More and more industries are using cryogenically cooled liquids and gases, which is increasing the demand for transfer systems that can handle those kinds of temperatures.
In this blog post, we are going to talk about cryogenic seals for loading arms, beginning a discussion of cryogenic fluids loading arms encounter, the industries that require cryogenic fluids, types of loading arms, and the most common polymer material choices for the cryogenic seals.
Cryogenic Fluids and Loading Arms
Cryogenic seals must be used in loading arms to transfer liquid natural gas (LNG, –260°F), as well as other liquid media such as liquefied petroleum gas (LPG, which is usually at -48°C), liquid nitrogen (-196°C), liquid helium (-269°C), liquid hydrogen (-253°C), cryogenic ethylene, or liquid oxygen (-183°C).
Industries Involving Cryogenic Fluids
There are a variety of industries where loading arms that can handle cryogenic temperatures are needed. Hospitals and medical research centers commonly make use of liquids at cryogenic temperatures for various treatments and tests, such as cryosurgery and MRIs. Chemical processing plants also need large supplies of cryogenic fluids. There are many different aerospace applications, for everything from satellites to space shuttles. Scientific research centers use cryogenic fluids for projects involving superconductors. Cryogenic fluids are used in many different manufacturing processes, from semiconductors to heat treated metals. Transportation, with the increased use of LNG as a fuel, is yet a another example of where cryogenic loading arms are increasingly in demand.
Loading Arms and Cryogenic Seals
Loading arms are flexible piping systems that are used to transfer chemicals in liquid or gas form. The flexibility of the piping system is due to its use of swivel joints. These swivel joints are typically made of stainless steel with a seal that is either a polymer or elastomer. If the chemicals being loaded involve cryogenic temperatures (such as liquid nitrogen), then special cryogenic seals are necessary.
Marine Loading Arms
One of the common areas where cryogenic seals are required for loading arms involves marine loadings arms, also known as mechanical loading arms. A good example of this would be unloading LNG from a marine tanker to an onshore storage tank. They are used with marine tankers, ocean going super tankers, ships, and river barges.
Distribution Loading Arms
Distribution loading arms requiring cryogenic seals are also common. Distribution loading arms, also known as land loading arms, are primarily used for unloading chemicals from tank trucks and railcars. Distribution loading arms are available as either top loading arms or bottom loading arms (which are usually reserved for handling more dangerous chemicals).
Seals for Cryogenic Loading Arms
Most polymer-based cryogenic seals used in loading arms are spring energized and made from a variant of PTFE, such as low-temperature PTFE, PCTFE, TFM. Another common polymer for these spring-energized seals is UHMW PE, which has properties comparable to PTFE. PTFE is often a first choice because it offers excellent chemical compatibility, has an extremely low coefficient of friction, and is thermally stable.
Conclusion
Any time cryogenic liquids must be transferred in bulk, there is a need for either marine loading arms or distribution loading arms that have cryogenic seals at the swivels. As the number of applications that make use of cryogenic fluids continues to grow, so does the demand for reliable seals. Keep in mind that spring-energized polymer seals have a proven track record for use in loading arms.