Research On Recognition Method Of Stress Signal Features Based On Strong And Weak Magnetic Field Coupling

Oil and gas pipeline transportation is the main means of oil and gas energy transportation,and the integrity of pipeline is directly related to the transportation safety of oil and gas energy.During the service period of long-distance oil and gas pipeline,under the action of long-term Environmental Corrosion and internal pressure,there will be defect area.Because the defect will spread rapidly under the action of stress,the pipeline will burst,therefore,the pipeline will be tested for the stress at the defect area,it is of great significance to reduce the occurrence of pipeline accidents.It is a safe and effective method to detect the stress concentration and corrosion defects in the pipeline by in-pipe inspection technology.The common nondestructive testing technologies include magnetic flux leakage testing,weak magnetic testing,magnetic particle testing,Eddy current testing,penetration testing,ultrasonic testing,x-ray testing,etc.,these detection techniques play an important role in oil and gas pipeline defect detection,stress concentration detection,pipeline safety and so on.But the in-pipe inspection technology needs to meet the requirements of non-contact,dynamic inspection and on-line inspection,so the magnetic flux leakage inspection technology and weak magnetic inspection technology are widely used in the oil and gas pipeline inspection technology at present.However,because the MFL detector works in magnetic saturation environment,the recognition rate of stress signal is low,and it is easily covered by defect signal,so it is difficult to identify The signal measured by the traditional weak magnetic detection technology based on geomagnetic field is weak and easy to be disturbed by the external environment,so it is difficult to distinguish the defect signal from the stress signal,and even more difficult to distinguish whether the stress exists in the defect.In this paper,the strong and weak magnetic detection method is used to identify the stress signal at the defect.The mechanism of strong and weak magnetic testing technology is to identify the stress signal at the defect by combining the testing signals of different external magnetic fields,it is of practical significance to improve the flexibility and accuracy of inpipe inspection of oil and gas.Based on the J-A theory,the magnetic mechanical model of ferromagnetic material defect is established,and on the basis of the relationship between the external magnetic field and the magnetic signal characteristics of the stress concentration area,the best applied magnetic field region is calculated,that is,the region where the ratio of pure stress signal to total stress signal is the largest by comparing the characteristics of strong magnetic signal with that of weak magnetic signal,the stress signal at the defect can be identified,and the stress signal at the defect can be identified The ferromagnetic steel bar is used to carry out the test of strong and weak magnetism and is analyzed systematically.The results show that the magnetic signal characteristics in the stress concentration region of ferromagnetic materials increase first and then decrease with the increase of applied magnetic field until the stress signal in the magnetic saturation region is almost covered,the maximum of stress signal and the maximum of stress signal in the mixed signal,and the stress concentration at the defect will enhance the magnetic signal characteristics,and the higher the stress,the stronger the magnetic signal intensity;There is a corresponding relationship between the eigenvalues of strong magnetic signal and weak magnetic signal at the defect,by which the stress signal at the defect can be identified.