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Pipeline walking is a global axial movement caused by the asymmetric distribution of axial force along the pipeline during the repetitive operational loading cycle. The pipeline walking rate, increasing with the loading cycles, may lead to high stress thereby the failure of connectors at PLETs or PLEMs. Current research studies and design guidelines focused on free-end pipelines and neglected changes in the pipeline walking rate and axial resistance with effects of pipeline end structures. However, in practice, several pipelines are adjacent to PLETs or PLEMs, which potentially affect the pipeline walking and expansion behaviour thereby walking rate and axial displacement. This study analyses the walking phenomenon considering the effects of mobilisation of the resistance at the pipeline end structures and develops new analytical solutions for the present problem, in terms of different walking mechanism, maximum axial resistance Pmax, and positions of pipeline end structures. The analytical solutions are validated through numerical simulation results. The case study results indicate the axial resistance generated by PLETs/PLEMs can effectively mitigate pipeline walking rate compared with free-end pipeline walking. In particular, the influence of PLETs/PLEMs is investigated, highlighting the sensitivity of the pipeline walking to the end boundary conditions covering different design scenarios.

Pipelines are widely used for transporting oil resources in offshore oil exploitation. As burying an entire deep-water pipeline is not possible owing to the large water depth, an on-bottom pipeline inevitably exhibits lateral global buckling deformation under high temperature and pressure in practice. Triggering several controllable mitigatory global buckling deformations by installing sleepers under pipelines is a more effective alternative to prevent cross-sectional failure caused by excessive buckling. While sleepers may trigger vertical global buckling and this risk must be verified before they are installed in practice. This study analysed the feature of lifting deformation for a pipeline laid on a sleeper. Nine influential factors of the variation in the lifting displacement were analysed. Based on the nonlinear relationship between lifting displacement and temperature difference, three key points and four relevant key parameters for describing the lifting displacement curve were proposed and calculated for the conditions of a pipeline with different combinations of influential factors. A back propagation neural network was trained to model the relationship between the locations of the three key points and the values of the nine influential factors. The error analysis indicated that the trained network can effectively predict the vertical lifting deformation and is suitable for a pipeline that experiences no lifting deformation. Based on the feature points predicted by the trained network, the approximate profile of vertical lifting displacement during the heating process can be described, and the assessment of whether the lifting displacement with the loading conditions in practice is allowable can be conducted.

With the development of submarine oil and gas resources, research on global pipeline buckling caused by high temperature and pressure in the process of oil and gas transport is becoming an important issue. Owing to human factors or to uneven seabed conditions, local bends are produced in the process of pipeline manufacturing and laying. Those bends are called geometric initial imperfections whose deformation forms can be divided into a single arch symmetric deformation and a double arch antisymmetric deformation. In this paper, the energy method is introduced to calculate the analytical solution of pipeline lateral buckling with a single arch initial imperfection, and the cause of snap buckling phenomenon is discussed. A FEA model is established, and the difference between the analytical solution and numerical solution is also presented.