Finite Element Analysis On Creep Damage For Hot The Manifold Of Steam Reform Furnace Based On Damage Mechanics

Steam reformer is the core equipment of hydrogen plant in chemical industry.In order to improve production efficiency,its operating parameters have been continuously improved.As the key component of steam reform furnace,the working environment of the manifold is very harsh,the temperature of the medium in the pipe is as high as 890?.At the same time,due to the internal pressure,temperature difference thermal stress and various constraints between the piping systems,the stress of the whole pipe system of steam reform furnace is extremely complex.In addition,the material deterioration of the manifold in the long-term high temperature service process leads to the problems of bending,bulging and cracking of the manifold.During the operation of the equipment,the sudden rupture of the manifold will not only lead to unplanned shutdown,but also bring huge economic losses,and even cause production accidents and endanger workers'lives.At present,the domestic research on the key components of the manifold of the high-parameter steam reform furnace is still in its infancy.There are lots of blanks in basic research and pre-research on key technologies,especially the research on the life prediction of the manifold.Therefore,the research of creep damage analysis on the 20Cr32Ni1Nb manifold of the high-parameter steam reform furnace is of great engineering application value to ensure the long-term safe operation of the high-parameter steam reform furnace.In the dissertation,according to the uniaxial creep test data of 20Cr32Ni1Nb manifold of the high-parameter steam reform furnace and on the basis of the creep damage mechanics,a constitutive model of creep damage based on the dual damage mechanism is proposed.The creep damage of the 20Cr32Ni1Nb manifold is analyzed by using finite element method.The service life of the 20Cr32Ni1Nb manifold of the high-parameter steam reform furnace is predicted.The main research work and the conclusions obtained are as follows:(1)A new creep damage constitutive model was established based on sinh function by considering the influence of carbide coarsening and void nucleation and growth on creep behavior of Fe-Cr-Ni based austenitic stainless steel.On the basis of the model,a nonlinear least square method was used to develop a model material parameter optimization program.The results show that the proposed creep damage constitutive model can accurately reflect the uniaxial creep behavior of 20Cr32Ni1Nb alloy at 890?/30MPa,35MPa,40MPa,45MPa and50MPa;the parameter optimization program realizes the automatic optimization of each parameter in the model.(2)On the basis of Kachanov-Robatnov,Liu-Murakami and Proposed Model,combined with the finite element numerical solution method,the UMAT subroutine is compiled to analyze the creep damage of typical high temperature components(round steel,straight pipe and elbow),and the results are discussed.The results show that compared with the Kachanov-Robatnov and Liu-Murakami creep damage constitutive models,the proposed creep damage constitutive model can reflect the nonlinear relationship between stress and failure time in a wide stress range under the double logarithmic coordinate,and the prediction results are more conservative.(3)Based on the actual size of the 20Cr32Ni1Nb manifold of the high-parameter steam reform furnace,a finite element analysis model for the creep damage of the manifold was established.Based on the Proposed Model,the creep damage finite element analysis of the manifold is carried out,and the results are discussed.The results show that:after 10~5h service in ideal condition,the maximum damage location occurs at the place where pigtail crosses with manifold,and the maximum cavities damage value reaches 0.186,that is,the service life(10~5h)is 58.1%of the total service life of the 20Cr32Ni1Nb manifold,which suffices the design life of 10~5h.