PSI - Issue 60

M.K. Sahu et al. / Procedia Structural Integrity 60 (2024) 390–401 M. K. Sahu et.al./ Structural Integrity Procedia 00 (2019) 000 – 000

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Above approach was proposed to be applied for the LBB qualification to avoid unstable cyclic tearing under reversible loading cycles for design basis earthquake events. It may be noted that all these investigations and proposed CTFAD are based on cyclic tearing test data conducted at room temperature. To validate this proposed methodology on reactor operating temperatures, the present investigation has been performed. The last two columns of the Table 3 present the load reduction factors and total number of loading cycles which are obtained from the current cyclic tearing tests conducted on reactor operating temperature. The present test data points are plotted along with the best fit curve and lower found fit curve of CTFAD Gupta et.al. (2014) in Fig. 4. It may be observed that for the SA333Gr6 CS pipe tests the data is falling little below the lower bound curve. This indicate that the temperature associated material degradation due to delayed strain aging (DSA) is more for cyclic tests than that in the monotonic tests. 5. Conclusions In this work, total six numbers of straight pipe specimens with through wall crack have been tested under four point bend loadings under reactor operating temperature i.e., 300 C. This includes total two numbers of monotonic fracture testing on one 8-inch carbon steel (SA333Gr6) pipe and one 12-inch similar metal weld (SMW) pipe specimen of SS304LN material. The monotonic tests are performed for finding out the monotonic loading capacity of the both type of pipe specimens under reactor operating temperature environment. To estimate the damaging effect due to reversible cyclic loadings three numbers of 8-inch pipe specimens have been tested under different magnitude of peak load values related to cyclic loadings. It should be noted that ideally the 8-inch pipes tested under monotonic and cyclic loadings are identical by material, geometry and loading configurations. This approach has singled out the • For 8-inch pipes, on decreasing the peak load values results in to increasing of endured loading cycle numbers. This observation is consistent with the room temperature findings. • For carbon steel pipes, the load reduction values are significantly lower than room temperature based CTFAD. Hence, high temperature cyclic tearing damage seems to be enhanced compared to room temperature. • This additional damage at high temperature may be due to the delayed strain aging (DSA) under cyclic loadings, which is commonly observed in carbon steel material in this temperature range. DSA causes additional embrittlement in the material which may cause additional reduction in load capacity under cyclic loadings. • The load reduction factor for stainless steel weld SMW is close to the best fit curve of CTFAD. Hence, the load reduction is similar at room temperature and high temperature for this material. However, for confirming this observation a greater number of cyclic fracture tests need to be performed for stainless steel weld pipe specimens. Boiler, A.S.M.E, 2007. ASME boiler and pressure vessel code: an international code. Section III, Division 1, Rules for construction of nuclear facility components, New York: American Society of Mechanical Engineers. Chattopadhyay, J., Dutta, B.K. and Kushwaha, H.S., 2000. Experimental and analytical study of three-point bend specimen and through wall circumferentially cracked straight pipe. International Journal of Pressure Vessels and Piping, 77(8), pp.455-471. Chattopadhyay, J., Dutta, B.K., Kushwaha, H.S., Roos, E. and Herter, K.H., 2004. Load bearing capacity of flawed piping components-comparison of experiment with calculation. International Journal of Pressure Vessels and Piping, 81(7), pp.599-608. Gupta, S.K., Bhasin, V., Chattopadhyay, J., Ghosh, A.K. and Singh, R.K., 2015. Cyclic-tearing behaviour and J – R curves of Indian NPP pipes under displacement-controlled cyclic loading. International Journal of Pressure Vessels and Piping, 132, pp.72-86. Gupta, S.K., Bhasin, V., Chattopadhyay, J., Ghosh, A.K. and Vaze, K.K., 2014. A proposal on cyclic tearing-based stability assurance for LBB demonstration of nuclear piping. International Journal of Pressure Vessels and Piping, 119, pp.69-86. Kramer, G., Veith, P. and Marschall, C., 1997. Stability of cracked pipe under seismic/dynamic displacement-controlled stresses. Subtask 1.2 final report (No. NUREG/CR--6233-VOL. 2). Nuclear Regulatory Commission. References damaging effect of cyclic loadings compared to monotonic loadings. The main findings of this work can be concluded with following points: