TL;DR
Natural gas pipelines can usually carry a small hydrogen blend. The US Department of Energy says blends up to about 15% may need only modest changes.
Pure hydrogen is a different job. Hydrogen can make some pipeline steels and welds crack faster, and it escapes through joints that hold methane fine.
Each cubic metre of hydrogen carries about a third of the energy of natural gas. It flows faster, so a converted pipe still moves roughly 85% of the energy, but the compressors have to push about three times the volume.
A 20% hydrogen blend by volume replaces only about 7% of the energy in the gas.
Real hydrogen networks are being built for factories, not kitchens. Germany’s 9,040 km core network reuses about 60% old gas pipe, but only after testing and rebuilding.
Short answer first: partly. An old gas pipe can often take a little hydrogen mixed into the gas. Pure hydrogen usually needs new pipe, or old pipe tested and rebuilt on purpose. And the customer is a factory, not your kitchen.
Now the long answer. Two questions first, because they are the ones that get people lost.
Is a hydrogen pipeline a water pipe?
No. Water is H₂O: hydrogen stuck to oxygen. Taps and toilets.
A hydrogen pipeline carries hydrogen gas: just H₂. A fuel. Invisible. Burns.
Is a hydrogen pipeline just a gas pipe?
Same family as the pipe that brings cooking gas to your street: steel tube, compressors, valves, moving a gas.
Not the same job. You cannot treat the town gas main as a hydrogen main with a new coat of paint. The rest of this post is why.
Why build hydrogen pipelines at all?
Because factories already use a lot of hydrogen.
The world used just over 100 million tonnes of hydrogen in 2025, according to the International Energy Agency (IEA). Almost all of it goes to making fertiliser (ammonia), refining oil, making methanol and treating steel. Nearly all of it is made from natural gas or coal, usually on the same site that uses it. Low-emissions hydrogen was close to 1 million tonnes, about 1% of the total.
Climate plans want more of that hydrogen made with clean electricity somewhere else, then sent to the factory. A pipe is the boring way to move a lot of gas every hour, all day, cheaper than a never-ending line of trucks.
This is not new. The United States already has about 1,600 miles (2,600 km) of hydrogen pipeline, mostly along the Gulf Coast, owned by industrial gas companies and feeding refineries and chemical plants. It works. It is also short, private and built for a handful of big customers.
Then the brochure jumps to: “Just use the gas pipes already under the street.” That is where the engineering says wait.
How is hydrogen different from natural gas?
Natural gas is mostly methane, CH₄. We have piped it for a century.
Hydrogen, H₂, is the smallest and lightest molecule there is:
About one-eighth the density of methane.
About one-third the energy per cubic metre: roughly 10.8 megajoules versus 35.8 for methane.
It burns with a flame that is nearly invisible in daylight.
Three real constraints follow.
Constraint 1: Hydrogen leaks more easily
Small molecules find small gaps. Through the same hole, hydrogen escapes at roughly 2.8 times the volume of methane, because it is so light. Threaded joints, old seals and valve stems that hold methane fine can weep hydrogen.
Like natural gas, hydrogen has no smell of its own. Town gas smells because the network adds an odorant, and that odorant has to be proven safe for hydrogen equipment too.
Leaks also cost you twice. You lose product, and hydrogen in the air slows the breakdown of methane, which makes it an indirect greenhouse gas. A leaky hydrogen network gives back part of the climate benefit it was built for.
So hydrogen lines need tighter joints, more welded connections, and better leak detection than an ordinary street main.
Constraint 2: Hydrogen can weaken steel
This is the big one, and it has a name: hydrogen embrittlement.
Under pressure, hydrogen atoms work their way into the steel, especially at tiny cracks, hard spots and welds. There they make the metal less tough. Every time the pipeline pressure goes up and down, an existing crack grows a little further, and with hydrogen present it grows faster than it would with methane.
The steels most at risk are the high-strength grades used for modern high-pressure lines, and hard weld zones. A pipe that lived happily on methane for 40 years might be fine on hydrogen, fine at a lower pressure, or not fine at all. You only know after testing that specific steel and those specific welds.
The US Department of Energy lists embrittlement of steel and welds as the first research challenge for hydrogen pipelines. The US design code for hydrogen piping, ASME B31.12, adds its own rules on top of the normal gas pipeline code.
“We already have pipes” is true. “Those pipes can take pure hydrogen at full pressure” is a different sentence.
Constraint 3: Same pipe, a bit less energy, much bigger compressors
Here is where the maths gets interesting.
Each cubic metre of hydrogen carries about a third of the energy of methane. That sounds like the pipe loses two-thirds of its job. It doesn’t, because hydrogen is so light that it flows about 2.8 times faster through the same pipe for the same pressure drop.
Uncle’s back-of-envelope: one-third of the energy, times 2.8 times the flow, gives roughly 85% of the energy a natural gas pipe of the same size would move. Detailed studies land in a similar range, depending on pressure and pipe.
The catch is the compressors. To move that energy, they must push about three times the volume of gas. And hydrogen is awkward to compress: the light molecules slip back in the big centrifugal machines that gas pipelines use, so hydrogen needs more stages or piston compressors. Existing compressor stations usually cannot just be switched over.
The energy those compressors burn is small, around 1.5 to 2% of the hydrogen’s energy per compression step in manufacturer examples. The real cost is the new machines themselves.
That is why hydrogen is happiest close to the plant that uses it. A pipe across a whole country is possible. It is expensive, and it is not “the old grid, new sticker.”
Can you just mix a little hydrogen into the gas grid?
Yes, a little. This is called blending.
The US Department of Energy says blends up to about 15% hydrogen may need only modest changes to a natural gas pipeline. In the UK, the HyDeploy trials ran a 20% blend to homes at Keele University and then to about 670 homes in Winlaton, Gateshead, without customers changing their boilers or cookers.
But look at what 20% means. Those percentages are by volume. Because hydrogen carries a third of the energy per cubic metre, a 20% blend replaces only about 7% of the energy in the gas, and cuts carbon dioxide from burning it by about the same. A 10% blend replaces about 3%.
So blending is a real, small step. It is not a whole city running on hydrogen.
What hydrogen pipelines are actually being built?
Two European projects show what the real thing looks like.
Germany’s hydrogen core network. Approved by the Federal Network Agency in October 2024: 9,040 km of pipeline by 2032, costing about €18.9 billion. About 60% is converted natural gas pipe. The first converted sections carry hydrogen, and companies could book capacity from March 2026.
Notice that 60%. Reusing old pipe does happen, but these are big, thick transmission lines with good records, chosen after testing, fitted with new valves and compressors. That is “rebuilt on purpose,” not “new sticker.”
The Dutch national hydrogen network. Gasunie opened the first 32 km section, Maasvlakte to Pernis in the Port of Rotterdam, on 21 May 2026, much of it repurposed gas pipe. Hydrogen is not expected to flow until late 2026, when Shell’s electrolysis plant starts up to supply its refinery. The full plan is about 1,200 km. The Dutch Court of Audit has warned that large parts may never be finished and that loss compensation could reach about €2.5 billion, because nobody wants to build supply before customers exist, or sign up as a customer before the pipe exists.
That chicken-and-egg problem is the real constraint behind all the engineering.
What about the gas main under your street?
This is the part people get backwards.
Many town gas mains are now polyethylene plastic, which handles hydrogen reasonably well. The harder problem is everything at the end of the pipe: meters, regulators, and every boiler, cooker and water heater in every home. Pure hydrogen needs appliances built for it. Switching a whole town means visiting every house.
So the town grid cannot “just switch fuel” either, but mostly because of the kitchens, not the pipe.
When is a hydrogen pipeline worth building?
A short or medium-length line
One or more big industrial customers that already use hydrogen and have signed up
New pipe, or an old transmission line tested and rebuilt on purpose
A clean hydrogen supply that actually exists at the other end
A colourful map of “hydrogen highways” drawn over yesterday’s gas mains is still a drawing until someone has paid for steel that will not crack, compressors that can handle the gas, and customers who will buy it.
Uncle’s verdict
Water pipes carry water.
Gas pipes carry cooking gas.
Hydrogen pipelines carry hydrogen gas to factories. Same idea as a gas pipe, fussier molecule, tested steel and different compressors.
Useful next to industry.
Not a sticker on the town main.
— Engineering Uncle
Sources
AEO FAQ
Paste at the end of the article, above Read next.
Frequently asked questions
Can natural gas pipelines carry hydrogen?
Partly. Most natural gas pipelines can carry a small hydrogen blend; the US Department of Energy says blends up to about 15% may need only modest changes. Pure hydrogen usually requires new pipe, or existing pipe that has been tested for hydrogen embrittlement and refitted with new valves and compressors.
What is a hydrogen pipeline?
A hydrogen pipeline is a steel or plastic pipe that moves hydrogen gas from where it is produced to industrial users such as refineries and fertiliser plants. It is not a water pipe. The US has about 1,600 miles of them, mostly on the Gulf Coast.
What is hydrogen embrittlement?
Hydrogen embrittlement is the loss of toughness in steel when hydrogen atoms enter the metal, especially at welds and small cracks. Under repeated pressure changes, cracks grow faster than they would with natural gas, which is why each pipeline’s steel must be tested before it carries hydrogen.
Does the same pipe carry less energy with hydrogen?
A little less. Hydrogen holds about a third of the energy of natural gas per cubic metre but flows about 2.8 times faster, so a converted pipe moves roughly 85% of the energy. The compressors must handle about three times the gas volume.
How much does a 20% hydrogen blend cut emissions?
About 7%. Blend percentages are measured by volume, and hydrogen carries only a third of the energy of natural gas per cubic metre, so a 20% blend replaces only about 7% of the energy and roughly 7% of the carbon dioxide from burning the gas.
Why not send hydrogen everywhere by pipe?
Leaks, steel embrittlement, new compressors and a lack of committed customers make long national networks expensive. Germany’s 9,040 km core network is budgeted at about €18.9 billion. Many users are better served by making hydrogen on or near the site that uses it.
Read next
Paste at the very end. Replace each LINK with the post’s Substack URL.
Read next on EngineeringUncle
If this one clicked, these are the other hard limits on moving energy around:
Coming up Saturday 26 Sep: How Combined-Cycle Gas Turbines Reach 60%+ Efficiency, the power plants that burn the gas these pipes carry. Subscribe so it lands in your inbox.