Finite Element Analysis Of The Directly Buried Small Angle Bend Section

Along with the continuous expansion of the central heating,higher requirements is also put forward for the directly buried heating technology.So far,technology in the buried heating field has been improved gradually,however,there are some key problems to be solved,such as the stress analysis of tee joint,stress analysis of adapter bonnet and stress analysis of small angle bend,etc.Among them,the O°-10° small angle bend section design is often encountered as problems by designers.How to analyze the stress of the small angle bend in directly buried heating pipe network and find out appropriate processing method,a set of complete system method haven’t come up at home and abroad.Aiming at this phenomenon,using the finite element simulation method,this thesis has analyzed the directly buried heating small angle bend section stress distribution characteristic and change rules under various influence factors.The thesis is briefly described as follows:Chapter One introduces the background and significance of this thesis.Current research is introduced and analyzed.A brief introduction to research methods and contents is also given in Chapter One.Chapter Two analyzes functions and features of different kinds of load in directly buried heating-pipe and classify the stress and failure forms that may appear.Three forms of failure are pointed clearly,one is plastic deformation,one is local buckling,another is low cycle fatigue.Chapter Three introduced stress calculation method of small angle smooth bend,and compared stress check methods for the three main failure mode of the small angle bend at home and abroad,namely the plastic deformation,local buckling damage and low cycle fatigue damage.After explaining the European standards,the author uses Palmgren-Miner formula and S-N curve to calculate the critical stress of small angle bend pipe.Based on the calculation,one can know whether the small angle bend pipe can meet the safety requirement of low cycle fatigue.Chapter Four established 0°-10° finite element model of single mitred pipe bend and small angle smooth bend using ANSYS finite element analysis software,by exerting displacement load,temperature load and internal pressure load and axial pressure load to small angle bend local thin-walled shell model,it is concluded that the small angle bend’s capacity to absorb the displacement is very weak;axial pressure load in the size of nominal stress can replace temperature load in check of small angle bend in anchorage section;by simulating the influence of the curvature radius and soil spring for small angle bend pipe stress,the result shows that increasing curvature radius and soil elastic effect reaction can reduce stress of small angle bend,the method had better effects on larger small angle bend.Chapter Five summarized some small angle bend approach in the actual directly buried heating engineering,such as increasing the radius of curvature,using compensator and fixed piers to protect single mitred small angle bend;replacing small angle bend with elastic bending Angle;and setting combination of bend Angle and other bend to replace,thus it is convenient for design personnel to choose economic and save processing means in specific work condition.Chapter Six introduced research results of this thesis,and put forward some valuable Suggestions for small angle bend research in directly buried heating field.