Sealing issues of pipeline valves for hydrogen-containing gases
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Regarding valve sealing for pipeline systems in hydrogen-containing media: The hydrogen composition is 99.99%, the temperature is at room temperature, the pressure is 2.0 MPa; ball valves are to be used, and soft-sealing valves that are fire-resistant and anti-static are desired. However, according to Table 12.03 of GB 50177-2005, the sealing surface of hydrogen valves is required to be made of high-quality steel or the same material as the valve body; this implies the use of a hard seal. The sealing performance of hard seals is inferior to that of soft seals, and owners have reported that hard seals are more expensive, with their sealing surfaces being prone to scratches. I would like to ask everyone how to make the choice? Additionally, in another operating condition where raw hydrogen accounts for only about 20%, with the remainder being nitrogen, is it still necessary to comply with GB50177-2005? I appreciate your advice, thank you!
"And stainless steel” – it’s a typo; it should be corrected to “alloy”.
The sealing surface and the valve seat are two different things; the valve seat can use a soft seal, while the sealing surface of the valve core ball is made of metal
The LOL value of hydrogen is 5.9%, and its lower explosion limit is 4.1%. Based on these figures, it can be estimated that under certain conditions, the hydrogen used as a raw material can create an explosive environment; therefore, I believe it is also necessary to comply with GB50177-2005； As for the claim that hard-sealed surfaces are prone to scratching, I don’t agree; under the same conditions, PTFE-sealed surfaces are more likely to get scratched and to suffer from wear due to pressure. The key is to ensure that the pre-commissioning work is carried out properly before the pipeline is put into operation.
This post was last edited by leo_0088 on 2020-7-10 21:43. In fact, I think soft seals are more prone to damage; once they come into contact with metal shavings, they stop sealing properly； Those who think hard-sealed ball valves are prone to damage do so because the ball valves in question use the simplest nitriding process – the ball is nitrided, and the valve seat is either nitrided or made of STL; the nitriding layer is relatively thin. After long-term use, the nitrided layer wears off and detaches, affecting the sealing performance and also increasing the risk of injury. The hydrogen balloon valves I use currently are all hard-sealed ball valves; depending on the pressure, either a floating or a fixed type is chosen. The ball surface is coated with a nickel-based alloy – the ball and the valve seat are welded using a two-step flame spraying process with this nickel-based alloy, giving an HRC value of 60 for the ball and 55 for the valve seat. The thickness of the sprayed layer can reach 1 mm on each side. ), currently, the ball valves we have been using for several years all ensure zero leakage. Also, the reason I use a hard seal is that, in my opinion, if a valve catches fire, a soft seal will fail easily due to its inability to withstand high temperatures; a hard seal is more reliable. Although it is more expensive, it reduces risks (which also serves to protect oneself).
This post was last edited by dpclove21 on 2020-7-11 at 16:15. Hard-sealed types have better fire resistance than soft-sealed types; soft-sealed types offer better sealing performance and can reach ANSI VI level. On the hydrogen pipelines in the out-of-bounds area, we use forged steel ball valves with metal seals, giving priority to fire resistance.
The temperature is at room temperature, the pressure is 2.0 Mpa; both metal seals and soft seals are available, depending mainly on the customer’s preference. As for the mixture of hydrogen and nitrogen you mentioned later, you can consider using the hydrogen partial pressure; both metal seals and soft seals work well in this case. In fact, there’s no need to worry too much about hydrogen as a medium at normal temperature and pressure. It is mainly the high pressure and high temperature that are very dangerous, such as in hydrocracking processes.
The temperature is at room temperature, the pressure is 2.0 Mpa; both metal seals and soft seals are available, depending mainly on the customer’s preference. As for the mixture of hydrogen and nitrogen you mentioned later, you can consider using the hydrogen partial pressure; both metal seals and soft seals work well in this case. In fact, there’s no need to worry too much about hydrogen as a medium at normal temperature and pressure. It is mainly the high pressure and high temperature that are very dangerous, such as in hydrocracking processes.