Fatigue Analyses of a Flexible Riser Considering End Fitting Effects

Abstract

During the end fitting (EF) mounting process, the tensile armor wires of flexible pipes are folded and then unfolded. This process usually leaves plastic deformations and generates sharp curvatures on these wires just at the EF entrance. Dissections performed in several flexible risers, which were in operation or subjected to qualification tests, revealed that this region is especially prone to fatigue failure thus affecting the overall performance of these structures. In this work, an analytical approach devoted to predict the stresses induced in the tensile armor wires at the EF entrance is combined with a previously presented methodology to compute the fatigue life of flexible risers in order to account for the EF mounting process. A parametric study is also conducted aiming at evaluating the effect of the folding radius, the stress level induced during pre-operational tests and the contact conditions between the epoxy resin and the tensile armor wires on the fatigue resistance of a free hanging flexible riser. These analyses indicate that the choice of the mean stress correction model, the folding radius and the stress level induced during the pre-operational tests significantly modify the fatigue resistance of the tensile armor wires. The contact conditions also influence the fatigue resistance, but their effect is less significant.