Hydrogen is showing up on more job sites every year: fueling stations, fuel cell skids, lab gas panels and plant process lines. The fittings and tubing look the same as any other instrument job, but hydrogen is less forgiving. Here is what I check before building a hydrogen line, so you can get it right the first time.
Why Hydrogen Is Different
Hydrogen is the smallest molecule there is. It will find a leak path that air or water never would. A fitting that passes a soap test on nitrogen can still weep hydrogen. Hydrogen can also make some metals brittle over time, especially high-strength and carbon steels. That is why material choice and workmanship matter more here than almost anywhere else.
Start With the Right Material
For most hydrogen instrument lines, 316/316L stainless is the starting point. Many hydrogen specs go further and call for 316/316L with a higher minimum nickel content, because more nickel helps stainless resist hydrogen embrittlement. Read your project spec before you order, and make sure the tubing, fittings and valves all meet it. Avoid carbon steel and mixing in parts of unknown material.
A-Best Industrial Inc. Fittings, Valves, and Tubing stocks 316/316L and 304/304L stainless tubing (DFARS compliant), plus Inconel when the job calls for it. See our tubing page for what we carry.
Wall Thickness and Pressure
Hydrogen systems often run at high pressure. Size the tube wall for the working pressure with a safety margin, and confirm that the tube OD and wall fall within the fitting manufacturer's recommended range. Our fractional stainless tubing pressure chart lists working pressure by OD and wall, with welded and temperature derating factors. Too thin a wall and the ferrules may not hold. Keep tubing capped until you use it so dirt and moisture stay out.
Tube Prep Is Where Leaks Start
On hydrogen, a scratch on the tube where the ferrule seals is a leak waiting to happen. Cut square with a RIDGID tube cutter made for stainless, and lock the GRIP-IT TOOL onto the tube so it doesn't spin in your hand and get scored. Then clean up the ID and OD with a deburring tool and blow out any chips. You'll find all of these on our tools page.
Make Up Every Fitting the Same Way
Bottom the tube in the fitting body, follow the manufacturer's turns, and check every connection with a gap inspection gauge. If the gauge fits in the gap, the fitting isn't made up. On a hydrogen line, there's no such thing as "close enough."
If your site already runs Swagelok, you don't have to rip it out to use DK-Lok. DK-Lok had its tube fittings tested to ASTM F1387-99(2005), witnessed by TÜV Rheinland, using 14 combinations of intermixed DK-Lok and Swagelok nuts, ferrules and bodies in 1/4" through 1" OD. Tests included hydrostatic burst, impulse, thermal cycling and vibration, with the result "No failure observed." DK-Lok also backs intermixing with a written guarantee for same-size, same-material Swagelok parts assembled per the DK-Lok catalog. Read the ASTM F1387 test report or see our DK-Lok page.
Leak Test Like You Mean It
For the bubble check, we use Gator Leak Detector. It's made for oxygen and compressed gas systems, including hydrogen lines, contains no oil or grease, and dries clean without any residue. Leaks show up in 5 to 30 seconds as bubbles or a fine white foam.
A bubble check is a start, not the finish. Many hydrogen systems are leak tested with helium or checked with a hydrogen detector, because small leaks are easy to miss. Follow your site's test procedure, and retest after any fitting is remade.
We're Here to Help
If you are planning a hydrogen line and want a second set of eyes on materials or parts, call A-Best Industrial Inc. Fittings, Valves, and Tubing at 310-833-3353 or email sales@abesttube.com. We're open Monday–Friday, 8:00 AM–5:00 PM Pacific, with after-hours emergency service.