Finite Element Analysis And Research On Immersed Natural Gas Pipeline Construction

Due to various factors,the existing natural gas pipelines can easily lead to the phenomenon that the pipelines cannot reach the original design buried depth,or even partial bareness,which will threaten the safe operation of pipelines,so shallow buried or bare pipelines need to be rectified.One of the renovation methods is the elastic immersed pipe,that is to say,within the allowable range of elastic deformation of pipeline,by controlling the length of pipeline excavation,the pipeline will naturally settle by its own gravity,so that the pipeline can meet or approach the requirements of design depth.Based on the analysis of buried depth and exposed condition of natural gas pipeline,this paper divides the pipeline engineering problems into four types:shallow buried or bare point and shallow buried or bare section in flat section,shallow buried or bare point in uphill section and shallow buried or bare section.Based on these four engineering problems,the paper analyses the settlement of natural gas pipeline.The main work is as follows:(1)According to the engineering situation of natural gas pipeline,the mechanical characteristics of natural gas pipeline are analyzed,and the pipeline beam element model is established according to the condition that the pipeline span in settlement area is far larger than the diameter of pipeline and the pipeline beam element theory;(2)By using finite element method,the excavation distance and deformation stress required for pipeline settlement to design depth are studied,and the finite element analysis method including grid,material,analysis layout,load and boundary conditions and the evaluation method of analysis results are established;(3)The excavation distance of natural gas pipeline settlement in flat section and upstream section is calculation under the influence of different working conditions,pipeline deflection,and pipeline size and pipeline material.During the construction process,the corresponding pipeline excavation distance can be selection according to the construction requirements;(4)Studied The influence of different deflection,pipeline size and pipeline material on the excavation distance and post-settlement stress of pipeline settlement under four engineering conditions,i.e.,shallow buried or bare point in flat section,shallow buried or bare point in uphill section,shallow buried or bare point in shallow section or bare section;(5)The influence of the length of shallow buried or bare section of pipeline on the settlement of pipeline is studied.(6)The influence of gas pressure on the internal stress of pipeline after settlement is studied.The main conclusions are as follows:(1)Under the same pipeline size,pipeline material and deflection,the excavation distance of the uphill section is slightly larger than that of the flat section;Compared with bare or shallow buried point,the excavation distance of bare or shallow buried section of pipeline is smaller at ?508 x 7.1 than that at bare or shallow buried point,but at ?762 x 7.1 and ?914 x 7.1,the excavation distance of bare or shallow buried section of pipeline is larger than that at bare or shallow buried point.After settlement,the stress of the pipeline does not reach the ultimate yield strength of the material and the pipeline does not fail.(2)The deflection of pipeline has great influence on the excavation distance of pipeline.Under the same pipe size,material and working condition,the smaller the deflection is,the shorter the excavation distance is;(3)Pipeline size has a great influence on the excavation distance,that is,the larger the size of pipeline,the longer the excavation distances of pipeline settlement and the greater the stress after pipeline settlement.(4)Pipeline material has little influence on the excavation distance.Under the same pipe size,deflection and working conditions,the excavation distance of pipeline is almost equal for different pipeline material.(5)When the length of shallow buried pipeline or bare pipeline is longer than 85m,the excavation distance has no effect on the settlement distance,that is,only excavating the shallow buried part,the pipeline can settle to the predetermined height.(6)When gas pressure is applied to the settled pipeline,the internal stress of the pipeline is lower than the yield strength of the pipeline,and the pipeline is not invalid.