nd Preven.(2008)8: 41-47 DOI10.1007/sl1668-0079106-5 C·A·S·EH·I.s.T.0·R.Y-P·E.E·R.R·E.v·I·E.W·E·D Damage and residual life assessment of bends for X20CrMoV121 Main Steam Pipe after Long-Term Service Zheng-Fei Hu· Zheng-Guo Yang·Guo- Qiu He Cheng-Shu Chen Submitted: 30 June 2007 /in revised form: 5 December 2007/Published online: 31 January 2008 C ASM International 2008 165,000 h service at 550C under 13.73 MPa pressure. experience severe service conditions that lead to deg The residual life of the bend sections is determined by radation in the microstructure and properties. Because evaluation of the service stresses and testing to obtain creep of this degradation, it is necessary to assess the residual rupture data. Metallographic analysis and tensile, impact, life of exposed components. The creep damage of the nd hardness tests are also conducted. These combined materials from components in long-term service has tests show that the properties of the steel deteriorated been surveyed to evaluate the residual life. There are during service, displaying embrittlement tendencies: the few reports about residual life assessment of high corresponding microstructures exhibit grain boundary chromium( Cr) ferritic steels; however some weakening and creep damage characteristics. However, tions of creep damage have focused on considering no evidence of localized damage in the form of measurement, the recovery of lath structure, and creep cavitation or surface cracks was observed in the coarsening of precipitating carbides [1-3]. The hardness examined parts, considering the residual life of the bends at of high-Cr ferritic steels decreases during recovery of service condition, they are adequate for an additional the lath structure and coarsening precipitates during 44,000 h of operation. It is recommended that a health creep deformation. Additionally, the lath width assessment should be taken after 25,000 h service exposure precipitate size increase during accelerated creep for safety reasons the contrary, some of the investigations [1] of X20CrMoV12 1 steam pipes that have been in long Keywords Main steam pipe. Microstructure term service indicated that the properties degraded Finite element analysis. Residual life assessment severely but no softening occurred. It is believed that the precipitation hardening by fine carbide intralaths as well as stabilization of M23 C6 subgrain structure by Introduction carbides are decisive factors for the high creep strength of this steel [2]. Many power plants This paper describes the damage evaluation of the 20 years, and the components in these plants have been mechanical properties and microstructure as well as residual life assessment for bent pipe sections of a ZF.H(凶)·G.Q.HeC.S.Chen X20CrMoV12 1 main steam pipe in a power plant in School of Materials Science and Engineering, Tongji University, Shanghai. The steam pipe has been in service for Shanghai 200092. China 23 years, and it has been operating at isothermal and constant pressure condition (550C/13.73 MPa) Z.-G. Yang more than 165, 000 h. The chemical composition of Department of Materials Science, Fudan University the X20CrMoV121 steel investigated is given in Shanghai 200433, China Table 1 2 SpringC Æ A Æ S Æ E H Æ I Æ S Æ T Æ O Æ R Æ Y—P Æ E Æ E Æ R-R Æ E Æ V Æ I Æ E Æ W Æ E Æ D Damage and Residual Life Assessment of Bends for X20CrMoV12.1 Main Steam Pipe after Long-Term Service Zheng-Fei Hu Æ Zheng-Guo Yang Æ Guo-Qiu He Æ Cheng-Shu Chen Submitted: 30 June 2007 / in revised form: 5 December 2007 / Published online: 31 January 2008
ASM International 2008 Abstract The bent sections from a main steam pipe in a thermal power plant in Shanghai were examined after 165,000 h service at 550 C under 13.73 MPa pressure. The residual life of the bend sections is determined by evaluation of the service stresses and testing to obtain creep rupture data. Metallographic analysis and tensile, impact, and hardness tests are also conducted. These combined tests show that the properties of the steel deteriorated during service, displaying embrittlement tendencies; the corresponding microstructures exhibit grain boundary weakening and creep damage characteristics. However, considering no evidence of localized damage in the form of creep cavitation or surface cracks was observed in the examined parts, considering the residual life of the bends at service condition, they are adequate for an additional 44,000 h of operation. It is recommended that a health assessment should be taken after 25,000 h service exposure for safety reasons. Keywords Main steam pipe
Microstructure
Finite element analysis
Residual life assessment Introduction Many power plants have been operating for more than 20 years, and the components in these plants have been used at elevated temperatures up to or exceeding the original design life. High-temperature components experience severe service conditions that lead to deg￾radation in the microstructure and properties. Because of this degradation, it is necessary to assess the residual life of exposed components. The creep damage of the materials from components in long-term service has been surveyed to evaluate the residual life. There are few reports about residual life assessment of high￾chromium (Cr) ferritic steels; however some investiga￾tions of creep damage have focused on hardness measurement, the recovery of lath structure, and coarsening of precipitating carbides [1–3]. The hardness of high-Cr ferritic steels decreases during recovery of the lath structure and coarsening precipitates during creep deformation. Additionally, the lath width and precipitate size increase during accelerated creep. On the contrary, some of the investigations [1] of X20CrMoV12.1 steam pipes that have been in long￾term service indicated that the properties degraded severely but no softening occurred. It is believed that the precipitation hardening by fine carbide intralaths as well as stabilization of M23C6 subgrain structure by carbides are decisive factors for the high creep strength of this steel [2]. This paper describes the damage evaluation of the mechanical properties and microstructure as well as residual life assessment for bent pipe sections of a X20CrMoV12.1 main steam pipe in a power plant in Shanghai. The steam pipe has been in service for 23 years, and it has been operating at isothermal and constant pressure condition (550 C/13.73 MPa) more than 165,000 h. The chemical composition of the X20CrMoV12.1 steel investigated is given in Table 1. Z.-F. Hu (&)
G.-Q. He
C.-S. Chen School of Materials Science and Engineering, Tongji University, Shanghai 200092, China e-mail: huzhengf@mail.tongji.edu.cn Z.-G. Yang Department of Materials Science, Fudan University, Shanghai 200433, China 123 J Fail. Anal. and Preven. (2008) 8:41–47 DOI 10.1007/s11668-007-9106-5