Why the floor is the critical component
Above-ground storage tank floors corrode from both sides: product-side pitting and, more dangerously, soil-side corrosion that cannot be seen from inside. Visual inspection alone cannot find it, so a volumetric scanning technique is needed.
How MFL tank floor scanning works
Magnetic Flux Leakage (MFL) magnetises the floor plate close to saturation. Where metal loss exists, part of the flux leaks out of the plate and is picked up by sensors between the magnet poles. The scanner is pushed across the floor, covering wide strips quickly and flagging both top-side and bottom-side loss.
MFL is a screening technique: indications are then sized with ultrasonic thickness measurement to decide on repair.
What API 653 expects
API 653 covers inspection, repair, alteration and reconstruction of atmospheric storage tanks. During an internal inspection the owner must assess floor condition and minimum remaining thickness to set the next inspection interval. MFL scanning followed by ultrasonic confirmation is the common way to obtain that data. Compliance depends on the complete procedure, qualified personnel and the owner's acceptance criteria.
Inspection steps
1. Empty, clean and degas the tank. 2. Remove scale and debris from the floor. 3. Calibrate the scanner on a reference plate. 4. Scan the floor in overlapping strips, including near welds and the annular ring. 5. Prove up indications with ultrasonic thickness. 6. Report with a floor map and repair recommendations.
MFL vs other floor techniques
| Technique | Strength | Limitation |
|---|---|---|
| MFL | Fast coverage, detects top and bottom-side loss | Screening; needs UT confirmation |
| Ultrasonic spot/scan | Accurate thickness | Slow over a full floor |
| Visual | Simple, top-side only | Misses soil-side corrosion |
What to look for in an MFL floor scanner
Coverage width, plate thickness range, sensitivity to small pits, ability to discriminate top from bottom-side loss, performance near welds and the shell, data mapping software and ease of use in confined tanks. The TANK-4000ME M2 by EDDYSUN is one option designed for this work.
Frequently asked questions
Can MFL measure remaining thickness?
MFL estimates metal loss for screening. Remaining thickness for repair decisions is confirmed with ultrasonic measurement.
Does the tank need to be out of service?
Yes. Floor scanning is done from inside an emptied, cleaned and gas-free tank.
Is the TANK-4000ME available in Europe?
Supply to Portugal and other markets is subject to commercial conditions, availability and import requirements of each destination. Contact us to confirm.
Equipment and technical support
Synvor supplies non-destructive testing equipment and provides technical support in selecting the right method and configuration for your application. The inspection itself is performed by the asset owner or a qualified inspection company.