PSI - Issue 60

D. Sen et al. / Procedia Structural Integrity 60 (2024) 44–59 Deeprodyuti Sen/ Structural Integrity Procedia 00 (2024) 000 – 000

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Figure 7: Graphical plot of allowable nominal stress versus flaw tip root radius for (a) round bottom BPFF and (b) flat bottom BPFF showing the safe and unsafe regions. The flaw is assumed to be located in a region away from rolled joint (no residual stress) in a pressure tube used in 220MWe Indian PHWR. The axial flaw length “ 2c ” is kept as 20mm. It can be seen from Fig.7a that the allowable nominal stress increases with the increase in flaw tip root radius. Although the threshold peak stress, as shown in Figs. 4 to Figs. 6, decreases with increase in flaw tip root radius, the stress concentration factor ‘ k T ’ also decreases sharply with root radius ρ . The net effect of these two factors leads to an increase in allowable nominal stress with an increase in flaw tip root radius. As expected, the allowable nominal stress is lower for higher crack depths. Similar results for a flat bottom BPFF are shown in Fig.7b.

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Figure 8: Graphical plot of allowable nominal stress versus flaw tip root radius for (a) round bottom and (b) flat bottom BPFF showing the safe and unsafe regions. The flaw is assumed to be located in a region away from rolled joint (no residual stress) in a pressure tube used in 220MWe Indian PHWR. The radial flaw depth “ a ” is kept as 0.6 mm.