Around 1970, China imported some magnetic flux leakage detection devices from developed countries. After that, China gradually began to conduct research on magnetic flux leakage technologies. In 1999, given China's great demand for magnetic flux leakage detection technology for steel pipes, the Ministry of Metallurgy of the People's Republic of China reviewed the national standard GB/T 12606-1999 Magnetic Flux Leakage Detection Methods for Steel Pipes. This standard has greatly promoted China's research, promotion and application of magnetic flux leakage detection technology. Through endless efforts, China developed a magnetic flux leakage detection instrument for petroleum pipelines in 2002. In China, the research of magnetic flux leakage detection technology mainly focuses on the following aspects:
1. Numerical calculation of the leakage magnetic field
Luming Li and others used finite element methods to study the relationship between the internal induced magnetic field and the vertical component of the leakage magnetic field on the surface crack of the product, and the influence of the width of the rectangular groove defect on the vertical component of the leakage magnetic field was studied. The vertical component of the leakage magnetic field could be used to obtain the width of the defect. Xianmei Wu and Mengma Qian used the finite element method to analyze the leakage magnetic field around the pipeline, and obtained the distribution of magnetic field lines for the defective pipeline with different sizes. Zhiping Liu used the finite element method to study the partial magnetization of the steel plate, and obtained the influence rule of the width of the test piece on the magnetization of the steel plate, and verified the feasibility of magnetic flux leakage detection after the partial magnetization of the steel plate. Li Yingying and others used the finite element method to study the effect of the lift-off value of the magnetic sensor on the extraction of the leakage magnetic field, and optimized the magnetizer for the magnetic leakage detection.
2. The magnetization technology
Luming Li, Songling Huang and others from Tsinghua University have studied the AC and DC magnetization in magnetic flux leakage detection and the selection criteria of the magnetizing current frequency were obtained. Professor Kang from Huazhong University of Science and Technology has studied the magnetization technology in the magnetic flux leakage detection technology, explained the selection principle of magnetization modes and magnetization intensity, and analyzed the excitation magnetic circuit. Ying Tang and others used the finite element method to study the pulse magnetization technology, obtained the distribution of the three-dimensional component of the leakage magnetic field under pulse magnetization, and concluded that when the magnetization field was parallel to the main plane of the defect, the pulse magnetization technology can get richer information of the leakage magnetic field than the traditional magnetization technology.
3. The signal processing of magnetic flux leakage
Jiang Xu, Xinjun Wu and others from Huazhong University of Science and Technology conducted research on the signal transmission method for magnetic flux leakage inspection of steel pipes, the transmission technology based on multiple detection signals has been proposed, and the transmission links of the online magnetic flux leakage detection signal of the steel pipe have been developed. Lijian Yang, Fengming Ma and others from Shenyang University of Technology have combined wavelet technology and wavelet packet transform technology to develop a signal processing system for magnetic flux leakage. They developed a pipeline magnetic flux leakage detection system with high detection accuracy based on a single-chip control system. For submarine pipelines, Tao Jin and others used wavelet technology to denoise the picked-up magnetic flux leakage signal, and obtained relatively good experimental results. Songling Huang and others used a combination of software and hardware to process the pipeline magnetic flux leakage detection signal, and successfully removed some of the interference that couldn't be eliminated by digital filtering. Experiments have shown that this method could improve the signal-to-noise ratio of the detection signal and the sensitivity of the detection system.
4. Research on defect reconstruction technology
Tao Yang, Taiyong Wang and Xuda Qin from Tianjin University conducted research on online magnetic flux leakage testing for steel pipes. The reconstruction of the defect size's information was realized by using characteristic analysis and nonlinear methods based on the collected magnetic flux leakage signal. Yuan Xie and others used linear inversion methods to obtain the shape information of defects based on experimental data, and the equation was solved by the least square method. Qiong Li and others used the equivalent surface magnetic dipole array to form a defect reconstruction model, and at the same time used the inverse matrix solution algorithm to obtain the optimal solution of the equation. Tao Jin tried to use wavelet basis function neural network in the reconstruction application of defect parameters, and the results showed that the network could achieve the reconstruction of depth and width of defects.
5. The equipment for research and development of magnetic flux leakage
In 2005, Fuyun He, Yan Zhang, Haiyan Zhang and others from Hefei University of Technology developed a magnetic flux leakage detection system suitable for large-diameter steel pipes based on the two-dimensional inspection technology. The system consists of a magnetization system, a signal acquisition system for defects of steel pipes, a signal analysis and processing for defects of steel pipes and a recognition system for defects and a demagnetization system. Yanhua Sun, Yihua Kang and others studied the signal characteristic information of magnetic flux leakage detection of the pipeline's defects under the axial magnetization of a single coil. A magnetic flux leakage detection method that does not require the flux leakage probe of the rotation of the inspected object was proposed. The corresponding magnetic flux leakage detection equipment was developed at the same time, which could realize the high-speed on-line magnetic flux leakage detection of seamless steel pipes. Yilai Ma, Li Lin and others developed a magnetic flux leakage detection system for drill pipes, introduced the hardware and software of the detection system, and the device could meet the requirements for on-line magnetic flux leakage detection of drill pipes through experiments.
It can be seen from the domestic and foreign research status of the above-mentioned magnetic flux leakage detection technology that although the magnetic flux leakage detection technology has been greatly improved in recent years. However, there are still few researches on magnetic flux leakage detection technology for seamless steel pipes. In terms of theoretical research, many finite element simulations only carried out two-dimensional leakage magnetic field research, but the actual leakage magnetic field was three-dimensional. There were few studies on three-dimensional leakage magnetic field simulation for seamless steel pipes. There was non-detection zone at the end for magnetic flux leakage detection for seamless steel pipes, and there were relatively few studies on how to eliminate the non-detection zone. This article intends to conduct research on magnetic flux leakage detection technology for seamless steel pipes, applies emerging signal processing, magnetization and other technologies in the magnetic flux leakage detection system for seamless steel tubes, and conducts research on three-dimensional magnetic flux leakage field and elimination methods of non-detection zone at the end for seamless steel pipes.
