How Do We Apply Our Knowledge of Hydrogen Embrittlement?
Hydrogen embrittlement is not a new problem, but the ins and outs of Hydrogen Embrittlement can still be difficult to grasp for those new to dealing with hydrogen. That's why we put together a four-part Ask Swagelok video series detailing what it is, how components can be affected, and what can be done to counter embrittlement issues.
In the third video, Senior Scientist Buddy Damm explains how a component gets fatigued in real-world usage compared to lab testing, how cyclic loading results in a slow accumulation of damage that can eventually lead to component failure, and how proper material selection can help mitigate the issue.
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CRAIG GIFFORD:
Welcome to Ask Swagelok. I'm Craig Gifford, here today with Buddy Damm who's a senior scientist for metallurgy here at Ask Swagelok. And we've been talking about hydrogen embrittlement. One of the things we’re going to talk about today is, “How does Ask Swagelok apply our knowledge of hydrogen embrittlement?” It's a really good question.
BUDDY DAMM:
The first thing I'll say is the hydrogen economy and market is very much evolving. And the research and development going on at national labs and universities around the world and within corporations is very dynamic. There's a lot of new information coming out, so we're trying to stay on top of that. We're staying close to our customers. We’ve got a lot of successful projects in hydrogen service, and we want to keep learning from that.
When we go to try and make material selections, one of the tools we use is something called the relative reduction in area. So, if you were to take a material and test it in air, pull in tension until it fractures, you can measure the ductility as a reduction in area. If you repeat that test in the hydrogen (H₂) environment, you'll get a lower reduction in area. And that relative difference between hydrogen and air can be expressed as a percentage.
So, if you were to test—austenitic stainless steels are one of the more common, capable alloys in hydrogen service. If you were to test 304 stainless, you would get about a 50% relative reduction in area. If you take 316L off the shelf, you'll get around 80%. It's much better. Now, Ask Swagelok uses an enhanced 316L with a little bit more alloy, and that will give you a 90% relative reduction in area.
Now, some other things that are important are things like welding. A lot of our customers weld tubes together all the way—weld tubes to our components. We want to understand how that weld performs. When we test the weld in hydrogen (H₂), we get around an 85% relative reduction in area compared to 90%. That's not much difference. Still good.
Another area of concern is strain hardening. So we strain harden 316 stainless steel, or cold work it, in order to increase its strength. We do that so that we can contain more pressure. Pressure containment in hydrogen (H₂) can be on the order of 700 bars or 10,000 psi. When we tested our product cold hardened, we got an 85% relative reduction in area versus 90%. So, really good.
But of course, in a real component, we're not designing until we load until fracture. Instead, cyclic pressure cycles are external. Cyclic loading results in accumulated damage through fatigue. It's important to understand, “How does fatigue get affected by hydrogen (H₂)?”
If you test 304 stainless steel and compare its performance in air and in hydrogen (H₂), you lose about 90% of its fatigue cycle life. If you test 316L and 316L with a slightly better alloy content, you get about a 70% loss in cycle life. So, that's still significant, but a big difference. And if you make good design choices to manage the stresses, then you can reset. For example, a modest reduction in stress can give you a tenfold increase in cycle life. So, it can really be a game changer.
CRAIG GIFFORD:
Well, that's great. Thank you, Buddy. And thank you for joining us for Ask Swagelok.