Research On Magnetic And Acoustic Composite Detection Technology Of Boiler Water Wall Tubes

The water wall tube is the most important evaporation surface of the boiler.However,the tubes often run on hazard environment filled with flame,smoke and ash.Working in this kind of environment,water wall tubes are easy to generating various types of defects,which may lead to the boiler explosion accident.Therefore,focusing on the defect detection of the tubes is really important for ensuring the safe operation of the boiler.The types of defects in the inner and outer walls of water wall tubes are complicated.The traditional single non-destructive testing(NDT)methods all have their own limitations in regard to the defect detection capabilities,so it is difficult to achieve the goal of all-round defect detection.In order to solve this problem,in recent years,more and more scholars have begun to research on the composite non-destructive testing technology.However,due to the complicated working conditions of water wall tubes,the current theoretical research on the structural design of the composite NDT detecting sensors is insufficient.There are also lack of specific methods for designing the parameter of the composite detection sensors,and experiment platform for conducting more in-depth experimental research.In order to solve the above problems,this paper will research on magneticacoustic composite detection technology for boiler water wall tubes defect detection.Aiming at the fact that the current theoretical research on the structural design of the composite NDT detection sensors is insufficient,in this paper,a composite NDT detection sensor will be designed which is based on the electromagnetic acoustic testing(EMAT)method,magnetic flux leakage testing(MFLT)method and pulse eddy currents testing(PECT)methods.Based on the equivalence analysis,the simulation model for the magnetic-acoustic composite sensor will be proposed.Aiming at the fact that the specific method for designing the parameter of the composite detection sensor is lacked,in this paper,a design method will be proposed based on the simulation model of magnetic-acoustic composite detection sensor.Firstly,the optimal magnetic field working point corresponding to the three different kinds of detection methods is calculated.Secondly,the method for designing a static magnetic field excitation structure of the composite detection sensor will be designed.Thirdly,the influence of the sensor structural parameters on the leakage magnetic flux,pulse eddy current and electromagnetic ultrasonic detection signal is analyzed.The parameter design method of magnetic-acoustic composite detection sensor is proposed.Aiming at the fact that the experimental platform of magnetic-acoustic composite detection technology is lacked,in this paper,an experimental platform is designed basing on the principle of magnetic-acoustic composite detection technology.The platform is required to implement the following functions: Firstly,it can generate the electromagnetic ultrasonic and pulsed eddy current excitation signal generation.Secondly,the multichannel magnetic flux leakage signal,electromagnetic ultrasound echo signal and the pulsed eddy current detection signals can be collected,displayed and stored.Thirdly,a pipeline crawling device should be designed,using for fixing and moving magneticacoustic composite detection sensors.Based on the experimental platform of the magnetic-acoustic composite detection system,the defect detection capability of the sensor is verified.Firstly,based on the simulation model of magnetic-acoustic composite detection sensor,the influence of defect parameters on the characteristic quantity of detection signal is analyzed,and the detection method of magnetic flux leakage and pulse eddy current defect is proposed.Then,the water wall tube was taken as the research object,and the actual detection ability of the composite detection sensor for four artificial defects and wall thickness measuring was studied.The experimental results show that the magnetic-acoustic composite detection sensor designed in this paper can effectively detect the four types of artificial defects on the pipeline surface.