Study On Key Techniques Of Detecting The Defect Of Magnetic Flux Leakage Pipeling

With the development of economy in our country, the oil and gas pipeline application increasing, the length of buried pipelines caused increased operation will appear more mechanical scratch, deformation, corrosion effects, you need to in a timely manner to pipeline survey of the ways to improve, and improve the accuracy and efficiency, oil and natural gas pipeline defect detection method in magnetic flux leakage testing method is more effective and widely used method. In leakage detection of magnetic, magnetic circuit calculation, the magnetization direction and angle of crack defect size with the impact on the test results, pipe special components and the characteristics of defect signal analysis judgment and magnetizing device optimization and other problems. To solve these problems of leakage magnetic testing process and results analysis has important significance.In this paper, several key problems in the pipeline leakage detection are studied, the magnetic flux leakage detection technology and the preliminary study on the magnetic circuit calculation are studied. Of magnetic circuit calculation of preliminary research: choice of Maxwell’s equations as a magnetic circuit calculation based, magnetic materials, magnetic magnet’s operating point determine and selection and the final circuit approximate calculation, from the whole of magnetic circuit calculation with the description of the contour. Through the finite element simulation of a permanent magnetic excitation to the wall of the pipe with different orientations crack detection structure and to 10 mm thick steel plate for the different angles of crack detection experiment system. Contrast plate on different crack orientations of experimental data, it is concluded that the hall sensor and the plate surface distance of 1mm provided away from the distance, with the crack orientation and the direction of magnetization angle becomes smaller detected crack leakage magnetic signal amplitude is reduced accordingly, when a vertical state detection to magnetic flux leakage field maximum, when the magnetization direction and the angle between the crack at 90 degrees to 30 degrees signal is detectable, angle is less than 30 degrees could not be detected in the effective magnetic flux leakage signals; In addition, the effect of different steel brush, magnetic yoke material and yoke thickness on the detection effect is simulated by Comsol; Finally according to the structural characteristics of the specific part of the oil and gas pipeline, analysis of the magnetizing pipe leakage magnetic field characteristics, based on pipeline leakage magnetic detection principle and Maxwell’s equations. The finite element simulation software Comsol simulation of pipeline special components and defects. Studied to leak magnetic axial signal components Bx channel number, Bx positive and negative peak sequence, Bx amplitude and the curves of axial length as discriminant analysis pipeline special components and defects of the basis, of special pipe components(to fill in for example), there are some defects leakage magnetic signals Bx component feature analysis of Bx of defect signal amplitude is greater than or equal to fill in signal Bx need repair. The experimental results show that the analysis method of the magnetic flux leakage signal of the pipeline is feasible.