Methods of magnetic flux leakage internal detection

Magnetic flux leakage testing is a type of non-destructive testing technology that belongs to indirect measurement techniques. The theoretical basis of magnetic leakage detection is the high magnetic permeability of ferromagnetic materials. The tested material is magnetized under the action of an external magnetic field. When there are defects inside the material, the defects cut the magnetic field lines. Due to the low magnetic permeability and high magnetic resistance of the defects, the magnetic field lines change their path in the tested material. Part of the magnetic field lines will leak out of the material surface and enter the tested material after passing over the defect, thus forming a defect leakage magnetic field. Leakage magnetic technology detects defects based on the numerical values of leakage signals distributed on the inner and outer walls of pipelines using magnetic field lines. It belongs to indirect measurement and is suitable for pipelines in various corrosive states. It can be used for pipeline detection of various impurities in crude oil and refined oil, and is currently the only reliable detection technology for natural gas pipelines. When there is a defect, the intensity of the magnetic induction line changes, and a change in current/voltage is detected, resulting in a change in the value obtained through Hall components.
The theoretical basis of magnetic detection is the high magnetic permeability of ferromagnetic materials. The tested material is magnetized under the action of an external magnetic field. When there are defects inside the material, the defects cut the magnetic field lines. Due to the low magnetic permeability and high magnetic resistance of the defects, the magnetic field lines change their path in the tested material Part of the magnetic field lines will leak out of the material surface and enter the tested material after passing over the defect, thus forming a defect leakage magnetic field. Leakage flux: Any other magnetic flux that does not flow according to the magnetic circuit specified by the iron core is called leakage flux. Leakage magnetic detection technology: using the principle of leakage magnetic flux, a strong magnetic field is generated by a permanent magnet through a magnetic medium to magnetize the wall of a ferromagnetic pipeline to saturation. A magnetic circuit field is generated around the circumference of the pipeline wall. When there is an abnormal Q on the pipeline wall, some magnetic field lines will penetrate through the wall and produce leakage magnetic flux. Pipeline defects can be detected by detecting the leakage magnetic field through a magnetic sensitive probe. Instructions related to corrosion detectors:
Pipe bend ratio: It is the ratio of the radius (curvature radius) of the center arc of the bend to the diameter of the bend, as shown in Figure RD, which is the bend ratio.
Pipeline deformation ratio: (original inner diameter of pipeline - inner diameter after pipeline deformation)/outer diameter of pipeline X 100%.
Pipeline weld: The joint formed by welding two pipelines together. Pipe welds: a joint formed by the welding of soft pipes. Reducing pipes: (reducing short joints) are fittings used to connect two pipes of different sizes in a straight line, achieving pipe diameter changes. There are concentric reducing joints and eccentric reducing joints. The centerline of two pipes connected by concentric reducing joints is in a straight line, mainly used for upright pipelines. Eccentric reducers are commonly used on horizontal pipelines. Corrosion ratio of pipeline (as shown in the right figure): (original wall thickness of pipeline - remaining wall thickness of pipeline)/original wall thickness of pipeline x 100%.
Detector probe lift off value: the distance between the sensor recognition center point and the inner wall of the pipeline.
Saturated magnetic flux leakage of detector magnetization pipeline: The magnetic flux leakage at the distance position of the probe outside the pipeline after the detector magnetizes the pipeline.