PSI - Issue 68

Aleks Vainionpää et al. / Procedia Structural Integrity 68 (2025) 279–284 A. Vainionpää et al. / Structural Integrity Procedia 00 (2025) 000–000

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Figure 2 depicts the comparison of spacing measurements in log-log scales and crack depth against cycle evaluation for two sub-groups. It is possible to perform two types of direct comparisons on these specimens, i.e. RTA vs HTA vs PWR (environment and temperature) and CA vs PUL vs POL (waveform). Based on the study, it can be stated that specimens tested in HTA exhibit longer fatigue lifetimes, compared to those tested in a simulated PWR primary environment. Specifically, the N 25 of the CA specimens tested in PWR water and HTA are 23600 and 190000, respectively. For specimens tested with a CA spectrum, the PWR environment largely accelerates the FCGR compared to HTA (roughly 5×), see Figure 2(a). Furthermore, the specimen tested in HTA initiate a fatigue crack at a much later stage compared to the specimen tested in PWR water (a factor of 10). The exposure to a PWR environment results in a systematically higher FCGR of 316L austenitic stainless steel. Additionally, specimens tested in PWR water showed an increased presence of nucleation sites for secondary cracks compared to those tested in HTA.

Fig. 2. Comparison of striation spacing measurements and crack depth against cycle evaluation for (a) RTA vs HTA vs PWR and (b) CA vs PUL vs POL. Moreover, the study also highlights the negative impact of a PUL test over a CA test on fatigue lifetime. For specimens tested in HTA, the PUL waveform accelerates the FCGR compared to a CA loading (roughly 3×), particularly beyond a crack depth of 1 mm, see Figure 2(b). Specifically, the striation spacings for PUL and CA