Hydrogen embrittlement
The future technology of hydrogen poses a number of technical challenges. For example, the gas can have a negative effect on the mechanical properties of metallic materials and cause damage.
Hydrogen gas changes the microstructure of metal
Hydrogen embrittlement (HE) is caused by the penetration and incorporation of hydrogen atoms into metals or alloys. If hydrogen is formed on a metal surface in atomic form, it does not combine to form diffusion-incompatible H2 molecules, but diffuses into the microstructure of the material as hydrogen gas. The gas is preferentially deposited at the grain boundaries and defects in the metal lattice, where the atoms quickly recombine to form H2 molecules.
This reduces ductility and load-bearing capacity and leads to cracking and fractures below the original elongation and yield strength. The material then becomes unusable.
Three factors must interact for cracking to occur:
- Critical hydrogen concentration (CH)
- Tension level
- Material properties
In the case of hydrogen embrittlement, a distinction is made between environmental hydrogen embrittlement, which is caused by hydrogen from the environment, and internal hydrogen embrittlement, which is caused by residual hydrogen that enters the material during the manufacturing process.
The risk is influenced by the hardness of the material (HRC, measured in Rockwell). The harder the metal, the more susceptible it is!
High-strength steels with a high martensite content are particularly susceptible to hydrogen-induced brittle fracture. Stainless steels with a low carbon content, such as 1.4404 or 1.4571, with an HRC value <20, are largely insensitive to this and are used as a standard material in hydrogen technology. 316 grade stainless steel with a 12% nickel content is also particularly suitable for the special challenges in hydrogen systems.
Protection against hydrogen-induced brittle fracture
Possible preventive measures include protection against the conditions that cause corrosion, for example by selecting the right material or by applying a special coating to the material to prevent direct contact with hydrogen.
When using industrial valves, both the internal tightness of the valve and the tightness to the outside are of particular importance.
For use in hydrogen technology, Mankenberg valves made of deep-drawn stainless steel are extremely resistant to corrosion and hydrogen embrittlement also thanks to their compact design and pressure resistance.
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