Abstract
The authors have developed a new method for detecting position and direction in weld zone of steel structures such as oil-storage tanks and bridges without removing their anticorrosion paint. The method uses a special eddy current probe and detects the position and direction by utilizing the difference of electromagnetic characteristics between the base material and the heat affected zone. The probe comprises two large tangential exciting coils wound orthogonally each other and a small pancake detecting coil. The exciting coils induce uniform eddy current rotating its direction synchronizing to the alternating exciting current. The signal amplitude from the probe provides information on its position in the weld zone and the signal phase indicates the direction of the probe. Thus the probe generates the weld signal to effectively follow the weld line in steel structures. The experimental results have shown that the proposed method is promising because the probe provides clear weld signal with little noise and the change of the probe lift-off from the material causes little variation in the signal.
