Detection of External Stress Corrosion Cracking by Acoustic Emission

概要

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Acoustic emission (AE) from external stress corrosion cracking (ESCC) on a butt-weld 4 inch SUS 304 steel pipe of 4mm thickness was monitored as a function of internal hydrostatic pressure. AEs were detected by the resonant sensors with center frequencies of 50kHz and 450kHz and analyzed using the signal processing system developed. Among three types of AEs detected by the 50kHz sensors, Lamb wave AEs with broad frequency band were located near the ESCCs and found to be generated during pressure rise and reducing. Radiation pattern analyses of zero-th order symmetric Lamb mode suggested AEs from surface friction, crack of the rust in ESCC and falling-off grains of IG-ESCC. AEs monitored by the sensors with 450kHz center frequency were possibly produced by the falling-off of grains along IG-SCC. Though the primarily AEs from TG-SCC can hardly be detected by conventional AE system, we can detect secondary AEs associated with ESCC. This paper also discussed how to detect the secondary AEs from ESCC in process plants.
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