PSI - Issue 71

P.K. Sharma et al. / Procedia Structural Integrity 71 (2025) 66–73

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1.1. Design and fabrication of different specimen Specimens have been machined from hot-rolled plates of Alloy 690 material of 10 mm thickness. The material was taken from the processing plant at WIP, BARC. Chemical composition of the material was evaluated using ASTM E 3047:2016. Final composition of alloy 690 plates used is shown in Table 1. Table 1: Chemical composition of alloy 690 material used for the test. Material Nickel Chromium Iron Carbon Silicon Manganese Sulphur Copper Alloy 690 61.6 28.7 8.992 0.025 0.21 0.253 0.003 0.165 The smooth and notched specimen were designed to incorporate multiaxial state of stresses. Thickness of the specimen were around 3 mm that is obtained from 10 mm thick plates of alloy 690 material. Total height of the smooth specimen is around 90 mm and gauge length is 19 mm. The gauge section area is around 3x4 mm 2 . The specimen were designed according to ASTM E-8 standard. The design details of the specimen are shown in Fig. 1(a). The U type notched specimen were fabricated keeping the width (W) at the minimum cross-section same as that of the smooth specimen i.e., 4 mm. The thickness and gauge section were also same as that of smooth specimen. The notch root radius (R) were taken as 0.5 mm, 1 mm and 2 mm that resulted in notch acuity ratio (W/R) of 8, 4 and 2 respectively. The geometry of notched specimen is illustrated in Fig .1(b) and 1(c). Fig. 1: (a) Geometrical details of the smooth specimen (all dimensions are in mm); (b) Notched specimen (c) different notches used for the study. 1.2. Test matrix for evaluating the effect of multiaxial stresses Tests were conducted on smooth and notched specimens at different temperature and stress levels. The net section stress (stress divided by minimum cross-section) was kept same for smooth and notched specimen. The stress levels were chosen such that the steady state creep rate can be captured in small time (minimum 8 hrs) for all the specimens. This slope shall be used for evaluating the Norton’s creep equation paramet ers at different temperatures. Some of the tests were carried out till rupture for evaluating the creep rupture behavior of the alloy 690 material. The details of the test matrix used is shown in Table 2. Table 2: Test matrix used for determination of effect of multiaxial stresses on creep deformation behavior of alloy 690. Temperature (°C) Stress levels (MPa) Smooth specimen Notched specimen (R 0.5 to 2 mm) 800 40-90 50-90 (50, 70, 81 ,90) 900 20-83 40-50 (40, 45, 50) 1000 5-25 25-35 (25, 30, 35) 1.3. Experimental procedure The tests were conducted on smooth and notched specimens using high temperature creep testing machine. The tests on smooth specimens were conducted according to ASTM E-139 while ASTM E-292 standard was used for conducting tests on notched type of specimens. The universal testing machine has the capability to test the specimen upto 1200 °C with temperature control in the range of ± 2 °C. The split type furnace with 3 zone control is used for reaching the desired temperature. After reaching the desired temperature, specimen were soaked for minimum 1 hr to reach the equilibrium temperature with the surroundings. Image of machine used for tests is shown in Fig. 2(a). Tests were carried out on creep control mode where the desired stress levels and loading rate for reaching the desired stress were kept as input. After running the start test program, the machine reaches the desired stress level and start the test while maintaining the constant stress condition. The tests were conducted for a minimum duration of 8 hours when the specimen did not fail earlier. This duration was chosen to simulate the accelerated deformation behavior occurring under the high temperature and stress conditions typical of nuclear processing vessel operation. It was sufficient to capture the secondary creep regime enabling accurate determination of minimum creep strain rates (a) (b) (c) R0.5 R1 R2