Research On The Crack Propagation Forecast And Preliminary Study On Turbine Runner Saftey Assessment

Fatigue crack is one of the main sources of component fault accident, Francis turbine runner blades often run a lot of fatigue cracks; seriously endanger the safe operation of power plants. The accident of Francis turbine runner blade cracks or faults is still commonplace, but the measures of detecting runner cracks, such as the ultrasound, magnetic detection, the Francis turbine need to be shut down at maintenance time, the crack monitoring on line and dynamic forecast crack growth trend is still a technical problem. At present, the shortcomings of turbine runner inspection by regular have been more and more significant, and the state of the runner blades cracks monitoring has become increasingly urgent.In this paper, the project 'Research of Theory and Method on Monitoring Crack of Francis Turbine Runner Blade' supported by national fund of natural science (50465002) as the background, research on fatigue crack propagation forecasting approach; using acoustic emission technology dynamic monitoring fatigue crack, according to analysis by the crack of the AE signal to analysis the crack state; application acoustic emission and vibration technology to runner safety assessment, which established the basis of theory in realizing on-line monitoring the status of the turbine runner.Firstly, the fatigue crack growth mechanism and the fatigue crack growth prediction method were discussed. Also, the grey model and neural networks were used for the fatigue crack growth forecast, and gives the turbine crack forecast method, and made the adaptation Analysis.Faced to Francis turbine runner blades the fatigue crack on the fatigue crack growth mechanism, using acoustic emission technology detect metal fatigue crack on the rise, development, fracture process, through the stretch and three-point bending fatigue test to prove that with the traditional Compared to detect cracks, AE can not only real-time capture of a fatigue crack, and can be theoretically and fatigue crack growth rate curve similar to the changes in the law. The introduction of the AE parameters and crack growth rate between the formula and the establishment of a crack AE signal characteristics and parameters of stress intensity factor between the mathematical relationships. Neural networks were used to the crack expansion phase of the pattern recognition.After analyzing the turbine runner structure, the crack of the causes and prevention measures to crack the traditional overhaul of the deficiencies, and the turbine runner crack the online monitoring and fault diagnosis of necessity were discussed, too. According to Francis turbine runner crack the overhaul of the actual situation, to launch technology based on AE and vibration technology to conduct a security assessment runner, and the runner-line monitoring and fault diagnosis.