Eddy Current Impedance Analysis for Testing of Defect Depths on Stainless Steel Pipes

An encircling coil had been employed to test the defects of stainless steel pipes in eddy current testing. However, the defects with depth of 0.10, 0.15 and 0.20 mm could not be distinguished with the corresponding differences in phase-angles of testing signals which was always true according to the principle of skin effects. Aiming at dealing with this problem, impedance analysis which could show the calculating phase-angles and amplitudes of simulating signal of defects was applied. We calculated phase-angles with depth of defects ranging from 010 mm to 190 mm and amplitude of three depths as shown above. The stainless steel pipes with man-made defects on the surfaces were also made for eddy current testing. The results indicated that defects of 0.10 mm could be found and depth differences of 0.05 mm could be distinguished with the amplitudes which were much more stable and reliable than the phase-angles.