PSI - Issue 68

M. Zarazovskii et al. / Procedia Structural Integrity 68 (2025) 391–397

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M. Zarazovskii et al./ Structural Integrity Procedia 00 (2025) 000–000

The processing of only SE(B) specimens yielded insufficient data since the sum of the weighting factors ∑r i ·n i was found to be equal to 0.476 for the model alloy E and 0.309 for the model alloy H. In the case of processing only the C(T)0.16T specimens, sufficient data were obtained for the model alloy E ( ∑ r i ·n i =1.51). For model alloy H, even after accounting for the data screening, the sum of the weighting factors is less than 1. In order to obtain reliable values of the reference temperature, the results of the SE(B) and mini-CT samples were combined. Following the combination of the results, they were subjected to the same screening process as described above for the miniature crayfish. The results of the multitemperature evaluation of T 0 for the all test results are presented in Tab. 3 and Fig. 4 (included are the 5% and 95% tolerance limits, along with the median K JC(1T) ). Upon combining the results for model alloy E, the sum of the weighting factors ∑r i ·n i is calculated to be 2.23. Similarly, for model alloy H, ∑r i ·n i is determined to be 1.42.

Table 3. Summary of T 0 the all results in agreement with ASTM E1921-17a (2017).

Property

Model alloy E

Model alloy H

Type specimen Initial T 0 (°C) Total Sapecimens Screened Specimens

SE(B) -155.4

CT0.16T

SE(B)+ CT0.16T

SE(B) 136.7

CT0.16T

SE(B)+ CT0.16T

-132.0

-139.1

99.8

115.6

5 0 5 3 2 1 0

20

25

4 0 4 2 1 1 0

16

20

6

4

8 8 6 1 2 3

6

Number of Samples Between +50/-50°C ( N )

14 11

21 14

14 10

Number of Uncensored Data ( r )

0.48

1.51

2.23

0.31

0.83

1.42

∑r i ·n i

Sapecimens Between T i - T 0 50 to -14 °C Sapecimens Between T i - T 0 -15 to -35 °C Sapecimens Between T i - T 0 -36 to -50 °C

1 5 5

2 8 6

2 5 3

The estimated Т 0 for 15Kh2NMFAA steel allows us to draw conclusions regarding its crack resistance. Fig. 4 show the FT curves according with the WWER nuclear standards PNAE G-7-002-86 (1987), SOU NAEK 177:2023 (2023), and VERLIFE (2008), with the CBT in the initial state according to PNAE G-7-002-86 being T k0 =-25 °C. It is seen that the all the considered standard FT curves exhibit a high degree of proximity in comparison with the lower 5% confidence interval of the Master-Curve. This indicates a significant reserve of the brittle strength resource of a particular RPV metal, which is calculated with respect to FT curves specified in above mentioned standards. Thus, the introduction of the Master-Curve concept will allow for a more adequate assessment of the brittle strength of NPP equipment and piping, and thus a reasonable increase in their service life.

a

b

Fig. 4. Master-Curve evaluation of the combined results: (a) for model alloy E, (b) for model alloy H