Analysis Of Inner Pressure Of Liquid-filled Elbow Pipes And Study Of Tube Bending Of Equal Strength By Induction Heating

As one of the modern transportation system, pipeline is extensively used in power, oil, natural gas, chemical, city gas and heating system, it is of great importance for modern transportation industry. In practical engineering, it has the following problems when analysing the stress for the liquid-filled elbow pipes:1) The inner pressure is uneven distribution:the pressure on the convex edge is larger than that on the concave side considering from the flow regularity of the fluid in the elbow bend.2) It will thin easily on the convex edge because of tensile stress, on the contrary, it will help thicking on the concave edge because of pressure stress in the process of machining considering from processing technology. From the problems above we can see:the wall thickness of high pressure area of the elbow pipe is thin than that of the low pressure area. Therefore, it is relatively weak for elbow pipes in pipeline nets. The defect problems of the elbow pipes become more noticeable because they are out of repair for long years, so accidents often occur caused by pipeline failure. Especially for pressure piping, whose transport medium is high temperature, high pressure, highly combustible liquid and gas, will cause serious economic losses, and a large number of casualties in the event of an accident.In view of the ticklish problems above, numerical simulation of the process in which liquid medium flows through the elbow pipe is simulated by FLUENT of the CFD software package based on the computational fluid dynamics. The inner pressure formula of the elbow pipe is fitted out by the software named 1stOpt according to the pressure value, then the wall thickness formula of the elbow pipe is figured out by the strength theory after analyzing the stress of the elbow pipe combining with the knowledge the plastic mechanics. Finally, the ox horn mandrel is designed, in the meantime, the forming process simulation is simulated by software named MSC.MARC and finally we get the tube bending of equal strength. The following research contents are included in this article:1. The pressure simulation data of the ninety degree elbow pipe is simulated under different flow conditions by the software called FLUENT. The inner pressure formula of elbow pipe is fitted out by the software named 1stOpt after analyzing the pressure simulation results and summarizing the influence of various parameters (inlet velocity v, outlet pressure Po, the liquid density p, the degree of curvature k, the axial angle a and the circular angle β) to the regularities of distribution of inner pressure of the elbow pipe.2. According to the formula of the inner pressure of elbow pipes, the wall thickness formula of elbow pipe is figured out by the third strength theory after analyzing the stress(axial stress σz, circular stress σβ, radial stress σr) of the elbow pipe at work combining with the knowledge the plastic mechanics.3. The 3d models of ox horn mandrels (horn mandrel with ellipse sections and horn mandrel whose central axis is Archimedes spiral) are designed and the corresponding straight tube blanks are selected, then the forming process of induction heating is simulated by the finite element software named MSC, by comparing the regularities of distribution of the wall thickness of the two types of horn mandrels by hot pushing, finally we find that the best solution whose finished product has equal strength is the ox horn mandrel whose central axis is Archimedes spiral.