Improving wear and galling in hydrogen applications

Due to its unique properties, hydrogen gas poses several technical challenges for the components with which it comes into contact. This necessitates the use of corrosion-resistant stainless steel, which in turn can be susceptible to wear and galling.

Text & image by Expanite

With a mass fraction of about 70%, hydrogen is the most common chemical element in the universe. On Earth, however, its mass fraction is only 0.87% and it is largely bound in water. Starting with production, over to transport ending with the actual usage, wherever hydrogen is involved, stainless steel components are also used. Some of these are subject to extreme wear and galling, depending on the application. In the past, this problem was countered with traditional wear protection methods such as component coatings (e.g. hard chrome plating, DLC or chrome carbide) or classic plasma nitriding or salt bath diffusion layers. However, these processes are generally known to negatively affect the corrosion resistance of the stainless steel parts. One solution to this dilemma is a surface hardening that protects against wear and galling while at the same time maintaining or even improving the corrosion resistance of the materials. This solution was developed by the founders of the Danish company Expanite and is increasingly being used in the hydrogen sector; for example, components of high pressure and control valves used in hydrogen infrastructure up to components for fuel cells are hardened.

Sustainably prevent hydrogen embrittlement

“Our customers often ask whether the Expanite technology increases the risk of hydrogen embrittlement, which is not the case,” explains Dr Holger Selg, application expert and Expanite Sales Director DACH. “The cause of the hydrogen embrittlement can be traced back to the diffusion of the hydrogen into the material, and in theory the Expanite layer acts as a diffusion brake to a certain extent. Charged with nitrogen and carbon, the surface is harder for the hydrogen to penetrate than an untreated surface.”
The gas-based diffusion process from Expanite is significantly more energy-efficient and environmentally friendly than comparable wear protection processes, and thanks to the treatment in a vacuum, no time-consuming cleaning of the parts, e.g. with aggressive chemicals, is necessary after hardening. Specially developed for corrosion resistant materials, the technology offers a solution for austenitic, martensitic, ferritic and duplex stainless steels as well as for expensive nickel-based alloys such as Inconel and Hastelloy. The new special process Expanite Hard-Ti, which the Expanite team of experts in Denmark has developed to market maturity in recent years, is used for titanium materials.

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