Magnetic Flux Leakage inspection (MFL) is based on electromagnetism and the measurement of permeability variations. The Magnetic Flux Leakage analysis confirms the presence of potential flaws due to wall thickness loss caused by corrosion or surface flaws such as cracks.

For ferromagnetic tube inspection performed with MFL, a probe made of a single strong magnet induces a magnetic field in the tube until saturation. Magnetic sensors strategically positioned between the magnet poles detect the flux leakage when a thickness loss happens in the pipe. The magnetic field “leaks” out of the tube because of its incapacity to be magnetized beyond the point of saturation. This technique is mainly used in refineries.