by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Benefits of Spring-Energized Seals for Wind Turbines

According to Statista, installed wind power worldwide reached a cumulative capacity of almost 743 GW (gigawatts) in 2020 and is expected to reach almost 841 GW by 2022. As it remains a competitive source of renewable energy, engineers are looking for ways to enhance the efficiency and reliability of wind farms and the turbines that comprise them. One design aspect under consideration is the seals that are used in these turbines. This week, we will discuss the various benefits of spring-energized seals for wind turbines. 

Sealing Challenges in Wind Energy

Wind turbine seals face many challenges during their lifetime:

  • Wide range of temperatures and temperature variations
  • Abrasive materials that can wear down a seal jacket and damage the sealing surface over time
  • Complications arising from below freezing temperatures
  • Regular exposure to moisture and rain
  • Constant exposure to UV that can degrade the seal jacket material

In addition, there are issues related to seal failure: maintenance and repair, a potential domino-effect of damage to internal components (e..g, gear box, electronics),efficiency errors, downtime, and technician safety.

One potential sealing solution for wind energy applications is the spring-energized seal. Spring-energized seals are commonly used in renewable and green energy applications, and wind energy is no exception.

What Are Spring-Energized Seals

Unlike traditional seals, spring-energized seals have an energizer (usually in the form of a spring or rubber) that enables the seal lip to maintain contact with the sealing surface. As with traditional lip seals, they are available in a wide variety of configurations. And there are different types of spring energizers to choose from, allowing for a fairly customized sealing solution for various renewable energy applications.

Benefits of Spring-Energized Seals

The resiliency made possible by the energizing spring enables the seals to provide very reliable performance in high pressures as well as wide environmental pressure variations. In fact, when configured correctly they provide an almost leak-proof seal, which can be critical not just for the wind turbine as a whole but for the precision components inside. 

Spring-energized seals can continue to provide an effective seal even in cases of hardware misalignment, out of rounders, eccentricity, and some degree of jacket wear and changes in sealing surface condition due to wear  (often caused by abrasive materials in the environment). They can also account for dimensional changes that result from wide temperature differentials such as those experienced by wind turbines, as well as extreme heat and cryogenic environmental conditions that can range between 140°F and -65°F.

Implementing spring-energized seals results in several benefits. More reliable seals reduce overall maintenance requirements for a wind turbine, and this can have a very positive financial impact for wind farms with multiple wind turbines at work. Effective, durable seals also lead to significantly less downtime and associated costs as well as more continuous electricity output. In fact, investing in spring-energized seals as opposed to more traditional seals will undoubtedly save money over time and extend the useful life of the wind turbines.

When a polymer material such as PTFE, PEEK, and UHMW PE is used for the seal jacket, there are no complications due to lubricants because these materials are self-lubricating. They have extremely low friction, do not exhibit stick-slip behavior, and have an extremely low starting torque and prevent the seal from freezing to the sealing surface. In addition, PTFE and PEEK exhibit excellent chemical compatibility with the various lubricants they may come into contact with. 

They also possess good UV resistance, which can be critical for seals that are constantly exposed to sunlight. Because wind turbines are often exposed to abrasive materials such as sand, dust, and saltwater, their wear properties are a definite benefit. The low levels of moisture absorption exhibited by these materials means that they will not change shape when exposed to humidity, moisture, and water.

Both materials also work well in the presence of extreme temperatures (including cryogenic) and exposure to moisture, humidity, and rain. In addition, PTFE and PEEK are available in high PV (Pressure-Velocity) grades that are ideal for dynamic sealing solutions. When combined with the proven performance of a spring-energized seal, they lead to more efficient wind turbines.

Finally, the use of spring-energized seals also has a positive effect on technicians’ safety by reducing the maintenance and repairs that must be performed at dangerous heights.

Conclusion

The use of spring-energized seals for wind energy should be considered as an option to 

increase efficiency and useful life while reducing downtime and maintenance costs. These seals along with a polymer jacket can provide an almost leak-proof solution that can withstand the many challenges of seals in the aggressive environments where wind turbines are found.

by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Spring Energized Seals in the Food and Dairy Industries

The food and dairy industries are tough on seals, whether its extreme pressures and temperatures or the limitations posed by using only FDA-approved materials. Spring-energized seals, however, can prove an excellent solution for the challenges posed by these industries. In this week’s blog post, we will discuss spring energized seals in the food and dairy industries.

Issues for Spring Energized Seals in the Food and Dairy Industries

There are several key issues involving seals for the food and dairy industries. The most obvious is FDA approval, but these seals are also exposed to both extreme temperatures and high pressures. Sanitation procedures are extremely harsh, often involving steam, hot water, and aggressive chemicals to achieve hygienic conditions. In addition, the seals will often be exposed to water for extended periods of time, which could be absorbed by the seal material and result in compromising dimensional changes. Lubrication can also be an issue, which means seals may have to be self-lubricating. Finally, the seals must be reliable, able to perform in less than ideal circumstances.

Spring-Energized Seals

Unlike traditional seals, spring-energized seals include an energized seal provides permanent resilience to the seal jacket. The energizer compensates for hardware misalignment, jacket eccentricity, and wear. These seals are typically made of strong, corrosion-resistant stainless steel with a polymer jacket.

FDA Approved Materials

FDA CFR 177, contained in Title 21 of the Code of Federal Regulations, deals with indirect food additives (i.e., substances that inadvertently make their way into food) in the form of polymers. In addition to FDA regulations, there are other standards in place that apply, including (EU) 1935/2004, NSF/ANSI standard 61 for drinking water systems, and 3A Dairy sanitary standards 18-03 and 20-27.

Spring-energized seals are available in materials that are FDA approved. These materials include UHMW PE (Ultra High Molecular Weight Polyethylene) and PTFE (both virgin and certain grades of mineral-filled) and are both known for low friction, chemical inertness, and the ability to handle rugged sterilization and cleaning procedures that can involve steam, hot water, and aggressive chemicals. Other polymers that might be considered  dependent on the application are certain grades of PEEK and Acetal. In addition, UHMW PE, PTFE, and Acetal are also 3A-Dairy and USDA compliant.

Extreme Temperatures and Extreme Pressures

Food and dairy seals must provide reliable performance in extreme pressures and temperatures. Spring-energized seals are able to maintain a tight seal in temperatures and pressures that would cause more traditional seals to fail. This is primarily due to the spring-energizer that keeps the seal lip intact regardless of dimensional changes due to temperature variation as well as pressure fluctuations. Spring-energized seals are well known for their sealing ability at extreme pressures, including vacuum pressures. In addition, they work extremely well in cryogenic temperatures.

Sanitation Procedures for the Food and Dairy Industries

Food and dairy applications almost invariably involve harsh sanitation procedures that can compromise the performance of typical seals. For example, steam and hot water can cause a significant temperature difference, but the spring-energizer is able to maintain a positive seal even if the seal lip changes dimensions. The right choice of an FDA-approved material can ensure that the seal jacket will remain undamaged in the presence of any aggressive chemicals used.

Hygroscopic Effects

When seals are exposed to moisture, water, or humidity for extended times, the seal jacket material may absorb that moisture. This can lead to dimensional changes that compromise the performance of the seal. However, with a spring-energized seal, the energizer allows the seal to maintain contact regardless of those dimensional changes. And with a material such as PTFE or UHMW PE for the seal jacket, the possibility of moisture absorption and associated hygroscopic effects is further reduced.

Lubrication

In food and dairy applications, it may not be possible to lubricate seals because of the possibility of contamination. Choosing the right FDA-approved material for a spring-energized seal can eliminate the need for a lubricant because both UHMW-PE and PTFE are dry running, self-lubricating materials.

Reliable Performance

Seals are critical in food and dairy processing: a failed seal can contaminate goods and, if undetected, can put consumers in danger. Spring-energized seals are extremely reliable, both for the reasons already discussed as well as their ability to compensate for issues such as wear, out-of-roundness, eccentricity, and issues with the surface of the shaft. These seals can perform where traditional seals would fail, again thanks to the spring-energizer that keeps the lip of the seal in contact with the shaft.

Additional Benefits of Spring-Energized Seals

Spring-energized seals can also be used as direct replacements for traditional seals that have failed, even for failures. Because of their durability and resistance to corrosion and contamination, spring-energized seals last longer which in turn leads to reduced downtime and repair costs.

Conclusion

Spring-energized seals are needed in various applications related to the food and dairy

Industry, including blenders, homogenizers, mixers, process vessels, and hygienic piping systems. For reliable, durable, high performing seals for the food and dairy industries, consider the use of spring-energized seals.

by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Best Materials for Spring Energized Seals

The polymers most commonly used in spring-energized seals are PTFE, PEEK, UHMW PE, Vitron, and Hytrel. All of these are high-performance engineering polymers, but some are better adapted for certain applications than others. In this week’s blog post, we will discuss the best materials for spring energized seals, and how they can be applied for each industry. 

Spring-Energized Seals with Polymer Jackets

Polymer sealing jackets are often chosen over their rubber counterparts for various reasons, including better performance at extreme temperatures, a wider range of chemical compatibility, and lower friction. And, depending on the material under consideration, polymers often provide better specific strength and stiffness. Because of these and other properties, they are often used as the sealing jacket for spring-energized seals.

However, knowing which polymer is best adapted for a specific application can be challenging, especially since there are a wide range of engineered polymers that offer excellent mechanical and chemical properties. What follows is a discussion of the most popular spring-energized seal materials for five industries.

Food and Dairy 

Food and dairy applications can make the design of spring-energized seals more challenging, especially when it comes to the choice of the seal jacket material. Materials must be compliant with FDA CFR 177, contained in Title 21 of the Code of Federal Regulations. And other standards may also apply, such as NSF/ANSI standard 61 for drinking water systems,  3A Dairy sanitary standards 18-03 and 20-27, and (EU) 1935/2004.

Because of such regulations, the two most commonly used jacket materials for spring-energized seals in the food and dairy industry are PTFE (both virgin and certain grades of mineral-filled) and UHMW PE (Ultra High Molecular Weight Polyethylene). Besides their FDA approval, these materials also provide low friction, compatibility with most cleaning and sanitation routines, and a good range of operating temperatures. In addition, both materials are self-lubricating, which eliminates the problem of finding a lubricant that is safe to use.

Aerospace and Defense

Aerospace and defense applications that require a spring-energized seal often turn to materials such as PEEK (Polyether ether ketone)  and PTFE. Spring-energized seals are used with hydraulic systems, fuel systems, actuators, and gimbal pods in everything from massive airliners and space rockets to lightweight, nimble drones. Operating environments may involve extreme temperatures, exposure to aggressive chemicals, and mission-critical performance. Some operating conditions may also involve cryogenic temperatures, for which PTFE and Hytrel work extremely well. Note that Hytrel is a TPC-ET thermoplastic polyester elastomer.

In space applications, temperatures can range from cryogenic vacuum conditions to extremely high temperatures and pressures. For spring-energized seals used in rockets, PTFE is the most common due to its wide operating temperature range, outstanding chemical compatibility, and extremely low friction. In addition, PTFE lends itself to the weight constraints and pressure fluctuations involved with space travel, and has been proven over and over that it can provide mission critical levels of reliability.

Automotive

Automotive seals must withstand rugged, extreme environments that may involve everything from corrosive chemicals to extremely high temperatures. When selecting a seal material for automotive applications, properties such as low friction, wear resistance, resistance to abrasion, and durability are major concerns. 

For automotive applications, the most common choice of seal jacket material for spring energized seals include PTFE and Viton (fluoropolymer elastomer). To provide the best performance in the demanding environment of automotive seals, additives such as MoS2 (Molybdenum Disulfide) or carbon may be added to increase strength, wear resistance, and stiffness or achieve low friction.

Renewable Energy

One of the most common areas in renewable energy that requires the use of spring-energized seals is wind energy. Seals for wind turbines can be extremely challenging to design because of the wide range operating temperatures involved, problems with lubricants that can freeze in cold temperatures, extremely low friction so that energy is not wasted, and reliable performance over a long life. Seals must also exhibit low moisture absorption. 

Wind turbine seals typically use PTFE and UHMW PE, known for their low friction and self-lubricating properties. They also offer extremely low moisture absorption, a good range of operating temperatures, and good wear resistance. In addition, they have good resistance to degradation under constant UV exposure.

Oil and Gas

In the context of the oil and gas industry, LNG plants figure heavily in applications that require the use of cryogenic spring-energized seals. For such cryogenic applications, PTFE and UHMW PE have been found extremely effective. For non-cryogenic environments, Hytrel (thermoplastic polyester elastomer) is another commonly used material along with PTFE. These materials offer good performance in sub-freezing temperatures and are reliable enough to support the spring-energized seal design as it prevents leaks that could be devastating not just to humans but to the environment as well.

For other applications, issues of extremely high temperatures and pressures are involved, such as sealing solutions for wellheads. For those jobs, PEEK is often the preferred material. It possesses low friction, excellent chemical compatibility, a wide operating temperature range, and high strength. In addition, it is also one of the few polymers that can maintain its performance in sour gas environments.

Conclusion

Spring-energized seals can provide gas-tight, highly reliable sealing solutions for some of the most difficult operating environments imaginable when combined with the right material. For many sealing solutions out there, high performance polymers are a perfect complement to the ruggedness of a spring-energized seal in many different industries. If you need a spring-energized seal, regardless of industry, we can help you select the right material to provide a durable, effective seal. Contact Advanced EMC today!

by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

PTFE Spring Energized Seals for Cryogenic Applications

When cryogenic temperatures are involved, a failed seal can have extremely serious repercussions that can include personal safety, explosions, damage to local ecosystems, and highly expensive downtime. One of the most dependable solutions to date for sealing in cryogenic environments is PTFE spring-energized seals. In this week’s blog post, we will discuss PTFE spring energized seals for cryogenic applications!

https://www.dailymotion.com/video/x12638r_teflon-spring-energized-ptfe-seals-by-advanced-emc_tech

Cryogenic Applications of Spring-Energized Seals

There are a host of cryogenic applications that depend on spring-energized seals. In the medical field, they are indispensable for MRI (Magnetic Resonance Imaging) equipment. In space applications, spring-energized seals can be found in equipment for radio astronomy and infrared telescopes as well as rocket propulsion systems. LNG fueling systems and compressors depend on them, as well as speciality gas manufacturing. Spring-energized seals are also needed in both pharmaceutical and medical research and can be found in scientific instrumentation for a wide range of disciplines. They are also critical for many food, dairy, and pharmaceutical applications.

But why do so many cryogenic environments require the use of a spring-energized seal?

Sealing Issues at Cryogenic Temperatures

The temperature range for cryogenic applications ranges from below freezing at -32°F down to absolute zero at -460°F. At these cryogenic temperatures, many seal materials begin to behave unpredictably, often exhibiting stiff or even brittle behavior. And changes in temperatures will cause dimensional changes in the seal, often compromising the integrity of the seal. To complicate things further, media at cryogenic temperatures may be chemically aggressive toward certain seal jacket materials. Finally, lubricants are usually prohibited at cryogenic temperatures because of issues with freezing, which means that a suitable material should be low friction and dry running.

Using the right sealing solution, however, can provide a reliable, gas-tight sealing system. And that, in turn, supports compliance with applicable safety and environmental regulations. 

Spring-Energized Seals

Unlike traditional seals, spring-energized seals include an energizer that applies a near-constant load throughout the circumference of the seal. This allows the lip of the seal to remain in contact with the mating surface in a variety of situations, including …

  • Eccentricity
  • Out of round 
  • Misalignment
  • Wear
  • Pressure fluctuations
  • Temperature fluctuations

In the context of cryogenic applications, spring-energized seals are used to maintain contact with the surface during the dimensional variations that result from temperature changes. In addition, spring-energized seals can be used in both static and dynamic applications, including rotating and/or oscillating movement.

Spring-Energizers Suitable for Cryogenic Temperatures

Spring energizers come in many different geometries, but for cryogenic applications, metal V ribbon springs are typically used. V springs, also known as cantilever springs, are used in extremely harsh operating environments and work extremely well in both cryogenic and vacuum pressure applications. 

A key feature of metal V springs as an energizer is their ability to provide a moderate yet very consistent load over a wide range of deflection. This aids in securing the lip of the seal against the mating surface even during dimensional changes due to wide temperature variations. For cryogenic environments, the spring-energizer is typically manufactured from either stainless steel or Inconel, Elgiloy, or Hastelloy.

However, in some instances, elastomeric o-rings can be used as the energizer as opposed to using a metal spring. O-ring energizers are durable and work well under a wide range of temperatures, but are best used when metal must be avoided in an application. 

Media Involved in Cryogenic Applications

As discussed earlier, there are a wide range of applications that require highly reliable sealing solutions. Spring-energized seals are excellent at maintaining seal integrity under such conditions, but thought must also be given to the seal jacket material, which will be in direct contact with media at cryogenic temperatures.

The most typical media of concern include …

  • LOx (Liquid Oxygen)
  • LHE (Liquid Helium)
  • LH2 (Liquid Hydrogen)
  • LAR (Liquid Argon)
  • LN2 (Liquid Nitrogen)
  • Liquid Xenon
  • LCO2 (Liquid Carbon Dioxide)
  • LNG (Liquid Natural Gas)
  • LPG (Liquid Petroleum Gas)
  • LMG (Liquid Methane Gas)
  • Various refrigerants and coolants

When a spring-energized seal is being specified, it is extremely important to select a material that not only has excellent properties at cryogenic temperatures but is compatible with the chemicals involved.

PTFE Spring-Energized Seals

One of the most widely used seal jackets for cryogenic applications is PTFE, better known by the trade name Teflon. PTFE provides excellent performance at a range of operating temperatures, including cryogenic, as well as pressure fluctuations. Its wide operating temperature range is complemented by a wide operating pressure range that includes vacuum pressures.

Virgin PTFE has the lowest coefficient of friction of any solid material, and even with the addition of filler materials it still remains extremely low. Lubricants will not be needed when a PTFE sealing jacket is used because it is self-lubricating, dry running, and exhibits no start and stop behavior. PTFE is also the most chemically compatible polymer available, solving the problem of chemical resistance issues. And for food, dairy, and pharmaceutical applications, PTFE is available in FDA-approved grades.

Conclusion

Where reliable sealing is critical in the presence of cryogenic temperatures, PTFE spring-energized seals are a proven solution in applications ranging from the rocket propulsion systems to MRIs. If you are looking for the right seal that offers superior performance in a cryogenic operating environment, contact Advanced EMC today. Our team of sealing experts can guide you in the process of specifying the right kind of cryogenic PTFE spring-energized seal.

by Jackie Johnson Jackie Johnson No Comments

Energizers used in Spring Energized Seals

PTFE spring-energized seals are one of the most popular choices for engineers in a variety of industries including oil and gas, medical, food and more. The reasons for their popularity are many, including their long service life, even wear, and their ability to perform in some of the harshest environments.  They work well in extreme temperatures; can even perform well in situations where operating conditions can vary significantly.  They usually offer a low compression set, have a long shelf life, and work very well in non-lubricated applications. One of the main reasons for these is the use of energizers, of which there are several different kinds.

As one of the key components of spring energized PTFE seals (it’s even in the name!), each of these energizers offers a different set of characteristics that allow engineers to find just the type of seal to suit their application’s needs.

In this week’s blog post, we are going to look at five different types of energizers, and where they are best used: coil springs, V springs, helical flat springs, cantilevered finger springs, and elastomeric O-rings.

Coil Spring

When people picture the spring energizing seal, the first image that comes to mind may well be the wire coil spring, also known as a spiral pitch spring.  One of its outstanding characteristics is low friction.  The angled coil spring works well where low friction and high pressure are involved, and works best in medium speed applications

V Springs

The V Spring is a cantilever, general-purpose energizing spring, which offers good performance at a relatively low cost.  The V ribbon spring (V ribbon spring energized seal) is the one to look at for the harshest, most severe applications your industry has to face.  It has been accepted as an excellent candidate for cryogenic and vacuum applications.

The v shape of this spring provides a moderate load over a wide deflection range and is used in dynamic and static applications.

Helical Spring

The helical flat spring, also known as a compression spring, is another commonly used alternative. It is typically a cylindrical shaped spring, and uses it’s coiled, mechanical form to store and release energy, which then absorbs impacts or shocks to resist compression or pulling objects.

This energizer is well adapted to a wide range of pressures, from high all the way down to vacuum conditions. It has been found especially suitable for sealing in lightweight gases or liquids. It performs the best under medium speed conditions.

Finger Spring

One outstanding performer is the cantilevered finger spring, also known as a finger spring (probably because it the shape of it reminds you of the end of your finger).

Finger spring energized seals are suited for sealing viscous media as the load is applied to the edge of the sealing lips. Seals energized by this spring also have extremely low friction, and offer low to high pressure sealing. They are best adapted to applications with speeds ranging from low to medium.

Elastomeric O-Ring

While elastomer is often synonymous with rubber, it is actually a highly modifiable polymer. Because of its affordability, ease of installation, and small space requirements, the Elastomeric O-ring is known as one of the most widely adapted sealing solutions. Known for their durability and versatility, elastomeric O-rings are suitable for dynamic or static applications with a wide range of temperature requirements.

An elastomeric O-ring energizer is especially useful when the use of metal must be avoided. It’s adapted well to extreme pressures, much like the helical flat spring.  It also works well when dead volume needs to be minimized.

In Conclusion

PTFE spring energized seals offer extreme temperature, high pressure, chemically inert static and dynamic sealing for the most demanding applications. They achieve this by using a variety of energizers, each with their own benefits depending on the application.

Whether your application is dynamic or static, low pressure or high, there is a spring energized seal for you. And Advanced EMC Technologies can help you find it!

Want to learn more about spring energized seals? Visit our product page HERE! Need sealing solutions? Contact us today.

by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Spring Energized Sealing Solutions For Cryogenic Services in LNG Plants

There are a limited number of reliable sealing solutions for cryogenic services in LNG plants, two leading polymers in use are spring-energized PTFE or UHMW seals.

Challenges of Working with LNG

Leaks involving LNG (Liquified Natural Gas) at cryogenic temperatures are dangerous to the health and safety of workers and to plant operation. Issues such as toxicity, extreme cold, asphyxiation, flammability, and explosions resulting from rapid expansion of LNG all point to the need for a reliable, leak-proof seal.

Finding an effective sealing solution for use in the cryogenic work environment of LNG plants can be extremely challenging. Keep in mind that nitrogen exists in liquid form under normal atmospheric pressure between -346°F and -320.44°F. It’s liquid to gas expansion ratio is very high at 1:694, which means as it boils (starting at its boiling point of -320.44°F) it will expand 694x its original volume. This can lead to an extremely high-pressure change if it occurs in a sealed environment, and most LNG seals must remain functional at either vacuum pressures or extremely high pressures.

Cryogenic Seals for LNG Plants

The temperatures involved with LNG happen to lie where many elastomeric and polymeric materials lose their elasticity and begin to behave as brittle materials. Some seals will also experience dimensional fluctuations related to temperature changes, further increasing the probability of failure. If temperature fluctuations are cyclical, there are going to be problems related to cyclic stress. Yet another issue related to dynamic cryogenic seals is lubrication: at such low temperatures, standard lubrication solutions simply will not work.

The Options For Sealing are Limited two either UHMW or PTFE Polymers and a Full Contact- Anti-Shrink Spring is Essential.

Both seal jacket materials can be specified PTFE, often known by its trade names Teflon or Flourolon 1000. The Ultra High Molecular Weight PE or UHMW, Fluorolon 5000 can handle the low temperatures involved in cryogenic service without becoming brittle (some grades can handle temperatures as low as -350°F) or succumb quickly to the effects of cyclical stress. In addition, both UHMW and  PTFE are self-lubricating, low friction supports dry running, and is a nonstick/slip material. In addition, both products are compatible with a wide range of chemicals, including those it would encounter in an LNG plant.

A spring-energized seal is a seal assembly that includes an energizing spring that forces the seal lip against the mating surface to achieve a highly leak-proof seal. This seal design, when combined with a PTFE lip, has been found ideal for cryogenic applications involving LNG. The spring energizer adds permanent resilience to the seal and can compensate for lip wear, eccentricity, hardware misalignment, and (perhaps most importantly when working with LNG) extreme pressures and dimensional changes. 

The recommended geometry for the spring energizer is a simple helical spring when cryogenic temperatures and either static, reciprocating, or rotary motion is involved. However, oscillatory or static motion may require the use of a solid spring. Recommended spring materials include  17-7 precipitation hardening stainless steel, 301/304 stainless steel, or, in some applications, Hastelloy, 316 stainless steel, Inconel, or Elgiloy.

Conclusion

The design of cryogenic seals for use in LNG plants can be challenging and must meet extremely high standards for reliability and safety, but PTFE spring-energized seals are an excellent starting point.