Pulsed eddy current nondestructive testing of ferromagnetic tubes

In sinusoidal eddy current nondestructive testing (NDT) of thick ferromagnetic tubes, wall thickness is measured with the coils displayed for 2-3 tube diameters (remote field eddy current technique). The tube inner diameter is measured at higher frequency with another pair of coils displaced for around 1 tube diameter (electrical caliper). In this paper, we give a thorough analysis of the excitation frequency and the distance between the coils for measurement of the tube inner diameter and wall thickness as a background for the application of pulsed eddy current (PEC). We propose application of one pair of coils displaced for 1-2 tube diameters for measurement of those tube parameters employing the features of response to the pulsed excitation. Results of our experimental work confirm that PEC technique provides a significant improvement of present eddy current systems for NDT of the ferromagnetic tubes.