Analysis Of Several Prediction Techniques For High Temperature Creep Life Of Sanicro25 Steel

Sanicro25 steel has high creep strength and high corrosion resistance at high temperature.It has become an important material for superheater and reheater pipes in the new generation ultra supercritical thermal power unit.However,the component is prone to creep fracture during long time working under high pressure and high temperature corrosion condition,which makes the component failure.Accurate prediction of creep damage life is of great significance to the use and design of the pipeline.This paper takes the Sanicro25 steel as the research object,the creep constitutive models are applied to predict the high temperature creep life of the steel by the calculation method of finite element simulation and analytic calculation.Relationship between creep strain rate and creep ductility parameter,which used in the creep ductility model with better prediction effect on life extrapolation was analyzed.The main contents of this paper are as follows:(1)Based on the creep data of Sanicro25 steel,Manson-Harferd model of time temperature parameter method,Kachanov-Rabotnov creep damage mechanics model including a damage variable,Dyson creep damage mechanics model with three damage variables,Creep Ductility model based on creep hole growth and microcrack action,are analyzed.The creep life under different stress levels was predicted,and the accuracy of creep rupture life prediction of different constitutive models was analyzed.It is found that the creep ductility model is more consistent with trends of experimental data points than the other three models,the other three models will be different degrees of overestimate or underestimate the creep life of Sanicro25 steel,from the point of view of engineering application,using the model to predict the creep ductility of high temperature component life can ensure the safe use of equipment.(2)The correlation between creep ductility and creep stress / creep strain rate was considered,the quantitative relationship between creep ductility value and creep strain rate was established,differential creep ductility values under varying stress values were obtained.The above results were substituted by the finite element method.It is found that the correlation between the creep ductility,the mean creep strain rate and the minimum creep strain rate is not the same as that of the original simulation results.Compared with the prediction results based on the average creep strain rate,the prediction results based on minimum creep strain rate for creep ductility and stress values are better than those predicted by experimental data.(3)According to the principle of conservation of energy and the principle of entropy conservation,the variation law of creep ductility with creep stress was considered,and based on the theory of creep activation energy,the relationship between stress and activation energy was constructed,two analytical models for life prediction were deduced.Compared with the experimental data,these models are not only simple,but also have higher prediction accuracy,which provides a new method and idea for damage evaluation and life prediction of high temperature components.