Gulfstar - Porches and Pull Tubes - Comparing Two Riser Interface Options

摘要

Historically, Spar platforms have utilized both riser porches and riser pull tubes for interfacing steelrncatenary risers (SCRs) to the floating system. The riser porch requires a stress joint at the hang-off endrnof the SCR to withstand tension and bending loads at the fixed connection. The pull tube requires specialrnhardware (e.g., a double-tapered stress joint) near the keel of the Spar where platform motions are firstrntransferred to the riser system. Each of these options for the riser interface has advantages and disadvantages.rnThe Gulfstar FPS utilized both pull tubes and a riser porch for riser interfaces.rnThis paper evaluates the experience designing and building the two different types of riser interfacesrnfor the Gulfstar FPS and the experience offshore during installation of the risers. The paper quantifies thernstructural appurtenances required for each interface in addition to the equipment required for riserrninstallation, which is significantly different for each interface type. The evaluation results in importantrnlessons learned and recommendations for both types of riser interface strategies.rnThe paper also summarizes the keel interface utilized on the Gulfstar FPS. The Gulfstar FPSrnincorporates a different approach for the keel interface with the pull tube support compared to other recentrnSpar projects in the Gulf of Mexico. The results demonstrate the compatibility of the riser keel interfacernwith the platform motions.rnThe information and results presented in this paper are applicable to engineers, designers andrnfabricators when evaluating riser interface options for floating systems, particularly Spar platforms.