Structural analysis and modifications–2 tankers for offshore FPSO and FSO service

Abstract

This paper addresses the unique structural requirements for successful conversion of tankers for floating production storage and offloading (FPSO) or floating storage and offloading (FSO) service. A description is given of the steps undertaken during two recent and very different conversions of a highly optimized 1980s VLCC to FPSO service, and a typical robust 1970s ULCC to FSO service. The paper describes the steps needed for ensuring the FPSO or FSO requirements are successfully met during conversion of the two tankers – each having its own history, e.g. date of build, original design, material choices, class society, voyage history and repairs. Firstly, the paper describes the procedure and results of an early initial structural assessment procedure on the basis of an American Bureau of Shipping (ABS) Phase A analysis, past tanker voyage history and a review of past survey records and thickness gauging data. Secondly, the paper describes the procedure and results of a detailed structural finite element analysis of the two vessels considering past tanker service and future FPSO or FSO service, including the effects of on-and offloading of crude oil. Since the abstract was first written, a third FPSO of similar configuration to the 1980s FPSO described in this paper has been analysed with the same procedure.