How Do You Choose a Pressure Gauge for Hydrogen Applications?

Choosing a pressure gauge for hydrogen applications requires careful attention to safety, pressure range, wetted materials and gauge construction. Hydrogen has a wide flammability range, requires relatively little energy to ignite and can interact with certain metals, so the pressure instrument must be appropriate for the specific operating conditions.

These considerations are important because the wrong gauge or material selection can contribute to equipment damage, inaccurate measurements or unsafe operating conditions. Factors such as hydrogen permeation, hydrogen embrittlement and overpressure should all be considered as part of the selection process.

Ashcroft has decades of experience designing pressure measurement instruments for demanding industrial applications, including gauges used in hydrogen systems. Understanding how hydrogen behaves and how it can affect pressure instruments can help you make a more informed gauge selection.

Read this article to learn:

• What challenges pressure gauges encounter in hydrogen applications
• Why hydrogen flammability and overpressure require special consideration
• How hydrogen permeation and embrittlement can affect pressure instruments
• Which materials and gauge construction features are important for hydrogen service
• What other factors to consider when selecting a hydrogen pressure gauge

What challenges do pressure gauges encounter in hydrogen applications?

Pressure gauges used in hydrogen applications must be able to withstand conditions related to hydrogen's flammability, potential overpressure, permeation and interaction with certain metals. Understanding these challenges can help you select a gauge that supports safe operation and expected measurement performance.

Hydrogen flame risks

Hydrogen is highly flammable and has a wider flammability range in air than many common fuels. Hydrogen can burn at concentrations of approximately 4% to 75% by volume in air.

Figure 1. Flammability range of hydrogen

Under optimal combustion conditions, approximately a 29% hydrogen-to-air volume ratio, the energy required to initiate hydrogen combustion is much lower than for many other common fuels. A small spark can provide enough energy for ignition under favorable conditions. At hydrogen concentrations near the lower flammability limit, however, more ignition energy is required.

Figure 2. Minimum ignition energy of hydrogen

These characteristics make controlling potential leaks and ignition sources important considerations when designing and operating hydrogen systems.

How can hydrogen create explosion and overpressure risks?

Hydrogen can create hazardous overpressure when pressurized gas is released or when a flammable hydrogen-air mixture ignites. The resulting pressure can create a direct hazard and may also damage nearby structures or equipment.

There are two primary overpressure conditions to consider.

1. Overpressure from unignited releases

Liquid hydrogen expands significantly when it warms and changes to a gas. This large volume change can cause pressure to increase rapidly if hydrogen is confined within a vessel, pipeline or enclosed space.

Heating a container of pressurized gaseous hydrogen can also increase its pressure. If the pressure exceeds the design rating of the container or other system components, mechanical failure may occur.

Pressure-relief devices (PRDs), such as rupture disks or relief valves, are commonly incorporated into hydrogen systems to help protect against overpressure. These devices should discharge to an appropriate safe location as determined by the system design and applicable requirements.

2. Overpressure from ignited releases

Hydrogen can also produce overpressure when a released cloud of hydrogen gas mixes with air and ignites. Rapid combustion can generate pressure that affects equipment, structures and personnel.

Because of this risk, hydrogen installations require careful management of potential ignition sources in areas where a release could create a flammable mixture. Applicable codes and standards establish requirements such as separation distances based on the specific installation.

Gauge construction can also provide an additional layer of protection if the pressure element fails. The Ashcroft® 8008S pressure gauge and Ashcroft® 8009S pressure gauge, for example, use a solid-front design. A baffle wall and rear blow-out feature help direct pressure away from the operator if the Bourdon tube ruptures.

Figure 3. Ashcroft® 8008S solid-front gauge

What is hydrogen permeation, and how can it affect a pressure gauge?

Hydrogen permeation is the movement of hydrogen through a material, and it can affect the wetted components inside a pressure gauge. Material selection is therefore an important consideration when specifying an instrument for hydrogen service.

Here's why it matters: 

• Hydrogen atoms are extremely small and can move through the structure of certain materials.

• Pressure and temperature, as well as the properties and thickness of the material, can influence permeation.

• The socket and Bourdon tube in the pressure gauge are continuously exposed to the process media.
• As application pressure increases, stress on the pressure-containing components also increases, making proper material selection and pressure rating especially important.

Because of this, materials such as 316 and 316L stainless steel are commonly considered for hydrogen pressure measurement applications. However, material compatibility should always be evaluated for the application's specific pressure, temperature and hydrogen conditions.

Figure 4. Hydrogen permeation example

What is hydrogen embrittlement?

Hydrogen embrittlement is a reduction in the ductility and fracture resistance of susceptible metals caused by exposure to hydrogen. Under certain combinations of material, stress, temperature, pressure and hydrogen exposure, this effect can increase the potential for cracking and brittle failure.

Hydrogen can enter susceptible metals and interact with their microstructure, reducing their ability to deform without cracking. The susceptibility and mechanism vary considerably among materials and operating conditions.

This makes material selection an important part of designing pressure instrumentation for hydrogen service.

Figure 5. Hydrogen embrittlement example

For pressure gauges, several factors should be evaluated together:

• Wetted materials: Materials exposed directly to hydrogen should be compatible with the application's operating conditions.
• Pressure range: The gauge and its pressure-containing components must be rated appropriately for the system pressure.
• Operating temperature: Temperature can influence hydrogen-material interactions and should be considered along with pressure.
• Gauge construction: Features such as solid-front construction can provide additional protection in the event of pressure-element failure.

The Ashcroft® 8008S and 8009S pressure gauges are available with 316/316L stainless steel wetted components and pressure ranges up to 20,000 psi, providing options for certain high-pressure hydrogen applications.

What other factors should you consider when selecting a pressure gauge for hydrogen?

In addition to material compatibility and pressure rating, gauge construction and manufacturing methods can influence suitability for hydrogen applications. The entire pressure-containing system should be evaluated rather than selecting an instrument based on one feature alone.

Consider how pressure-containing components are joined

Welding methods can affect the properties of pressure-containing components. Laser welding provides precise, localized heat input and does not require the electrode used in some conventional welding processes.

Controlling the welding process is particularly important when manufacturing components intended for hydrogen service because contamination, defects and changes to the material can influence performance.

Select the appropriate gauge size and construction

Gauge size and safety construction should also match the application.

For applications requiring a larger dial, the Ashcroft® 1279 pressure gauge is a 4.5-inch ASME-style process gauge available with 316 stainless steel wetted parts. It also incorporates solid-front construction and is available for pressure ranges up to 20,000 psi.

The appropriate gauge ultimately depends on the application's operating pressure, temperature, materials, installation requirements and other process conditions.

Ready to learn more?

Selecting a pressure gauge for hydrogen requires more than matching an instrument to the system pressure. Hydrogen's flammability, potential for overpressure, ability to permeate materials and interaction with susceptible metals all make material compatibility and gauge construction important parts of the selection process.

If you have questions about selecting a pressure gauge for your hydrogen application, contact Ashcroft to speak with a product expert who can help you evaluate your application requirements.

In the meantime, feel free to download our Hydrogen Applications Guide to learn more about pressure measurement considerations and instrumentation for hydrogen applications.