Finite Element Analysis of Ultimate Strength of Flexible Risers Subject to Axial Compression Using Simplified Model

Abstract

Flexible risers are pipes connecting the offshore platform to the subsea flow line and transporting gas and oil. Flexible risers can encounter many uncertain factors during their installation and operation process. Especially, during installation process, due to the pressure unbalance, flexible risers can be subject to axial compression, which is an undesirable force. Axial compression can result in failure modes such as radial buckling. Therefore, it is very necessary to analysis failure modes and to evaluate the ultimate strength of flexible risers. Ultimate strength assessment of flexible risers is very complicated and time-consuming. This is because it includes many difficult points such as material nonlinearity, large deformation, and nonlinear contact mechanism. Also, it is difficult to understand structural behaviors under various loads. This paper introduces practical and stable methods for ultimate strength assessment using simplified FE models. In particular, numerical methods are provided to increase convergence of nonlinear analysis. In addition, the effects of ovalizations and external pressure are examined.