Flaw Detection in Copper Tubes Using Longitudinal Wave by Electromagnetic Acoustic Transducers

Electromagnetic acoustic transducers (EMATs) are developed for flaw detection in copper tubes. Longitudinal wave is propagated along length of the tubes. First, we use the square wave pulse, to find that the unidirectional transmission is possible with the array-type EMATs. Then, we apply the EMATs for U-bend tubes. Since low frequency components reflect at the U-bend section, the burst wave excitation is thus recommended. After finding the optimum excitation signal, flaw detection is executed. It is revealed that the flaw, which occupies 12% of the cross section, can easily be detected even in the U-bend tube, and that the flaw detectability is improved up to 3% by taking the correlation of the received signal with end reflected echoes. For straight pipe, the flaw occupying 1.5% of the cross section can be detected from 2 m distant.