Análise numérica de enrijecedor à flexão para I-tube

Abstract

Flexible risers have played an important role in the offshore oil and gas industry. During the operation phase, these pipelines are subjected to dynamic loads from marine currents, winds and waves which generate undesirable bending moment at the upper connection with the platform. Bending stiffeners are used at this connection to limit the curvature, in order to avoid riser failure due to overbending and fatigue. The function of this ancillary equipment is to ensure a smooth stiffness transition between the flexible riser and the platform. The propose of this work is to evaluate the behavior of the riser at the upper connection when subjected to an axial load combined with an angular variation between the longitudinal direction of the pipe and the neutral position of the bend stiffener. In this work, finite element models were developed using ABAQUS®, mainly to verify the differences between the standard configuration, which considers the riser and the bend stiffener fixed at the same position, and the I-tube configuration, which considers a significant length of flexible pipe above the bend stiffener position. The bend stiffener (polyurethane) was evaluated with three different elastic modulus, considering the elastic linear behavior, as well as with the nonlinear elastic symmetric behavior. In the numerical analysis, different gaps between the pipe and the bend stiffener, and the influence of the use of the sleeve on the behavior of the riser were also analyzed. Finally, a study was carried out to evaluate the impact of bend stiffener rotation at the bell mouth region.