Optimization And Performance Study Of Right Angle Bend Pipe Of Direct Buried Heating Pipeline

With the rapid development of clean heating,the direct burial method has been widely used in heating pipe networks due to its advantages of low cost,long life and convenient operation and management.Due to the road conditions and the inevitable obstacles,the elbows have been used to some extent in the direct buried uncompensated pipe network.However,the length of the curved arm of the elbow may be the maximum transition length and the lateral displacement is constrained by the soil,making it difficult for the elbow to meet the stress checking conditions.In the project,some measures are often taken to protect the elbow and it is difficult to achieve a true uncompensated laying.At present,domestic and foreign scholars have carried out a lot of research on traditional elbows,but there is a lack of optimization research on the elbow structure itself.In view of this,this paper carries out an optimization study of the elbow structure,aiming to provide a strengthened elbow structure that can fundamentally reduce the maximum stress value.In this paper,the finite element model of ordinary curved pipe and three kinds of reinforced curved pipestructures is established,and a comprehensive numerical simulation work is carried out.Firstly,the structural parameters of the three strengthened elbows are optimized respectively,and three optimized strengthened elbow structures are obtained.Then,by comparing and analyzing the stress performance of the ordinary elbow and three optimized strengthened elbows,the most The optimized strengthening of the elbow structure is carried out.Finally,the optimal strengthening elbow structure is studied under different influencing factors,and the stress distribution law of the elbow is obtained,which provides a reference for the practical engineering application of the optimal strengthening elbow structure.The main research work and main conclusions of this paper are as follows:(1)Based on the simplified soil spring model,the pipe material is regarded as an infinite elastic body,and a finite element model is established for the pipe structure,and the model is checked for grid independence.By applying a surface effect unit to simulate the axial friction between the pipe and soil,a displacement load is applied in a direction perpendicular to both end faces of the pipe to simulate the length of the compensated arm outside the straight pipe section of the model,and the pipe is uniformly applied with uniform pressure load and temperature Load.(2)In this paper,three types of strengthened elbow structures are proposed.By analyzing the influence of structural parameters of each strengthened elbow on the stress value of the elbow,At the same time,the stress performance ofordinary curved pipe and three optimized strengthened bending pipes are compared and analyzed to obtain the optimal curved pipe structure.(3)The numerical simulation of the optimal pipe structure of pipe diameter DN800 is carried out.the influence law of different influencing factors on the maximum stress value of the pipe structure is obtained.(4)Stress analysis results of curved pipe structures:1)For the elbow structure 2(wall thickness enhancement type),as the wall thickness of the elbow increases,the maximum stress value at the elbow shows a decreasing trend,but the stress reduction range is different.2)For the elbow structure 3(rib reinforcement type),as the height of the rib increases,the maximum stress value of the inner elbow decreases,the maximum stress value of the outer elbow increases,and there is a reasonable rib height,so that the inner and outer layers The maximum stress value of the elbow is small and the stress values of the two are balanced;the thickness of the rib has little effect on the stress value of the elbow structure.3)For the elbow structure 4(rib and straight arm reinforced),as the length of the straight arm increases,the stress values of the inner and outer elbows tend to decrease,but the stress reduction is different;with the increase of the rib height The maximum stress value of the inner elbow is reduced,and the maximum stress value of the outer elbow is increased.There is an optimum combination of the length of the straight arm and the height of the ribs,so thatthe maximum stress values of the inner and outer bends are small and the stress values of the two are balanced.4)Under the same pipe diameter,compared with the elbow structure 1,the elbow structure 2,the structure 3 and the structure 4 can effectively reduce the maximum stress value of the elbow,but the reduction ratio of the three is different,and the elbow structure 2 has the smallest reduction.The curved pipe structure 3 is secondarily reduced,and the curved pipe structure 4 has the largest amplitude in the reduction.5)With the temperature difference of the medium circulation and the decrease of working pressure,the maximum stress values of the inner elbows and outer elbows of the elbow structure 4 are all decreasing,and the maximum stress values of the inner elbows and outer elbows are balanced.6)With the increase of the radius of curvature and wall thickness of the elbow,the maximum stress value of the inner elbows and outer elbows of the elbow structure 4 is significantly reduced,and the maximum stress values of the inner elbows and outer elbows are balanced.