Assessment of SYMS Survival Limit for “Peng Bo” FPSO During Installation

The ConocoPhillips “Peng Bo” FPSO in Bohai Bay, China, is one of the largest FPSOs in the world. It was installed in early 2009 and first oil was achieved in May 2009. The FPSO is moored to a jacket platform in about 27m water depth via a Soft Yoke Mooring System (SYMS). The mooring system consists of two yoke arms (port and starboard) connected at the jacket end to a turn-table that sits on a main bearing at the top of the jacket. The other ends of the yoke arms are integrated with two large ballast tanks which are attached to two pendulums supported by a rigid frame mounted on the forward end of the FPSO. The ballast weights give rise to the necessary system surge restoring force while the turntable and bearing allow the FPSO to weathervane. The yoke arms and ballast tanks are pre-installed with empty ballast tanks mounted on two temporary support barges while awaiting the arrival of the FPSO. Upon arrival, the ballast tanks are attached to the pendulums from the FPSO side. The tanks are then filled with solid concrete ballast to achieve the design weight. Before the tanks are completely filled, the SYMS may not have sufficient restoring force in partially filled condition to prevent excessive pitching of the yoke arms and severe bearing load on the jacket beyond the design limit due to large FPSO offset in the event of an unforeseen storm event. An analysis was carried out to estimate the maximum bearing load and yoke arm pitch angle when the ballast tanks were 0%, 25%, 50%, and 75% full for 10-year and 100-year return period events. This paper describes the analysis methodology and results from the analysis. The overall project and installation experience are also discussed.Copyright © 2010 by ASME