Magnetic flux leakage is a magnetic method that is used to detect corrosion and pitting in steel structures. As one of the nondestructive testing techniques, MFL is widely applied to the inspection of defects in oil and gas pipelines and aboveground storage tanks made of ferromagnetic material.
The basic principle is that a powerful magnet is used to magnetize the steel. At areas where there is corrosion or missing metal, the magnetic field leaks from the steel. Therefore MFL can detect corrosion by sensing magnetic leakage.
Magnetic Flux Leakage system is mainly composed of magnetizing device, yoke and sensor array. Permanent magnets are high magnetic energy product, small size, light weight and no external power required. So the magnetizing device usually uses permanent magnets.