High Temperature Flowline Thermal Design Using Rotating Buoyancy Modules

A rotating buoyancy modules (RBM) system was developed as an improvement to the non-rotating buoyancy from the collaboration between a major oil company and Trelleborg Offshore. In this system, a finned external shell rotates around an inner core strapped to pipeline. The rotating buoyancy reduces berm build-up, decreases friction for pipe-soil interaction, and ensures the robustness of buckling mitigation for HPHT thermal design. In the contrast, for a non-rotating buoyancy module, seabed soil berms can build up after the initial flowline lateral movement which can limit further lateral movement. As result of berm build-up, the effectiveness of non-rotating buoyancy modules to control pipeline buckling reduces. RBM was applied for the first time in a tie-back flowline for a Gulf of Mexico (GOM) deepwater development project. In this paper, flowline thermal design using RBM for the project is presented. The project field conditions that impacted the tie-back flowline design included existing crossings and limited space for subsea structures and flowlines. The pipe-seabed interaction and RBM-seabed model is presented along with the axial and lateral friction parameters used for peak and large displacement on normal pipe sections and RBM sections. The main loads for the flowline were from the operational conditions in term of temperature and pressure profiles. Lateral buckling mitigation results include the RBM location configurations, buckling locations, effective axial forces and von Mises stresses. Recommendations for situations when RBM should be used for high temperature high pressure thermal design are presented.