Study Of Magnetic Flux Leakage Inspection On Steel Tube

Along with the high-speed development of oil-gas industry, the corrosion of pipes and pipelines used for transporting oil and gas is more and more serious. Also is the menace of them. The cost of corrosion is enormous, including shuttling down of the factory, loss of products and materials, power waste, etc. Corrosion can even result in pipeline leakage accident, polluting environment, threatening people's safety. So it is necessary to inspect the pipeline corrosion condition to avoid pipeline accidents.This paper focuses on smaller diameter pipelines ( φ89mm steel tube). After investigating the domestic and abroad magnetic flux leakage technology at home and abroad, contrasted analysis of several non destructive testing methods, such as eddy current testing (ET), ultrasonic testing (UT), magnetic particle testing (MT) and magnetic flux leakage (MFC) etc. The method of MFL is selected the mathematical modal of pipeline (steel tube) under magnetization with magnetic dipole theory. Analyze the corrosion magnetic field of steel tube, and magnetic field influence factors, such as defects direction, dimension, position and material etc. By analyzing several magnetizing manners, we make choice of permanent magnetizing matter along pipeline, design magnetic circuit, and calculate the mainly parameter of permanent magnetic during equivalent magnetic circuit method. Development the magnetic flux leakage inspect system, with high integration level, linearity great and direction well using Hall sensor. This inspection system is highly sensibility, small fabric and light. We developed the data acquisition and data analysis software. The software realize the data acquisition with real-time display, filtering the disturbance signal with program, such as high frequency and irregular pot etc, and make the data analyzing result to accuracy. We carry out experiments in steel tube and semi-steel tube, analyzing the magnetic flux leakage field difference and feature in steel tube and semi-steel tube, getting the identify method inside and outside of steel tube. Studying the factors that influencing magnetic flux leakage signal, that is lift-off, corrosion deepness, corrosion area and coat thickness, etc.The result shows that, the steel tube magnetic flux leakage inspecting system can test the corrosion defect in the steel tube, and experiment results are in accord with theory. The inspecting sensitivity comes up to 20% about the wall thickness of the steel tube. All these have practical application value to analyze the corrosion defect and identify the defect.