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<p>Ammonia is emerging as a promising carbon-free fuel that can be converted to energy using combustion engines and fuel cells or converted to hydrogen in a cracker. The structural alloys in these applications are exposed to harsh conditions, notably high temperature and presence of NH<sub>3</sub> and H<sub>2</sub>O, under which their behavior remains insufficiently understood. In this work, the nitridation behavior of seven alloys (625, 600, 800HT, AISI 316L, AISI 310S, AISI 444 and EF101) was systematically studied as a function of temperature (495–670&#xa0;°C), NH<sub>3</sub> concentration (6–85%) and H<sub>2</sub>O content (0–2%). Mass gain measurements combined with microstructural characterization were used to quantify nitridation and identify degradation mechanisms. Nitridation resistance increased with decreasing Fe-content and increasing Ni-content of the alloy, with alloy 625 showing the highest resistance across the investigated conditions. Increasing temperatures and the presence of 2% H<sub>2</sub>O accelerated nitridation in alloys 600, 800HT and 316L, but suppressed it in alloy 444. The improved nitridation resistance of alloy 444 is attributed to the formation of a protective oxide scale, highlighting the critical interplay between oxidation and nitridation in environments containing both NH<sub>3</sub> and H<sub>2</sub>O.</p>

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Nitridation Resistance of Alloys in Pressurized Ammonia Operation: Effects of Temperature and H2O

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年8月3日

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  • Belma Talic,
  • Per Martin Rørvik,
  • Yngve Larring

摘要

Ammonia is emerging as a promising carbon-free fuel that can be converted to energy using combustion engines and fuel cells or converted to hydrogen in a cracker. The structural alloys in these applications are exposed to harsh conditions, notably high temperature and presence of NH3 and H2O, under which their behavior remains insufficiently understood. In this work, the nitridation behavior of seven alloys (625, 600, 800HT, AISI 316L, AISI 310S, AISI 444 and EF101) was systematically studied as a function of temperature (495–670 °C), NH3 concentration (6–85%) and H2O content (0–2%). Mass gain measurements combined with microstructural characterization were used to quantify nitridation and identify degradation mechanisms. Nitridation resistance increased with decreasing Fe-content and increasing Ni-content of the alloy, with alloy 625 showing the highest resistance across the investigated conditions. Increasing temperatures and the presence of 2% H2O accelerated nitridation in alloys 600, 800HT and 316L, but suppressed it in alloy 444. The improved nitridation resistance of alloy 444 is attributed to the formation of a protective oxide scale, highlighting the critical interplay between oxidation and nitridation in environments containing both NH3 and H2O.