Development Of MFL NDT System For Automatic Inspection Of Water-Cooled Tubes Of Boiler

The water-cooled tubes play an important role in power generation of power station boiler,its interior is a flowing high temperature water vapor mixture.High-temperature mixture of water and steam flowed through and outer surfaces heated by the finance.It will lead to generate various flaws of the water-cooled tubes in such an environment for a long time,Eventually,it will cause the safety accident of tube-burst.According to the failure mechanism and complex working conditions of boiler water-cooled wall tubes,the magnetic flux leakage(MFL)detection technology is used to realize the high-efficiency detection of water-cooled wall tubes to ensure the safe operation of power station boilersFirstly,By comparing various non-destructive testing(NDT)methods,the outstanding advantage of MFL testing technology is that other NDT methods cannot be replaced,which is suitable for the detection of water-cooled wall tubes.The generation mechanisms of these flaws described in the thesis have been deeply studied under the consideration of working condition and structural feather of the tubes.Essentially understood the formation mechanism of its defects.Secondly,COMSOL Multiphysics numerical simulation software is used to verify the principle of MFL detection technology.The relationship between the influencing factors of MFL detection and MFL signal is analyzed and calculated.It provides a theoretical basis for the determination of magnetic flux leakage detection signals of water-cooled wall tubes.Thirdly,solutions for magnetic leakage testing are proposed.The parameters of the magnetization device are determined by analytic calculation and finite element simulation,and then the software and hardware of the detection system are optimized according to the detection scheme and magnetization device parameters,so as to ensure the stability and reliability of the crawler in the process of detecting the water-cooled wall tubes.Finally,the detection hardware and software are reasonably combined to design a image analysis and multi-channel detection system.The system has been tested experimentally on the water-cooled tubes in the laboratory.The experimental results meet related testing standards of the boiler tube.