Conventional eddy current testing is applied when testing non-ferromagnetic heat exchanger tubes. The test is performed with a bobbin coil that produces an electromagnetic field in the tube. This allows the inspection to have greater sensitivity on the inside diameter of the tube where defects are most likely to occur and with the use of multiple frequencies we are able to penetrate 100% of tube wall thickness in order to detect flaws at variable depths. When the probe is pulled across a discontinuity, the electromagnetic field is distorted in per portion to the discontinuity size and relationship to the field. This distortion in magnetic field changes the coil impedance that is related to the discontinuity. Because of this coupling effect of the eddy current probe to the material it is crucial to have a properly cleaned tube and to know tube dimension prior to commencing the inspection. The eddy current testing method detects pits, wall loss and cracks
Eddy Current inspection is a very fast technique with data acquisition rates of up to 2m/sec being feasible, making it an ideal technique for the inspection of equipment with large numbers of tubes. Between 600 -1000 can be inspected during a shift depending on the tube lengths.