Study on Magnetic Flux Leakage Testing Probe and Device for Tubes
|School||Research Institute of Mechanical|
|Course||Measuring Technology and Instruments|
|Keywords||Pipe MFL Probes Test Equipment|
Steel magnetic flux leakage detection equipment manufacturing concentrated in several large foreign NDT equipment manufacturing company, such as Germany and the United States FORSTER TUBOSCOPE. Their equipment used to detect and injury through transversal longitudinal wound rotary probe detection methods. Rotate the probe works fast detection speed, high sensitivity, but due to probe high-speed rotation of the mechanical system design and manufacture high demands put forward, processing and manufacturing difficulties, the current domestic machinery manufacturing level is difficult to meet the rotation of the probe accuracy requirements. Beijing Institute of Iron and Steel Research analysis and testing of the probe fixed / steel spiral forward work carried out research indicating that as long as the testing device designed to detect parameter settings properly, effectively check out the defects in the steel pipe is entirely possible, and be able to meet the national standard steel pipe magnetic flux leakage detection performance requirements, this pipe magnetic flux leakage detection method is feasible and suitable for China's national conditions. The topics developed pipe magnetic flux leakage testing device used in the steel-situ rotation / linear scanning probe work, the purpose is to study the AC and DC magnetic flux leakage probe tube aspect to the defect detection, the detection feasibility and MFL testing the reliability and to study the impact of magnetic flux leakage factor for the development of functional magnetic flux leakage detection equipment to prepare. Study of this subject is theoretical research from beginning MFL combined model calculation, the device is designed after the experimental tests. Firstly, the paper analyzes the main drawback of steel, outlining the basic principles of magnetic flux leakage, leakage magnetic field and the formation mechanism of the process of magnetic flux leakage testing tube introduced MFL main technique to study the magnetic flux leakage detection technology at home and abroad Status and trends and pipe magnetic flux leakage testing equipment overview, finalized the magnetic flux leakage testing device technology research programs as well as the main content. Then, we calculated defect leakage field test ring model of the air-gap magnetic field, magnetic flux leakage through joints and limited deep slit leakage field was calculated, and then analyze the magnetization of magnetic flux leakage testing tube method, pointed out the magnetization , magnetization and magnetization direction of magnetic flux leakage testing, and analysis of the principle of electromagnetic induction sensors and scanning factors, the final analysis of the AC and DC magnetic flux leakage detection, and pipe magnetic flux leakage detection probe model analyzed and calculated. Then, the paper model of the probe using ANSYS finite element analysis, the burial depth and size of defects, pipe wall thickness, the magnetization intensity and lift-off clearance on the influence of magnetic flux leakage detection simulation analysis. After this magnetic flux leakage detection probe is designed, including the design of the sensor coil, the excitation coil design and the design of the field core, and then calculating the parameters of the excitation coil, the final production of the probe. Finally, in the production of steel rotating scanner device and testing sample tube, the realization of the magnetic flux leakage testing devices. Then on the magnetic flux leakage detection probe and test equipment experimental tests carried out on the impact of MFL factors studied experimentally. The conclusion that the magnetic flux leakage inspection speed characteristics, lift-off characteristics, frequency characteristics ac magnetization results. This study shows: how to make pipe defect leakage field is MFL inspection of the premise. Pipe leakage magnetic flux leakage detection probe is detected core, it is the role of magnetic excitation field and receive signals to achieve these two features are the sensor and exciter. For steel pipe magnetic flux leakage detection, they need to ensure adequate magnetization magnetization can not be too large, otherwise it will affect both the sensitivity and signal to noise ratio. Either AC or DC magnetization magnetized, when magnetized steel too, SNR was significantly reduced. Magnetization direction is perpendicular to the long axis defects, leakage magnetic field the strongest. When the magnetization direction of the long axis parallel to the direction and defects, almost no leakage magnetic field signal. For steel axial injury, should be used longitudinal coil sensor scanning, for pipe circumferential injury, should be used horizontal coil sensor scanning. MFL is key to achieving the relative movement of the probe and the tube, the subject line using the scanning probe / tube was rotated detection methods, this method, although rotation and scanning speed is limited, but the steel pipe can be achieved as the defect detection aspect . ANSYS finite element simulation analysis showed that: specific surface defects near surface defects leakage magnetic field is weak, for the same shape and size of defects, burial depth and magnitude of the leakage magnetic field is approximately linear. For the same deep defects in the same magnetization condition, width-to-peak amplitude of defect not have great impact, only a slight increase only. The width of the defect in certain circumstances, in a certain range, the vertical component of the leakage magnetic field peak - the defect depth substantially linear relationship. Pipe wall thickness distribution of the magnetic field lines on the main lines of magnetic force that inclusion on the wall, the wall is thinner wall leakage magnetic field lines more easily. When the applied current density load, found that the current density to a certain size defect leakage magnetic field lines only, and with the increase of the current density, but reaches a certain extent and no magnetic flux leakage increases. Axial component of the magnetic flux leakage baseline and peak values ??with the sensor lift-off increases rapidly decreased radial leakage field peak - peak with the sensor lift-off value increases also decreases rapidly when large lift-off, the drain magnetic field changes slowly. The lift-off relationship between the leakage magnetic signal is nonlinear, the smaller the lift-off, reduced faster. That is, the smaller the lift-off, lift-off fluctuations in the value the greater the impact on the detection sensitivity. Experimental tests show that: AC current probe and probe signal characteristics, magnetization, detection sensitivity, there are differences. AC current probe of the probe signal to noise ratio higher than the required magnetization is low, detecting liftoff same clearance, the sensitivity is higher. The magnetic properties of magnetic flux leakage testing of ferromagnetic magnetization theory consistent with the magnetic flux leakage sensor detects the speed characteristics in line with the theory of electromagnetic induction. Lift-off characteristics consistent with the ANSYS simulation analysis conclusion, with the lift-off increases the sensor signal decreases rapidly acquired defect in the lift-off is small, it is obvious for the detection of adverse fluctuations in the actual detection should avoid higher volatility big lift-off clearance. For this magnetic flux leakage inspection subject developed a test device, the DC probe proper clearance liftoff 1-3mm. AC leakage magnetic probe suitable lift-off values ??ranging from 1-10mm. AC magnetic flux leakage testing appropriate frequency range 1kHz-10kHz. Lift-off at the appropriate clearance, testing speed and magnetization, this project developed steel situ rotation / linear scanning probe-type magnetic flux leakage detection device, enabling steel longitudinal and transverse defects.