Research On On-line Monitoring Technology Of Weld Cracks In Steam Cooler Based On Acoustic Emission Principle

Steam cooler is an important equipment in the regenerative system of modern large-scale coal-fired power plants.The weld zone is affected by welding residual stress or other welding defects.Under the action of alternating running load,there is a risk of crack occurrence in the area due to weld crack propagation.Therefore,effective monitoring of the weld crack state of the steam cooler is of great significance for its long-term stable operation.The main research contents of this paper are as follows:(1)Taking the weld zone of steam cooler as the research object,the crack propagation process of the metal material was simulated by the crack propagation finite element method.The acoustic emission signal generated by the crack propagation of the metal material was obtained,and the response characteristics were analyzed.Design the weld crack fatigue expansion test,analyze the acoustic emission signal characteristics of the weld crack crack fatigue expansion of steam cooler and analyze the relationship between the acoustic emission signal characteristics generated by crack propagation and the crack propagation process,and the acoustic emission signal monitoring characteristics corresponding to the crack propagation of the weld of the steam cooler are proposed.Design control experiments to further investigate the effects of metal materials and crack defect types on the characteristics of crack propagation acoustic emission signals.(2)The guided wave characteristics and thermal conductivity of the waveguide rod are analyzed.The numerical simulation method is used to establish the numerical analysis model of the guided wave characteristics of the waveguide rod.The guided wave performance of different size waveguide rods is explored,and the reliability of the simulation results is verified by experiments.Based on the principle of thermal conductivity analysis,the thermal conductivity analysis model of waveguide rods with different sizes was established by numerical simulation method.The influence of the structure on the thermal conductivity was analyzed,and the influence of the fin structure on the thermal conductivity of the waveguide rod was investigated.In order to further study the guided wave characteristics of the waveguide under the hot state,based on the thermo-mechanical coupling analysis method,the guided wave characteristics are simulated on the basis of the thermal analysis of the waveguide rod,which provides guidance for the optimal design and selection of the waveguide rod.(3)The overall design of the acoustic emission monitoring scheme for the weld crack of the steam cooler is carried out.By constructing the on-line condition monitoring and evaluation system of the acoustic emission,the crack propagation acoustic emission signal of the weld zone of the steam cooler is captured and processed.Through signal analysis to determine the location of the acoustic emission source,analyze the nature of the acoustic emission source,determine the time of acoustic emission to monitor the crack propagation,and combine the experimental research and monitoring results to assess the severity of the acoustic emission source,suggest and appropriate treatment methods to achieve the purpose of monitoring the weld crack of steam cooler.