The Finite Element Analysis Of Large Diameter Heating Directly-buride Elliptic Elbow

The local components of elbow, tee and reducer are the stress weak links in the heating directly-buried pipelines, and how to protect these components from being damaged is the key in the reasearch of heating directly-buried technology field when the pipeline network is in the condition of operation. In the process of production, the elbow will appear such uncontrollable defects that the cross-section is elliptical and the wall thickness is not equal, however, the domestic and foreign scholars have yet not made researches on the problem that how the ellipticity would influence the elbow stress.In view of this situation, this paper analyzed the influence and change rule of the heating directly-buried elbow which is caused by the ellipticity. The work of this paper is briefly described as follows:The first chapter basically narrated the research backgrounds of this paper, and briefly introduced the author’s research methods and the research contents aimed at the present situation of the elliptical elbow stress analysis at home and abroad.The second chapter presented the methods of the stress situation and intensity calculation of the ideal elbow, and also introduced the stress condition which the ellipticity elbow is only under the action of pressure that has been researched by the scholars at home and abroad.According to the different diameter, ellipticity and radius of curvature of the heating directly-buried elbow, the third chapter simulated and analyzed the influence of bend sress when the elbow is under the comprehensive function of different pressure load、displacement loads and temperature loads by using the ANSYS finite element software.The simulation results shows that the elbow cross section have certain ellipticity and the ellipticity is controlled in a certain range can reduce the sress size of the elbow dangerous area;the thermal displacement that is caused by temperature change is the main factor of making the elbow be destroyed; the higher the internal pressure is, the smaller the ellpticity that is corresponded to the elbow stress minimum value is; the effect of big bend curvature radius can not only reduce the size of the elbow stress, but also can weaken the elbow stress that is influenced by the ellipticity.The fourth chapter introduced two different fatigue analysis methods aimed at the heating directly-buried elbow at home and abrod, and also analysed how to determine the elliptical elbow’s fatigue life according to the simulation result.The fifth chapter introduced this paper’s research results,and put forward some meaningful suggestion in the light of the later elbow research work.