Analysis Of The Mechanical Properties Of The Buried Steel Pipeline Crossing The Fault In The Frozen Soil Area

The demand for oil and natural gas in various countries is increasing,and the supply and demand of oil and natural gas have a large span.Considering strategic,safety,cost and other factors,long-distance pipeline transportation becomes the preferred solution.However,long-distance pipeline transport will inevitably have to cross the tundra,seismic belt and other complex terrain environment.Frost heave and fault of permafrost will cause serious damage to oil and gas pipelines.Therefore,it is necessary to deeply study,analyze and summarize the failure modes and mechanisms of buried steel pipelines crossing faults in frozen soil areas,so as to play a helpful role in pipeline design and maintenance under such working conditions.This article first to the frost heave and strike-slip fault mechanism analysis,the pipe using scaled finite element software ADINA.the thus,the buried steel pipelines across the fault simulation on temperature field calculated in frozen soil frost heave,as the initial condition into strike-slip faulting structure in the simulation,the distribution and variation rule of the pipeline displacement stress and strain under six different working conditions were simulated and analyzed,based on the stress and strain analysis of the formula of ultimate strain of pipeline and comparison analysis,the conclusion is as follows:1)Frost heaving is the effect of the volume expansion of frozen soil on the pipeline.The fault makes the position of the pipeline change by dislocation,and the permafrost restrains the pipeline,resulting in the pipeline deformation and finally failure.The buried pipeline through the fault in the permafrost area,where the fault is the main influencing factor.2)Under different working conditions,small fault displacement,thick pipe wall,fault intersection Angle of 45*,small outside diameter,thick insulation layer thickness and high grade pipe are all favorable for buried steel pipe crossing the fault in frozen soil area.With the increase of the displacement of the fault,the deformation of the pipe changes from "one" to "Z" of 45* line.The displacement cloud map is 45* wavy and aggregated to 45* line.It can be seen from the upper part of the pipe(Y-axis)that the displacement cloud map is "bullet".The strain cloud map of pipeline gradually changes from "V" to "snake head",and the stress cloud map shows the distribution of "eight" and double "eight".The insulation layer can effectively reduce the stress,strain and displacement of the pipeline,reduce the impact on the surrounding frozen soil,and play a good role in buffering and heat insulation of thepipeline.3)Stress-based pipeline design is suitable for pipelines in general terrain environment,and strain-based pipeline design is more suitable for pipelines in terrain prone to displacement changes.The formulae of ultimate strain generally take into account diameter-thickness ratio,steel grade and pipe pressure.In the Norwegian and American codes,the calculated limit strain is high,Japan is in the middle,and China and Canada are low,which are also closest to the simulation value in this paper.In the Chinese codes,the pipeline design through fault can meet the requirements of the pipeline through fault in permafrost regions.When the fault rupture is greater than 1.5m,it needs to be designed separately.For the design of long-distance transportation pipeline,different pipe diameter,wall thickness,steel grade,insulation layer thickness should be adopted.