What are the Different Pressure Classes for Hydrogen and CNG Products?
Global investment into hydrogen and compressed natural gas powered vehicles and their supporting infrastructure continues. That means selecting and specifying high-performance components is essential. But where to start? On-vehicle systems require dozens of components to operate reliably. Each of these components should be tested and proven to deliver reliable performance. In a new four-part Ask Swagelok video series, we look to make sense of the current landscape.
In the second video of our four-part Ask Swagelok series focused on clean energy standards, Chuck Hayes explains the differences in hydrogen and CNG pressure classes.
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CRAIG GIFFORD:
Welcome to Ask Swagelok. I’m Craig Gifford here today with Chuck Hayes, who is Swagelok’s global hydrogen expert. And Chuck, we've been talking about clean energy standards and certifications and kind of everything revolved around that. So, Chuck, help us understand the pressure classes around both hydrogen and compressed natural gas.
CHUCK HAYES:
Sure. It's a great topic and a lot of people get really confused on this. So we'll start and we'll make it really easy. CNG’s pressure class is 248 bar. That's pretty simple and straightforward; there's no real changes to it and that's been around for a long time. In hydrogen, we have two different pressure classes we typically use: H35 and H70. They're defined in international standards. There are a few other ones that we don't use, usually on-vehicle H50 and H25. And what those are is actually they're in megapascals. So, 35 megapascals is 350 bar. So, that's to start with. That is a nominal working pressure. Nominal working pressure means the settled pressure at ambient temperature; that's what the pressure will be.
But there's a difference here. So, let's talk your barbecue grill. If you ever have a big party and you're on your grill for a long time, if you look at your propane tank, it frosts over. It gets cold because most gases go through, when it goes through pressure change, something called the Joule-Thomson effect. And it gets cold. There are only three gases that don't, and that is hydrogen, helium, and neon. They get hot. So when we're fueling the vehicle, we fuel that vehicle and the gas gets hot going into the tanks. So, in the 350 bar, we go to 437 bar when it’s hot. And when it cools back down and settles, it's back down to 350. And at 700, it goes up to 875 bar and cools back down to 700. So, we have to make sure all of our components meet those particular pressures.
CRAIG GIFFORD:
Right, right. Oftentimes, 350 bar product—
CHUCK HAYES:
I said it has to go to 437. If you were to get stuff that was just certified or just available for 350, it may not be available for that working pressure that’s a lot higher. That's because a lot of products in the world were rated for oil and gas, and that was 6000 psi. That's just slightly higher than that. So, you have to go to a different class of product.
And then the last thing is that the station and the vehicle are different. So, let's talk about the H75 for on-vehicle for H70 pressure class. But the station is higher. It actually goes to 962 bar because you need more pressure to be able to push it in. So understand that when you're looking at them. And the 700’s a really tricky one, too, because there's a lot of product that goes to 10,000 psi. 700 is actually 10,200 psi, but you really need to go to much different products to be able to get up that next round in the medium range. Because you have to account for the reverse Joule-Thomson effect. Okay. When it gets hot, yeah.
CRAIG GIFFORD:
Well thank you, Chuck. We really appreciate it. And thank you for joining us at Ask Swagelok.