Magnetic Flux Leakage (MFL) is the industry-standard screening tool for in-service floor inspection of above-ground storage tanks. TechCorr uses MFL to map corrosion across a tank floor without draining or entering the vessel, supporting API 653 inspection intervals and risk-based integrity programs.
What is Magnetic Flux Leakage (MFL)?
MFL magnetizes the tank floor with a bridge of strong permanent magnets and sweeps the floor surface. Where the steel is full-thickness, the magnetic flux stays inside the plate. Where wall loss, pitting, or laminations reduce the cross-section, flux "leaks" out of the surface, and sensors detect that leakage. The result is a color-coded thickness map of the entire floor.
When should MFL be used instead of conventional UT?
MFL is a rapid screening method — it covers thousands of square feet of floor in a single shift and flags every suspect area for follow-up. Conventional ultrasonic thickness (UT) gives a precise point measurement but only where you place the probe. The two are complementary: MFL finds the damage, UT confirms the remaining wall. For API 653 external and internal inspection intervals, MFL lets you defer or target internal entry by proving the floor condition from outside.
Does MFL require the tank to be empty?
No — that is its main advantage. MFL can be performed on the external bottom of an in-service tank, provided the underside is accessible and the floor is dry and clean enough for magnetic contact. For tanks that cannot be taken offline, MFL combined with Online Monitoring keeps your integrity program on schedule without lost production.
How accurate is MFL?
MFL reports wall loss as a percentage of nominal thickness with typical detection thresholds around 20% of wall loss for isolated pitting and better for broad corrosion. It is a screening tool, not a code-acceptance method by itself. Every MFL indication is confirmed with conventional UT before retirement thickness decisions are made under API 653.
What tank types and sizes can TechCorr inspect with MFL?
TechCorr deploys MFL on API 650 and API 12F tanks from a few hundred barrels up to over one million barrels, including floating-roof and fixed-roof configurations. Our crews mobilize from regional offices across North America and pair MFL with Rope Access for shell and roof inspection without scaffolding.
What certifications do TechCorr's MFL technicians hold?
MFL crews are led by API 653-certified inspectors and supported by ASNT Level II/III technicians trained on the specific MFL platform in use. Reports are reviewed and signed by an API 653 inspector before issue. Request a quote to scope an MFL campaign for your tank fleet.