Cryogenic temperatures require cryogenic materials. This is not only a simple fact of physics, it’s a key mandate. When working in this challenging environment, design and selection of the cryogenic material such as seals become important factors in not only the performance and cost, but the success and safety of the project. This is especially true when engineering polymer seals for cryogenic applications in the aerospace and oil & gas industries. Ever wonder what goes into making quality sealing materials for this type of specialized environment? Which characteristics should you look for when using polymer materials? From rocket propulsion systems to LNG tank applications, today we’re sharing some important features to consider when using sealing materials for extreme temperatures:
Cryogenic seals are designed to work in temperatures ranging from -320°F (-196°C) in applications with liquid nitrogen to -425°F (-254°C) for liquid hydrogen applications. They also seal other gasses such as liquid natural gas, liquid oxygen and helium; all of which need to be isolated and tightly secured.
Cryogenic seals are most often incorporated in two key industries:
- Aerospace industry
Critical in the rocket thrust and lift-off process, polymer seals control the escape of a volatile mix of the many gasses needed to launch and propel the rocket. The seals are commonly found on rocket tanks and valves as well as the feeding lines that transfer fuel to the rocket engine. On NASA’s SLS (Space Launch System) — the world’s most powerful rocket — the massive tanks hold 733,000 gallons of propellant and feed the engines to produce 2 million pounds of thrust!
- Oil and gas industry
Cryogenic seals are used throughout the complex journey of LNG (liquefied natural gas) and LPG (liquefied petroleum gas) value chains that include liquefaction, transfer to transportation in export and import terminals, carriers and bunkering. The PTFE seals are found in demanding applications such as cryogenic valve transfer equipment where reliability is crucial to avoid any downtime.
When sourcing cryogenic seals for either industry, we recommend that you consider these key indicators of quality:
- The rate of leakage
Although a certain level of gas leakage is inherent to any seal. (no sealing material can guarantee 0% leakage rate), leakage rates must be kept in the micro range given the very volatile gasses and liquids they are designed to isolate. Seal designers take particular care to closely consider the shrinkage rate of materials at cryogenic temperature and find the best solutions to maintain sealing forces to minimize leakage rates. One of the most-ideal solutions can be found when metal springs are inserted into jackets of spring energized seals specifically designed to compensate material shrinkage and keep sealing efficiency.
- The precise packaging / handling
Quality seals should be packaged and handled with extreme care in a cleanroom environment to block any impurities from entering the system. Contaminants such as dust or debris will hinder a close bond between the seal and the mating surface. For best results, look for seals that are vacuum sealed to eliminate any impurities. Packaging is particularly important with large diameter seals, which are challenging to move and install.
- The ease of installation
The difference between an “easy” seal install and a “hard” one is determined by the level of force needed to compress the seal between the two surfaces.
Metal seals are much more difficult to install since they do not compress as polymer seals do. Metal seals also require more nuts and bolts to secure the seal with the right amount of torque. Polymer spring-energized seals offer a distinct advantage given their easy compression rate and ability to resist aggressive media.
One sealing solution that easily meets the needs of both the aerospace and the oil & gas industry is the OmniSeal® RACO® spring-energized seal, as it adds a level of reliability and lifetime confidence to the customer. The RACO® seal tolerates extreme pressures from vacuum to a few thousands bars and handles cryogenic temperature requirements. Design flexibility is also a hallmark of the OmniSeal® product, which can reach a 9-foot diameter or more.
All OmniSeal® RACO® cryogenic seals are pre-validated in order to reduce OEM development time and cost. With this strict design process, products are delivered to market more quickly (often saving several months or more), and OEMs realize a substantial cost savings by eliminating repeat testing.
If you thought the RACO® seal is a new spring-energized seal design, think again! It has a proven record of performance in space discovery. The technology was originally developed in the 1950s, and eventually evolved to become the go-to cryogenic seal material for the Space Shuttle Program, the International Space Station, Atlas V launch vehicles, Delta IV Heavy rocket, Mars rover Curiosity, and now the SLS project.
Could the OmniSeal® RACO® seal provide the right functional qualities for your cryogenic sealing application? Count on our experts to help you find out – let’s start with some testing!