Hey everyone, it’s Jake from the O Seal Ring shop, and over the last few months, I’ve gotten a question that pops up more often than you’d expect from industrial clients, aerospace techs, and even people working on cryogenic energy projects: “Can O Seal Rings be used in cryogenic applications?” O Seal Ring
I get it—when you’re dealing with temperatures that plunge well below what your freezer can hit (think -150°F, -300°F, even lower), every tiny component matters. A leak in a seal can cost thousands of dollars, delay projects for weeks, or even be a safety risk. I’ve been selling O seal rings for 12 years now, and cryogenic use is one of the trickiest, most interesting areas we work in, so let’s break this down straight, no jargon that’ll make your head spin.
First, let’s get one thing clear: not all O seal rings are the same. When someone asks about cryogenic O seals, they’re not talking about the standard nitrile rubber (Buna-N) rings you’d use for a pool hose or a car’s fuel line. Those would crumble into dust at -40°F, easy. Cryogenic O seals are built for extreme cold, and the big question I always have to answer is: what makes a seal ring work when temperatures drop so low that materials lose their flexibility? That’s the key. Seals need to stretch, compress, and bounce back to form a tight barrier. If a material gets glassy and rigid at low temps, it can’t do that—it cracks, gaps, and leaks.
Over the years, I’ve walked clients through two main types of O seal rings that work for cryogenic use: elastomer (rubber-based) and metal O seal rings. Let’s start with elastomers because that’s what most people first think of, and they’re still the workhorse for a lot of low-end cryo applications. For cryogenic elastomers, we rely on two materials almost exclusively: fluorocarbon rubber (FKM) and silicone rubber, but wait—even within those, there’s a difference. Standard FKM can go down to around -20°F to -40°F, which might be cold for a beer fridge, but not for a liquid nitrogen line. We use low-temperature FKM (sometimes called “LT FKM”) that’s formulated to stay flexible as low as -80°F. That’s good for applications like liquid nitrogen storage tanks, small medical cryo units, and even some aerospace fuel lines that don’t get super cold.
But for really extreme cryo? Like liquid hydrogen, which is -423°F, or liquid oxygen at -297°F? Elastomers just can’t cut it. Even the best low-temp rubbers will go glassy once you get below, say, -100°F. Silicone is a little better—some high-grade silicones can go down to -150°F, but still way above liquid hydrogen temps. That’s where metal O seal rings come in, and these are the ones I get most excited about because they’re actually pretty clever.
Metal O seals are different from regular rubber O rings. They’re made from solid metal, usually stainless steel, Inconel, or even copper for softer, more conforming seals. The ring has a custom cross-section—sometimes oval, sometimes with a slightly wavy face—that’s designed to deform just a tiny bit when you tighten the fittings, creating a metal-to-metal seal that’s impermeable even at super cold temps. The reason they work is simple: metals have a much lower glass transition temperature than rubber. A standard 316 stainless steel ring won’t lose its strength or flexibility at -423°F; in fact, some metals get stronger at extremely cold temps, which is why they’re used in rocket fuel systems all the time.
But here’s the catch I always warn clients about: metal O seals aren’t a one-size-fits-all solution either. You can’t grab a random stainless steel O ring from a hardware store and throw it in a liquid oxygen line. For one thing, compatibility with the media matters. Liquid oxygen is highly reactive, so you need metal O seals made from oxygen-grade materials that won’t spark or degrade when exposed to it. We supply 316L stainless steel O seals for LOX lines, but we also have copper O seals for applications where you need a softer metal that can conform to slightly rough surfaces—common in older piping systems that aren’t perfectly machined. Inconel O seals are for the hottest cryo applications, like liquid hydrogen lines, where temps hit that -423°F mark, and Inconel maintains its strength better than stainless steel there.
Another big part of cryogenic O seal performance is what happens to the seal when the temperature fluctuates. A lot of people forget that when you go from room temp to -300°F, materials contract a lot. If you pick the wrong material, the seal will contract too much, leaving a gap between it and the pipe or the fitting. For elastomer seals, we calculate the compression set at cryo temps. Compression set is how much a material stays deformed after being squeezed. If a rubber O ring has high compression set at -80°F, it’ll lose its shape and not seal tight once it’s cold. That’s why we test every batch of our low-temp FKM to make sure it has less than 15% compression set at -80°F—we don’t want clients calling us at 2 a.m. because their nitrogen line started leaking.
For metal seals, thermal contraction is actually a plus if you pick the right metal for the mating parts. If your pipe is made of carbon steel and your seal is 316 stainless steel, their thermal expansion rates are close, so when they both contract at the same rate in the cold, the seal stays tight. If you mix a stainless steel seal with a pipe made of something like cast iron, the expansion rates are different, and one might shrink more than the other, creating a gap. That’s a mistake I see new clients make all the time—they grab a cheap stainless steel O ring for a cast iron cryo tank, and it leaks because of mismatched contraction rates. So we always ask clients what their mating materials are before recommending a metal seal.
Let me also talk about some real-world examples to make this concrete. Last year, I worked with a team from a university physics lab that was building a new particle accelerator. They needed seals for liquid helium lines, which operate at -452°F—super cold, way below liquid hydrogen. They first tried silicone O rings, which leaked within an hour of cooling down. We swapped them for 10mm Inconel O seals, and they’ve had zero issues for 18 months now. Another client was a medical equipment maker who produces portable liquid nitrogen freezers for blood storage. They were using standard FKM O rings that cracked every 6 months. We switched them to LT FKM O rings, and their maintenance rate dropped by 90%. That’s the stuff that makes my job worth it—solving problems that other seal suppliers can’t.
I should also address a common myth I hear all the time: “O seal rings can’t handle cryo because they’re too simple.” People think gaskets are better for cryo, but no—O seals are actually superior for dynamic applications, like pumps or valves that cycle cold fluid. Gaskets can shift, crack, or lose their seal when you open and close a valve, but O seals have a circular shape that distributes pressure evenly around the joint, so they hold up through repeated cycling. For static applications, like a fixed tank fitting, gaskets work, but O seals are cheaper and easier to replace. The key is picking the right material and sizing correctly.
Sizing is another thing that’s non-negotiable with cryo seals. When a rubber O ring contracts at low temps, its cross-section gets smaller, and its inner and outer diameters shrink. If you size it for room temperature, by the time it’s cold, it’ll be too small. We use a specialized sizing chart that accounts for thermal contraction for both elastomer and metal seals. For example, a 1-inch LT FKM O ring at room temp will shrink about 0.02 inches in diameter when cooled to -80°F, so we size the groove slightly deeper to account for that. For metal seals, it’s a smaller contraction—stainless steel only shrinks about 0.005 inches per inch of diameter at -300°F—but we still account for it in our machining specs.
Now, I know a lot of you are probably thinking: this sounds great, but where do I get a cryogenic O seal that actually works? A lot of suppliers will sell you a “cryogenic O seal” without testing it, and that’s how you end up with leaks. We don’t do that at our shop. Every batch of our cryo O seals—whether elastomer or metal—goes through a pressure test at the actual operating temperature of the application. For FKM seals, we test them at -80°F with nitrogen at 100 psi to make sure they don’t leak. For metal seals, we test at -320°F with liquid helium to simulate the toughest conditions. We also keep records of every batch, so if a client has an issue, we can trace exactly what material was used, how it was manufactured, and test a sample to find out what went wrong.
I also want to be honest about the limits here. If you’re working with temps below -450°F—near absolute zero—even Inconel O seals might not be the best choice. For those super specialized applications, we work with a partner that makes custom cryogenic seals using materials like titanium or even beryllium copper, but that’s for very specific projects, not standard industrial or lab use. For 99% of cryogenic applications out there—from medical freezers to aerospace fuel lines to industrial liquid nitrogen storage—our LT FKM and stainless steel/Inconel O seals work perfectly.
So to circle back to the original question: yes, O seal rings absolutely can be used in cryogenic applications, but only if you pick the right type, material, and size. A standard household O ring won’t cut it, but a high-grade low-temp elastomer or properly machined metal O seal is often the most reliable, cost-effective solution for cryogenic sealing.
At the end of the day, the last thing you want in a cryo system is a seal that fails. I’ve seen projects delayed, products ruined, and even safety hazards because someone used the wrong seal. That’s why I take the time to talk through every client’s specific needs: what’s the temperature, what fluid are they handling, what are the mating materials, is it static or dynamic? No two cryo applications are the same, so a one-size-fits-all approach never works.
If you’re working on a cryogenic project—whether it’s building a lab freezer, upgrading industrial piping, or fixing an aerospace component—and you’re not sure what seal you need, I’d love to chat. No sales pitch, just straight advice. I’ve spent 12 years learning the ins and outs of O seals, and cryogenic use is my favorite part of the job. Drop me a line, and we can figure out the right solution for your needs.
Stainless PTFE Shaft Seal References:
- O’Connor, R.T. (2008). Seal Design Handbook. Marcel Dekker, Inc.
- ASME Boiler and Pressure Vessel Code, Section VIII: Pressure Vessels, 2023 Edition. American Society of Mechanical Engineers.
- South, R.P. (1994). Rubber Compatibility and Performance at Cryogenic Temperatures. Journal of Elastomers and Plastics, Vol. 26, No. 3.
- Materials Properties Council. (2019). Metal Seal Performance at Cryogenic Temperatures. MPC Technical Report 19-04.
- Aerospace Materials Handbook. (2021). NASA Marshall Space Flight Center.
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