Prediction of creep damage life for 2.25Cr1Mo welded joint and assessment by ultra-sonic noise analysis
Nakashiro Masashi; Shibata Saburo; Yoneyama Hiroshi; Umaki Hideo; Sakuma Naokatu; Watanabe Terutugu; Okuyama Yoshihiro
Abstract:For evaluating the creep damage of 2.25Cr1Mo steel(JIS STPA24) welded joint, degradation mechanism and non-destructive analytical methods (Ultrasonic test noise analysis methods: UT noise analysis) were studied on the welded joint creep specimens interrupted at various test periods. Degradation of the heat affected zone (HAZ) prior to the base metal degradation was calculated from the simplified computation formulae simulating the stress relaxation curve. Creep void formation was remarkable in the middle of HAZ of the specimen, rather than near the surface, followed by the formation of linkage called Type IV cracking. UT noise analysis method, especially effective for detecting fine defects, could be used to measure the degradation of the welded joint HAZ. The measured results of welded joint in fossil power plant indicated the usefulness of UT noise analysis method. Key Words:creep, life assessment, welded joint, NDE, relaxation curve, ultrasonic, boiler, header, Cr-Mo steel