Research On Mechanical Behavior Of Global Buckling And Active Control Theory Of Steel HT/HP Subsea Pipeline

As the number of easy-to-extract oil reserves diminished,it became an inevitability that oil exploitation would move from land to sea and from shallow water to the deep ocean.Deep-ocean drilling and oil/gas transport comes with a set of a set of unique challenges that require unique solutions.In addition,it is more challenging to use single layer subsea pipeline under deep water condition.Therefore,pipe-in-pipe system and sandwich pipe are becoming more popuplar in deep water condition.However,their global buckling response and control method are more complex.For the control method of global buckling,passive control methods,such as bury,are gradually replaced by active control methods,such as snaked-lay and sleeper methods.These new trends in pipeline and global buckling control method bring us new subjects and challenge.In this paper,theoretical and numerical methods,together with different optimization methods are used to conduct a systematic research related to above subjects.Several research results with importance in scientific research and engineering application have been obtained:Bending model of pipe-in-pipe system is proposed and verified by related experiment results.The main factors which influence the bending performance of pipe-in-pipe system are studied in details.The bending behavior of pipe-in-pipe system is uncovered.The equivalent bending stiffness formula of pipe-in-pipe system is proposed to simplify the global buckling calculation process.Dynamic buckling model of subsea pipeline is built to analyses the dynamic effect of upheaval buckling process.The formula for critical buckling force of pipeline,which takes imperfection and non-linear behavior into consideration,is proposed.Numerical model of pipe-in-pipe system and sandwich pipes are established to study main factors which influence the critical buckling force and post-buckling responses.On the basis of simulated results and dimensionless analysis,the critical buckling force formulas of pipe-in-pipe system and sandwich pipe are proposed to calculate critical buckling force of pipeline with initial imperfections.Numerical models of global buckling for snaked lay pipeline and pipeline with imperfection and sleepers are built.The influence of imperfection shape,sleeper properties and seabed conditions are studied in detail for both models.The best shape of snaked lay pipeline is obtained by genetic algorithm,which reduces the critical buckling force dramatically therefore increase the probability of active control method.Critical buckling force,buckling displacement and post buckling stress formulas for pipeline with imperfection and sleepers are proposed by gene expression programming technique,which can be used in the design of this kind of active method.