Fatigue life improvement of scallops in ships/FPSOs using finite element analysis

Floating production vessels are planned to mainly be on the same location without scheduling any shutdowns for maintenance and repair. This implies stricter requirements to a reliable fatigue design than the standard procedure that is used by the ship industry, with inspection and repair every fifth year. One of the areas that has been subject to improved fatigue design requirements is scallops in a three perpendicular plate intersection. A general model applicable for several structural details in ships is used in the present study. Four different methods of calculating hot spot stress have been considered. Five different geometries of scallops have been modelled by three-dimensional 20 node isoparametric elements and analysed. The results from these analyses are presented and discussed in this paper.