Rotary seals are essential to maintaining the life of the equipment. While choosing the appropriate rotary seal materials, the rotary shaft mating surfaces are equally important.
Below, we will discuss rotary seals, materials used for seals, and rotary shaft properties.
Rotary Seals
Rotary seals work to help keep the system lubricated while excluding contaminates. A properly fitting seal can positively impact the life of the lubricant. Oil’s life span at 86°F (30°C) is 30 years. However, as the oil heats up, the life span diminishes rapidly to no more than a 30-day life span.
The addition of contaminants and water also limits the life of the oil and the ball bearings. For example, adding .002% water into the oil lubricant will reduce the ball bearing’s life by 50%. The cause of the ball-bearing integrity loss is called hydrogen embrittlement.
Common Materials Used for Rotary Seals
Rotary seals come in several different materials. The optimal choice is dependent on the environment in which it is used. The most common materials include nitrile rubber, polyacrylate rubber, fluoroelastomers (FKM), and PTFE.
While these materials are a good choice for rotary seals, conventional rubber seals are common in static applications where temperature and chemical compatibility are not a concern. PTFE is the solution in high-speed dynamic service requiring low friction seals or where exposure to severe temperature or chemicals exists. There are different types of PTFE used for rotary shaft seals. Users can choose from
Virgin PTFE
Molybdenum Disulfide Filled PTFE (MoS2)
Carbon Filled PTFE
Carbon and Graphite Filled PTFE
Carbon and MoS2 Filled PTFE
Glass Filled PTFE
Glass and MoS2 Filled PTFE
Polymide Filled PTFE
Properties of Rotary Shafts Mating Surfaces That Affect Sealing Performance
Most often, rotary shafts are metal. However, the rotary shaft mating surface could be made from plastics. No matter what material the shaft is made from, some properties will affect the sealing performance of the shaft.
The properties of the rotary shaft that affect sealing performance are the shaft harness and the shaft roughness. The sections below explain in greater detail how the hardness and roughness of the rotary shaft can affect the rotary shaft’s sealing performance.
Rotary Shaft Hardness
The hardness of the rotary shaft is how deep an indenter can penetrate the surface of a shaft. The shaft’s hardness is measured in the Rockwell C scale. The higher the number, the more complex the surface.
As a general rule, the rotary shaft should always be harder than the seal to ensure the seal wears out before the shaft. Additionally, if you choose a harder surface, there are more options for seal materials.
With a rotary shaft with a hardness exceeding 45 Rockwell C, the seal doesn’t have time to polish and “bed in.” That means that any roughness on the surface will cause issues with the seal, wearing it down quicker than average. A shaft with a hardness under 45 Rc requires a softer seal which doesn’t have as long of a life.
The choice of hardness depends on the environmental pressure and shaft speed. For example:
In environments of 1000 psi with rates up to 150 sfpm, a shaft with 70Rc or greater is necessary
Settings using shaft speed 2500 sfpm and 0 psi need a hardness of 60Rc or greater.
Rotary shaft speeds of up to 150 sfpm and 0 psi need a hardness of at least 35Rc, with lubrication, or 44, with no lubrication.
Rotary Shaft Mating Surface Roughness
The rotary shaft’s roughness refers to the shaft surface’s unevenness. To measure the roughness, measurements of high and low points of the shaft and taking the difference to determine the machined tolerance.
Ideally, a smoother surface will increase the seal life and offer outstanding performance. But on the other hand, when the surface is exceptionally smooth, there is no way for the oil to flow between the mating surface and the seal. As a result, the seal wears out quicker without lubricant between the seal and the mating surface.
Of course, a high roughness level can allow leaks through low points on the shaft. Therefore, the rotary shaft roughness needs to be relatively smooth but not so smooth that the seal cannot be lubricated.
Rotary shafts work with the rotary seals to keep lubrication from dirt and water. Understanding the properties of the rotary shaft mating surfaces helps determine the type of seal material chosen. Contact us today for your rotary seal and shaft mating needs.
High-performance liquid chromatography is the ideal method for analyzing various solutions in different fields. This machine, however, requires HPLC spring energized seals that adhere to strict guidelines with slight variation.
Different Liquid Chromatography Types
There are a few different types of liquid chromatography. The primary liquid chromatography types include high-performance liquid chromatography (HPLC), preparative HPLC, and ultra-high-performance liquid chromatography.
High-performance liquid chromatography is used in multiple different industries. HPLC is found in food science, drug development, and forensic analysis. It is used to separate compounds and used for quantitative and qualitative analysis.
Preparative HPLC is used in purification applications as it requires a higher flow rate. This liquid chromatography is also used to separate and collect high-purity compounds. It is also used for large quantities of compounds needed for evaluation and analysis.
Ultra-high-performance liquid chromatography (UHPLC) is similar to HPLC. It is used to separate different constituents of a compound and to identify and quantify the different components of a mixture.
Operating Conditions
HPLC pumps operate in conditions with variable flow rates and small shaft diameters. They have tight leak criteria and operate under a wide range of pressures. HPLC pumps have a medium-speed reciprocation.
Seals in HPLC pumps must withstand the solvents used to separate compounds dissolved in the liquid sample. Solvents used in HPLC include
MeOH (Methanol)
ACN (Acetonitrile)
H2O (Water).
The expected lifetime for seals in HPLC pump environments is a minimum of one million cycles. Seals may last longer depending on the flow rate, pressure, and media.
Seal Designs
HPLC seals prevent leaks from occurring. Should the mile phase lack into the back of the pump, it will impact consistency, accuracy, and pump precision. To effectively prevent leaks, seals should have effective leak resistance in pressures up to 20 kpsi.
Seal Geometry
The geometry of the seal is an important factor. For HPLC pumps, a flange design helps reduce the pump’s pulsation. HPLC spring energized seals have a longer seal ID lip and a polymer backup ring to increase the amount of contact stress.
UHPLC seals have a non-flange design and a shorter seal ID lip. Instead of a polymer backup ring, it uses a ceramic or metal backup ring. These seals have a concave back for higher-pressure distribution.
Jacket Materials
HPLC pumps’ seals have a PTFE or UHMW PE jacket. The UHMW PE material is used in systems with pressures greater than ten kpsi. UHMW PE is an FDA-compatible material for both food and pharmaceutical analysis.
PTFE jackets are the most chemical resistant of the common materials. The PTFE jackets are filled with graphite or polyimide. These fillers are heat and wear-resistant and work well in liquids and steam.
Performance Factors
Sealing performance factors are affected by the different surfaces in the HPLC pump. The housing surface has a suggested static sealing surface between 9.1 to 14.5 μin Ra.
On the plunger surface, a smoother surface is best. For virgin PTFE or UHMW PE, a minimum shaft hardness is 40Rc. The suggested dynamic surface is 7.3 – 14.5 Ra μin.
Medium
Dynamic Surface
Static Surface
Reciprocating
Rotary
RMS
Ra μin
RMS
Ra μin
RMS
Ra μin
Liquids
8 to 16
7.2 to 14.4
8 to 12
7.2 to 10.8
16 to 32
14.4 to 28.8
Plunger alignment needs to have a minimal shaft-to-bore misalignment with tight concentric guidance between the wash body and pump head. For best sealing performance, the shaft-to-bore misalignment should be kept to a minimum.
Shaft To Bore Misalignment at the Seal Area
Shaft Diameter (in inches)
Shaft to Bore Misalignment (in inches)
0.000 – 0.750
0.0020
0.751 – 1.500
0.0025
1.501 – 3.000
0.0030
3.001 – 6.000
0.0035
6.001 – 10.000
0.0045
HPLC Spring Energized Seal Recommendations
The HPLC spring energized seal requirements should be considered during the pump design process. Designers should collaborate with seal engineers early in development. Contact us today to get a quote on your next custom seal needs.
There is a push for more people to drive electric vehicles. While they are more environmentally friendly, the motors differ significantly from traditional combustion engines. Electric vehicle seals must keep lubrication confined to the gearbox, dirt, and debris out of the motor while providing engine efficiency.
In this article, you will gain a basic understanding of
How electric vehicles and internal combustion engines differ
Design considerations for electric vehicle seals
Types of materials used in making seals for electric vehicles
Differences in Electric Vehicle and Internal Combustion Engines
If you are standing outside an electric vehicle looking at it, you may not notice many differences between it and a gas-powered automobile. The overall external design is the same, except the electric car has no exhaust pipe.
However, below the surface, the two engines are significantly different. Gas-powered have a gas tank, gas pump, motor, carburetor, alternator, smog controls, and hundreds of other moving parts. In addition, the engine requires seals to keep oil and other fluids from leaking out.
An electric vehicle engine only has one main moving part: the motor. Despite the motor being in a dry environment, seals are still required to help keep dirt and dust out of the engine and the lubricants needed for the vehicle gearbox.
Both electric vehicles and internal combustion engines require specialized seals to keep the motors/engines working efficiently.
Electric Vehicle Seal Design Considerations
Electric vehicle motors work more efficiently and require seals that can handle their unique needs. The seals used in electric vehicles often exceed the minimum requirements of seals found in internal combustion engines. In addition, many of them must work in dry environments.
Friction
Friction is one of the primary design considerations for electrical vehicle seals. While friction in any engine is not desired, electric vehicles need a lower friction seal than traditional gas-powered engines. Any friction created by seals causes efficiency loss in power output.
If the engine isn’t efficient, the battery won’t be able to have the range that it should. A motor working harder to make up for the efficiency loss won’t be able to travel as far as it should. Lower friction is essential to gain better efficiency and long distance.
Dry Running
Electric vehicles require both dynamic and static seals. The dynamic seals are often called rotary lip seals. While they don’t require oil seals, electric motors need seals that work in a dry-running environment.
The primary shaft uses a rotary seal to prevent dirt, dust, and water from entering the electric motor. If fluid and debris enter the motor, it can damage the engine and cause it to break down or damage some of the highly charged electrical components so that it won’t work efficiently.
In addition to running in a dry environment, the rotary seals must withstand the higher speeds electric motors run. The components spin up to 18,000 rpm, about three times faster than a traditional combustion engine. As a result, seals in these engines have to withstand high-speed running without lubrication.
Electric Vehicle Seal Materials
Not all materials common seal materials work well in electric vehicles. However, two of the more common types are PTFE and molded rubber. The materials are used for different applications but are necessary as part of the vehicle’s makeup.
PTFE Seals
Polytetrafluoroethylene (PTFE), more commonly known as Teflon, is a nonreactive material with a low coefficient of friction. Therefore, it is ideal for high-temperature environments found in an electric vehicle motor.
Seals made from PTFE are usually found on the e-axle and help to act as a barrier between the motor and gearbox. The engine is a dry environment, while the gearbox requires lubrication. The PTFE seal keeps lubricant from seeping into the motor. In addition, the seal’s dry side has a lip that keeps dust and dirt out of the engine.
In addition to keeping the lubricant in the gearbox and dirt out of the motor, the PTFE rotary seal can withstand the high speeds in the car’s engine. Additionally, it provides low friction to keep the motor running efficiently.
Molded Rubber
While PTFE is the ideal seal material for the e-axle, molded plastic is the perfect solution for valve housing. The valve housing needs a seal that will withstand high temperatures and pressure in the area. The T-junction area of the seal is the most problematic area known for failure.
Molded rubber seals are push-in-place rubber gaskets that perform well under pulsating pressure. These gaskets can handle temperatures of up to 302°F (150°C) and 50 Bar pressure. In addition, it requires more gland space than seals used in a traditional combustion engine.
Conclusion
Electric vehicles are rising in popularity. However, due to the nature of their engines, they require different seals than a traditional combustion engine. These seals need to have lower friction and handle high-speed rotation.
Need seals for your electric vehicle manufacturing? Contact us today to find out how we can create custom seals for your project.
Seals used in the oil and gas industry must withstand high temperatures, high pressure, and a chemically hostile environment. The conditions limit the material used to make the seals for this industry. The most common types of materials include
PTFE
PEEK
UHMW
PCTFE
Hytrel
Let’s look further into these materials, their benefits, and their limitations.
What is PTFE?
Polytetrafluroro Ethylene (PTFE) is a synthetic fluoropolymer with high-temperature resistance, commonly known as Teflon. It is a hydrophobic, high-molecular-weight polymer consisting of carbon and fluorine.
Benefits of Using PTFE
PTFE is ideal for use in the oil and gas industry as it is resistant to extreme high and low temperatures. In addition, PTFE has a low coefficient and a low dielectric constant. Finally, the hydro resistance nature of the material makes it a top choice for working with steam or heated seawater.
One of the most significant benefits of using PTFE is the resistance to harsh chemicals. It has the broadest chemical resistance of commercial polymers. For example, seals made of this material are resistant to hydrogen sulfide, ferric chloride, ferrous sulfate, hydrochloric acid, and hydrofluoric acid.
Limitations of PTFE
PTFE’s limitations make it unsuitable for some uses. For example, it is sensitive to creep and abrasion, requiring regular maintenance. PTFE also has low radiation resistance and can corrode and produce toxic fumes as it breaks down.
Properties of PTFE
PTFE has a density of 2200 kg/m3 with a melting point of 327°C (620°F). PTFE maintains self-lubrication, strength, and toughness at temperatures down to -268 °C (-450.67°F). Additional properties include:
What Are Some Common Oil and Gas Applications of PTFE?
PTFE is one of the more common materials used in oil and gas seals. For example, O-rings, slipper seals, backup rings, piston rings, and spring-energized seals use PTFE material. In addition, natural gas, cold media seals, bearings, and wear components also use PTFE for manufacturing.
What Is PEEK?
Polyetheretherketone, or PEEK, is a colorless organic thermoplastic semi-crystalline polymer with excellent mechanical and chemical resistance properties. It’s high-resistance to terminal degradation makes it useful in oil and gas environments.
PEEK has high mechanical strength and is ideal for high vacuum applications. Its robust nature makes it suitable for demanding applications such as the oil and gas industry. It works well in compressors, pumps, and pistons.
Limitations of PEEK
Despite PEEK’s many benefits, there are some drawbacks to using this material. It has low UV light resistance. It is also unsuitable for nitric acid, sulphuric acid, sodium, and halogens. In addition, it is expensive to make and requires high temperatures to process.
Properties of PEEK
PEEK has a high tensile strength of 25000 to 30000 psi. It has a V0 flammability rating of 1.45mm and can withstand high loads for extended periods without residual damage. Additional properties include:
What Are Some Common Oil and Gas Applications of PEEK?
Labyrinth, spring-energized piston seals, backup rings, and seal packing in the oil and gas industry are manufactured using PEEK materials. In addition, it is the material most often chosen for the face seals at the wellhead to contain the high-pressure production of gas and fluid.
What is UHMW Polyethylene?
Ultra-High Molecular-Weight, UHMW, Polyethylene seals are thermoplastic, semi-crystalline materials. It is lightweight with a high-pressure tolerance that makes it ideal for spring energized seals used by the oil and gas industry.
Benefits of Using UHMW Polyethylene
Seals made from UHMW have the benefit of being both abrasion and impact resistant. This self-lubricating material has a low friction coefficient. It withstands extreme colds and high temperatures.
It has a high molecular weight, meaning UHMW is not likely to melt and flow as a liquid. This material cannot be molded by traditional methods, thanks to the high molecular weight. Instead, it is compression molded to make it stronger.
Limitations of UHMW Polyethylene
While UHMW Polyethylene has many benefits for the oil and gas industry, there are some limitations, such as having a lower maximum continuous surface temperature than other materials.
UHMW Polyethylene has a compressive strength of 3000 psi. In addition, it has a maximum safe workload of 1000 psi in some industries. Overload can cause UHMW polyethylene to crack or break.
Properties of UHMW Polyethylene
UHMW polyethylene seals are self-lubricating and have low surface energy, which makes them ideal for the oil and gas industry. Other UHMW polyethylene properties include
What Are Some Oil and Gas Applications for UHMW Polyethylene?
UHMW polyethylene material is used for seals in the oil and gas industry. It is used to make spring energized seals. It is also used for cargo dock impact bumpers and liners.
What is PCTFE?
Polychorotrifluoroethylene (PCTFE) is a chemical compound with a high tensile stretch and good thermal properties. Its chemical-resistant properties make it ideal for use in the oil and gas industry for seals and other components.
Benefits of Using PCTFE
Seals made with PCTFE are nonflammable and heat resistant up to 175°C (347°F). They are also resistant to acetone, hydrochloric acid, sodium peroxide, citric acid, and sulfuric acid. It is water-resistant as well.
PCTFE has a board temperature range with a useful temperature range of -204.4°C (-400°F) to 193.3°C (380°F). When comparing PCTFE vs PTFE, PCTFE is a stronger polymer with better mechanical properties.
Limitations of PCTFE
PCTFE has many beneficial properties for the oil and gas industry. However, some limitations, such as a lower melting point when compared to PEEK or PTFE, might make it less desirable. Seals used in extreme temperatures may need to be a different material.
Additionally, PCTFE is a stiffer material. While this does allow it to maintain its dimensions better, it does break easier than PTFE. Along with being stiffer, it is not as non-stick when compared to PTFE.
Properties of PCTFE
PCTFE has V-0 flammability and a hardness of 67 at 100°C and 80 at 25°C. Other properties include
What Are Some Oil and Gas Applications for PCTFE?
Like PEEK or PTFE, PCTFE is a great material for seals in the oil and gas industry. It’s chemical resistance, which means it can be used in the most volatile industries. Fillers within the seals can enhance some of the properties. PCTFE is also used in component designs and valve seats.
What is Hytrel?
Hytrel is a thermoplastic polyester elastomer that is plasticizer-free. It is a stable material with needed flexibility while handling high temperatures. It is a worthwhile option to consider for the oil and gas industry.
Benefits of Using Hytrel
As a seal material for the oil and gas industry, Hytrel has good chemical resistance. It can withstand exposure to fuel, hydrocarbon solvents, and oil. Additionally, as the material is exposed to higher temperatures, it becomes more rigid. At lower temperatures, it is more flexible.
Hytrel is abrasion resistance. It offers impact and creep resistance to the seals. It also is resilient and excels at providing flex fatigue and tear resistance. Hytrel has a natural spring-like property and has low hysteresis.
Limitations of Hytrel
As there are several models of Hytrel, only a few are best for use in seals. Hytrel 4556, 4056,4068,4069, and 6356 are the ones that work best. However, these don’t always work well in the oil field, so you should know which ones to look for.
Properties of Hytrel
Hytrel has V-0 flammability and a hardness of 67 at 100°C and 80 at 25°C. Other properties include
What Are Some Oil and Gas Applications for Hytrel?
Hytrel is useful as a seal material in the oil and gas industry. As it is resistant to many chemicals, including hydrocarbon solvents, it is ideal for hazardous conditions.
Which Seal Type is Best for the Oil and Gas Industry?
Each seal type has its uses and benefits for the oil and gas industry. However, the best options are PEEK, UHMW, PCTFE, and Hytrel. It is because they have the best physical properties to withstand the harsh conditions in the oil and gas field.
At Advanced EMC Technologies, we offer custom-engineered sealing systems that provide reliable sealing solutions. Our seals perform under high temperatures, high pressure, and chemically hostile environments. Contact us for more information.
Seals for Oil and Gas Industry FAQ
IS PEEK environmentally friendly?
There is no evidence that PEEK has a significant environmental impact in its service life, disposal, or manufacturing. Toxicity is low and does not contain anything known to be toxic. There is low smoke, poisonous gas emissions, and fire when involved in a fire.
What are spring-energized seals?
Spring-energized seals can store mechanical energy by compressing the spring. As a result, they withstand more pressure and heat than their conventional counterparts. In the end, the mechanical energy stored in the seal keeps it from leaking.
Fluorinated ethylene propylene (FEP) is one of the most popular jackets for encapsulated rings used in cryogenic, corrosive environments, and even FDA-approved food grades. It is well-known by many of the trade names Teflon FEP, Neoflon FEP, and Dyneon FEP. FEP encapsulated helical springs are one type of these seals.
Let’s take a closer look at what an FEP encapsulated helical spring is, the properties of these seals, and the benefits of using them.
What is an FEP Encapsulated Helical Spring
FEP Helical spring seals are created from helical springs. These are elastic coiled mechanical devices. Most consumers are used to seeing helical springs in equipment and devices that store and release energy.
A helical spring seal provides sealing solutions for industries operating in extreme conditions. These seals provide a gas-tight sealing system that meets environmental regulations and reduce fugitive emissions.
FEP encapsulated helical springs seals are housed within a durable, chemical jacket made from fluorinated ethylene propylene. The FEP jacket allows the spring seal to work in chemically corrosive environments or extreme temperatures.
What are the Properties of FEP Encapsulated Springs
FEP encapsulated helical spring seals’ properties make them ideal for use in extreme conditions. A wide variety of industries can use these spring seals to meet their needs.
Property
Test Method
Units
Results
Encapsulation Max Service Temperature
8,000-hour aging tests
°C / °F
204 / 400
Encapsulation Tear Strength
ASTM D1004 (Initial)
N / Kg
2.65 / 0.270
Encapsulation Tensile Strength
ASTM D638 @ 24°C / 75°F
PSI / Bar / MPa
3,400 / 234 / 23.0
Encapsulation Impact Strength
ASTM D256 @ 24°C / 75°F
J/m2
No Break
Encapsulation Hardness
ASTM D2240
Shore
56
Encapsulation Specific Gravity
ASTM D792
g/cm3
2.15
Encapsulation % Elongation @ Break
ASTM D638 @ 24 °C / 75°F
%
325
Encapsulation Flex Modulus
ASTM D790
PSI / Bar / MPa
85,000/5,860 / 586
Encapsulation folding Endurance
ASTM D 2176
Cycles
100,000
Encapsulation Ignition Temperature
Vul045
°C / °F
≥530 / ≥986
Encapsulation Color
Visual
N/A
Off Clear
Moisture Absorption
Vul046a
%
<0.01
Advantages of FEP Encapsulated Spring Seals
FEP encapsulated spring seals have many advantages for industrial settings such as cryogenics, aerospace, and oil. It has some of the same advantages as using PFA encapsulated seals.
FEP encapsulated helical spring seals’ properties make them ideal for use in extreme conditions. A wide variety of industries can use these spring seals to meet their needs.
The FEP jacket protects from corrosive chemicals. FEP has an excellent resistance rating for several chemicals, including the following.
Gasoline
Hydrochloric Acid (1-5, 20, and 30%)
Isobutyl Alcohol
Isopropyl Alcohol
Propane Gas
Sulfuric Acid ( 1-6, 20, 60, and 98%)
Sulfuric Hydroxide (1 and 50%)
FEP also has a wide operating range. It works in a temperature range of -420°F (-251°C) to 400°F (204°C). At cryogenic temperatures, FEP encapsulated helical springs remain flexible. This flexibility makes it preferable to O-rings in a cryogenic environment.
The FEP encapsulated helical springs have low friction. It gives them a minimal stick-slip behavior. A low compression set allows the seal to return to its original shape after deformation.
Best FEP Encapsulated Helical Springs
FEP encapsulated helical seals have several advantages in cryogenic and corrosive environments. They withstand temperatures as low as -251°C (-420°F) and are flexible even at low temperatures.
Advanced-EMC will work with you to find the encapsulated helical spring solution your application needs, from FDA-approved solutions for use with food processing equipment or a reliable, cryogenically compatible solution for a rocket. Contact us today to learn more.
FAQ
Is FEP silicone?
No, FEP stands for fluorinated ethylene propylene. A Teflon coating protects the seal from hazardous conditions such as extreme temperatures and chemical environments. FEP can encase silicone rings, but it is not silicone itself.
Is FEP the same as PTFE?
No, while both are Teflon substances, there are several key differences. FEP is better with gas and vapor permeability, while PTFE has a lower coefficient of friction.
A marine loading arm is a flexible, mechanical arm that assists with 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 either 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, liquified natural gas, liquid oxygen, liquid nitrogen, liquid hydrogen, and liquid helium. The table below shows at what temperatures 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 that has 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 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 can typically withstand 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.
The ability of cryogenic seals to maintain integrity is often critical not just for the processes involved but for the safety of humans, other equipment, and the environment. Seal failure could lead to expensive damage, hefty lawsuits, and even loss of life. Finding reliable solutions that can handle cryogenic temperatures and the pressures involved is challenging but not impossible.
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 standardFDA 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.
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.
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 extremelychemically 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.
In addition to the growing market for commercial applications, Statista estimates that 80 countries will have their own space program by 2025. And a critical factor in the success of any space venture is the type of seals used, including those for space vehicle propulsion systems.
However, finding the optimum sealing solution that provides highly dependable performance can be formidable for several reasons, including extreme pressures and temperatures, chemical compatibility, SWaP, and outgassing, not to mention vendor requirements involving seal size manufacturing.
Extreme Pressures
Depending on the applications, the pressures faced by seals can involve not only high pressures in the range of 100 bar but ultra-high vacuum conditions as well. For example, consider a typical hypergolic rocket propulsion system where pressures can reach between 1,500 and 16,000 psi during Stage 2. To further complicate matters, pressure fluctuations make it much more challenging to retain a reliable seal.
Extreme Temperatures
One of the challenges involved in designing seals for propulsion systems often involves wide temperature ranges from cryogenic to extreme heat. For example, the fuel tanks on many modern rockets must provide sealing at cryogenic level temperatures at which many polymeric and elastomeric materials become brittle and unreliable. And when temperatures fluctuate, traditional seal solutions can experience significant dimensional changes, leading to leaks.
Material Compatibility
Seals for vehicle propulsion systems must be compatible with the fuels involved. For example, cryogenic hyperbolic bipropellants often require seals resistant to oxidizers. Also, keep in mind that, according to a NASA Lesson Learned on Static Cryogenic Seals for Launch Vehicle Applications, seal materials must also be compatible with any anticipated purge or cleaning material that they may come into contact with.
SWaP
SWaP (Size, Weight, and Power) is a significant factor in both space vehicle engineering and aerospace in general. Designs must fall within tight constraints for weight to minimize fuel requirements and size to reduce the overall volume of the space vehicle. In addition, seals, including those for the propulsion systems, must also be optimized to meet SWaP requirements.
Outgassing
Vacuum conditions make outgassing, the release of gasses from solid materials, a serious problem. This phenomenon not only introduces new chemicals to what may already be a volatile environment but can also lead to the deposition of chemicals on critical surfaces. Therefore, NASA makes available spacecraft material outgassing data to aid in selecting safe materials.
Size
Large fuel tanks necessitate large seals. For example, some of the seals for NASA’s SLS (Space Launch System) are over 6’ in diameter, and other fuel tanks have similar requirements. Such seals are challenging to both manufacture and test. Such large seals must usually be custom manufactured with small production runs, making it difficult to balance cost and performance. In addition, not all seal vendors have the manufacturing capabilities required for creating seals of this size at the proper levels of accuracy and precision.
Spring-energized seals, widely used in aerospace, are a practical solution for space vehicle propulsion systems. They can retain seal integrity even when subject to extreme pressure and temperatures due to the energizer. In addition, these seals can account for misalignment, eccentricity, thermal expansion and contraction, wear issues, and other dimensional changes. And they provide a consistent force over a wide deformation range.
The most commonly used materials for spring-energized seals in space environments include PTFE, FFKM, and Hytrel. However, when outgassing is a concern, materials such as PEEK, PAI, PI, Acetal, PCTFE, and antistatic PTFE can be considered. And many of these materials are also available with fillers to enhance their properties.
There are also a variety of choices regarding the spring energizer used. For example, cryogenic and vacuum pressure environments most often implement V ribbon springs (also known as V-springs), helical springs work exceptionally well for static cryogenic applications, and high-pressure conditions usually employ coil seals. And remember that canted coil springs can be highly customized to produce consistent forces.
Advanced EMC: Your Source for Space Vehicle Seals
When it comes to vendor concerns, Advanced EMC has the equipment and experience required to manufacture large seals accurately. Our sealing solutions team has the knowledge and understanding needed to help you at every step of selecting propulsion system seals for everything from small LEO satellites to passenger-laden space vehicles. Contact us today!
Many associate canted coil springs with spring-energized seals, but they can be used for much more. For example, canted coil springs provide a lightweight, easy-to-install alternative to traditional mechanical fasteners.
Canted Coil Springs Fasteners
Canted coil springs can perform three different fastening tasks:
Latch: fastens two parts together
Lock: permanently fastens two parts together
Hold: holds and aligns two parts together
Note that both holding and latching allow for the parts to be disconnected and reconnected. However, if two pieces are locked together, they cannot be separated without either damaging the canted coil spring or the connected parts. Also, note that canted coil springs can be used for quick-release locking, which allows the lock to be bypassed for a quick, simple release. And in all fastening applications, the force required to latch, lock, or hold can be specified by the engineer and accomplished by varying the coil space, wire diameter, spring width, and height.
Advantages of Using Canted Coil Springs as Fasteners
There are several benefits to using canted coil springs instead of more traditional mechanical fasteners. For example, they are easy to install and require no special tools, shortening assembly time. They are also highly reliable and provide dependable performance over thousands of insertion/removal cycles.
Canted coil spring fasteners experience almost no compression set and provide precise, predictable forces even when subject to a wide range of temperatures. Furthermore, the individual coils compensate for mating surface irregularities, misalignment, and dimensional variations.
Their lightweight, compact nature makes them ideal for use in applications where weight and available space are at a premium, and they can also reduce the complexity of assemblies. Finally, and perhaps most importantly, they can serve other functions besides fastening, such as grounding, service as multi-point conductors, and providing tunable EMI/RFI shielding.
Applications of Canted Coil Fasteners
In the medical industry, canted coil springs are used for both latching and holding in various applications, including implantable and non-implantable devices and surgical devices, such as customized tools for use by specific surgeons. An example of an implantable device would be joint replacements that require highly reliable locking.
The oil and gas industry depends on canted coil springs’ highly reliable mechanical fastening capabilities for advanced downhole tools where insertion and breakaway forces must be controllable. In the renewable energy market, canted coil springs work well as connectors within the highly confined environment of turbine nacelles.
The automotive and aerospace industries find them an ideal approach to fastening in applications where SWaP (Size, Weight, and Power) is critical. In addition, canted coil springs are regularly used in the defense industry, where specific applications include aircraft system connectors and optoelectronics connectors. Finally, canted coil springs also work well for underwater, fluidic, and satellite/orbital connectors.
Conclusion
Canted coil springs are a simple, reliable, multi-use alternative to traditional mechanical fasteners. Benefits include the ability to compensate for dimensional changes, lightweight and compact nature, and their ability to reduce the complexity of systems. They can also serve as not only fasteners but EMI shields and multi-point conductors. And keep in mind that their use ranges from medically implantable devices where their ability to respond to particular insertion/removal forces is critical as well as the harsh and dangerous world of downhole tools in the oil and gas industry.
FlexForce Canted Coil Springs
Advanced EMC’s FlexForce Canted Coil Springs are available in 300 Series Stainless Steel, Hastelloy, and copper alloys with gold, silver, or nickel plating. In addition to light, medium, and heavy load spring forces, the forces can be customized. Our FlexForce canted coil springs are available in wire diameters between 0.25 mm (0.010 inch) and 1.50 mm (0.059 inch) and coil widths between 1.5 mm (0.039 inch) and 15 mm (0.591 inch). However, other materials, finishes, and dimensions may be available.
Contact us at bvardeman@gmail.com or call us at (918)-994-7776 to learn more about the FlexForce canted coil springs and how they can benefit your designs.
In addition to the growing market for commercial applications, 
