Research On Numerical Simulation Of Multi-Layer Wrapped Vessel's Stress Field Based On Finite Element Method

To high pressure vessel, multi-layer wrapped structure as kind of pressurized equipment is common and supposed can't be damaged. But now this kind of vessel has induced many disastrous accidents. So how to evaluate the wrapped layer vessel's remaining life became an urgent problem. In order to establish a feasible test to evaluate wrapped layer vessel's remaining life and detect the defect efficiently, Qingdao University of Science &Technology with other three units apply for the 863 project named test evaluation for wrapped layer vessel's remaining life. This article mainly worked on wrapped layer vessel's numerical simulation in aspects of stress field and temperature field to estimate and evaluate wrapped layer vessel's remaining life.When performing numerical simulation, I had to establish lots models, and it was very difficult especially presented a model of contact through manual operation when considering the layer gap. So based on ANSYS, I developed a finite element parametric analysis program in wrapped layer urea converter, and integrated modeling&division grid&load solution and so on various functions into the system. Then I can complete the urea converter finite element numerical analysis quickly through inputting few parameters. All of these reduced the analysis work load and the difficulty greatly.I carried out a detailed finite element analysis for urea reactor by using parametric program, and analyzed with the experimental results. The results showed that the calculation stress of numerical simulation and P.G.Pimshtein Formula have the same trend, the data are in good agreement with each other, but the result of Lame Formula has a greater deviation. With the Laminate's gap increasing, the external laminates number that doesn't bear pressure is growing and Laminates rupture possibility occurred more easily. Multilayer girth weld connecting is the most complex parts of Stress distribution since the existence of laminate's gap. The more around the both sides of welding seam, the more pull stress and the compression. Shelf space and deep girth weld parts intersect produce a cusp, the most vulnerable stress parts is the top laminates gap and deep girth weld fusion line. Analysis also shows that change in the Slope angle has a certain impact to the distribution of stress field of deep girth weld fusion line.Therefore, the layer gap and the welded joint form and so on have the very tremendous influence to the multi-layer wrapped urea converter stress field's distribution. The urea converter strain test result also indicated that gaps between the urea converter layers have the tremendous influence to the urea converter stress distribution. And there is a basically good agreement between the actual strain value and the theoretical value. So, when carrying on the multi-layer wrapped urea converter design, should consider the stress concentration's influence which caused by gaps to urea converter overall intensity.I found that the Local Stress at deep seam weld toe ring site has already exceeded the yield strength while I was doing structure linear elastic numerical simulation of urea reactor, Therefore I did a elastic-plastic finite element analysis for urea reactor. The results showed that it has the largest von Mises stress at Blind and both sides of the first layer. It can prove that lining layer, blind lamellar gap between the inner core and the corresponding deep seam weld toe Central location may be a limited yield under actual operating pressure.Because urea reactor's operating temperature is high, I got thermal- structure coupling analysis at last. The result showed that temperature load on urea reactor has little affection on stress field under the operating temperature.