Creep-fatigue Strength Research For An Ultra-Supercritical Steam Turbine Valve Based On Different Assessment Specifications

Under the background of energy saving and emission reduction,the high-parametric trend of power plant steam turbine become more obvious.The valve is one of the most crucial parts of a steam turbine,normal operation of which is the guarantee of safety for the steam trubine.The valve not only endures the creep under high temperature more than 600? and the fatigue problem during the start-shutdown process,but also the interactive effect of these two which can accelerate the damage speed.Therefore the assessment for valve strength is vital for safe operation of the valve.In this paper,FEA software Abaqus is used to calculate the valve of an ultra-supercritical steam turbine,and the results of stable operation and startstop operation are analyzed respectively.For the stable operation stage,the temperature field,displacement field,stress field and equivalent creep strain of the valve are obtained.The characteristics and causes of the results are analyzed,and the location of significant creep is pointed out.For startup and shutdown stage,the reasons of temperature field and stress field change are mainly analyzed.FEA paves the way for strength assessment.On the basis of FEA,the characteristic locations are selected for the defect-free structure assessment procedures of R5 volume 2/3,and the general strength analysis of the valve strength is completed.Afterwards,Abaqus post-processing programs are compiled based on the fatigue and creep damage algorithms of R5 code,ASME code and continuum damage method,respectively.The programs are written in Python language.Finally,these programs are used to calculate the fatigue damage,creep damage and coupling damage of the valve,to assess the life of the valve,and to complete the final step of the strength assessment of the valve.The results obtained by different methods are compared and analyzed,and their respective characteristics are summarized.