This is a technique of electromagnetics method, which consists of the “scanning” of all the length of the tube using probes which emit a magnetic field which measures the lift-off or the fill factor and converts it in signals based on amplitude (without analysis of phase). It is applied only to ferromagnetic materials, including tubes with external rooms. It can detect and measure pits, loss of isolated or gradual thickness.
Due to the penetration of Eddy currents being limited to the internal surface of tubes, the testing by NFT is not affected by rooms in the external side of tubes.
– Allows the inspection of tubes partially embedded
– A little sensitive to support plates and tubesheets
– Speed in testing is superior to Iris
– Tubes external rooms do not interfere with result
– Sizing is not needed, variables interfere very often
– It requires high fill factor
– Exam execution and analysis require experience and ability
– Standard tubes manufacturing is required to all types of examined tubes
– It does not make the difference between internal and external discontinuities