| With the development of the offshore oil and gas resources, especially for the exploitation of deep water and marginal oil fields, more and more high temperature and high pressure (HT/HP) pipelines are used in practice. Global buckling of pipeline under HT/HP is becoming key factor for pipeline design. Thus, it is of significance to study thermal buckling mechanism and controlling methods of submarine pipeline. Combined with theoretical deduction and numerical simulation, the study on global buckling of HT/HP submarine pipeline is carried out in the paper.Critical axial compressive forces of lateral buckling mode 1 and mode 2 of flexible pipeline without initial imperfection are derived on the base of energy theory. The comparison of the results from energy method and Hobbs's method is conducted. Based on the theory of thermal buckling, and considering the effect of initially imperfect geometry on lateral buckling of pipeline installed on the flat seabed, analytical solutions to critical axial forces in buckling segment and out of buckling segment as well as critical temperature are proposed. The comparisons between analytical and numerical results validate analytical solutions suggested in the paper. Through the analysis, initial imperfections have great effect on critical buckling force and temperature.Nonlinear finite element (FE) model of subsea pipeline laid on even seabed is established to analyze critical buckling of pipeline, post-buckling deformation, bending moment and strain. Two methods are introduced to simulate initial imperfection corresponding to practical engineering. The effects of residual stress due to initial imperfection on pre-buckling and post-buckling are carried out. The results show that residual stress can increase critical temperature and axial strain of post-buckling pipeline. Considering the effects of initial geometry imperfection, lateral and axial frictional coefficient between soil and pipe, yielding soil deformation, ratio of diameter to wall thickness of pipe, steel strength on lateral buckling, sensitivily is completed. Interaction between pipe walking and lateral buckling is studied in this paper, it can be seen that lateral buckling can effectively decrease pipe walking. Buckling distance between two potential buckling positions is the key to initiate lateral buckling at the positons at the same time. Based on analytical studies in imperfect pipeline lateral buckling, control criterion of minimum distance between two adjacent buckles is presented. Sine shape as a new shape of snaked-lay pipeline is presented in this paper. FE analysis display the new snaked-lay shape can effectively reduce critical buckling force and control bending moment and strain of post-buckling pipeline. The effects of pipe-lay radius, length, angle and distance are discussed. Based on FE results, the optimum offset angle and pipe-lay length of sine shape are suggested.Considering the characteristics of snaked-lay method and sleeper method, a new lateral buckling controlling measurement combined with snaked-lay and sleeper (SS) is proposed. Using ANSYS, nonlinear FE model considering the interaction of seabed, sleeper and pipeline is established. SS method can overcome deficiencies of snaked-lay method and sleep method through FE analysis. Numerical results show that sleeper height has significant effect on pre-buckling and post-buckling of pipeline. The controlling criterion of sleeper height is proposed.Due to scour and erosion of wave and current or pipeline laied on uneven seabed, span is inevitable during operation. Nonlinear contact FE model is established to study the effect of spanning depth and length on global buckling of pipeline with single span. For the pipeline with double spans, spanning distance is studied, and the controlling criterion of spanning distance is presented to reduce the interaction risk of the double spans. For snaked-lay pipeline with single spanning, the crest of snaked-lay pipeline should avoid locating at spanning segment.
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