An acoustic emission (AE) monitoring system with real time noise reduction function using a spectral subtraction (SS) process was developed, in order to monitor AE in a noisy environment. To evaluate the noise reduction performance of the SS, we monitored artificial AE signals in various noise environments. The S/N ratio of the AE signal in background noise, which includes electrical noise of a pre-amp and/or an A/D converter, was improved by 18.4dB using the SS process. Periodic noise was reduced and the S/N ratio increased to 40dB. We also reduced the noise with wide frequency band and the S/N ratio increased by 8-10dB. We then monitored the cylinder wave AE signals produced by a pencil lead breaking in the noise generated by the air flow in the pipe. The system improved the S/N ratio of the AE signal by 9.2dB and was able to detect AE signals.

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In large-scale structures such as bridges or coastal steel structures, the total length of the welded joints of the thick girder is very long. Therefore, improvement of the inspection speed of ultrasonic testing (UT) for the welded joint is required.Conventional UT needs mechanical movement of the probe to scan all sections of the weld. The phased array UT technique can replace this mechanical scanning movement in a right-angle direction against the welded line with high speed electrical scanning. In this study, we evaluated the UT condition based on JIS Z 3060 for the phased array UT techniques applying to the weld practically.

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In large-scale structures such as bridges or coastal steel structures, the total length of the welded joints of the thick girder is very long. Therefore, improvement of the inspection speed of ultrasonic testing (UT) for the welded joint is required. The phased array UT technique can achieve high speed inspection by the electrical scanning. In the previous study, we reported the effective UT conditions for phased array. In this study, we developed the logic for judging weld defects using the inspection data of automatic UT. In addition, we evaluated the detectability of phased array UT inspection for the welded joints of thick plates using test pieces of imitated slit defects and natural weld defects.

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