J Fail. Anal and Preven. (2008)8: 41-47 Fig 1 (a)Scanning electron fractographs of exposed sample from tensile test at room Temperature.(b) Scanning lectron fractographs of of thin foil from thin fo exposed sample. (d) TEM micrograph of thin foil from in foil from exposed sample Table 4 Stress rupture properties of service exposed bend pipe at 1000 550°C 菲丰 Sample No. Stress(os), Rupture EL(A),% EA(2), %o MPa time. h 000 23456789 824 35.6 82.8 l190.5 35.1 10 82.1 100000 394 Time(hours) 10 Fig 2 Plot of stress with rupture time for service exposed bend at Sample is not ruptured 550° 131 MPa This threshold strength of virgin material is less than the d bent tube sectio properties of determined by extrapolation from accelerated testing., The mechanical tests and rupture data as well as the strengt the exposed material, 0559 C=131 M Finite-element analysis is used to calculate the stress damage compared with those of the virgin pipe distribution in a pipe section. The model comprises a pipe bend(90%) to which straight pipes were attached to both ends. Thus numerical influences from boundary conditions Residual Life assessment on the calculated stresses and strains in the pipe bend co be minimized. The stress analysis takes into account only Standard EN10216-2 [10] gives the creep rupture stre the internal pressure and ignores all other loads. Further, it of X20CrMoV121 under 550C GR.100000= 128 was decided to fix one straight pipe end and load an axial 2 Springerr550 C 105 ¼ 131 MPa ð1Þ The mechanical tests and rupture data as well as the corresponding microstructure indicate that the properties of the parent metal of exposed bent tube sections show creep damage compared with those of the virgin pipe. Residual Life Assessment Standard EN10216-2 [10] gives the creep rupture strength of X20CrMoV12.1 under 550 C rR,100,000 = 128 MPa. This threshold strength of virgin material is less than the strength of the exposed material, r550 C 105 ¼ 131 MPa, determined by extrapolation from accelerated testing. Finite-element analysis is used to calculate the stress distribution in a pipe section. The model comprises a pipe bend (90) to which straight pipes were attached to both ends. Thus numerical influences from boundary conditions on the calculated stresses and strains in the pipe bend could be minimized. The stress analysis takes into account only the internal pressure and ignores all other loads. Further, it was decided to fix one straight pipe end and load an axial Table 4 Stress rupture properties of service exposed bend pipe at 550 C Sample No. Stress (rs), MPa Rupture time, h EL (A), % EA (Z), % 1 260 17.0 33.1 79.6 2 250 24.5 34.0 79.8 3 220 171.5 35.8 82.0 4 210 366.0 39.6 82.4 5 200 605.0 35.6 82.8 6 190 1190.5 46.5 83.2 7 180 1695.0 35.1 83.4 8 170 3334.0 30.4 82.1 9 160 5346.0 39.4 82.5 10 150a –– – a Sample is not ruptured Fig. 2 Plot of stress with rupture time for service exposed bend at 550 C Fig. 1 (a) Scanning electron fractographs of exposed sample from tensile test at room Temperature. (b) Scanning electron fractographs of exposed sample from tensile test at 550 C. (c) TEM micrograph of thin foil from thin foil from exposed sample. (d) TEM micrograph of thin foil from thin foil from exposed sample (magnified) 44 J Fail. Anal. and Preven. (2008) 8:41–47 123