While hydrogen is gaining rapidly in popularity as a sustainable fuel and energy carrier, the versatile substance comes with some concerns too. One is the hydrogen embrittlement that may occur in austenitic stainless-steel pipelines and infrastructures.
In this blog, we focus on hydrogen embrittlement. We will explain exactly what this phenomenon entails, the risks involved and how to reduce the risk of brittleness in stainless steel infrastructures.
Definitions: brittleness and hydrogen embrittlement
Before we go more in-depth into risk factors, hazards, and solutions, first a few definitions:
What is brittleness?
Brittleness can be defined as “the property of breaking with minimal elongation. If a significant amount of force is applied to a brittle material, it will shatter or crack. Some examples of highly brittle materials are glass and ceramics. At the slightest of strain or shock, these materials break up instantly.
The opposite of brittleness is ductility. Ductile materials eventually show plastic deformation with increasing strain or shock, which does not result in immediate fracture.
What is hydrogen embrittlement?
Hydrogen embrittlement is the brittleness of material due to the influence of hydrogen. This phenomenon occurs due to the diffusion and dissolution of hydrogen in the microstructure of metal piping or infrastructures. In combination with mechanical stress, the hydrogen creates hairline cracks that grow progressively larger over time.
The phenomenon of hydrogen embrittlement is not new. As early as 1875, Johnson discovered changes in iron’s elasticity and fracture stress after it was temporarily immersed in acid.
Johnson’s findings led to further research, which showed that only acids that produce hydrogen deteriorate the properties of iron through their impact. The link with hydrogen was thus quickly established.
We are 146 years on, and the research is still ongoing. However, we have become much more knowledgeable about the effect of hydrogen embrittlement and the vulnerability of austenitic stainless steel to this phenomenon. We now know that the following risk factors increase the risk of hydrogen embrittlement:
- An increase in hydrogen pressure in transfer lines or applications.
- The formation of martensitic and ferritic structures in materials by plastic deformation.
- The application of non-stabilized forms of stainless steel.
- Operating temperatures between -173 °C (100 K) and 27°C (300 K), as shown in the figure below.
Plastic stretch ratio at failure as a function of test temperature
Why is hydrogen embrittlement destructive?
There is a reason why so much research is being done on hydrogen embrittlement. Many industries depend on steel structures, which may come into contact with hydrogen in operation or during construction. These include oil and gas structures, steel parts of wind turbines, architectural structures, and, of course, infrastructures for storing and transporting hydrogen.
When hydrogen damages the quality of the steel, these structures would need to be replaced or repaired relatively quickly, and, over time, there is a risk of collapse. Within the oil and gas industry, there is also a second danger: leakage. When large quantities of hydrogen leave an infrastructure, there is a risk of fire and explosion.
The forming of hydrogen embrittlement takes time. It can take years before an infrastructure is damaged to the point of collapse. However, when that time comes, the consequences are often severe. The relatively slow process does not imply that the proper safety measures to prevent hydrogen embrittlement are not essential.
How to prevent hydrogen embrittlement?
But what can be done to reduce the risk of hydrogen embrittlement? What do hydrogen infrastructures need to comply with to remain solid and free of cracks for as long as possible?
Choice of material
First, proper material selection is essential. For example, increasing the Ni percentage and decreasing the C percentage in the material reduces the chance of hydrogen embrittlement. The addition of Ti also helps. These atoms occupy critical locations in the crystal structure of austenitic stainless steel. In other words, the added elements stabilize the desired microstructure. For safe use with hydrogen, a minimum nickel content of 10% is often maintained.
The difference in the plastic strain ratio of various materials can be seen in the earlier shown figure by G.R. Caskey. The types of steel in this figure demonstrate very different reactions at various temperatures. One material remains considerably more stable in the critical temperature range than others.
Which type of steel is most suitable for a specific pipeline or infrastructure varies considerably. For example, if an infrastructure is subject to regular temperature changes, the material choice is essential to prevent hydrogen embrittlement. An example of an infrastructure where the temperature change is prevalent is a gas station.
In addition to choosing the best steel grade, the employed welding technique also affects whether or not hydrogen embrittlement occurs. By making the wrong choice of material and alloy, sensitization can occur. Sensitization is the formation of carbides at the crystal boundaries of the material during welding.
Fortunately, sensitization is preventable by using stainless steel with a low carbon percentage (<0.03%), such as stainless steel 316L or 1.4404. The addition of Ti to the alloy, as in stainless 316Ti or 1.4571, is also an excellent method to prevent this problem.
At Demaco, we are aware, like no other, of the risks that hydrogen entails. We closely follow research in the field of hydrogen embrittlement and know exactly which materials are and are not suitable for various applications. That is why we can guarantee optimum quality and safety.
Would you like to know more?
Demaco is an expert in developing the most optimal infrastructures for hydrogen. Do you have questions about our work? Feel free to contact us or take a look at our products and projects for more information.
Would you like to know more about our work with liquid hydrogen? Please look at this page or read our recent blog about liquid hydrogen. In that blog, you can read all about this versatile cryogenic liquid and the years of experience Demaco has with various advanced hydrogen projects.