Research And Application Of The Speed-effect Of Magnetic Flux Leakage Pipeline Detector

Nowadays, petroleum and natural gas have become the most important sources ofenergy. China, as a major energy power, focuses on the safety and the efficienttransportation of petroleum and natural gas because of their important significance. Today,the usual manner to transport petroleum and natural gas is pipeline transportation. With thetime flies and the causticity of the soil and seawater, it is certain that these pipes will bedamaged with different factors such as, corrosion and deformation by the force. So,recurrent accurate detection of the pipeline in service is very important. In the process ofdetecting the gas pipeline, due to the greater pressure between the two pumping stations,the operating speed of the detector which is working inside the pipe to detect the pipelinemagnetic flux leakage is very unstable and can be changed easily by the influence of thegas expansion, the pipe structure changes and other factors. The high speed reduces themagnetization level and decreases the magnetic flux leakage signal amplitude. Therefore, itis difficult to finish the magnetic flux leakage detection.According to the questions above, this paper studies the speed-effect of magnetic fluxleakage detector of the inner pipeline deeply. Theoretically，the paper researches theprinciple of magnetic flux leakage inspection, the principle of ferromagnetic materialmagnetized and the principle of the velocity effects. On the basic of Becker Eddy Model,the paper analyzes the principle of magnetic flux leakage inspection to make amathematical model, meanwhile, calculates and analyzes the effects made by high-speed.Through the theory of ferromagnetic, the paper solves the influence caused by the eddyeffect which is made by the detection device and the wall of the pipeline when they areoperating relatively. The Maxwell equations lead to differential form of the speed effect.According to the magnetic flux leakage detector specific parameters, establishes anaxisymmetrical two-dimensional simulation model in ANSYS finite element simulationsoftware to analyze the influence to the pipeline magnetic flux leakage signal because ofspeed-effect. In the process of the simulation, different defect length, different defect depth, wall thickness and other factors lead to different effects.The calculation and simulation show that the faster the speed is, the smaller the radialmagnetic flux leakage signals shows; meanwhile, with thicker of the wall thickness, greaterof the length and shallower of the depth of the defects, its speed effect would be more andmore obviously. When the speed rate is more than6m per second, it is impossible to carryon the inspection of magnetic flux leakage because the high speed is incapable tomagnetize the wall of the pipeline. Increasing the intensity of the excitation can reduce theimpact of the speed-effect to a certain degree.