Composite Riser and Export Line Systems for Deep Offshore Applications

Composite materials offer an interesting alternative to classical steel solutions in the deep offshore risers and export lines systems. They are able to bring lightness both with high mechanical and compliance resistance, and important developments have been made by the industry to qualify them for offshore use. Most applications planned up to now have been however for TLPs, SPARs or Drilling Risers, where saving weight has direct influence on the design of the floating supports and corresponding equipment. However new riser system concepts have appeared, such as catenary risers, hybrid towers, or “Lazy W” export lines, used for instance on the Girassol field. The objectives of the present study are, starting from operational hypothesis, to design and verify feasibility of steel and composite risers for these types of applications in the very deep offshore (down to 2500m), including laying conditions. Composite and steel solutions are then compared and the advantages induced by the composite version can be evaluated. An acceptable cost of the composite version can then be deduced. Main conclusions are that both steel and composite versions are technically feasible in the mild conditions of the Gulf of Guinea or of Brazil. Steel is however close to its limit and may not work in more severe conditions. The cost advantages of the composite version are found essentially during the laying phase, and may justify the use of such an application. An important issue will be however the industrial availability of long length composite joints.