Magnetic Flux Leakage (MFL) Testing

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Magnetic Flux Leakage (MFL) Testing

An inspection technique that detects volumetric changes, Magnetic Flux Leakage (MFL) testing is facilitated by tank floor mapping utilizing today's latest computerized equipment. With MFL, a strong magnet induces a magnetic field in the material. On a corrosion spot, a leakage field will arise. The larger the corrosion, the larger the leakage field. 

After the fairly quick MFL inspection is complete, the suspect areas of the tank floor surface will be quantified by slower but more accurate Ultrasonic Testing (UT).

Silver Wing Floormap MFL 2000

The Floormap MFL 2000 tank floor scanner is one of a new generation of MFL systems designed for the inspection of bulk liquid storage tank floors. The system takes advantage of the latest developments in magnet design to deliver enhanced performance on thicker floor plates (10mm and above).

The 2000's ergonomic mechanical design allows the magnet carriage to be "broken" from the floor with much less effort than previous designs, despite its increased magnetism. An onboard computer allows full data acquisition of signals detected by MFL in such a way that mapping of defect indications can then be carried out through graphical reporting software. This software allows the grouping of defects according to severity in operator-definable color-coded bands.

The 2000 allows the cross-checking of pitted areas through an ultrasonic technique in order to confirm material loss (as a percentage of plate thickness) and verify MFL banding. Any variation between the MFL banding and the ultrasonic results can be corrected for in the reporting software. The 2000 is designed to detect under-floor conical pit or lake-type corrosion represented by an artificial reference hole 40% deep. Under ideal conditions pitting of approximately 20% loss in a 6mm plate can be detected and sized.

Floor thicknesses over 12.5mm and up to 20mm can be inspected by switching the 2000 to manual mode. It is not possible to quantify or map corrosion in these thicker plates due to the lower flux levels induced in the plate. It is however possible to detect corrosion 50% deep or greater in material up to 15mm thick and between 60 and 70% deep in materials up to 20mm thick. A secondary NDT method, normally UT, is then used to quantify the material loss.