EC - NEAR FIELD
It is an electromagnetic method technique, which consists of “scanning” the entire length of the tube using probes that emit a magnetic field that measures the “lift-off” or filling factor and converts it into amplitude-based signals ( without phase analysis). It is applied only to ferromagnetic materials, including tubes with external fins and can detect and size pits, isolated or gradual thickness loss.
Due to the penetration of eddy currents being limited to the internal surface of the tubes, the NFT test is not affected by fins on the external side of the tubes.
Due to the penetration of eddy currents being limited to the internal surface of the tubes, the NFT test is not affected by fins on the external side of the tubes.
MAIN ADVANTAGES
– Allows the inspection of partially encrusted tubes;
– Little sensitive to baffles and mirrors;
– External tube fins do not interfere with the result;
– Higher test speed than IRIS.
MAIN DISADVANTAGES
– Dimensioning is not precise, many times variables interfere;
– Requires high filling factor;
– Performing the exam and analysis requires experience and skill;
– Requires standard manufacturing for each type of tube examined;
– Does not differentiate between internal and external discontinuities;