Stress Concentration Factors of Damaged FPSO Side Panels Under Cyclic Loads

FPSO (floating production, storage and offloading) units can be subjected to mechanical damage in their side panels caused by collision with supply vessels. Even if the ultimate strength of the panel is not significantly affected by small damage, the stress concentration in the collided region may lead to the initiation of fatigue cracks, considering the long period of operation undergone by these vessels. The aim of this work is to evaluate stress concentration factors (SCFs) in damaged FPSO side panels and estimate their effect on the fatigue life through a theoretical study. A finite element model is developed to reproduce a supply vessel collision and evaluate resulting SCFs under in-plane compression load. A parametric study is carried out considering different damage magnitudes and the results obtained are used to develop an analytical expression to provide SCFs as a function of dimensions of damage and panel. SCFs provided by this expression could be used in a theoretical fatigue life study that can estimate the residual fatigue life of collided FPSO side panels and help to forewarn a fatigue failure under the event of an accidental collision.