Probabilistic Inspection Planning of the Åsgard A FPSO Hull Structure With Respect to Fatigue

Abstract

Probabilistic methods has been used to develop a basis for an in-service inspection program for the A˚sgard A FPSO hull structure with respect to fatigue cracks. A˚sgard A is a floating production unit constructed for Statoil and was installed on the A˚sgard Field during the winter 1999. Hot spot areas showing the shortest calculated fatigue lives have been selected for probabilistic analyses. This implies areas at doubling plates and transverse stiffeners in the deck structure and the connections between the side longitudinals and the transverse frames. In FPSOs, there are a number of details with similar geometry that also are fabricated in the same way. Some of the details like those in the deck structure are also subjected to the same magnitude of loading. Consequently, there will be correlation in fatigue life when several components are considered at the same time. The effect of this correlation has been investigated for components that have a welded surface and components that are ground. A number of analyses have been performed to investigate the effect of this correlation on required amount of in-service inspection. And it is shown how results from these analyses are transferred into an in-service inspection program for the A˚sgard A FPSO. [S0892-7219(00)00302-2]