Near field testing (NFT) is used for the inspection of fin fan carbon steel tubing in heat exchanger tubes it was first developed as an alternative to magnetic flux leakage (MFL). Specifically designed to detect internal corrosion, erosion, or pitting on the inside of carbon steel tubing. Because the eddy current penetration is limited to the inner surface of the tube, NFT probes are not affected by the fin geometry on the outside of the tubes.

NFT is a technology that uses two coils — a transmitter and a receiver. Typically the receiver coil is close to the transmitter coil, taking advantage of the transmitter's near-field zone — that is, the zone where the magnetic field from the transmitter coil induces strong eddy currents, axially and radially, in the tube wall. NFT is also much more sensitive to defects close to structures such as support plates and tube sheets.

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