Near field testing (NFT) is a non-invasive, electromagnetic technique used to inspect the internal surfaces of tubes for corrosion, erosion, pitting, and axial cracking:

How it works

NFT uses two coils, a transmitter and a receiver, to generate eddy currents in the tube wall. The receiver coil is placed close to the transmitter coil to detect discontinuities in the near-field zone of the transmitter’s electromagnetic field.

What it’s used for

NFT is often used to inspect fin-fan tube heat exchangers, carbon steel tubing, and other ferromagnetic tubes. It’s also useful for detecting defects near structures like support plates and tube sheets.

Benefits

NFT is a rapid and cost-effective method that’s not affected by the external support structures or tube sheets. NFT probes measure lift-off, or “fill factor”, and convert it to amplitude-based signals.