Abstract: Seeing that there was no automatic detection means for defects in large tank bottom plate weld seam, the authors devoted themselves to developing an automatic detector based on the electromagnetic acoustic detection method. As for the key detection transducer, an electromagnetic acoustic transducer for exciting oblique incident SV waves was developed. The transducer's detection capability was tested on weld seam test panels. An echo signal wavelet noise reduction method was investigated and experiments were carried out on the simulated tank bottom plate to test the detector's walking-recording ability. The results show that the transducer can accurately find the defects in the weld seam whether there is anti-corrosion paint on the test panel or not, that according to the minimaxi threshold method, the noise reduction of the echo signal can be realized by using the db4 wavelet, and that the detector can implement the non-contact inspection of the tank bottom weld seam, record and mark defects to form a test map with the defect mark, which can replace the manual detection and reduce the casualties that may be caused by the personnel entering the tank cleaning and repairing.

Key words: tank bottom weld seam, non-contact detection, automatic detector, electromagnetic acoustic transducer, wavelet de-noising, detecting map