The last couple of decades have seen the conversion of a large number of trading tankers into floating production, storage, and offloading units (FPSOs). ABS records indicate that about a fifth of the worldwide FPSO fleet is approaching the end of its designed service life, with a significant number of these operating in Brazilian waters. Meanwhile, new discoveries in pre-salt reservoirs and the recent proven technologies for oil recovery have been pushing operators and concessionaires to extend oil production in these fields beyond their originally predicted life. Additionally, recent pre-salt oil developments offshore Brazil have increased the demand for new units. The result of these developments is a stated industry need to extend the service lives of existing FPSOs.
This need in association with the refinement of environmental data and enhancement of Rules requires the verification of the adequacy of the FPSO unit to withstand the design operational loads, and its updates, refurbishments and additional equipment using currently available engineering tools for numerical simulations and the current Code and Class Rule requirements.
A new methodology to review these units employing state-of-art technology tools was developed using studies comparing existing FPSO arrangements based on prescriptive classification rule requirements and finite element analyses. Comparisons were performed between the results of these analyses and the original approved design data. Such comparisons are significant in understanding FPSO structural capacity at the conversion stage, its performance during its intended service, and its remaining service life. Differences were mapped and the reasons for these differences were investigated to determine typical engineering procedures needed for predicting the estimated remaining service life. The resulting approach is a new method for evaluating the remaining structural life of existing FPSOs.
This approach also enlists an in-service inspection program to provide the necessary information regarding structural degradation during years of operation, previous repairs, and the most current condition. A similar approach also can be used for other hull forms.