Hydrogen-Induced Steel Damage

metal
Hydrogen-induced fractures, © RUB

Hydrogen has the potential to assume an especially important role during the technological shift away from fossil fuels toward renewable and alternative sources of energy. Plans for using renewably sourced hydrogen as an energy carrier (e.g., power-to-gas) to deal with periods of excess power have posed special challenges for the energy industry. In addition to environmental and economic considerations, the increase in the amount of hydrogen creates hurdles for material use, as the hydrogen may cause spontaneous failures of metallic components, a process that is known as “hydrogen embrittlement.”

Through humid furnace lining, additives and alloying elements, hydrogen may diffuse into components or semi-finished products as early as casting to cause damage such as flakes or fish-eyes. There is a similar risk during welding. Most hydrogen-induced damage, however, occurs when the component has been put in place.

If the hydrogen causing the damage originates from the time the component was manufactured or processed, such as during pickling or galvanizing, and is only “activated” due to strain on the component during actual use, it is called a “delayed fracture.” If the hydrogen is only introduced during use of the component, as in the case of cathodic partial reactions during corrosion, it is called “sulfide stress cracking.” In both cases, most of the components fail spontaneously and there are no warning signs such as deformation.

Atomic, trapped or molecular

Most hydrogen-induced damage is triggered by atomic (diffusible) hydrogen (H+). Because of the small size of the atoms, diffusion occurs at a very fast pace in steel at room temperature, similar to carbon at 800 °C. Externally induced stresses, which may overlap with internal ones, will stretch the metal lattice structure, establishing the force for atomic hydrogen to diffuse into and accumulate in weak spots. This process, called Gorsky effect, is made worse by indentations and cracks causing a localized surge in tension.

Conversely, so-called trapped hydrogen (H+T) accumulates at energy-intensive points in the metal lattice structure (caused by defects such as dislocations, inclusions, grain boundaries, etc.). This means that it is no longer diffusible at room temperature and usually does not pose a risk. Only by introducing activation energy in the form of rising temperatures typical for each type of trap can it again diffuse into the metal lattice structure and cause damage …

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