What Is SLOFEC?
SLOFEC (Saturated Low Frequency Eddy Current) is an advanced electromagnetic inspection
technique that combines two physical principles: the magnetic saturation of MFL — which
enables penetration of the full wall thickness — with the phase-sensitive signal analysis of low
frequency eddy current — which provides enhanced defect characterisation and top/bottom
surface discrimination.
In conventional MFL, a strong magnetic field saturates the material and flux leakage is detected
at wall loss locations. Standard MFL is effective up to approximately 12–15mm wall thickness.
Above this, the magnetic circuit cannot achieve full saturation, and sensitivity degrades
significantly.
SLOFEC extends this limit to approximately 30mm wall thickness by combining the magnetic
bias field of a permanent magnet yoke with eddy current sensor arrays positioned between the
magnet poles. The eddy current signal — superimposed on the saturated magnetic field — is
sensitive to both surface and sub-surface metal loss, and the phase angle of the eddy current
response allows discrimination between top-surface (internal, product-side) and bottom-surface
(external, soil/foundation-side) corrosion — a capability that standard MFL does not provide.
SLOFEC key capabilities:
- Wall thickness inspection range: 0 to approximately 30mm
- Effective through non-metallic coatings up to 10mm (GRP, rubber, paint, epoxy)
- Top-surface and bottom-surface corrosion discrimination
- Applicable to coated, lined, and thick-wall storage tanks, vessels, and piping
- High-speed scanning — comparable to standard MFL floor scanning rates
- C-scan colour map output for clear, quantitative condition visualisation