Research On Forecast And Assessment Of Steam Turbine Blade Life

With the development of power industry, people put forward higher requirements on the strength and life of steam turbine blades. The operation practice of steam turbine show that the fatigue failure is the main failure reasons of blade, and the turbine blade is complex in structure and operation conditions, the stress to the qualitative description is difficult, all these increase the difficulty of the research on the life of the blade. Using finite element analysis method to study the fatigue performance of the blade is a useful method of fatigue analysis, and its result to the blade design, the manufacture, the optimization and reliability evaluation has important reference value.The domestic 135MW/100 MW steam turbine blade prone to failure is taken as research object, combined with finite element method, utilized finite element analysis software HyperMesh and Ansys to calculate the static and dynamic stress field of blade, then paper proposes a theory combined with the finite element simulation analysis and fatigue life evaluation vulnerability analysis method of the blade. First of all calculating stress of the blade, then the result is imported into the MSC.Fatigue to predict the life of the steam turbine blade, lastly putting forward the evaluation method of fatigue life. The result has guiding significance and application value for design and life management of steam turbine unit. The main research works are as follows:1) Through the analysis, we find that there are two kinds of common failure mode of blade fatigue. Then illustrate how to use mathematical defining material characteristics curve, according to these mathematical formula study the process of material fatigue performance parameters, and relationship between each of these fatigue parameters, all above provide the basis for the analysis of fatigue.2) In view of the low cycle fatigue of blade, the paper analyzes and summarizes the effects of the low cycle fatigue of two kinds of main load, static steam force and centrifugal force load, and studies the calculation methods of the static steam force. We established the finite element model of the blade by using HyperMesh and Ansys. Then calculate the static stress distribution of blade, on the basis of the static stress field, combining with the blade material strain fatigue characteristic curve and load spectrum, using the Neuber strain correction method on Miner linear fatigue cumulative damage theory, the blade low cycle fatigue life was calculated and predicted. Then low cycle life evaluation method of the blade are given3) In view of the high cycle fatigue of blade, the paper analyzes and summarizes the influence of the main load of high cycle fatigue is the steam excited vibration. With single blade as the research object, the paper uses the modal analysis to determine the speed and frequency of the blade when resonance occurs. Then the harmonic response analysis was carried out on the blade, on the basis of the analysis results of the harmonic response of blade dynamic stress distribution, combining with the blade material stress fatigue characteristic curve and load spectrum, using the Goodman mean stress correction method on Miner linear fatigue cumulative damage theory, the blade high cycle fatigue life was calculated and predicted. The life of the fractured blade of 100 MW turbine is calculated, and the results are in agreement with the actual results. Finally, how to use the research content to evaluate high cycle fatigue life of the blade is given.Through research, this paper calculated the blade of 100 MW steam turbine of high and low cycle fatigue life, its result is in agreement with the actual result and provided a feasible simulation analysis method for the blade fatigue life calculation and evaluate. This has some guidance for the future calculation of the life loss of other conditions.