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Hydrogen embrittlement is the loss of toughness and ductility in a metal that has taken up hydrogen, so that it cracks or fractures at stresses it would otherwise tolerate. It is documented most heavily in steels, nickel alloys and titanium alloys, and in some metals (zirconium, niobium, vanadium, tantalum) it involves brittle hydride phases.
Short answer
Hydrogen embrittlement is cracking or fracture of a metal caused by dissolved hydrogen together with stress. It matters to engineers, lab staff and facilities teams wherever hydrogen is produced, stored or piped, or wherever steel parts are exposed to hydrogen-generating processes. The mechanism is not a single settled process: published reviews describe several, and combinations are likely.
Definition and scope
S.P. Lynch’s review for NACE Corrosion 2007 (Paper 07493, hosted by the US pipeline safety regulator’s R&D site) treats hydrogen embrittlement (HE) as a family of failure modes, especially in steels, nickel alloys and titanium alloys. The same review notes that the mechanisms operating in HE and in liquid-metal embrittlement are the same in steels, and it traces the history back to W.H. Johnson’s 1874 paper on changes in iron and steel produced by hydrogen and acids.
This page is a concept explainer. It does not give procedures, bake schedules or acceptance limits, which belong to the governing standard, the part specification and the material supplier.
How hydrogen embrittlement is described in practice
Reviews and engineering programmes describe the problem by where the hydrogen comes from and which materials are exposed. Two named sources show the range.
Mechanism research (Lynch, 2007)
The review distinguishes a hydride mechanism from three mechanisms that do not need hydrides, and concludes that the dominant process depends on the fracture mode.
Gaseous hydrogen infrastructure (US DOE, 2023)
M. Kass and colleagues at Oak Ridge National Laboratory presented a compatibility assessment at the DOE Hydrogen Program 2023 Annual Merit Review (7 June 2023). It states that hydrogen embrittlement of pipeline steels “has been extensively studied”, and that the US natural gas transmission network (over 300,000 miles, about 1,800 compressor stations, pipe up to 1.2 m / 48 in. diameter) is composed almost entirely of low-carbon steels. The presentation asks whether that existing infrastructure can be repurposed for hydrogen and for gas blends, and notes that much less is known about polymers than about steels.
Mechanisms compared
The table is limited to what Lynch (2007) states.
| Mechanism | Idea in brief | Where the review says it applies |
|---|---|---|
| Hydride formation | Brittle hydrides form ahead of the crack tip | Widely accepted for Zr, Nb, V and Ta (first proposed by Westlake, 1969) |
| HELP (hydrogen-enhanced localised plasticity) | Hydrogen promotes localised plastic deformation | Slip-band fractures |
| HEDE (hydrogen-enhanced decohesion) | Hydrogen weakens atomic bonds | Possibly some brittle intergranular fracture |
| AIDE (adsorption-induced dislocation emission) | Adsorbed hydrogen eases dislocation emission at the crack tip | Cleavage-like and dimpled intergranular fracture |
The review adds that combinations of these mechanisms are likely in many cases. It also records the historical lineage of the decohesion idea (Pfeil, 1926; Troiano, 1960) and of localised plasticity (Beachem, 1972).
Where it matters for labs, clinics and supply decisions
- Hydrogen pipelines and repurposed gas lines. The DOE presentation reports that ASME B31.12 recommends a maximum steel grade of X52, and that API guidelines call for a maximum yield strength of 827 MPa. It also summarises studies suggesting natural gas blends with up to 17% hydrogen are suitable for existing pipelines. That figure is the project’s own summary of studies, not a guarantee for any specific line.
- Material selection in lab equipment. Where hydrogen generators, gas manifolds, high-pressure fittings or electrolysis cells are specified, material compatibility with hydrogen is a question for the manufacturer’s documentation and the applicable code, not for general knowledge. For general material-compatibility thinking see CASRAI’s guides on 316 stainless steel and the chemical resistance chart for plastics.
Common misunderstandings
- “There is one agreed mechanism.” The literature describes hydride, HELP, HEDE and AIDE processes, and combinations are likely.
- “It only affects steel.” Lynch’s review covers nickel and titanium alloys and describes hydride-forming behaviour in Zr, Nb, V and Ta.
- “A blend percentage is a safe-for-all figure.” The 17% finding is a summary of studies for natural gas pipeline steels, not a design allowance.
FAQ
What causes hydrogen embrittlement?
Hydrogen taken up by a susceptible metal, combined with stress, leads to cracking. Lynch’s review describes the processes by which the hydrogen produces fracture.
Which metals are affected?
The review focuses on steels, nickel alloys and titanium alloys, and describes hydride formation in zirconium, niobium, vanadium and tantalum.
Can existing natural gas pipelines carry hydrogen?
The DOE project cited above evaluates this question; it reports studies suggesting blends up to 17% hydrogen are suitable and recommends limits on steel grade (X52) and yield strength (827 MPa) under ASME B31.12 and API guidance. Specific decisions rest with the operator and applicable codes.
Sources
- S.P. Lynch, “Progress towards understanding mechanisms of hydrogen embrittlement and stress corrosion cracking”, NACE Corrosion 2007, Paper 07493: PHMSA R&D copy (read 2026-11-08).
- M. Kass et al., “Compatibility Assessment of Natural Gas Pipeline Infrastructure Materials with Hydrogen, CO2, and Ammonia”, DOE Hydrogen Program 2023 Annual Merit Review, 7 June 2023: DOE presentation (read 2026-11-08).
