This article was originally published on January 30, 2023, and updated on August 6, 2025.
Liquefied gases, such as nitrogen, oxygen and helium, are used in many cryogenic applications. These systems operate at extremely low temperatures, typically below -150 °F, and introduce a unique set of pressure measurement challenges. Instruments exposed to these conditions must withstand intense thermal stress, potential material brittleness and design limitations due to space constraints.
At Ashcroft, we understand the implications of these conditions and know how to take precautions to prepare for potential pressure gauge failure. Our pressure measurement expertise relating to industrial systems, including cryogenic applications, helps ensure reliable performance, process safety and long-term instrument protection.
Read this article to learn more about cryogenics, how to measure pressure in these applications, and how to protect your instruments from the effects of very low temperatures.
What is Cryogenics?
Cryogenics is the field of science and engineering that deals with the production and behavior of materials and systems operating at very low temperatures. While definitions vary slightly, the National Institute of Standards and Technology (NIST) defines cryogenics as anything involving temperatures below -153 °C (-243.4 °F). One of the most common uses is for liquid Nitrogen, where the temperature is -195 °C (-320 °F).
At such low temperatures:
- Gases, such as nitrogen, oxygen and hydrogen become liquids
- Most metals, with the exception of 316 stainless steel, contract and may become brittle
- Common elastomers and polymers can harden or crack
- Standard fill fluids and materials may become unstable
Under these extreme conditions, standard instrumentation is often unsuitable without modification or protection.
Where Cryogenic Pressure Measurement Is Used
Cryogenic systems are found across a variety of industries where low-temperature fluids are processed or stored. A few application examples include:
- Liquefied natural gas (LNG) transport and storage
- Hydrogen energy systems and fueling infrastructure
- Medical gas cylinders and delivery
- Cryopreservation of biological materials
- Food product freezing and transportation
- Inert gas cooling during industrial heat treatment
- Aerospace propulsion and rocket fuel systems
One particularly sensitive cryogenic application involves liquid oxygen, used in aerospace, medical, and pharmaceutical environments. In oxygen-enriched atmospheres, materials that are combustible in air can ignite more easily and burn more intensely.
Pressure instruments used in oxygen service must be properly cleaned for oxygen compatibility. This includes the removal of oils, greases, or other contaminants that could ignite and cause catastrophic failure.
Challenges in Measuring Cryogenic Pressure
Measuring pressure in cryogenic systems is more complex than in standard temperature applications. The extremely low temperatures affect not only the process media but also the performance and durability of the measurement instrument. Without the right precautions, even a well-constructed pressure gauge or transducer can fail quickly or deliver inaccurate readings.
In addition to the temperature issues discussed earlier, here are two other common challenges engineers face in these environments, and why proper isolation and material selection are essential.
1. Direct mounting is not recommended for cryogenic applications
While wetted parts may be 316 stainless steel, most instruments include gaskets, seals or internal components that are not designed for exposure to extreme cold. Exposure to these conditions can lead to:
- Seal cracking or hardening
- Freezing of fill fluids
- Mechanical deformation of sensing elements
These risks can result in rapid and complete instrument failure. Protecting the instrument from these low temperatures is critical for reliable measurement.
2. Process materials must be compatible in cryogenic applications
Provided the media is compatible, stainless steel is typically the best material for cryogenic and low-temperature service. Additional acceptable materials include:
- Bronze
- Monel
However, steel tube gauges should be avoided, as the ductility of carbon steel diminishes significantly in cryogenic conditions, increasing the risk of brittle failure.
How to Measure Pressure in Cryogenic Applications
To measure pressure accurately in cryogenic systems, instruments must be thermally isolated from the cold process. This is typically achieved using siphons or capillaries that allow the pressure signal to reach the instrument while keeping it at or near ambient temperature. Here is more detail on both approaches:
1. Capillary siphons for remote mounting in cryogenic applications
Accessories, like the Ashcroft® 1115A Capillary Line, are flexible, stainless-steel tubes that connect the instrument to the process at a distance. This allows heat from the ambient environment to protect the gauge or transmitter. Capillary lines are ideal for remote mounting and installations requiring vibration isolation or easier access to instruments.
They offer:
- Pressure ratings up to 10,000 psi
- Operating temperature range: –300 °F to 750 °F
- Stainless steel construction with optional PVC sheathing
- Lengths from 1 to 100 feet
2. MicroTube™ and Mini-MicroTube™ siphons for compact spaces
Where space is limited or remote mounting is impractical, Ashcroft® 2098 and 2198 MicroTube™ Siphons provide a compact method to isolate instruments from the cryogenic process. These coiled siphons dissipate heat effectively in a small footprint, allowing safe direct connection to the process line without compromising measurement integrity.
They offer:
- Protection up to 800 °F (model 2198) and 600 °F (model 2098) provided they are being used in an ambient temperature environment
- Pressure ratings of 5,000 psi and 3,000 psi, respectively
- 316L stainless steel wetted components, preferred for extremely low temperatures
- Compact installation for tight system footprints
Figure 1: Cryogenic Pressure Gauge Checklist
Ready to learn more?
Using what you learned about measuring pressure in cryogenic applications, you have a better idea of how to protect your instruments and your system. For more information about temperature protection, here are a few related articles:
- Heat Dissipation: Pressure Gauge Accessories for Non-Steam Applications
- How Does Temperature Affect Pressure Gauge Performance?
- How Does Media Temperature Affect Pressure Transducer Performance?
- What’s the Right Pressure Instrument Mounting Assembly for Me?
Contact us directly to speak with one of our industry experts and get all of your questions answered. In the meantime, download our guide to learn more about how to avoid pressure equipment failure.