of storage, handling and installation.
The objective of this study is to select the minimum spool radius without inducing damage in the tube during storage on the spool. This is accomplished though experimental and analytical studies utilized to assess the influence of different material systems, lay-ups and tube geometry on the stress-strain response induced in bending. This is accomplished by experimentally determining the moment-curvature relationships for several types of filament-wound tubes. Four point flexure tests are preformed on [± 45]4 and [± 55]4 orientations of carbon/epoxy and glass/epoxy tubes. Finite element models are then created to simulate the loading scenario. The models utilize two-dimensional shell elements and incorporate non-linear geometry effects as well as a progressive damage subroutine that predicts failure initiation and its progression. The models are compared with experimental data and are used to conduct parametric studies of the effects of lay-up, geometry, and constitutive material on the flexural behavior of the composite tubes.
Related Publications: Ochoa, O. O. and Rodriguez, D.E., “Flexure behavior of composite spoolable tubes”, OMAE2002-28263, Oslo, Norway, June 2002.
Ochoa, O. O. and Rodriguez, D.E., “Hybrid spoolable tubulars- damage initiation and progression during bending”, American Society of Composites 17th Annual Technical Meeting, Purdue University, October 2002.
Ochoa, O. O., “Unrealized Potential of Composites in Offshore Applications”, Proceedings of 13th International Conference on Composite Materials, Paper ID 1686, Beijing, China, June 2001.