Design And Analysis Of The Keel Joint For Top Tensioned Riser

Top tensioned riser (TTR) is very important for the deep offshore oil and gas exploitation, which is in relatively complex environment. Therefore the floating structure would subject to a variety of environmental loads. The top tensioned riser system would be the weakest part in offshore oil and gas exploitation. Security and integrity of the riser will affect the marine oil and gas exploration, and in the Spar platform and the free-standing riser due to the particularity of its structural design, resulting in the generation of stress will appear in the riser keel joint portion and the stress joint contacts subsea wellhead. So study of these two parts will become a hot issue in the field of academic research and engineering fields. This article studied a traditional Spar platform and its drilling riser systems research in the South China Sea environment. In this article, we use OrcaFlex analysis software and Ansys finite element analysis software making numerical simulation for system riser keel joint portion. In this paper, we make use of the method for Global to Local model analysis, in which we use Ansys building a local model of the keel joint which get the boundary condition from the global model built in OrcaFlex software. In addition, we studied three different types of the keel riser joints for their von-Mises stress, bending stress distribution in the joint portion of the keel. In further we discussed the stress distribution of the riser in a particular Keel Joint with changing one of the parameter for the Keel Joint. The results show that:the keel joint for top tensioned risers makes an influence for von-Mises stress in riser. Furthermore, different types of Keel Joint make different contribution. So in the design project of the riser, the influence of the keel joint for stress in the top tensioned riser must be considered to avoid large local stress happening. In addition, stress in the riser system will redistribute with using thickened keel joints; compared to the riser without keel joints, in which a high stress will happen, the riser with a tapered keel joint will change the stress distribution greatly (peak stress produced three points); Meanwhile, the stress level in the region could be reduced by increasing thickness of the keel joints. For flexible keel joint, compared to the displacement brought about obvious constraints, its peak value in reducing stress riser is not obvious contribution to the riser on. For Out-sleeve keel joints, two stress risers peak point will move. The von-mises stress at the lower point contacting the riser and Out-sleeve will be reduced in a certain region.