PSI - Issue 68

Birhan Sefer et al. / Procedia Structural Integrity 68 (2025) 1121–1128 Sefer et al. / Structural Integrity Procedia 00 (2025) 000–000

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hydrogen uptake for the specimens tested in H 2 at high temperature as compared to the ones tested at room temperature for both conventionally and AM alloys. © 2025 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of ECF24 organizers Keywords: Hastelloy X; hollow specimen method; SSRT; TDMS; fractography; high-pressure hydrogen gas; high temeprature; hydrogen embrittment. 1. Introduction Hydrogen gas (H 2 ) as a green energy carrier is considered to be crucial in the transition to a fossil free society. It can be produced by electrolysis of water using renewable energy and utilized as a fuel without any carbon dioxide emission. It may also play a key role in an energy system relying on intermittent weather dependent power generation. The production of H 2 can be based on the power access from renewable sources. By an H 2 storage system, the gas can then be used for power generation in gas turbines when the demand is high. This has great potential to stabilizing the power grid and the price fluctuations of electricity. However, when having hydrogen gas in contact with components in metallic materials the risk of hydrogen embrittlement must be addressed. For conventional gas turbines, fuelled with natural gas, solid solution strengthened Ni-base alloys are normally used for components in the combustion zone, due to their high-temperature strength and oxidation resistance. These alloys are in general also known to have high resistance to HE and have great potential to be used for hydrogen gas turbines (San Marchi and Someday (2012). AM has high potential to be used for production of structural components in various applications, especially where the freedom to design complex geometries is vital to the optimization of the component performance and is a key enabler for the design of efficient H 2 combustion systems. Furthermore, it drastically reduces the need for welding, which may also be beneficial. There is however lack of knowledge on how AM Ni-base components behave when used in high-pressure H 2 environments (Yao et al. (2023) and Behvar et al. (2024)). The present work aims to evaluate the differences between conventionally manufactured hot rolled and AM Hastelloy X with respect to hydrogen uptake and hydrogen embrittlement susceptibility in SSRT with hollow specimen method. Solid solution strengthened Ni-base alloys are frequently used at temperatures where significant microstructural changes occur in service, e.g. precipitation and growth of carbides. The in-service aging of the material has been shown to have significant impact on the hydrogen solubility (Gao et al. (1992)) and hydrogen embrittlement susceptibility (Hasegawa and Osawa (1981)) of conventionally manufactured Hastelloy X. Mechanical testing under the influence of hydrogen in combination with service-like thermal exposure is of key importance for relevant assessment of the hydrogen embrittlement susceptibility of solid-solution strengthened Ni-base alloys. In this context, the authors expect elevated temperature mechanical testing using hollow specimens to play an important role, not only due to the relative simplicity, low cost and reduced safety concerns compared to autoclave testing systems, but also due to the freedom of testing conditions when it comes to maximum testing temperature, heating/cooling rate and accessibility for strain measurement. The aim of the 800°C SSRT testing performed in the present work is not only to assess the hydrogen embrittlement susceptibility, but also to contribute to the development of mechanical testing methods relevant for Ni base alloys used in H 2 combustion applications. 2. Materials and methods In this work Hastelloy X in hot rolled and solution heat treated condition was compared to as-printed AM condition. Hastelloy X is a nickel-chromium-iron-molybdenum alloy with exceptional combination of oxidation resistance, fabricability and high-temperature strength as well as high resistance to stress corrosion cracking (SCC). It is widely used in gas turbine engines for combustion zone components because of its high resistance to oxidation. The nominal chemical composition for Hastelloy X in hot rolled condition is shown in Table 1. © 2025 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of ECF24 organizers