This paper gives an overview of the latest developments of advanced finite element analysis (FEA) tools that are used for the design of subsea pipelines. It focuses on the deepwater and high pressure / high temperature conditions. The paper demonstrates through the use of FEA, that designs can be undertaken for complex scenarios that were not previously possible.
This paper includes three main sections. The first section looks at the ‘global’ analysis of pipelines using a set of highly non-linear finite element programs based on ABAQUS. These programs have been widely utilized for over ten years in oil and gas industry and for hundreds of field developments around the world, in various design stages, from pre-FEED, FEED, to final detail design. The programs are used to undertake the complex design cases, such as lateral buckling, upheaval buckling, pipeline walking; pipe-in-pipe (PIP); thermal buckle management; and pipeline span identification, as well as span stress and collapse screening. The programs have been calibrated against the observed pipeline structural responses in the field. The simulation process covers from installation to operation and can be expanded to pipeline span analysis, route curve stability, and pressure-thermal load fatigue assessment.
The second section demonstrates how FEA can be used to undertake ‘local’ modeling of pipelines to address local issues and provide verification and support for a reliable global pipeline design. Pipeline end structure behavior, thermal mitigation buoyancy and soil interaction, thermal mitigation sleeper embedment and installation tolerance, PIP inner pipe lock-in load, field joint stress/strain localization, and free span VIV analysis, are some typical applications. These works can be in component level or represent some local pipeline section. Such detail analyses ultimately relies on the ‘global’ FEA to provide trustworthy loading and boundary conditions.
This paper also presents the analysis strategies based on the project experiences, the lessons learned, and future improvement. The presentations include, the route selection versus thermal expansion and global buckling, the FEA modeling process (1-D, 2-D versus 3-D), the pipeline-soil interaction, the selection of mitigation for lateral buckling, and related design issues. The combination of these analysis advancements and extensive project experiences will provide the strong supports on solving the most complex engineering problems presently faced in the offshore industry, and in some cases have allowed significant cost savings to be achieved in the engineering.