Hydrogen embrittlement

A challenge for valve manufacturers and plant engineers

The demand for renewable energy sources and sustainable systems that replace fossil fuels is huge. Hydrogen is seen as playing a key role in this context: The gas enables clean mobility and also plays an increasingly important role in numerous industrial processes.
Hydrogen is nothing new in industry, especially in the chemical industry and in refineries. What is new, however, is that hydrogen has become part of the German government's national strategy to combat climate change and is thus gaining in importance.
But the gas places demanding requirements on valves, piping and plant components.

One reason is hydrogen embrittlement. Find out what this is, which materials are particularly affected by it, and what to look out for when choosing valves in the article!

Hydrogen - a challenging medium

Hydrogen is the lightest element in the periodic table, and at the same time has a high gravimetric energy density. In atomic form, the diffuse gas can easily penetrate a wide variety of materials and cause them to become brittle. Carbon steels are particularly susceptible to this.
Other aspects to consider when dealing with the gas are: Hydrogen is highly volatile. Therefore, special attention must be paid to the internal tightness of a control valve and to the tightness to the outside.

What is hydrogen embrittlement?

If the strength of a material changes or a material becomes brittle due to the penetration and storage of hydrogen, this is called hydrogen embrittlement. This is followed by material fatigue, which leads to the formation of cracks.

When does hydrogen embrittlement occur?

Whether due to hydrogen corrosion or other chemical reactions: Hydrogen embrittlement occurs when atomic hydrogen is formed on a metal surface. Instead of combining to form non-diffusible H₂ molecules at the surface of the material, the hydrogen diffuses during the process. In the process, it becomes trapped in the metal structure, preferentially at defects or grain boundaries.

If hydrogen atoms concentrate at the grain boundaries, they quickly recombine to form molecules (H₂). The resulting increase in pressure significantly reduces the ductility of the material. The result: embrittlement and even failure of the material.

Which materials are particularly susceptible to hydrogen embrittlement?
And which are more resistant to it?

The key factor in determining a material's suitability for hydrogen is its hardness (HRC measured in Rockwell). The harder the material, the more susceptible it is to hydrogen embrittlement.
A material with an HRC value of over 41 is particularly vulnerable to hydrogen embrittlement. In particular, higher-strength steels with a high martensite content and a yield strength greater than approx. 800 MPa are at risk of hydrogen-induced damage.

Austenitic stainless steels (e.g. CrNi steels), on the other hand, have proven to be suitable materials and are therefore predominantly used as standard materials in hydrogen technology. As studies show, a high nickel content has a positive influence on resistance to hydrogen-induced brittle fracture.

How can hydrogen embrittlement be prevented?

By …

Minimizing contact between the metal and any sources of atomic hydrogen.
Protecting against corrosion-causing conditions, e.g., by applying special coatings.
the implementation of heat treatments, also called hydrogen low annealing or annealing/tempering - suitable for certain processing operations where a large amount of hydrogen is absorbed.
the correct choice of materials, i.e. the use of materials less susceptible to embrittlement.
The right material quality. Homogeneous metal grids with small voids significantly reduce the likelihood of embrittlement.
regular and careful inspections of critical points.

What needs to be considered when choosing control valves?

Whether valves, piping or plant components - each element must be resistant to the medium hydrogen. It is also important that they comply with the current requirements (PED, ATEX, ISO 15848/ TA Luft, etc.). These norms, guidelines and standards provide initial indications for specifications - whether for plant engineers planners or operators of industrial plants.

A good reference point is also the term "H₂-ready", which is used by many manufacturers - including A. Hock - for valves that are suitable for the medium hydrogen.

In summary, hydrogen valves should have these characteristics:

Internal and external tightness
Hydrogen resistant materials
Meet ignition protection requirements
In short: "H2-ready"

Generally speaking, to ensure safe operation in the plant, all components that come into contact with hydrogen must meet the stringent requirements. This means that all materials used must be tested for suitability, leak tightness and functional safety, and selected accordingly.

Safe hydrogen valves from A. Hock

The following applies to all valve series from A. Hock:

High material quality: By means of dye penetration and X-ray testing, the cast housings are inspected and categorized for the smallest defects. This virtually eliminates embrittlement. We achieve the highest quality levels for hydrogen applications.
Precise material selection: Only suitable steels with low carbon content and hardness levels below 25 HRC are used. NACE certification is standard for us.
Tightness to the outside: Tightness is ensured by TA Luft packing or bellows.
Tightness inside: Internal tightness is provided by high leakage class V (metal sealing) or class VI (soft sealing) on our hydrogen valves.
Finest dosing of hydrogen via low KVS value 0.010 at DN15

Read more interesting articles about hydrogen and valves.

Hydrogen

What is hydrogen simply explained? How is it produced? And why is it so important for the energy transition?

Hydrogen control valves

Two-way and three-way valves for control of hydrogen

Control valve sizing

Sizing of control valves for your hydrogen application

Do you have further questions about hydrogen in industry?

Do not hesitate to contact us.

Dominic Hock

Managing Director

I’m happy to support you with projects and enquiries in the field of valve technology as well as measurement and control technology. My areas of expertise are automation technology and networks.

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