by Jackie Johnson Jackie Johnson No Comments

Guide to Cryogenic Seals for Marine Loading Arms

cryogenic seals for marine loading arms

A marine loading arm is a flexible, mechanical arm that assists loading or unloading ships. Typically, they transport petroleum and other chemicals between vessels and containers at the docks. 

Marine loading arms are an alternative to using direct hookups. Like direct connections, you must completely drain the loading arms before breaking off the links by using high-pressure air to blow out traces or stripping the line using a pump.

Due to what these loading arms carry, they can operate at cryogenic temperatures. Choosing the appropriate seals for this use is essential to ensure the safety of operators and machines alike. Let’s look further into cryogenic seals for marine loading arms.

Why Use Cryogenic Temperatures

Some liquids are too volatile to transport naturally. That is why they are cryogenically cooled into their liquid form. Cooling the air to cryogenic temperatures requires a process of compression, cooling, and expansion.

Moving cryogenic liquids instead of gas is safer and less likely to explode or cause a fire in the event of an accident. However, as these liquids are at sub-zero temperatures, you should use protective equipment when handling them.

There are many types of gasses transported using cryogenic temperatures. The most common use of marine loading arms to load onto ships include liquified petroleum gas, natural gas, liquid oxygen, liquid nitrogen, liquid hydrogen, and liquid helium. The table below shows the temperatures at which these gasses are transported.

Gas Temperature °C Temperature °F
Liquified Petroleum Gas -48°C -54.4°F
Natural Gas -162°C -259.6°F
Liquid Oxygen -182°C -295.6
Liquid Nitrogen -196°C -320.8°F
Liquid Hydrogen -253°C -423.4°F
Liquid Helium -269°C -452.2°F

Cryogenic Seal For Marine Loading Arms Design Consideration

The most common cryogenic loading arm seals are a polymer material with a metallic energizer. These materials include

  • PTFE
  • PCTFE
  • TFM
  • UHMW PE

PTFE is often the first choice because it is compatible with a wide range of chemicals, has an extremely low coefficient of friction, and is thermally stable. Another valuable material for cryogenic seals is Torlon® Polyamide-imide. Torlon PAI is rigid even at cryogenic temperatures. 

These materials have excellent chemical compatibility, low friction, dry-running, and good dimensional stability. Dimensional changes can be accounted for using a spring-energized seal or sizing the seal by accounting for the plastic’s coefficient of thermal expansion. 

Cryogenic seals made with PTFE and its variants offer a high strength-to-weight ratio, excellent durability, and self-lubricating properties.

What Cryogenic Seals Materials to Avoid

Traditional compression seals are not a viable choice for cryogenic use. Natural rubber, silicone, Buna-N, fluorocarbon, and ethylene-propylene can handle sub-zero temperatures. However, they cannot correctly seal at cryogenic temperatures. Temperatures below -32°C (-25.6°F) cause the rubber to become brittle.

If you use an inappropriate seal, it will eventually fail. Upon failure, the hazardous liquids flowing through the marine loading arm will escape and can be life-threatening. Some dangers include explosion, fire, asphyxiation, or frostbite.

In addition, there will be dimensional changes between when the seal is installed and when it experiences cryogenic operating conditions. You must ensure that the chosen polymer or elastomer doesn’t become brittle at the cryogenic temperatures involved.

Cryogenic Seal Maintenance Considerations

Periodically, cryogenic seals will require maintenance and replacement. Some things to ensure a longer seal life include understanding conditions, knowing what the seal can withstand, and knowing what to look for when it comes to wearing and lubricating.

Understand Conditions 

The conditions in which your marine loading arm works will affect the seals. Temperature, movement, and pressure will eventually cause the seal to wear out and increase leak rates.  If you know and understand the exact conditions where the seals will work, you can pick the suitable material for longer-lasting usage.

Knowing What the Seal Can Withstand

All seals have a limit to what they can withstand. Cryogenic seals can withstand temperatures from -269°C (452.2°F) to 148°C (300°F). They typically resist chemicals, natural gas, petroleum, and liquid nitrogen. They can also withstand high-pressure conditions.

Know What to Look for When It Comes to Wear

All seals wear out. Eventually, cryogenic seals are not excluded. Seals begin to wear on the seal face, causing a leak. You should inspect seals regularly for signs of distress, such as chips and grooves. If there are any indications of wear, then you should replace the seal immediately.

Lubricate

The cryogenic fluids themselves usually make for poor lubricators.  Any added lubricants or even moisture can freeze onto the face of the seal, causing the seal to shatter or, worse yet, the system to lock up and experience catastrophic damage.  However, not using lubrication can result in issues like slip-stick vibration.  

Lubricating cryogenic seals is virtually impossible. As a result, using unfilled polymer materials or a modified material may be the only option.

Best Cryogenic Seals for Marine Loading Arms

Choosing the best cryogenic seals for marine loading arms will depend on what you are transporting. Most cryogenic seals will work in marine loading arms, but some materials work better than others. The most common materials are PTFE, PCTFE, TFM, and UHMW PE.

Advanced EMC offers a wide array of cryogenic seals. If you are interested in purchasing cryogenic seals, contact us today!

FAQ

How do you seal liquid nitrogen?

Sealing liquid nitrogen requires either silicone or PTFE seals. If the seal comes into contact with the liquid nitrogen, PTFE seals are the better choice as this material can handle cold flow without causing creep.

What is the purpose of marine loading arms?

Marine loading arms load or unload vessels carrying petroleum products. They are made of several sections of pipes connected by quick-connect fittings and swivel joints. Cryogenic seals are used between the fittings and joints when transporting liquid nitrogen, liquid petroleum, or any other liquid stored at cryogenic temperatures.

Food Processing and PTFE Spring-Energized Seals
by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

PTFE + Spring-Energized Seals: A Reliable Solution for Food and Pharmaceutical Processing

The primary challenge in specifying a seal is finding a solution that achieves consistent seal integrity for the operating conditions involved. However, when food or pharmaceuticals are involved, additional challenges arise — and can be met using PTFE spring-energized seals.

Design Concerns for Food and Pharmaceutical Seals

There are a number of critical design considerations involved with any type of sealing application, such as operating temperature, pressure, velocity, wear rate, friction, and chemical compatibility.

When food, dairy, or pharmaceuticals are involved, however, there are additional criteria. The first of these is finding a material that is compliant with relevant standards. In the United States, the main standard is the Food and Drug Administration standard FDA 21 CFR Part 177. This standard covers indirect food additives and thus applies to seals. For a material to be considered FDA compliant, it must be safe for human consumption and chemically inert.

Another potential challenge related to food and pharmaceuticals is MRO (Maintenance, Repair, and Operations): 3-A (Dairy and Milk) sanitary standards 18-03 for rubber materials and 20-27 for polymers, as well as NSF (National Sanitation Foundation) sanitary practice standards such as NSF/ANSI 2-2021. Such standards and practices deal with CIP (Clean-In-Place) and SIP (Sanitize-In-Place).  CIP/SIP processes often involve …

  • Extremely high temperatures, which can affect seal integrity and dimensional stability if the right material is not selected
  • Exposure to hot water and steam, which can prove problematic for materials that have a significant water absorption rate
  • Aggressive media, which can permanently compromise seal integrity if the jacket material is not compatible with the cleaning media

Wear resistance is also a critical factor: as the seal begins to wear, its particles become a potential source of contamination. This is particularly problematic when food, dairy, beverage, or pharmaceuticals are involved because those wear particles will likely be ingested. The seal material must, therefore, have a low rate of wear and be safe for occasional ingestion.

Extreme temperatures are often involved and can range from cryogenic (where elastomers and polymers may develop brittle behavior) to extreme heat (where the strength and stiffness of the seal material may be significantly reduced). Seal materials for food and pharmaceutical applications may experience both temperature extremes during regular operation, which may involve the CIP/SIP procedures discussed earlier.

Lubrication is also a major design choice for food and pharmaceutical sealing solutions. But, again, contamination must be considered and the chances are not good when it comes to finding a food-safe lubricant that is compatible with the sealing material and provides the necessary reduction in friction. A better solution would be a material with an extremely low coefficient of friction that is also self-lubricating.

Finally, any application involving food, beverages, or pharmaceuticals must have highly reliable seals. A seal failure can result in ruined products, dangerous contamination, and the potential for lawsuits.

PTFE Spring-Energized Seals

One highly reliable solution for food, dairy, and pharmaceutical applications is spring-energized PTFE seals. Spring-energized seals include an energizer that maintains seal integrity during …

  • Extreme temperatures and temperature variation, including temperatures related to CIP/SIP processes
  • Changes in pressure as well as reliable performance over a range of pressures (including vacuum conditions)
  • Seal or shaft wear
  • Shaft misalignment, eccentricity, or dimensional changes

In addition, spring-energizers add permanent resilience to the seal jacket — and an excellent option for the seal jacket is PTFE.

Virgin PTFE (also referred to as unfilled PTFE) is both FDA and USDA approved. PTFE also provides excellent high-temperature performance, experiences no water absorption, and is extremely chemically inert, all of which combine to give it the ability to maintain seal integrity during the most aggressive CIP/SIP procedures. In addition, PTFE is hydrophobic, thus repelling water and making it even easier to keep clean.

PTFE also exhibits good wear resistance, and what wear the seal jacket does experience will be compensated for by the spring energizer. And virgin PTFE provides excellent performance over a range of temperatures, from cryogenic -450°F to high temperatures up to 450°F. PTFE also has the lowest coefficient of friction of any solid at 0.1. Furthermore, it does not require lubrication because it is self-lubricating.

Conclusion

PTFE spring-energized seals are an excellent solution to the sealing challenges of food, dairy, beverage, and pharmaceutical processing. Combining the outstanding properties of FDA-approved virgin PTFE with the reliability and integrity of spring-energizers leads to high integrity and consistent sealing even in aggressive or extreme operating conditions.

If you are looking for seals related to food or drug processing, contact Advanced EMC today. Our sealing solution experts will work with you to find the right type of spring-energized seal for your application, including everything from the seal jacket geometry to the spring material and configuration.