This article was originally published on March 13, 2023, and updated on November 20, 2024.
Hydrogen has rapidly become a leading source of alternative energy, but it presents unique challenges that require careful consideration. For example, hydrogen is flammable, which can lead to explosions. It can also cause hydrogen embrittlement, and hydrogen permeation, both of which can also damage the instruments that are designed to ensure the safety and efficiency of your hydrogen system.
As the product leader of Industrial Gauges at Ashcroft with 15 years of industry experience, I wrote this article to help you better understand the dangers associated with hydrogen and provide my recommendations for selecting the best pressure gauge for these applications. When you are done reading, you will also find additional resources that can help deepen your knowledge of this timely topic.
Four challenges pressure gauges can encounter in hydrogen applications.
Selecting a pressure gauge that can withstand the harsh demands of hydrogen systems is crucial to maintaining safe operations and achieving expected performance levels for these applications. Choosing the wrong pressure gauge, on the other hand, can lead to equipment damage, inaccurate measurements and worker injury. The following are some of the dangerous conditions your pressure instrument will expected to endure:
1. Hydrogen flame risks.
Hydrogen is flammable at concentrations between 4% and 75% in air, which is a very wide range compared to other common fuels, as shown in Figure 1.
Figure 1. Flammability Range of Hydrogen.
Under optimal combustion conditions (a 29% hydrogen-to-air volume ratio), the energy required to initiate hydrogen combustion is much lower than that required for other common fuels (e.g., a small spark will ignite it), as shown in Figure 2. However, at low concentrations of hydrogen in air, the energy required to initiate combustion is similar to that of other fuels.
Figure 2. Minimum Ignition Energy of Hydrogen.
2. Hydrogen explosion and overpressure risks.
When hydrogen is present in sufficient concentrations and quantities, it can lead to overpressure. This is the result of either unignited releases of pressurized gas or the ignition of a cloud of released flammable gas. In both scenarios, the resulting overpressure can be hazardous, posing direct threats from the pressure itself and indirect threats from structural damage or airborne debris.
- Overpressure from Unignited Releases
As with any cryogenic fluid, if liquid hydrogen is warmed and vaporized into a gaseous state, it occupies significantly more space. From its liquid phase to its gas phase, hydrogen expands to about 850 times its size. Therefore, a confining vessel, pipeline, or sealed space could easily become over-pressurized during a liquid-to-gas phase change.
If a pressurized gas container is heated, the gas will expand even further. If the pressure exceeds the container design rating, mechanical failure will occur.
Pressure-relief devices (PRDs), such as rupture disks or relief valves, should be installed and vented to a safe location to prevent overpressure.
- Overpressure from Ignited Releases
Beyond overpressure associated with the stored gas, flammable gases like hydrogen can burn. If a cloud of hydrogen gas is ignited, the rapid combustion (i.e., explosion) can create overpressure.
As with gasoline vapors at a fueling station, certain precautions must be taken to limit the number of ignition sources (such as lit cigarettes or unclassified electrical equipment) in areas where a release of hydrogen could form a hazardous cloud with sufficient concentration to create an ignited overpressure. These areas are often referred to as “exclusion zones” or “separation distances.”
Solid-front instruments like the Ashcroft® 8008S Pressure Gauge and 8009S Pressure Gauge provide an extra layer of safety on a small, 63 mm gauge. The baffle wall feature with a rear blow-out plug diverts pressure away from the operator if the Bourdon tube should rupture.
Figure 3. Ashcroft® 8008S Solid-Front Gauge.
3. Hydrogen permeation
Hydrogen permeation refers to the penetration of hydrogen ions through the lattice structure of a particular material. This can cause concerns in pressure gauges when selecting internal wetted materials as certain materials can help reduce this problem.
In addition to the lattice structure of a material, hydrogen permeation is also influenced by the pressure of an application. The higher the pressure of the application, the larger the force that is applied to the socket and bourdon tube.
This force stretches the lattice structure of the material, allowing more hydrogen ions to permeate the material. Therefore, your pressure gauge should use a material like 316L stainless steel or variants of 316 stainless steel that not only has a tight lattice structure but is well suited to handle the pressure range of the application.
Figure 4. Hydrogen Permeation Example.
4. Hydrogen embrittlement
Hydrogen embrittlement, also known as hydrogen-induced cracking or hydrogen attack, is a phenomenon that causes loss of ductility and, consequently, brittleness in a material. Highly susceptible materials include high-strength steels, titanium and aluminum alloys, and electrolytic tough-pitch copper.
Due to its small atomic size, hydrogen can infiltrate metals through minute imperfections on their surfaces. Once inside, hydrogen atoms combine to form hydrogen molecules (H2). These molecules then aggregate, creating a larger hydrogen mass that applies outward pressure within the flaw. When the stress applied is below the yield stress of the vulnerable material, it can lead to cracking and potentially catastrophic brittle failures.
To help prevent both hydrogen permeation and hydrogen embrittlement from affecting the efficiency of your operation, make sure your pressure gauge uses strong materials like 316/316L stainless steel with pressure ranges up to 20,000 psi. These features are available in both the Ashcroft® 8008S Pressure Gauge and 8009S Pressure Gauge.
Figure 5. Hydrogen Embrittlement Example.
Other factors to consider for pressure gauges used in hydrogen applications.
Laser welding is used to reduce the possibility of contamination. Its precision allows less of a chance of deforming or damaging nearby areas to not reduce wall thickness. With some metals such as stainless steel, brittleness could result from conventional welding if the electrode used for welding contains traces of moisture.
The heat of the welding causes the water to decompose and release hydrogen that enters the metal causing it to become brittle. This can’t happen with laser welding because there is no electrode.
If you require a larger gauge, Ashcroft’s 1279 pressure gauge with 316 stainless steel wetted parts is also a good option for hydrogen applications. The 1279 is a high-performance 4.5-inch ASME-style process pressure gauge with a comprehensive design for maximizing safety and reliability. It also comes with a solid front safety feature and can handle pressure gauges up to 20,000 psi.
Ready to learn more?
Now that you know the factors to consider when choosing the right pressure gauge for hydrogen applications, you can research the best solution. Keeping these factors in mind can help ensure that you avoid problems or downtime with continuously reliable and accurate measurements.
If you want to learn more about pressure gauges, read some of our other blogs:
- Solid Front vs. Open Front Pressure Gauges
- How To Identify Your Pressure Gauge and Get the Proper Replacement
- How Does Temperature Affect Pressure Gauge Performance?
- How Do I Select the Right Pressure Gauge Range?
- Why Did My Pressure Equipment Fail? 6 Instrument Killers
Feel free to contact us today to talk to one of our industry experts and get your questions answered.
And if you’d like to learn more about hydrogen applications, download our guide: