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Applications
Published in Cameron Coates, Valmiki Sooklal, Modern Applied Fracture Mechanics, 2022
Cameron Coates, Valmiki Sooklal
The magnetic flux leakage (MFL) method is used to detect anomalies in normal flux patterns created by discontinuities in ferrous material saturated by a magnetic field created by a powerful magnet [17]. A sensor is used to detect fluctuations in the magnetic field caused by differences in material properties. This technique can be used for piping and tubing inspection, tank floor inspection, and other similar applications. It can be done without removing the insulation, resulting in a fast, economic way to inspect long runs of pipe or tubing. MFL is very effective at detecting surface and subsurface flaws. However, it is limited to ferromagnetic materials only and produces very poor results when detecting axial cracks or deep flaws.
Preventive maintenance and testing of mining ropes
Published in Tad S. Golosinski, Mining in the New Millennium Challenges and Opportunities, 2020
Mark J. Bergander, Roman Martyna
The principle of the magnetic flux leakage (MFL) test is based on detection of magnetic field distortion around the damage. It is illustrated in fig. 1. The rope moves through the test sensor where it is magnetized. If there is a continuity of metallic cross section, the entire magnetic flux is enclosed within the rope. Any sharp defect, like broken wire, will distort the magnetic flux to the extent that its small portion will protrude onto the rope outer surface. The amount of this “leaking” magnetic field depends on the severity of metallic loss and its location, i.e. inside vs. outside of the rope. The outside loss produces sharp and large magnitude leakage while internal one results in wider but much weaker magnetic field on the surface.
Data collection, processing, and database management
Published in Zongzhi Li, Transportation Asset Management, 2018
Magnetic flux leakage: Magnetic flux leakage (MFL) testing is a widely used method for detecting corrosion and pitting in steel structures. MFL is often used for assessing the integrity of pipelines and storage tanks, but the principle can also be applied to transportation industries. The elementary principle of MFL involves magnetizing a ferrous metal object to saturation level with a powerful magnetic field. The magnetic flux will stay undisturbed if the test object is flawless. However, if there exist internal or external metal defects (such as cracks or corrosion), the magnetic flux leaks from the object.
The Effect of Motion-Induced Eddy Current on High-Speed Magnetic Flux Leakage (MFL) Inspection for Thick-Wall Steel Pipe
Published in Research in Nondestructive Evaluation, 2020
Guanyu Piao, Jingbo Guo, Tiehua Hu, Henry Leung
The magnetic flux leakage (MFL) inspection technology is widely used in the oil and gas pipeline transmission industry. Pipelines are mainly composed of ferromagnetic materials and are prone to generate various metal losses, such as defects, corrosions, and fatigues [1–3]. The pipeline inspection gauges (PIGs) inside the pipe propelled by the oil and gas transmission medium are used to detect these metal losses to ensure the pipeline safety. The defects on the pipe wall will generate MFL signals when the pipe wall is magnetized to saturation by the permanent magnets equipped in the PIG [4,5], and the MFL signals are measured to quantify the defect sizes [6–9]. Nowadays, to meet the rapidly growing demands of oil and gas, the building of trunk pipelines operated under high-speed and high-pressure conditions has been greatly increased, causing the transmission speed up to 8 m/s and the pipe wall thickness up to 15 mm [10–12]. The MFL is considered to be the highest speed inspection technology comparing to other widely adopted technologies such as ultrasonic (UT), electromagnetic acoustic transducer (EMAT), and eddy current (EC) [13,14]. However, the inspection speed of MFL is usually limited to 4 ~ 5 m/s because the relative motion between the permanent magnets and the pipe wall will cause strong motion-induced eddy current (MIEC) that significantly distorts the MFL signals, which restricts its application in high-speed inspection [15,16].
Modeling and Experimental Studies on 3D-Magnetic Flux Leakage Testing for Enhanced Flaw Detection in Carbon Steel Plates
Published in Research in Nondestructive Evaluation, 2019
W. Sharatchandra Singh, S. V. Sagar Kumar, C. K. Mukhopadhyay, B. Purnachandra Rao, P. Ravindar
In the field of nondestructive testing and evaluation, magnetic flux leakage (MFL) technique is widely used to detect the presence of surface and sub-surface flaws in ferromagnetic components such as oil and gas pipelines, storage tank-floors, wire ropes, etc. [1,2]. In this technique, leakage field from flaws is detected by magnetic field sensors [1]. The leakage field has three components (Figure 1) along the three perpendicular directions viz. tangential, HX (along the measurement surface and perpendicular to the length of flaw), circumferential, HY (along the measurement surface and parallel to the length of flaw), and normal, HZ (perpendicular to the measurement surface). Among the three components, the HZ component is generally considered to be the most significant component of the leakage field [3,4].
Magnetization Time Lag Caused by Eddy Currents and Its Influence on High-Speed Magnetic Flux Leakage Testing
Published in Research in Nondestructive Evaluation, 2019
Bo Feng, Yihua Kang, Yanhua Sun, Zhiyang Deng
Steel pipes and bars are extensively applied in the petroleum and energy industry or utilized as raw materials in additional processes. Defects that inevitably appear in steel pipes and bars during the manufacturing process may cause potential accidents. Therefore, nondestructive testing of steel pipes and bars is required prior to their use. The most efficient and cost-effective method of inspecting ferromagnetic materials is the magnetic flux leakage (MFL) testing method, in which the tested workpieces are magnetized by a magnetizer. A schematic of MFL testing is shown in Figure 1. A magnetizing coil is used to generate a magnetic field inside the workpiece; only half of the coil is shown in the figure for better visualization of the workpiece under testing. Direct current (DC) is applied to the magnetizing coil in the circumferential direction, so that the generated magnetic field inside the workpiece is mainly in the axial direction. The magnetic field concentrates in the workpieces, and when the magnetic field meets a defect it will leak into the nearby air [1]. Subsequently, magnetic sensors placed in the magnetizing region detect the leakage field.