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Everything You Need to Know About Hydrogen Safety and Preventing Embrittlement

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Global Hydrogen Review,

How can hydrogen professionals build systems that last? It’s important to remember that materials matter for hydrogen containment. Fluid systems made with specifically formulated, high-quality stainless steel better resist the challenges inherent to hydrogen containment. Swagelok’s FAQs explain how and what should be considered in materials selection for hydrogen components.

As the world searches for viable alternatives to traditional fossil fuels, hydrogen has emerged as a potential leading candidate—but it comes with unique challenges. The lightness and small size of its molecules make it difficult to contain. Further, when contained with metal, one of two phenomena may take place:

  • Low-temperature embrittlement: As temperature decreases, metals lose some ductility.
  • Hydrogen embrittlement: At higher temperatures where hydrogen is a gas, atomic hydrogen can diffuse into the metal and cause embrittlement.

Embrittlement makes metal more fragile and prone to failure. Hydrogen containment failures can increase downtime, safety risks and lower profitability. If the use of hydrogen as a fuel is to expand, experts have to address this specific problem. The keys are understanding the phenomenon and how to specify the right metals for the purpose.

Q: How does hydrogen penetrate metals? 

A: When hydrogen molecules dissociate into atomic hydrogen, they can infiltrate metals. Typically, these atoms collect at stress concentrations like crack tips or microstructural features like grain boundaries, inclusions, or precipitates.

When hydrogen molecules penetrate metals, they weaken their ductility, toughness, or fatigue and fracture resistance.

Q: What is low-temperature embrittlement?

A: Most commonly found in ferritic steels, low-temperature embrittlement weakens the steel as temperatures fall. The ductility, toughness, or fracture and fatigue resistance is lower, resulting in potential failure. In such instances, components are more often constructed from austenitic stainless steels, which are less susceptible to this kind of embrittlement.

For most hydrogen applications, austenitic stainless steels provide the best containment because they suffer only minor, low-temperature embrittlement.

Q: What is hydrogen embrittlement?

A: High-strength materials are more likely to experience hydrogen embrittlement, which reduces metal’s ability to resist fatigue and fracture. Once again, austenitic stainless steels perform best in these situations because of their face center cubic (FCC) crystal structure, moderate strength and high ductility. Hydrogen embrittlement is much less likely.

Q: What are the potential consequences of using more susceptible stainless steel? 

A: For hydrogen applications, using stainless steels that cannot stand up to the gas’ specific nature significantly increases the chance the components will fail. The concern is not ductility loss but fatigue capability reduction. Component failure, of course, causes a host of problems, including:

  • Potential safety issues
  • Excessive downtime for maintenance or repair
  • More frequent component replacement
  • Sustainability concerns due to hydrogen escaping into the environment
  • Higher total cost of operation and ownership for the asset

    Higher percentages of nickel in austenitic steel alloys resist embrittlement better than their ferritic counterparts.

Q: How can I differentiate higher-quality stainless steels versus lower ones? 

A: The best stainless steels for hydrogen applications include higher levels of nickel over time. Specifically, 316 stainless steel formulations with a minimum of 12% nickel handle hydrogen much more effectively. Nickel stabilizes stainless steel and reduces its susceptibility to hydrogen embrittlement. Though it is generally true that 316 stainless steels with high nickel content are better for hydrogen system construction, there are circumstances where another metal might be a better choice. If material strength or corrosion resistance is the goal, it may make sense to use another metal—but proper system design and maintenance are essential to reduce the effects of hydrogen embrittlement.

The American Society for Testing and Materials (ASTM) requires a minimum of 10% nickel in 316 stainless steel formulations, but 316 stainless steel with a minimum of 12% nickel is better for the specific challenges posed by hydrogen.

Q: How can I be sure I am selecting high-performance materials?

A: Deciding which materials to specify in any fluid handling applications is challenging, but that complexity ratchets up considerably when it comes to hydrogen systems—and it is crucial to get it right. Seek out suppliers that can demonstrate a thorough understanding of materials science and have developed products successfully used in hydrogen applications. Hydrogen’s reputation as a reliable and viable alternative to fossil fuels depends on it.

Written by Buddy Damm, Senior Scientist, Swagelok Company.

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