Research On Signal Analysis And Visualization Of Submarine Pipeline Defects

In this paper,the influence of pipeline defects on the distribution of leakage magnetic field during magnetic flux leakage(MFL)detection was studied.The defect was not highly recognized by traditional MFL inspection,in this case that finite element analysis of tri-axial MFL inspection was conducted using ANSYS.MFL signals of magnetic leakage field on three directions(radial,circumferential and axial)were obtained and the relation of MFL and defect geometric parameters was analyzed.The objects of traditional numerical simulation and experimental research were only single defect,in this case that secondary development was adopted based on ANSYS to analyze MFL inspection of pipeline with axial multiple defects.The models of pipeline with axial double defects and three defects were es-tablished.The impact of single defect on the leakage magnetic field is extended to the common effect of multi-ple defects.The influence of pipeline defects on the distribution of leakage magnetic field during MFL detection was studied by analyzing the sensitivity of the geometrical parameters,distance and the deviation of the sensor.The method of 3D profile reconstruction and visualization is summarized,and the basic framework of 3D contour reconstruction is put forward,which solves the problems of region segmentation recognition,defect contour detection and so on,and The model of three-dimensional contour is established.Based on the previous research,the main eigenvalues of MFL signal are extracted,and the framework of neural network iterative inversion is established.The results show that there is a certain relationship between the geometric parameters of the defect and the defect magnetic flux signal amplitude in a certain range.The influence of axial proximity defect on MFL signal detection can not be ignored.The value of lift off has a great influence on the result of MFL test.Limited sensor sensitivity,if beyond a certain range,will not be able to get the required test data.The amplitude of radial component in pipeline wth axial multi defects is similar to that with single defect pipeline,but there is a critical lift off value.When the lift off value is near the critical value,the depth of defect can not be effectively identified by the radial component amplitude.Therefore,in order to make the test data reliable and measure the depth of the defect,the appropriate reference value and lifting value should be selected,and the appropriate data analysis method should be adopted to make the detection data more accurate and comprehensive,and ensure the accuracy of defect identification.The selection of edge detection threshold has a great influence on the results of edge detection;only the reasonable threshold is selected,the accurate edge recognition result can be obtained.