J Fail. Anal and Preven. (2008)8: 41-47 Table 1 The chemical composition of examined pipe from the pipe samples. The methods of preparing the TEM samples are described in many references [4] Stress analysis was carried out using finite element C Mn S analysis software and reflects the stresses under service 0.23 0.64 0.006 0.02 0.36 11.23 1.00 0.32 0.72 0.08 conditions. The residual life assessment of the main steam pipe is determined from the comprehensive results, including mechanical tests, microstructure investigation, Experiment and procedures and stress analysis. The test material was cut from three bends at 45 outboard position of a 273 mm outside diameter(OD) by 26 mm Results and Discussion thick main steam pipe of X20CrMo V12 1. A sample from a section of virgin pipe in the as-received state was also Mechanical Properties studied. The mechanical properties were investigat under room temperature and at the service temperature of The mechanical properties of the examined materials tested machine operated at constant strain rate. Full-size Charpy strength oo.2 and ultimate tensile strength ob of exposed V-notch impact specimens were also tested. Hardness samples decrease about 30%o, and the toughness is less than measurements were performed at a standardized machine 20% of that of the material in the as-received state: how- load of 375 kg on testpieces. Tensile tests were carried out ever, the hardness shows no significant changes. These on the base metal in both the longitudinal and transverse results show that the properties of the exposed materials directions of the main steam pipe. The accelerated stress degraded, and the spectacular change of the rupture tests were carried out at 550C at various stress mechanical property decrease of toughness after levels in the range of 150 to 260 MPa. The variation of the long-term service exposure. This means that the base metal yield strength (0.2% proof stress) and ultimate tensile of the exposed pipe is much more brittle at room temper strength (UTS)with temperature of testing are shown in ature. The same result has been obtained by others [5, 6 later tables The mechanical properties of the samples tested at high The microstructural investigations were performed temperature are given in Table 3. The strength as well as using analytical transmission electron microscopy (TEM); toughness of exposed samples decreases slightly, and there the transmission microscopy was carried out on both foil is a distinct change in toughness. Toughness of the exposed samples and carbon extraction replicas using a PhiLIPs materials at high temperature is about 30% less compared CM200(National Microanalysis Center, Materials Science with the as-received sample tested at the same condition. It Department,Fudan University, Shanghai) transmission is shown that there is an increasing trend of toughness and lectron microscope operating at 200 kV. Both the foil and brittleness transformation temperature with prolonged carbon extraction replicas for TEM study were prepared exposure time at service condition Table 2 Mechanical properties of virgin and service-ex aterials at room temperature Material SI No and direction Tensile stren Pa EA(A), RA(Z). Toughness(Akv), J Hardness, HB Bend 21 4465149 21 24 l19 ENI0216-2 >490 690-840 axial; H, hoop 2 SpringerExperiment and Procedures The test material was cut from three bends at 45 outboard position of a 273 mm outside diameter (OD) by 26 mm thick main steam pipe of X20CrMoV12.1. A sample from a section of virgin pipe in the as-received state was also studied. The mechanical properties were investigated under room temperature and at the service temperature of 550 C. Tensile tests were conducted using a 100 kN machine operated at constant strain rate. Full-size Charpy V-notch impact specimens were also tested. Hardness measurements were performed at a standardized machine load of 375 kg on testpieces. Tensile tests were carried out on the base metal in both the longitudinal and transverse directions of the main steam pipe. The accelerated stress rupture tests were carried out at 550 C at various stress levels in the range of 150 to 260 MPa. The variation of the yield strength (0.2% proof stress) and ultimate tensile strength (UTS) with temperature of testing are shown in later tables. The microstructural investigations were performed using analytical transmission electron microscopy (TEM); the transmission microscopy was carried out on both foil samples and carbon extraction replicas using a PHILIPS CM200 (National Microanalysis Center, Materials Science Department, Fudan University, Shanghai) transmission electron microscope operating at 200 kV. Both the foil and carbon extraction replicas for TEM study were prepared from the pipe samples. The methods of preparing the TEM samples are described in many references [4]. Stress analysis was carried out using finite element analysis software and reflects the stresses under service conditions. The residual life assessment of the main steam pipe is determined from the comprehensive results, including mechanical tests, microstructure investigation, and stress analysis. Results and Discussion Mechanical Properties The mechanical properties of the examined materials tested at room temperature are given in Table 2. The yield strength r0.2 and ultimate tensile strength rb of exposed samples decrease about 30%, and the toughness is less than 20% of that of the material in the as-received state; how￾ever, the hardness shows no significant changes. These results show that the properties of the exposed materials degraded, and the most spectacular change of the mechanical property is the decrease of toughness after long-term service exposure. This means that the base metal of the exposed pipe is much more brittle at room temper￾ature. The same result has been obtained by others [5, 6]. The mechanical properties of the samples tested at high temperature are given in Table 3. The strength as well as toughness of exposed samples decreases slightly, and there is a distinct change in toughness. Toughness of the exposed materials at high temperature is about 30% less compared with the as-received sample tested at the same condition. It is shown that there is an increasing trend of toughness and brittleness transformation temperature with prolonged exposure time at service condition. Table 1 The chemical composition of examined pipe Composition, wt% C Mn S P Si Cr Mo V Ni Cu 0.23 0.64 0.006 0.02 0.36 11.23 1.00 0.32 0.72 0.08 Table 2 Mechanical properties of virgin and service-exposed materials at room temperature Material SI No. and direction Tensile strength, MPa EA (A), % RA (Z), % Toughness (Akv), J Hardness, HB Rp0.2 Rm Bend 1 A 575 778 20 44 20 220 H 556 766 21 44 20 227 2 A 566 775 20 46 23 230 H 568 776 20 45 20 232 3 A 561 774 19 47 21 230 H 567 777 19 41 21 224 Virgin 1 A 695 777 26 59 113 230 2 A 702 776 26 59 114 234 3 A 685 776 24 60 119 229 EN10216-2 [490 690–840 [14 [27 A, axial; H, hoop 42 J Fail. Anal. and Preven. (2008) 8:41–47 123