J Fail. Anal and Preven. (2008)8: 41-47 est data and extrapolated curve surface cracks or cavitation. Additionally, it is recom Master curve from ref 9 mended that another health check of the expected service of the exposed bent sections be carried out after 22,000 h of service. During shutdown of the plant, nondestructive tests, namely, dimensional(thickness and diameter)mea- surement, and in situ metallography may be carried out to assess the condition of the materials for their future serviceabil 10 202122232425262728 Larson Miller Parameter T(25+log(tr))/1000 An increasing trend of brittleness of the parent metal of X20CrMoV12. 1 is seen with prolonged exposure at service Fig4 Plot of stress vs Larson Miller parameter(LMP)for parent conditions. Corresponding microstructural investigations metal of bend show that carbide coarsening and martensite structure deterioration also occur during long-term exposure service Equation 8 means, from the redesign viewpoint, that the at 550C. The residual life of bent sections of main pipe of pipe could not meet the safety criteria for opera- X20CrMoV12I is about 44,000 h, provided there is tion for 100,000 h after 23 years service evidence of localized damage in the form of surface cracks The rupture data for the specimens have been plotted in or cavitation. Even though the straight sections of the main terms of log(stress) versus Larson-Miller parameter steam pipe appear to be in a reasonably good state of Fig 4, where LMP is expressed health. it is recommended that another health check be LMP= T(25+log tr) (5) carried out after 22,000 h of additional service. Addition- ally, during shutdown of the plant, nondestructive tests where T is the absolute temperature in K, and tr is the (NDT), namely, dimensional(thickness and diameter) rupture time in hours measurement. hardness measurement. and in situ metal- Analysis of rupture data indicates that the properties of lography should be carried out to assess the condition of the exposed steel are comparable to those of the master curve the materials for their future serviceability of virgin pipe [11], suggesting no appreciable creep damage The test data points of the stress versus LMP plot for the Acknow service-exposed material are fairly close to the master curve ural Science Foundation of China under contract no. 50771073 and for virgin material when the stress is less than 200 MPa. The 2007CB714705 esearch Program of China under contract no master curve for the virgin material has been extrapolated to a lower stress value that is below the operating hoop stress (on= PD/2t=72. 1 MPa)of the service-exposed main References steam pipe. The remaining life of the service-exposed steam pipe predicted at 72.1 MPa and at 550C is shown in I. Masuyama, F, Nishimura, N, Sasada, A: CAMP-ISD, 11. 614 Fig. 4. At the operating hoop stress of 72.1 MPa for the engthening mechanisms in high chromium service-exposed pipes, the LMP value as read from the graph steels. In: Bakker, W.T., Parker, J D(editors ). Proceedings of the is about 25,730. At this value of LMP, one would expect a Third Conference on Advances in Materials. Technology for very long life. As is customary, an inspection life of straight Fossil Power Plants. London (UK): The Institute of Materials, pp. 187-19402001). pipe after >100,000 h is recommended. However, consid 3. Sawada, K, Maruyama, K Hasegawa, Y, Muraki, T. Creep life ering that the maximum resultant stress on the bent section is assessment of high chromium ferritic steels by recovery of 01=125 MPa, the LMP value as read from the graph is martensitic lath structure. Proceedings of Eighth International about 24, 398 and the expected residual life is about Conf. on Creep and Fracture of Engineering Materials and Structures, Tsukuba, Japan, Nov. 1-5, 1999. 44,200 h. The results for the parent metal in the bent section 4. Hu, Z F, Wu, X F, Wang, C.X. HRTEM study on precipitates in predict a remaining life of about 44, 200 h at most highl high CoNi steel. J. Mater. Sci. Tech 20. 425/528 stressed locations, although failure of the straight sectior 5. Vodarek, V, Strang. A: Effect of nickel on the should not occur in 100,000 h of operation rocesses in 12CrMoV steels during creep at 550C. 38,101(1998) This analysis thus suggests that the remaining life at 6.Ennis, P.., Zielinska-Lipiec, A, Filemonowicz, A Quantitative 550C is a minimum of 44, 200 h for the service, provided omparison of the microstructure of high chromium steels for 2 SpringerEquation 8 means, from the redesign viewpoint, that the exposed pipe could not meet the safety criteria for opera￾tion for 100,000 h after 23 years service. The rupture data for the specimens have been plotted in terms of log (stress) versus Larson-Miller parameter in Fig. 4, where LMP is expressed: LMP ¼ Tð25 þ log trÞ ð5Þ where T is the absolute temperature in K, and tr is the rupture time in hours. Analysis of rupture data indicates that the properties of the exposed steel are comparable to those of the master curve of virgin pipe [11], suggesting no appreciable creep damage. The test data points of the stress versus LMP plot for the service-exposed material are fairly close to the master curve for virgin material when the stress is less than 200 MPa. The master curve for the virgin material has been extrapolated to a lower stress value that is below the operating hoop stress (rh = PD/2t = 72.1 MPa) of the service-exposed main steam pipe. The remaining life of the service-exposed main steam pipe predicted at 72.1 MPa and at 550 C is shown in Fig. 4. At the operating hoop stress of 72.1 MPa for the service-exposed pipes, the LMP value as read from the graph is about 25,730. At this value of LMP, one would expect a very long life. As is customary, an inspection life of straight pipe after [100,000 h is recommended. However, consid￾ering that the maximum resultant stress on the bent section is r1 = 125 MPa, the LMP value as read from the graph is about 24,398 and the expected residual life is about 44,200 h. The results for the parent metal in the bent section predict a remaining life of about 44,200 h at most highly stressed locations, although failure of the straight sections should not occur in 100,000 h of operation. This analysis thus suggests that the remaining life at 550 C is a minimum of 44,200 h for the service, provided there is no evidence of localized damage in the form of surface cracks or cavitation. Additionally, it is recom￾mended that another health check of the expected service of the exposed bent sections be carried out after 22,000 h of service. During shutdown of the plant, nondestructive tests, namely, dimensional (thickness and diameter) mea￾surement, and in situ metallography may be carried out to assess the condition of the materials for their future serviceability. Conclusions An increasing trend of brittleness of the parent metal of X20CrMoV12.1 is seen with prolonged exposure at service conditions. Corresponding microstructural investigations show that carbide coarsening and martensite structure deterioration also occur during long-term exposure service at 550 C. The residual life of bent sections of main pipe of X20CrMoV12.1 is about 44,000 h, provided there is no evidence of localized damage in the form of surface cracks or cavitation. Even though the straight sections of the main steam pipe appear to be in a reasonably good state of health, it is recommended that another health check be carried out after 22,000 h of additional service. Addition￾ally, during shutdown of the plant, nondestructive tests (NDT), namely, dimensional (thickness and diameter) measurement, hardness measurement, and in situ metal￾lography should be carried out to assess the condition of the materials for their future serviceability. Acknowledgments This work was supported by the National Nat￾ural Science Foundation of China under contract no. 50771073 and National Basic Research Program of China under contract no. 2007CB714705. References 1. Masuyama, F., Nishimura, N., Sasada, A.: CAMP-ISIJ, 11, 614 (1998). 2. Ennis, J.P.: Creep strengthening mechanisms in high chromium steels. In: Bakker, W.T., Parker, J.D. (editors). Proceedings of the Third Conference on Advances in Materials. Technology for Fossil Power Plants. London (UK): The Institute of Materials, pp. 187–194 (2001). 3. Sawada, K., Maruyama, K., Hasegawa, Y., Muraki, T.: Creep life assessment of high chromium ferritic steels by recovery of martensitic lath structure. Proceedings of Eighth International Conf. on Creep and Fracture of Engineering Materials and Structures, Tsukuba, Japan, Nov. 1–5, 1999. 4. Hu, Z.F., Wu, X.F., Wang, C.X.: HRTEM study on precipitates in high CoNi steel. J. Mater. Sci. & Tech. 20, 425/528 (2004). 5. Vodarek, V., Strang, A.: Effect of nickel on the precipitation processes in 12CrMoV steels during creep at 550 C. Scr. Mater. 38, 101 (1998). 6. Ennis, P.J., Zielinska-Lipiec, A., Filemonowicz, A.: Quantitative comparison of the microstructure of high chromium steels for Fig. 4 Plot of stress vs Larson Miller parameter (LMP) for parent metal of bend 46 J Fail. Anal. and Preven. (2008) 8:41–47 123