Development of Cylinder Type Concrete FPSO With Tangerine-Shaped Cross-Section

Abstract

Concrete platforms have proven to be a viable offshore solution for deep-water projects according to the documented performance of over 40 years [1]. Since concrete has resistance to seawater corrosion, reduced maintenance costs and motions, concrete structures have become attractive to the offshore oil and gas industry [2, 3]. There are many floating concrete structures such as barge, ship, platform and LNG/LPG terminals. While most concrete offshore platforms are the fixed structures, floating concrete platforms have been used for drilling, extraction /storage and production units for oil and gas including heavy lifter. There are two representative floating concrete facilities on the Norwegian shelf, Troll B and Heidrun A [4, 5]. Troll B is the first concrete semi-submersible product unit and Heidrun A is the floating concrete tension leg platform. The concrete FPSO (Floating Production Storage and Offloading), however, was assessed to be inferior to the steel FPSO in respect of feasibility. In this study, an optimization design of the cross-section for cylinder shaped concrete platform is presented in order to promote the feasibility of a concrete hull for an FPSO. Optimal aspect ratio (depth to diameter) with economic analysis is examined and tangerine-shaped section which can utilize the excellent material properties of the concrete in compressive strength is developed. Exterior wall having a small curvature are applied to transmit the load to interior bulkhead. A parametric sensitivity study was conducted to find the optimal curvature of the exterior wall. Subsequently, an arch-shaped wall is applied to center wall in order to improve the upper and lower tension force caused by bending moment. The tendon was placed in the center of any cross-section, taking into account the tensile force that can be caused by additional asymmetric loads. The effect of tangerine shaped cross-section can be clearly identified by comparing the results with the circular shaped cross-section.