MFL - Bottom Tank Inspection

Magnetic Flux Leakage Inspection techniques have been widely used in the Oil field Inspection Industry for over a quarter of a century for the examination of pipe, tubing and casing both new and used. It is only in the last ten years that this inspection technique has been applied to Above Ground Storage Tank Floors in an attempt to provide a reliable indication of the overall floor condition within an economical time frame.

In order to understand how this particular application of Magnetic Flux Leakage works it is necessary to understand the basic principles of the technique. Everybody is familiar with the ability of a magnet to “stick” to a carbon steel plate. This is due to the fact that magnetic lines of force (flux) much prefer to travel in the carbon steel plate than in the surrounding air. In fact this flux is very reluctant to travel in air unless it is forced to do so by the lack of another suitable medium.

For the purposes of this particular application a magnetic bridge is used to introduce as near a saturation of flux as is possible in the inspection material between the poles of the bridge.

Any significant reduction in the thickness of the plate will result in some of the magnetic flux being forced into the air around the area of reduction.

Sensors which can detect these flux leakages are placed between the poles of the bridge, our MFL equipment can detect in real time these material losses and help the inspector to identify the critic zones in the tank floor for a UT inspection.

MSB inspector were training in flux leakage and the use of the equipment.

The ultrasonic prove up necessary must be carried out by personnel who are adequately trained and qualified.

It must be remembered that this is not just “thickness measurement” but rather corrosion evaluation and the technician must have a full understanding of the technique that should be applied.

This is not a subject that we can cover within the limits of this paper. It will, however, be the subject of the next in a series of papers regarding the NDT of Storage Tanks.

MSB have carried out this MFL Inspection with excellent results in Panama to many clients, some of them three tanks belonging to ACP (Autoridad del Canal de Panama) and others to THE SHELL COMPANY.

MFL - Inspección de Fondo De Tanque

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