Research On The Key Technologies For Magnetic Flux Leakage Internal Inspection Of Gas Storage Wells

Clean energy that the natural gas represents plays a more and more important role inenergy structure of China. The gas storage well is most widely applied in the CNG(Compressed Natural Gas) car industry, which is used to store compressed natural gas. Thesafety of the gas storage well is closely related to the CNG filling station and the socialproperty and personal safety around it. Therefore, it’s important to detect the gas wellregularly in order to ensure it safe while in the service. To circumvent the difficulty of thedetection of corrosion defects, the magnetic flux leakage (MFL) testing method and tool forgas storage well is studied in detail in the thesis.Firstly, the structure and the testing technology of the gas storage well are introducedbriefly. The different parameters of the magnetizer are optimized with numerical simulationmethod by establishing MFL testing3D FEM (finite element model), including magnet length,iron cross-section and pole space, etc. Especially, the problem how to choose the optimizationobject is solved in the optimizing pole space process, which laid the foundation for designingand manufacturing lighter MFL testing device. Secondly, a magnetic circuit model based onthe Kirchhoff’s law and the multi-branch parallel method is established by analyzing thecharacteristic of the special lift-off form magnetizer offset, which can be used to analyze theinfluence on the magnetizing state inside the pipe wall when the magnetizers have eccentricityfrom the axis of the pipeline specimen. And the effects of the magnetizer offset on MFLsignals and MFL testing device designing are studied by3D finite element method. Then thevalidity of the magnetic circuit model and the simulation results are verified by experiment inthe pipe specimen. Finally, the lighter MFL testing device for gas storage well is designed andmanufactured on the basis of the above theoretical study. After that, the movementperformance and the detecting sensitivity of the device are tested by experiment in the lab.The results show that the device can detect the Φ1.6mm cylindrical through-hole artificialdefect and the movement performance of it is good that can pass the groove easily in the well.All the work in this dissertation enriches the research of the pipeline MFL internal testing,provides important support for the development of industrial standard NB/T47013.12and canhelp promote the application of the MFL testing technique.