PSI - Issue 14

Rajwinder Singh et al. / Procedia Structural Integrity 14 (2019) 930–936 Author name / Structural Integrity Procedia 00 (2018) 000–000

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Keywords: Hydrogen embrittlement, short crack, fatigue loading, SA 508 Grade 3 Class I low alloy steel

1. Introduction The reactor pressure vessel installed in nuclear power plants are manufactured from SA533 and SA508 LASs (Kim et al. (2015)). Due to the critical operation of these RPV steels in nuclear reactors, a continuous research is going on to improve the overall properties of these steels and thus different grades of these SA508 and SA533 RPV steels have been developed. During operation in nuclear power plants, these RPV steels are in continuous contact with high temperature water and thus are susceptible to HE due to corrosion reactions. As reported in literature, these RPV steels can absorb 2 ppm to 6 ppm of hydrogen during operation in nuclear reactors (Broomfield (1965); Chakravarny et al. (1986)). Therefore, to ensure the safe operation of these pressure vessels installed in nuclear reactors, it is important to investigate the effect of HE on the mechanical properties of these RPV steels. Extensive research has been carried out to understand the effect of hydrogen embrittlement on RPV steels with main focus on the effect of HE on tensile, fatigue and long crack growth properties of these steels. Wu et al. (Wu and Kim (2003)) investigated the effect of hydrogen on the tensile behavior of SA508 Cl. 3 LAS. The difference in the tensile properties were observed in hydrogen charged and un-charged specimens. The reason for this difference was explained by comparing the fractured surfaces of hydrogen charged and un-charged specimens for microvoid coalescence and dimple size. Mager et al. (Mager et al. (1977)) studied the difference in long crack growth behavior of A533 Gr. B Cl. I RPV steel tested in air and primary grade nuclear reactor water at 288 o C. Higher long crack growth rate was observed in high temperature than in air at same temperature. This difference was attributed to stress corrosion cracking in high temperature water environment by comparing the fractured surface of the specimens after testing. Similarly, Lee and Kim (Lee and Kim (2001)) investigated long fatigue crack growth in SA508 Cl. 3 RPV steel in high temperature water environment. In this study it was also concluded through fractography study that HE caused cleavage like facets with microvoids and brittle striation during crack propagation under cyclic loading. Huang et al. (Huang et al. (2008)) also explained the difference in long fatigue crack propagation in air and high temperature water environments by comparing the fractured surfaces of the samples tested in both these environmental conditions. The detailed effect of hydrogen on fatigue crack propagation cannot be completely understood by merely comparing the fractured surfaces of specimens tested for long fatigue crack propagation. Also, these long fatigue cracks do not interact with the microstructural features of the material. The detailed mechanistic understanding of HE on the fatigue and fracture behavior of these RPV steels can be understood well by investigating the effect of HE on short fatigue crack propagation. In general, these short cracks are of the order of 10 µm to 1 mm and during propagation under cyclic loading they highly interact with the microstructural feature in the material such as grain boundaries, inclusion, phase boundaries (Kaynak et al. (1996); Newman et al. (1999); Strubbia et al. (2014)). These interactions lead to high fluctuations in the crack propagation rate of these short fatigue cracks. The hydrogen present in the subject material may affect the interaction of short fatigue crack propagation with the microstructural features in the material. The aim of this research paper is to investigate the effect of hydrogen on short fatigue crack growth behavior in RPV steel SA508 Gr. 3 Cl. I LAS. The specimens are electrochemically hydrogen charged to investigate the effect of absorbed hydrogen on short fatigue crack propagation in the subject RPV steel. SENT specimens with an initial notch of the order of around 85 µm to 90 µm are used to investigate the short fatigue crack propagation. The effect of absorbed hydrogen on the subject RPV steel will be explained on the basis of difference in the interaction of short fatigue crack propagation with the microstructure of the subject RPV steel under hydrogen charged and un-charged conditions.

Nomenclature LAS Low Alloy Steel RPV

Reactor Pressure Vessel