2013 Volume 62 Issue 11 Pages 449-453
Stress corrosion cracks in steel specimen under high temperature and high pressure were monitored using an optical fiber AE monitoring system. The AE monitoring system was composed of an optical fiber interferometer, a feedback circuit and a digitizer. The optical fiber sensor was coated with a polyamide, which has high heat resistance. A sensing portion of the optical fiber was wound over a cylinder type sensor holder that acted as a wave guide for AE connected to a CBB jig. A sample was fabricated by welding a low alloy steel plate with a carbon steel plate. AE signals were monitored for 28 days（2.4 Ms）under a CBB test at 180℃ and 1.0 MPa. 119,460 AE signals were detected. Noise signals caused by the heater and autoclave were reduced by utilizing the correlation coefficient of AE waveforms and their frequency spectra. The characteristics of the waveform propagated along the wave guide were also utilized for eliminating noise signals. Only 96 AE signals were extracted after the noise reduction process. These AE signals were detected 1.2 Ms after start of AE monitoring. It was estimated that SCC was initiated during this time.