Floating Production Storage and Offloading (FPSO) units are becoming an evermore applied field development concept. Their use ranges from extended well testing and marginal field development to major development hubs in large deepwater finds. They have been proven suitable for operation in benign and harsh environments.
Their hulls are converted tankers, or new built barges with their structural design based upon the maritime tradition. However, there are differences in environmental loading, operational and durability requirements between trading tankers and FPSO hulls. Recognizing a shortfall in fatigue loading data for FPSO hull design, the Joint Industry Project (JIP) FPSO Integrity was formed in which oil companies, classification societies, shipyards, FPSO contractors and legislators participated. A 2.5 year measurement campaign was undertaken onboard an FPSO operating on the UKCS in order to establish a data base of FPSO motions and loads, together with a complete description of the environmental- and vessel loading conditions. Moreover, a software package was developed that predicts fatigue loads and damage, and that describes the non-linear phenomena around the waterline, the so called ‘intermittent wetting’.
This paper elaborates on the comparison between the data gathered during the measurement campaign and the predictive software developed during the course of this JIP. It describes the validation process in general and identifies in specific where the underlying assumptions of the software fall short of the measurements, and what effects these deviations have on the fatigue damage endured by the structure.