The magnetic flux leakage detection method can effectively detect defects on the surface, near-surface and inside of ferromagnetic materials, and is low-cost and easy to implement automation, so it is widely used in steel pipe inspection.
High speed and high-precision magnetic leakage testing magnetization for longitudinal damage of steel pipes.
In the magnetic flux leakage detection scanning of steel pipe spiral propulsion, the faster the detection speed, the longer the required axial length of the detection shoe, so that the scanning coverage
The coverage range exceeds the uniform magnetization zone, resulting in inconsistent signals.
To address the issue of mutual constraint between detection accuracy and speed in longitudinal damage detection of steel pipes, and with the goal of ensuring signal consistency for high-speed detection of longitudinal damage in steel pipes, a method combining finite element simulation and experimental verification is adopted,
Analyzed the influence of the structure of magnetic pole shoes in circumferential magnetization on the uniformity of magnetic field on the surface of steel pipes. On this basis, a longitudinal magnetic flux leakage detection method was proposed
The magnetization measurement method expands the uniform magnetic field area on the surface of the steel pipe and improves the consistency of the detection signal within the same detection area.
With the rapid development of China's petrochemical and energy industries, the demand for steel pipes is increasing day by day. However, steel pipes have been produced before
During the process, defects such as cracks and corrosion may occur due to the influence of processing technology, which may pose certain safety hazards during use. According to the American Petroleum Institute standards [1] and national standards [2], seamless steel pipes and welded steel pipes must undergo 100% non-destructive testing before leaving the factory.
The leakage magnetic detection method can effectively detect defects on the surface, near surface, and inside of ferromagnetic materials, and it is low-cost and easy to achieve automation, so it is widely used in steel pipe inspection. In order to ensure detection efficiency, it is necessary to continuously improve the speed of steel pipe detection.
The existing research on high-speed magnetic leakage detection mainly focuses on the influence of induced eddy currents on the detection signal [3]. In terms of magnetization methods, there are already orthogonal magnetization methods based on straight steel pipes [5]. But there is no literature that has conducted in-depth research on signal consistency in high-speed magnetic flux leakage detection. In magnetic leakage detection, the maximum magnetic leakage field occurs when the magnetization field is perpendicular to the defect. Therefore, when detecting longitudinal defects, circumferential magnetization of the steel pipe is required. Due to the lower circumferential magnetic permeability of the steel pipe compared to the axial magnetic permeability [6 飊 7], it is difficult to achieve saturation when magnetizing the steel pipe in the circumferential direction. Unlike the uniform magnetic field formed when magnetizing in the axial direction, the circular geometry of the steel pipe makes it difficult for the magnetic flux to fully pass through the interior of the steel pipe in the circumferential direction during magnetization, and some of the magnetic flux will diffuse into the air [6]. Therefore, the magnetic field is strongest at the magnetic pole and weakest in the area between the two magnetic poles, resulting in uneven distribution of the magnetic field in the circumferential direction. The length of the magnetic pole in the axial direction is limited, and the axial area covered by the magnetization field is also limited, which can only magnetize a local part of the steel pipe. Therefore, uneven magnetic field distribution may also occur in the axial direction of the steel pipe.
Through the analysis of the spiral forward motion model of steel pipes, it was found that in order to achieve comprehensive scanning and detection of longitudinal injuries, the faster the detection accuracy, the longer the distance along the axial direction of the detection array probe needs to be arranged. However, when using traditional magnetic poles to magnetize steel pipes in the circumferential direction, the uniform area of magnetic field distribution along the axial direction is small. If the range covered by the array probe exceeds the range covered by the uniform magnetic field, the signals obtained by the same defect passing through the various probes of the array probe will be seriously inconsistent, making it impossible to accurately evaluate the defect and affecting the detection accuracy. Therefore, this article proposes an optimized circumferential magnetization method, which optimizes the structure of the magnetized pole shoes, changes the excitation magnetic circuit, and obtains a uniformly distributed magnetic field in the detection of steel pipes, thereby improving signal consistency.
