Hydrogen embrittlement is a mechanism of material damage in which hydrogen penetrates materials and degrades their mechanical properties. The detrimental effects vary greatly depending on the material used.
This phenomenon is considered a major challenge in the development of hydrogen infrastructure and particularly affects piping and plant engineering. Its damaging effects were first scientifically documented as early as 1863 by Henri Étienne Sainte-Claire Deville and Louis Joseph Troost.
Mechanism and Effects
As the smallest atom in the universe, hydrogen can move into the interstitial sites of the crystal structure of metals. After atomic hydrogen is adsorbed onto the surface, it diffuses to areas of high tensile stress, such as notches or material defects. This is particularly critical at pressures of 700 bar, such as those found in the hydrogen tanks of fuel-cell cars.
Embrittlement can result from hydrogen in both the gas phase and aqueous media. Often, months or even years elapse between the initial hydrogen absorption and the eventual failure of the material.
A microscopic view of hydrogen embrittlement in Inconel. Image from Iannuzzi, Mariano, Barnoush, Afrooz, and Johnsen, Roy. (2017): Materials and Corrosion Trends in Offshore and Subsea Oil and Gas Production (© General Electric)
Material-Specific Susceptibility
Not all materials are equally susceptible to hydrogen embrittlement. In the case of steels, the risk depends heavily on their internal structure. High-strength steel grades—such as those used for heavy-duty machine components—are particularly problematic. Certain microstructures in steel—experts refer to“ferritic”and“martensitic”structures—also readily absorb hydrogen and consequently become brittle quickly.
So-called austenitic steels are significantly more resistant, as they absorb hydrogen much more slowly. The addition of various metals during alloying also affects susceptibility: nickel, for example, makes the steel more resistant to hydrogen, while additives such as chromium, molybdenum, or titanium increase the risk of embrittlement.
The Effect of Hydrogen on Non-Metallic Materials
Plastics do not exhibit conventional embrittlement; however, hydrogen can become trapped in the voids between the molecular chains. During rapid decompression, these gas bubbles can cause the material to rupture. Aluminum and magnesium alloys do not exhibit a tendency toward embrittlement in the presence of dry, gaseous hydrogen, but may suffer reversible hydrogen damage under other conditions. Their properties can then be restored through prolonged degassing.
Factors Affecting the Reaction and Reaction Conditions
Research and Prevention
Research into this phenomenon is gaining importance due to the planned expansion of the hydrogen infrastructure. While hydrogen embrittlement has so far occurred mainly in welds or as a result of small-scale corrosion, future hydrogen pipelines will be exposed to significantly larger quantities.
At Saarland University, for example, research has been conducted on standardized industrial testing methods. A key focus of this research is on various “loading methods”: Hydrogen can be introduced into the material either electrochemically or through pressure loading (200 bar, 200–300°C). For damage analysis, methods such as high-resolution computed tomography are used, which can capture structures at the nanometer scale. This non-destructive testing allows for real-time observation of crack initiation and growth.
Various preventive measures are available to avoid this problem. Heat treatment is key, particularly stress-relief annealing at 200–230 °C. Following electroplating processes, this treatment must be performed within four hours. Hydrogen-carrying systems are monitored through regular material testing in accordance with ISO standards, during which components are subjected to defined tensile stresses for 48 hours.
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