Study On Buckling Response Of Large Diameter Gas Pipeline Under Fault Displacements Based On ABAQUS

There is wide spread active fault distribution in China.Long-distance oil&gas pipeline will inevitablly cross some active fault area.Generally,most of buried pipelines will appear fracture failure due to the permanent ground displacement caused by the rupture of the crust.Under the fault movements,pipelines are prone to be squeezed by the soil mass of fault,resulting in the occurrence of local bucking of pipe and that means there is a sharp increase of axial strain of the cross-section of pipe near the fault plane.Then the buckling area will lose its bear capacity if the deformation develops further.Besides,the overlarged curvature of the pipe wall will often lead to cracks or leakage.In this paper,the local buckling behavior and parameter influence law of the large diameter gas pipeline are studied.Based on the simulation results,the critical buckling strain and critical fault displacement formula under the movement of strike-slip fault and the reverse fault is proposed.The main contents are as follows:Based on the theory of nonlinear finite element,shell theory and the parameters of China-Myanmar Gas Pipeline,ABAQUS was used to establish the 3D pipe-soil model of strike-slip fault,normal fault and reverse fault.The pipeline was modelled by the shell element and the soil was modeled by C3D8 brick element.The Ramberg-Osgood model is used to describe the elastic-plastic characteristics of the pipe.The constitutive model of the soil is described by the Mohr-Coulomb model and the size of pipe-soil is 60m × 10m×6m.The pipe-soil contact pairs were established to simulate the nonlinear contact behavior.Then through the comparison of the test results,the accuracy and validity of the model have been verified.Based on the analysis of the 10 sensitive parameters affecting the local buckling of the pipeline,the variation tendency of axial strain of the local buckling area,the overall deformation of the pipe and the maximum axial compressive strain with the fault displacement was obtained.Compared with the value of critical strain calculated by finite elment method under different operating conditions,the CSA limit compressive strain formula has some limitations and inaccuracies.Ultimately,the critical compressive strain formula and the critical fault displacement formula was proposed of the X80 gas pipeline crossing the active fault area by the analysis of multiple nonlinear regression theory.And the comparing results show that the calculated values of proposed formula are in good agreement with the simulated values,which could prove that the formula has a certain accuracy.The critical fault displacement formula can be used to assume the safety of the post-earthquake pipeline and estimate if it needs to be replaced in time.