9/21/2023 0 Comments Magnetic flux leakage![]() ![]() The lead coil will detect this leakage but it is not possible to deduce the location (ID or OD) of the defect. Then flux leakage occurs on the inside or outside surface of the tube depending on the pitting location. When the magnetic field comes across pitting, the flux lines are diverted and theses distortions cannot be contained in the tube wall. That coil is wound over the absolute coil, between the two magnets. So where there is general thinning such as erosion, even if no flux leakage occurs, the strength of the magnetic field decreases and this variation is detected. It measures the strength of the magnetic field produced by the magnets. ![]() That coil is wound around the steel core between the two magnets. ![]() To that, three coils are added each one being sensitive to specific defects.įor wall loss detection, we use the coil operating in the absolute mode. Two permanent magnets coupled to a steel core are used to magnetize the tube wall until complete saturation is reach. The principle of operation is based on magnetization. As for ECT, this technique requires a good fill factor as well as a good probe centering position to maintain a fair sensitivity to small volume defects. Inspection is quite fast the pulling speed can go up to 1 m/s. This makes MFL more of a detection method than a sizing one. The defect sizing capacity of MFL has some limitations the signal amplitude is affected by pulling speed variations and the signal has no phase component. This technique is typically used for the inspection of air cooler and heat exchanger tubes. Magnetic Flux Leakage (MFL) Testing is an NDT technique used to detect pitting, circumferential cracks, and wall losses in ferromagnetic tubes such carbon steel, nickel, and ferrous stainless steel. ![]()
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