Saturation Low Frequency Eddy Current(SLOFEC) Technique
Fast screening for local metal loss.
Similar to the Magnetic Flux Leakage, but with two major differences:
1) a more powerful electromagnet to establish a saturated magnetic field within the test component;
2) low-frequency eddy current sensors to measure magnetic flux distortion inside the material, rather than outside as with MFL Hall-effect sensors.
SLOFEC Equipment
General inspection capabilities
Suitable for fast screening of thick walled pipes (<30mm) and for inspection of thinner walls covered with non-metallic protection layers up to 10mm (e.g. glass fibre reinforced epoxy coatings).
SLOFEC uses the combination of magnetic field line and eddy current field line distribution to detect flux density changes within the material. Testing field line changes within the material is giving more sensitive results than conventional MFL techniques. The use of the eddy current technique allows variation of settings and analysis of signal amplitude & signal phase.
Good for local defect detection such as detecting pitting corrosion and localised microbiological corrosion (which is mainly present as localised corrosion but can rarely appear as general corrosion). Even small isolated pits are detected.
More sensitive defect detectability than Magnetic Flux Leakage techniques
especially on thicker walls.
Suitable for inspection of ferritic and non-ferritic materials; suitable for inspection of pipes, tank floors, vessel.
Ability to detect & distinguish both internal defects and outer surface breaking defects.
Inspection limitations
Tankfloors, vessels and drums: wall thickness up to 30 mm, coatings up to 10mm.
Pipes and pipelines (1”+ diameter): wall thickness up to 25 mm, coatings up to 7mm. (Values taken from Innospection website.)
Sensitive for corrosion detection but not used for absolute wall thickness
determination “Gradual” defects (greater than 300-400mm in length) are not as easily detectable.
Findings should be complemented by conventional ultrasonic inspection.
