MFL Tank Floor Mapping
The Floormap VS2i, a computerised magnetic flux leakage system designed to detect, size and map underfloor corrosion on above ground storage tanks. The Floormap VS2i magnetic flux leakage (MFL) floor scanner comes with up-graded magnets to improve corrosion detectability and sizing on thicker materials, faster data capture with a custom designed micro controller and all new software. The Floormap VS2i contains significant improvements in terms of defect positioning, electronic data processing and software manipulation.
Theory of operation
As floormap v2si moves forward, powerful permanent earth magnets which maintained at the bottom of the scanner, induces localized magnetic saturation at the tank floor plates, as the scanner moves over the area of corrosion, an array of 32 hall effect sensors mounted between the two magnet poles sense changes in the magnetic field, which then converted into electrical signals, the electrical signals is then processed before being sent to the on-board computer, once the scan has been saved, the location and severity of the corrosion is displayed on the color coded map of the plates.
Characteristics
- Detect corrosion using 32 hall sensors.
- Scan width is 250 mm.
- Method of propulsion is by DC motor.
- Speed is 0.5 m/ sec.
- Thickness range is 12.5mm maximum in case of automated sizing mode and 20 mm maximum in case of detection mode.
- The test could be performed through coating up to 6 mm thickness.
- Sensitivity is Adjustable up to 20% underfloor corrosion on coated 6 mm plate or 10% underfloor corrosion on uncoated 6 mm plate.
- The MFL Floormap v2si is provided with auto-stop upon detection option and real time analysis.
Reporting
- The off-line reporting software automatically produces a CAD drawing of the tank floor with the defects being positioned to within 3 mm accuracy. All captured data, over 20% loss of the nominal plate thickness, is re-analysed to identify the defect profile and separate the corrosion into 1 of 3 classes. Different sizing algorithms are applied to each class of corrosion ensuring enhanced defect sizing even on badly corroded floors where small diameter deep pits may otherwise have been undersized.
- Additional data from visual, ultrasonic, vacuum box and magnetic particle inspection can be added to the report generating a full fingerprint of the tank floor including the annular plates. An innovative feature of the software allows subsequent inspection data to be overlaid and corrosion growth identified.
- These features coupled together with a patch plate design function and full statistics package give a powerful, cost effective tool with which to carry out trending and asset life projections.
- Measurement tools for sizing areas of corrosion.
- Top / Bottom defect views.
- Ability to add previous inspection for comparison.
overall view
patch plates & photos
plates view
comparison from previous inspection
FAQ
Cleaning requirements for Magnetic Flux Leakage (MFL) Inspection Some preparation is required in order for a MFL inspection to take place. Any product should be drained from the tank and the tank should be cleaned. Cleaning techniques will vary depending on the type of product stored in the tank, the time since the tank was last cleaned and opinions held by the engineer in charge of the cleaning operation. Acceptable cleaning methods include shot blasting, grit blasting / sand blasting, high pressure water jetting, ultra high pressure water jetting etc. The media used in the blast cleaning process should be removed from the floor before the inspection takes place. It is very difficult to completely remove all of the shot from the surface of the floor. Two problems can occur if the MFL scanner passes over any loose shot (or any other loose ferrous material). The shot will become embedded in the scanner rollers and cause excessive vibration. Spurious defect indications will be detected / recorded if any shot passes underneath the sensor head. The aim of the cleaning process is to remove any contaminants such as product residue, corrosion build, scale and loose ferrous material from the surface of the tank floor which can affect the quality of a MFL inspection. Product residues can also give off toxic or flammable gasses. The floor should be clean enough for a good visual inspection (you should be looking at the surface of the steel, not a layer of product residue/scale etc – see examples below). Surface oxidization / rust will not present a problem for MFL inspections.
No, Magnetic Flux Leakage is used to inspect the parent plate material for corrosion defects and cannot be used for the lap welds. The most common method of inspecting storage tank floor plate lap welds is by use of a Vacuum Box.
Yes, the MFL flux leakage signal is a bi-polar signal which can be detected at the top (near surface) of the tank floor even when the corrosion originates on the bottom (far surface) of the tank floor.