Special Topic : Green Applications
The size of hydrogen molecules also poses a threat to lower-quality stainless steels because the molecules can diffuse into the material and cause it to weaken through a process called hydrogen embrittlement . When the stainless steel becomes weaker and is subjected to the high pressures necessary to use the fuel , it can cause cracks to occur in the valves , resulting in unsafe conditions .
That is why the valves in hydrogen fuel systems must be chosen carefully , with four specific considerations in mind :
• Pressures - To achieve desired density , H 2 must be stored in on-vehicle tanks at 350-700 bar .
• Stress and Vibration - Systems must be able to withstand fast speeds , bumpy roads , and inclement weather conditions .
• Safety - Refueling stations must be safely operable by the average consumer .
• Maintenance - On all valves it should be easy to recreate leak-tight joints during servicing .
No matter what the application , hydrogen valves must perform with those attributes in mind . All connection points must be leak-tight and should be able to withstand the stresses put on them in mobility operations . The following are examples of types of valves that can be chosen .
Hydrogen Ball Valves
The most common valves in hydrogen systems are ball valves , which provide users with the ability to stop and start the flow of hydrogen quickly ( Figure 1 ). If this valve is chosen , examine the stem seal carefully because it must be able to cope with challenging conditions . It may make sense to use a trunnion-style ball with a direct-load design , which can easily provide leak-tight performance as the valve opens and closes . Additionally , using a bottom-loaded stem design may enhance the safety of the valve by limiting the chances of stem blowout .
If there is any question about which ball valve to use , a supplier should be able to advise on which one is best for a specific application . Within the ball valve category , there are many options , including two- or three-way functionality , different mounting options , and multiple flow coefficient ratings that can be tailored to fit your system . Hydrogen ball valves should also be compatible with the appropriate fittings so leaks do not occur .
Hydrogen Needle Valves
If an application requires a more precise adjustment in hydrogen flow , needle valves may be the most effective option ( Figure 2 ). Specifying needle valves in hydrogen systems means additional considerations must be made . For example , needle valves often require significant force to seal correctly because they are usually all-metal construction . Though necessary , the applied force also has the potential to damage the needle and possibly the seat . Leaks could lead to potential fire hazards , resulting in costly maintenance . In addition , large air actuators may be required to open and close needle valves in hydrogen applications , which could delay the opening or closing by up to two minutes .
Choosing needle valves made from high-quality 316 stainless steel is a best practice to ensure the metal is not easily damaged over time by the process of hydrogen embrittlement . The needle valves must also be properly pressure rated to deal with the high pressures ( 350-700 bar ) that occur in most hydrogen applications . Finally , the needle valves should be compatible with hydrogen-qualified fittings just like the ball valves .
Hydrogen Check Valves
Check valves prevent backflow in hydrogen refueling systems , allowing consumers to use them safely ( Figure 3 ). Even if one understands check valves in other industrial applications , those used in hydrogen refueling stations must contend with hydrogen-specific conditions .
Once again , the steel matters . Most check valves have springs and are usually constructed with strain-hardened material , which is more susceptible to hydrogen embrittlement . Check valves used in hydrogen systems should be manufactured with high-quality 316 stainless steel to avoid these problems . In hydrogen refueling applications , check valves undergo rapid , severe changes in temperature and pressure , which can lead to damage of the valve ’ s elastomer seals . Ball check valves are the better option for hydrogen compressors for that reason , and they should also be compatible with other hydrogen system components .
As the world begins to view hydrogen as a viable alternative to fossil fuels over the long term , the safety , reliability , and durability of its corresponding infrastructure must meet high-performance standards . Working with a reliable valve supplier who can help choose the proper components for whatever hydrogen system is being built will help secure its long-term future .
About the Author
Chuck Hayes is the Global Technical Lead for Clean Energy for Swagelok Company .
Figure 3 : Using a proper check valve will help prevent backflow in the hydrogen compressors located in refueling stations . These leak-tight connections are designed to protect consumers from potential hazards .
Stainless Steel World Americas - December 2023 | www . ssw-americas . com 15