The lightest gas in the world contains small molecules that can be difficult to contain, but suitable components can make systems more reliable.
Scientists continue to seek new solutions to fuel the most diverse applications energy. If the reasons for this are multiple – whether it is to avoid geopolitical conflicts or the urgency of countering climate change – an idea is gaining ground: hydrogen is a promising solution (Figure 1). This zero emission energy source, however, poses unusual difficulties linked to the low density of this gas and the small size of the molecules that constitute it.
Figure 1. Countries and consumers around the world are looking for alternatives to traditional fossil fuels. Hydrogen is a promising solution, but systems responsible for transporting it must be built with the greatest care. © 2024 Swagelok Company
If hydrogen must replace fossil fuels in transport and other applications, companies will imperatively have to find ways to handle this gas in the liquid and/or gas state. Hydrogen liquefies at-253 ° C (-423 ° F) and it is approximately 140 times dense in the liquid state than in the gas state. It is therefore more efficient to transport and store hydrogen in liquid form. On the other hand, when used, hydrogen is in the gas state. These characteristics can harm metals in two ways:
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Low -temperature weakening : When the temperature decreases, the metals lose their ductility.
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The weakening by hydrogen : In the gaseous state and at higher temperatures, hydrogen atoms can diffuse in the metal and weakening it.
When engineers speak of weakening of a metal, they mean thereby ductility, resistance to rupture and resistance to fatigue considerably reduced by certain factors of the operating environment in relation to a situation free from such constraints. This weakening of metals can have consequences and in particular lead to a failure of the systems, endanger the staff or oblige to multiply the arresting of the facilities, with the financial losses that this implies. While the hydrogen sector is gaining importance, it becomes essential to be able to avoid problems of this type.
Hydrogen professionals must imperatively find for their systems components capable of managing the molecules of this volatile gas. More specifically, they should use components designed for hydrogen and made in quality stainless steel with high nickel and chrome content. The risk of weakening is less with these stainless steels which will be more effective in confining hydrogen.
The weakening process
Hydrogen enters metals when stable dihydrogen molecules turn into hydrogen atoms. In general, the hydrogen atoms are alleviated where constraints are concentrated – fissure ends, microstructural characteristics such as intergranular limits, inclusions, precipitates (Figure 2).
Figure 2. Hydrogen atoms easily diffuse in lower quality stainless steels, which can cause cracking and fatigue of metal. If nothing is done to remedy it, this can lead to a premature failure of the system. © 2024 Swagelok Company
The phenomenon of low -temperature weakening occurs when the temperature falls suddenly, which leads to a decrease in ductility, tenacity or resistance to fatigue and rupture. Austenitic stainless steels resist these conditions well and only undergo low degradation. In comparison, the effects on ferritic steels will be much greater under the same conditions. This is why austenitic stainless steels are favored in systems that transport liquid hydrogen, because it is likely that these systems will have to deal with temperature variations.
The weakening by hydrogen occurs when the molecules sink into the metals and will reduce the resistance to fatigue and the rupture of the component. High resistance materials are much more sensitive to the phenomenon. Austenitic stainless steels, which are characterized by their cubic crystalline structure with centered faces (CFC), their moderate resistance and their naturally high ductility, will therefore be more indicated for these applications. However, this does not mean that they are completely spared by the phenomenon of weakening by hydrogen and they will therefore have to be monitored accordingly.
Why more sensitive steels pose more problems
Like all forms of weakening reduce the performance of components and systems, the probability of premature failure is much more likely with these steels. Among the two most commonly encountered problems – the loss of ductility and the fatigue of components – fatigue is much more serious. Well -designed components do not undergo the effects of constraints capable of leading to a macroscopic plastic deformation, so that the loss of ductility is minimal.
Over time, cyclical charges resulting from pressure cycles, vibrations or other service charges can cause damage and cause the failure of components due to fatigue, which occurs when steel is weakened by constraints or repeated charges. Added to this is the fact that the components and systems that undergo these constraints will possibly be exploited in environments with difficult environmental conditions, which then increases even more the probability of a failure due to fatigue. The failure of a component can lead to safety problems for staff, expensive stopping of the system concerned, additional maintenance interventions, hydrogen leaks and an increase in operating costs and the overall cost of the system.
How to determine the quality of a stainless steel?
Trials have shown that stainless steels with high nickel and chrome content is better resistant to weakening by hydrogen compared to less strongly allied steels. If the American Society for Testing and Materials (ASTM) requires a minimum nickel content of 10 % in the composition of stainless steel 316, a steel containing at least 12 % nickel will be more suitable for particular problems posed by hydrogen (Figure 3). The nickel content helps stabilize the microstructure of stainless steel, which makes it more resistant to the phenomenon of weakening by hydrogen. During tests carried out by Swagelok, it was found that the effect of this phenomenon on the ductility in traction of stainless steel 316 containing 12 % of nickel was minimal.
Figure 3. When choosing components for systems that implement hydrogen, we favor stainless steels with high nickel (Ni) and chrome (CR) which are less exposed than other stainless steels at the risk of weakening by hydrogen. © 2024 Swagelok Company
For most systems that implement hydrogen, components made in steel with high nickel content are the most logical choice. However, it happens that other performance criteria require choosing a different material. For example, if the resistance of the material or its resistance to corrosion prevails over the prevention of the weakening phenomenon, it can then be more logical to opt for other materials. In these situations, it is all the more essential to design the systems correctly to avoid weakening. The weakening processes being better and better documented by research, a serious supplier should be able to help its customers choose the components best suited to a particular application.
Why it is important that hydrogen valves are ultraperformative
Systems that implement hydrogen as a source of energy include many valves that will have to be chosen with the greatest care. Engineers who write specifications for these systems will have to take into account the following elements before choosing valves:
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Pressures
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Constraints and vibrations
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Security
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Maintenance
Valves that do not meet the strictest standards in these four areas should not be used. In addition, suppliers must be able to prove that their valves are perfectly tightly tightly tight – connection points, stop device, regulation device – and that their components will be able to withstand the rigorous conditions encountered in applications that implement hydrogen.
The three most commonly used valves in systems that transport hydrogen are:
Spherical bushel valves. For these applications, the seals of the valves of the valves must withstand wear. It may be judicious to use direct compression Tourillon valves, which offer the necessary sealing performance. Otherwise, the valves with stem compressed by the base also make it possible to avoid ejection problems and make the system safer. If questions arise as to which valve will best suit an application, a serious supplier should know how to answer them.
Nean valves. In most applications that implement hydrogen, needle valves are not privileged due to the huge couple that must be applied to open and close them. As they are generally fully metallic valves, the repeated application of such a torque can eventually deform the needle, which generates leaks and causes expensive maintenance operations. A needle valve selected for this type of application should be manufactured in high quality 316 stainless steel, which will not be so easily deformed under the effect of the maneuver torque. In addition, these valves must have a nominal pressure adapted to the pressures used with hydrogen (generally 350/700 bar).
Anti-return valves. The filling systems generally include anti-return valves which will prevent any repression of hydrogen while a user fills the tank for their vehicle. This security function is essential and should in no case be neglected. The anti-return valves often contain a nutty steel springs, which makes them particularly sensitive to the phenomenon of weakening by hydrogen. These valves should be made in high quality 316 stainless steel and will have to withstand significant and sudden variations in pressure and temperature. As a rule, it is the anti-ball-rounding valves that work best with hydrogen.
Choosing high -performance materials with care
Without the advice of a recognized supplier, it can be difficult to determine the materials best suited to a particular application. However, it is essential to make the right decisions, especially when it comes to applications that implement hydrogen. If hydrogen must replace fossil fuels as a reliable and viable energy source, the systems designed for these uses should be of the best quality.
It is therefore essential to find suppliers who control not only the physics of materials, but also the constraints specific to these applications. Thanks to their experience and advice, you should be able to find the materials and solutions that will optimally meet the specific needs of an application.
