PSI - Issue 60

7

B Shashank Dutt et al. / Procedia Structural Integrity 60 (2024) 471–483 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

477

For SS 316 LN welds, estimated and determined fracture toughness values are plotted in Fig.6. Estimated K 1c and determined K j1c of the welds tested at RT are mentioned in table 3. The estimated K 1c values differ by 1-36 % compared to determined fracture toughness. Estimated K 1c for welds at 380 and 550 °C are included in tables 4 and 5 respectively. From tables 3-5, it is observed that out of nine aging conditions only for few aging conditions estimated K 1c are greater than 30 %, compared to determined K j1c values. Estimated K 1c results for similar (SS 316L, E308 and E347) austenitic welds (Hong et al. 2018), subjected to aging at 400 °C and tested at 25 and 320 °C are included in tables 6 and 7 respectively. From table 6 (tested at 25 °C) it is observed that only for 4 tested conditions out of total 9 test conditions, estimated K 1c are greater than 30 % of the determined fracture toughness. It is observed from table 7 (tested at 320 °C) that only for one (400 °C, 5000 h) aged condition (total 9 test conditions) estimated K 1c is greater than 30 %. Estimation of K 1c was also carried out for cast stainless steel (Yu et al. 2018) welds (SMAW and GTAW) and from different locations (fusion zone and heat affected zones). The estimated K 1c results are mentioned in table 8. From table 8, it is observed that (6 test conditions) only for 2 test conditions (heat affected zones) estimated K 1c is greater than 30 % of the determined values.

100 150 200 250 300 350 400 450 500 100 150 200 250 300 350 400 450 500 Present study Hong (2018) Yu (2018) SMAW welds GTAW welds tested at RT GTAW welds tested at 320 C Estimated K 1c , MPa.m 0.5 Determined fracture toughness, MPa.m 0.5 316 welds tested at RT 316 welds tested at 380 C 316 welds tested at 550 C

Fig.6. Estimated K 1c and Determined fracture toughness of austenitic stainless steel welds

From Tables 3-8, it is observed that estimated K 1c was within ± 30 % of determined values, for many tested conditions. In a previous study by Youn et al. (2021), estimation of J -R curves and fracture toughness ( J 0.2 , J 1.0 and J 3.0 ) was carried out for SS 316L welds (prepared by SMAW and GTAW processes) subjected to different aging (350 and 400 °C and maximum of 15,000 h durations) conditions and tested at two temperatures. Estimated fracture toughness values and determined fracture resistance, at various (0.2, 1.0 and 3.0 mm) crack extensions were compared (Youn et al. 2021). It was summarized that for GTAW welds tested at RT, estimated fracture resistance values were conservative. For SMAW welds, estimated fracture resistance values were not conservative. Previously, ratios of J 0.2 (predicted to determined) varied in the range of 0.4 to 0.7 (40-70 %) for GTAW welds (conservative) tested at RT (Youn et al. 2021). In a subsequent investigation, different estimation (based on aging constants) was applied for 316 L welds (Kim et al. 2022). For welds aged at 400 °C and tested at RT, difference between estimated fracture toughness and determined fracture toughness was in the range 9-30 % . For welds aged at 400 °C and tested at 288 °C, estimated