Numerical study on upheaval buckling for surface laid subsea pipelines with topographic step imperfection

Upheaval buckling may occur for subsea pipelines laid on the seabed with topographic step imperfection under high temperature. In order to predict the post buckling behaviour of upheaval buckling, a finite element model of ABAQUS is proposed to simulate upheaval buckling for surface laid subsea pipelines with step imperfection. Firstly, a new method to introduce a step imperfection from an originally flat seabed is presented. Then, the finite element model of ABAQUS proposed in this paper is verified through the analytical results. The results obtained by FEA and analytical method have a good agreement. The influence of temperature difference, model length and step height on configuration and post buckling behaviour is investigated in detail. Our results show that rigid seabed assumption is reasonable in this study. The model length of the pipeline must be larger than the feed-in length. Otherwise, displacement amplitude, maximum stress and axial thermal expansion will be underestimated. For larger step height, displacement amplitude and maximum stress are larger at lower temperature difference due to the initial deflection induced by step imperfection of seabed, however, they become smaller at high enough temperature difference. The influence of step height and thickness of the pipe on the critical buckling force can be fitted well by a simple formula. The critical buckling force is barely affected by the axial friction coefficient between pipe and seabed.