The basic principle of this Non-Destructive Test is that a strong magnet induces a magnetic field in the material. At areas where there is corrosion or missing metal, a leakage field will arise. The output from the detector can be electronically digitalized for automated inspection systems. All indications is stored as well as their location. Bad areas or spots in plates can easily be identified and repaired. In the range 6 to 20 mm, all ferro-magnetic tank bottoms can be inspected, and (limited) coated surfaces also can be tested.
Magnetic Flux Leakage (MFL) is a method of Non-Destructive Testing, which is used to detect corrosion and pitting in steel structures, most commonly pipelines and storage tanks. MFL is a detection technique, which detects volumetrically changes. The disadvantage of Magnetic Flux Leakage is that no absolute values but relative volumetrically changes are reported. However it is a very suitable tool for detecting bad spots in the plates. After the fast MFL inspection is done, only the “suspicious” areas of the tank bottom surface will be quantified by the slow but more accurate Ultrasonic Testing.