Stress Analysis And Countermeasures Of Buried Nature Gas Pipeline In Uneven Settlement

The pipeline transport of natural gas in China has been developed rapidly.Constrained by geologic condition,many pipelines have been buried in soft soil.With the weak bearing capacity,those pipelines buried in soft soil are prone to be destructed under uneven settlement.In order to ensure safety operation of natural gas pipeline,the stress analysis and countermeasures of natural gas pipeline under uneven settlement should be investigated due to inflammable and explosive properties of natural gas.The main contents of this paper are summarized as follows:(1)A mechanical analysis model of pipeline for natural gas transmission station is established based on elastic foundation beam theory and structural mechanics.The stress analysis of pipeline is carried out with analytic method,and the expression of additional stress of pipeline under uneven settlement is deduced.(2)A pipe-soil interaction analysis model is established.ABAQUS is adopted to analyse the influence of pipeline parameters and soil physical properties on pipeline stress,and the stress variation of pipeline under different settlement condition is ontained.According to finite element calculation results,the relation formula between maximum Mises stress and the length of settlement spool and ultimate settlement displacement is obtained by MATLAB.The maximum Mises stress of pipeline under different settlement conditions may be predicted by formula.(3)Based on the axial stress analysis,the thresholds of additional axial tensile stress and additional axial compressive stress are 171.3MPa,-148.5MPa respectively.A multilevel early warning for pipeline additional stress is set up,and safety protection measures are postulated.(4)The additional stress level of pipeline under non-uniform settlement and the validity of finite element analysis is obtained by resistance strain gague method.Maximum values of axial additional stress and hoop additional stress are 114.9MPa,142.0MPa.The rectification method is proposed for high stress area,combined the finite element analysis and the measured results of the pipeline stress,the overall additional stress level of pipeline is reduced,and the pipeline is in safe state.The results can be treated as an guidelines for stress analysis and safety protection of natural gas pipelines under uneven settlement.