Two coils are excited with a AC Current, producing a magnetic field around them. The magnetic field penetrates the tube material and generates apposing AC currents in the material. These currents are called “Eddy Currents”

Any defects that change the eddy current flow will change the impedance of the coils in the probe.

These changes in the impedance of the coils are measured and used to detect defects in the tubes.

Advantage

Suitable for nonferrous tubing such as SS304/316, brass, titanium, Inconel, Copper, Copper-nickel, etc.
Can detect pits, corrosion, erosion and axial cracking.
Very fast technique. Up to 2 m/s pulling speed. Able to inspect around 800 tubes per shift.