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Pulsed eddy-currents have been used successfully for a number of years to measure the wall thickness of thin-wall tubing. In studies of 88.9-mm (3.50-in.)-diameter stainless-steel tubing, wall thicknesses in the 0.254 to 0.762 mm (0.010 to 0.030 in.) range have been measured with an accuracy of ±10%. This paper describes an investigation of the relationship between the pulse length and depth of electromagnetic plane-wave penetration. Long pulses contain lower-frequency components than pulses of shorter duration. Therefore, longer pulses will penetrate much more deeply into a conductive material, assuring a 90 percent confidence level in the measurement of thicker materials. The pulsed eddy-current equipment used at Argonne National Laboratory (ANL) employs sampling of the detector waveform at discrete time intervals. Optimization of field-coil design for larger thicknesses of conductive material necessitates an increase in the pulse length. With a preliminary coil design, a penetration of 9 mm into stainless steel was achieved.
pulsed eddy current, electromagnetic plane wave, electromagnetic penetration, field coil, pickup coil
Engineering assistant, Argonne National Laboratory, Argonne, Ill.