Study On Upheaval Behavior Of Perfect Marine Pipelines

The upheaval buckling of marine pipelines caused by the temperature stress is one of the main failure modes of pipelines. When a pipeline is operated at high internal pressure and temperature, it will attempt to expand and contract for differential temperature changes. Normally the line is not free to move because of the plane strain constraints in the longitudinal direction and soil friction effects. For positive differential temperature it will be subjected to an axial compressive load and when this load reaches some critical value, the pipe may experience vertical (upheaval buckling) or lateral (snaking buckling) movements that can jeopardize the structural integrity of the pipeline. In these circumstances, an evaluation of the pipeline behavior should be performed in order to ensure the pipeline structural integrity during operation in such demanding loading conditions. Performing such analysis, the correct mitigation measures for thermal buckling can be taken into account either by acceptance of bar buckling but preventing the development of excessive bending moment, or by preventing any occurrence of bending.The present study concentrates on vertical upheaval of buried marine pipelines. An account of some researches of the upheaval buckling of buried pipelines has been given in great details. That very close relationship exist between the thermal buckling of components such as continuously welded rail-tracks, concrete road pavements or subsea and buried pipelines, and the simple buckling of columns has long been recognized.In association with the practical pipeline project, an approach for estimating the vertical upheaval buckling of perfect pipelines tendency has been established. The factors that may cause pipeline buckling, such as temperature, subsoil, buried depth and expansion bend are discussed. Finally, the finite element software named ANASYS has been applied to analyzing the upheaval buckling of perfect pipelines and the calculated results are compared with the analytic solution.The analyzing results show that stresses in the pipeline rise with the increase of temperature difference, friction between the pipeline and subsoil, and the buried depth. While the buried depth is deep enough, the pipeline vertical upheaval should been prevented.