Permanent Magnet of The Magnetic Flux Leakage（MFL）Magnetizing Device for Oil Pipeline

The Magnetic Flux Leakage（MFL）of  non-destructive inspections is the most widely used detection method to detect a variety of flaws in oil and gas pipeline. The MFL system consists of magnetizing device, yoke and hall sensors. Its working principle is (as below drawing): firstly, to magnetize pipeline detection range by strong magnetic force from magnetizing device. The leakage magnetic field will appear when there is flaw on the pipeline wall. Secondly, to convert MFL signal collected by hall sensors into current to test the flaw size and location.

Magnetizing is the first step for MFL and determines whether pipeline test area can produce enough magnetic field signals. Magnetizing device usually uses permanent magnet, such as ferrite, alnico, smco and ndfeb magnet, due to its different characteristics in high magnetic energy product, small volume, light weight and no external power required. Ferrite (ceramic) is cheap but low Br; AlNiCo is high Br but low coercive force; rare earth magnet which includes samarium cobalt and neodymium iron boron is high coercive force and remanence but expensive.

For different permanent magnets, the magnetic circuit should be designed according to their magnetic properties, give full play to its advantages, so that the magnetic circuit reaches to the optimum. For high remanence and low coercivity magnetic material, it should adopt an elongated magnet; but on the contrary, it should adopt stubby magnets. If the magnetization effect cannot meet the requirements and coercivity cannot increase, increasing the size of the permanent magnets (typically width and thickness) can meet the requirement. Common grades for MFL magnet are N38, N42, N45 and N50M, sizes 40x20x10mm, 25x25x25mm, 40x25x10mm and 45x45x45mm and so on. We also manufacture arc (segment), ring, and cylinder type magnet for magnetic flux leakage testing.

China Magnets Source Material Ltd. has many years production experience for MFL magnets; the magnets have been applied for the detection of the Pacific seabed pipeline. If you have such requirement, please feel free to contact us.