| 摘要 |
The technique is based on comparing the spectral response of the "suspect" signal with that of a reference signal. The "suspect" signal is a signal detected in the weld heat-affected zone by a high-frequency (10 MHz), angle-beam (typically 45 degree) shear wave transducer operated in the pulse-echo mode. The reference signal is taken from the base metal next to the weld or heat- affected zone with two matched transducers of the same kind as the pulse-echo transducer but operated in the pitch-catch mode. The two signals are gated and Fast Fourier Transformed to the frequency domain for comparison. Relative to the reference spectrum, the high temperature hydrogen attack spectrum has an amplitude which increases with an increase of frequency, while welding defects and inclusions have the same frequency dependence as the reference spectrum. Therefore, localized high temperature hydrogen attack can be easily differentiated from other defects due to its unique spectral response.
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