Storage Tank Floor Inspection Methods: MFL, UT and Robotic Crawlers Compared
PetroBot Technologies ·
Tank floors fail from the side you cannot see. Soil-side corrosion, product-side pitting and weld degradation all develop between inspections, and the method you choose determines what you find. The three workhorses — magnetic flux leakage (MFL), ultrasonic thickness (UT) measurement, and robotic UT crawlers — answer different questions.
MFL floor scanning
MFL scanners sweep the floor of an empty, cleaned tank and flag areas of metal loss quickly across large plate areas. MFL is a screening tool: it locates suspect areas but does not measure remaining thickness precisely, so findings are normally proven up with UT. It requires the tank out of service, cleaned to bare plate.
Manual UT measurement
UT gives a true remaining-thickness reading at the point measured. Manual UT on a tank floor is slow, coverage is sparse by necessity, and it requires entry into a cleaned, gas-freed tank — with all the confined-space cost and risk that entails. It remains the reference measurement for proving MFL indications and qualifying repairs.
Robotic UT crawlers — in service
Robotic crawlers bring the UT probe to the floor while the tank remains full and operating. Coverage is programmable, measurement density far exceeds manual spot readings, and every reading is position-logged for repeatable corrosion-rate trending between surveys. Because no person enters the tank, the inspection requires no cleaning, no gas-freeing and no confined-space controls.
The trade-off is access and product compatibility: robot deployment depends on tank openings, internal structures and the stored product, which is why a technical suitability review precedes every deployment.
How they combine
A modern integrity programme uses robotic in-service UT for trending and shutdown prioritisation, MFL for full-floor screening when the tank is opened, and manual UT to prove indications and verify repairs. The methods are complements, not competitors — the goal is the cheapest path to defensible floor-condition data at each point in the tank's life.