| Two of the most important loading conditions for pipelines in operation are ground movement and temperature change. Ground movement is caused by the factors such as fault settlement, slope movement, frost heave, and thaw settlement. The difference between the pipe temperature change in service and the tie-in temperature of the pipeline produces an axial compressive force in the pipeline. With a large enough temperature differential, the resulting compressive axial force can cause the overall buckling of the pipeline, leading to considerable vertical, lateral, or combined movement of the pipe. Many cases of thermal buckling have been recorded for both onshore and offshore pipelines. Pipelines subjected to ground movement or thermal buckling may deform into elastic-plastic range and form wrinkles.; In this research project, a two-dimensional, numerical model is developed for the analysis of pipelines under different loading conditions, and, in particular, under thermal loading. The finite element model features a new elastic-plastic, isoparametric C1 beam element capable of modeling large displacements and finite strains using an updated Lagrangian Formulation. The numerical model can handle highly irregular pipe and ground profiles in order to cover most practical cases. The resulting finite element model was implemented in the computer program ABP (Analysis of Buried Pipelines). The finite element model is verified through several examples by comparing the analytical results to those of closed-form solutions, experimental data, or other finite element programs. Two thermal buckling case studies, stemming from the investigations carried out on actual pipelines, demonstrate the application of the thermal analysis. |
