Research On Structural Integrity Of X80 Steel Natural Gas Pipeline Under Special Geological Conditions

With the development of the economy,the world's demand for natural gas is also increasing.Pipeline transportation is the safest and most economical of the five transportation methods.X80 pipeline steel has good mechanical properties,so it is widely used worldwide.China's geological conditions are complex,and long-distance natural gas pipelines inevitably need to go through complex geological environments.In recent years,due to special geological conditions,accidents caused by natural gas pipelines have continued to occur.Among them,faults and landslides have brought the most hazards.The most representative accident is the explosion of the China-Burma pipeline.In view of the above problems,this paper uses a combination of theoretical analysis,experimental testing and numerical simulation to study the strength failure mode of the X80 natural gas pipeline under the special geological conditions of faults and landslides.The main research contents and results are as follows:(1)Through tensile,Charpy impact,and three-point bending tests,in order to study the pipeline structure response and defects under special geological conditions safety assessment provides data basis,the constitutive relationship of X80 pipeline steel and the material's yield strength,tensile strength,fracture toughness and other mechanical performance data were obtained.(2)For the X80 steel pipeline under strike-slip fault,a pipe-soil contact model was established,the mechanical response of X80 steel under different influence factors was studied,and the critical strain and fault displacement of X80 steel under different fault displacements were obtained.Strain-based failure criterion for defect-free X80 pipeline steel was obtained.(3)For the X80 steel pipeline under the action of lateral landslide,a model of pipeline crossing through the landslide was established.The stress and strain of the pipeline under different landslide displacements were considered.Different factors(wall thickness,buried depth,internal pressure,landslide displacement,soil,body properties,etc.)on the strength of X80 pipeline were put forward.(4)For the pipelines with defects,based on the X80 mechanical performance data,the X80 special failure assessment curve was established,the safety evaluation of the defective welds under special geological conditions was carried out,and the weld seam geometry such as residual weld height,staggered edges,under-weld penetration,etc.The influence of dimensional factors on the evaluation of defect safety has obtained the allowable defect size of X80 girth weld under special geological conditions of faults and landslides,which provides technical support for the safe operation of defective pipelines.