The Cold Bending And Hot Bending Elbow Stress Analysis Of Long Distance Hot Oil Pipeline

With the development and utilization of the world energy,the extraction of oil and gas,transportation and storage has become an important symbol of national economic development,and has drawn more and more attention by countries around the world,and has become a barometer of world economic development.As a safe,economic and effective means of transportation of oil and gas,oil and gas long distance gas transmission pipeline transportation industry got rapid development all over the world.In the construction of long-distance pipelines,to meet the line to the design requirements,pipeline usually needs to turn to change direction.There are usually two types of steering,horizontal and vertical steering,mainly through methods such as by adding the elastic laying of elbow or bend.Cold bending and hot bending elbows are the most popular elbows.From the angle of stress analysis,the stress of the elastic laying pipeline section is equivalent to the straight section,but the stress of the bend section is very complex,so far there is not an accurate calculation method.Therefore,the long distance hot oil pipeline pipe bending stress analysis is of vital importance.This paper,by using ANSYS to establish the long distance gas transmission pipeline pipe bending model and the high and steep slopes in bend model,took the method of combining the theoretical analysis and numerical simulation,to study the following content,and draw the following conclusion:(1)This paper introduced the basic hypothesis of stress analysis,the load and stress of pipelines,summarized the common calculation models of pipe bending,namely,elastic flexure hinge model,soil resistance model,draw the calculation method of elbow hoop stress,and provided a theoretical basis for subsequent elbow stress finite element analysis.(2)Finite element model of elbows of different angles are established.The effect that different radius of curvature and different diameter-thickness ratio do to the elbow stress is analyzed.Conclusions are made that,the elbow hoop stress of elbow with the same diameter and thickness decreases with the increase of bending curvature radius,and the largest hoop stress appears in the bending section of the inner pipe wall.At the same time,with the increase of bending curvature radius,the hoop stress of the bent pipe tends to the hoop stress of straight pipe.When the bending curvature radius is certain,the diameter-thickness ratio varies with choosing different types of pipes.The maximum stress of X80 elbow increases with the increase of the diameter-thickness ratio.(3)Taking a long-distance pipeline project as an example,pipe model of high and steep slopes in long distance gas transmission pipeline has been established by using pipe soil coupling model with the shell-spring combination.Factors that affecting the maximum elbow stress of the high and steep slopes bending pipes are analyzed.Conclusions are made that,the maximum stress of the high and steep slopes bending pipes decreases with the increase of the wall thickness when the bending curvature radius is certain;and the stress also decreases with the increase of the radius of curvature when the wall thickness is certain.When the radius of curvature reaches 6.0,variation in stress value is small.The maximum stress of X80 pipe is obviously smaller than that of X70 when the radius of curvature and the wall thickness are certain.