THE LIGHTWEIGHT HYBRID RISER

摘要

This paper describes the lightweight hybrid riser concept shown in Fig. A overleaf. In thisrnconcept the riser tension is absorbed by aluminium conduit pipes in place of dedicatedrntethers. These conduit pipes also provide the buoyancy required during tow out andrninstallation. The conduit pipes confine the steel production risers so that differentialrnexpansion can be accommodated for pipes with fixed end connections both at the base andrnto the buoyancy tank. Flow assurance may be provided for by a combination of solidrninsulation and an insulating gel with long term stability as well as sufficient viscosity tornarrest convection, heating or pressure reduction as an alternative to injection of chemicalrnagents .rnThe paper addresses the corrosion aspects of this combination of steel and aluminium andrndemonstrates that they are at least equal to steel, as the full effect of the basically inertrnnature of cathodically protected aluminium is mobilised in this particular application. Thernconfiguration is also favourable to abating the effect of vortex induced vibrations.rnThe lightweight hybrid riser is monolithic in nature without mechanical couplings, bearingsrnand goosenecks. Neither does it have soft sealing systems or fibre strapping. This all-metalrnsolution makes for low sensitivity and exposure to damage. The multipurpose aluminiumrnconduits, the simplified pull-in of pipelines to pull-in porches on the fixed base and thernsingle operation tow out and installation leads to a cost saving of about 40% whenrncompared to current concepts.rnHybrid risers are applicable in deep water developments (>1000m) and accommodate thernuse of FP(S)O?s and semisubmersibles. The lightweight hybrid riser provides a solutionrnreducing both risk and cost. In ultra deep water these advantages tend to increase.