Tag Archives: spring energized seals

Spring-Energized Metal Seals Help Protect Equipment

Spring-energized metal seals provide numerous advantages in oil and gas applications, including but not limited to MWD and LWD tools, couplings, subsea compressors, enclosures/vessels, christmas trees, electronic submersible pumps and flowmeters. Extreme operating pressures and temperatures, together with more difficult resource recovery, zero tolerance for failure and environmental concerns, are placing unprecedented demands on this equipment.

Traditionally this industry has used solid machined seals that provide high compression loads but lack resilience. They also tend to have relatively high rates of leakage over time as flanges deteriorate. Recent advances in metal seal technology provide controlled compression, high resilience and reduced leakage.

Background

picture of spring-energized metal sealThe industry once used elastomeric seals extensively but discovered they work only within a certain temperature range, becoming brittle in cold and tending to flow at warmer temperatures. At elevated temperatures and pressures, seals can undergo a phenomenon called explosive decompression, extruding out of a flange and resulting in catastrophic failure of the seal. The porosity of elastomeric seals makes them subject to increased leakage over time.

In addition, they are limited in terms of chemical compatibility and have a tendency to degrade with age.

Metal seals, by contrast, offer greater chemical compatibility and longevity. They have no porosity problems and hold up better to aggressive media such as hydrogen sulfide. Metal seals have long been used by industry. Some companies even have their own sealing departments creating custom-machined metal and elastomeric seals to meet their specific requirements.

Among the machined metal seals these in-house departments produce are ring joint flange seals. These seals are inserted into trapezoidal-shaped grooves that allow them to tolerate bidirectional pressures. However, their lack of resiliency and plastic deformation results in extremely high seating loads.

Evolution of metal sealing

First used by the nuclear industry, metal O-rings were among the earliest types of resilient metal-to-metal seals. These were superseded by metal C-rings (Figure 1). Developed for the aerospace industry for weight reduction, these C-ring seals are more resilient than O-rings and require less load, allowing the use of smaller flanges and fewer bolts. Energized by higher pressures, C-rings are capable of achieving good sealing levels. Pressure-energized seals of this nature do not perform as well at lower pressures due to low seating loads and contact stress. In many cases, a silver coating can be used to improve sealing performance provided there is sufficient load to achieve plastic deformation.

Large-diameter spring-energized metal seals were originally developed for the French nuclear power industry. Unlike pressure-energized seals, they function by plastic deformation of a metallic jacket with greater ductility than the flange materials. This deformation occurs between the sealing face of a flange and an elastic core composed of a close-wound helical spring.

Spring-energized seals look similar to spring-energized C-rings but have a soft outer liner and open away from pressure (Figure 2). By contrast, spring-energized C-rings with plating have a hard outer layer and open toward the pressure.

The spring provides a specific resistance to compression, during which the pressure forces the jacket to yield, filling any machined finishes and imperfections on the face of a flange by making positive contact with it. Each coil of the helical spring acts independently, allowing the seal to conform to any surface irregularities on the flange.

Highly engineered with respect to pressure and leakage parameters, spring-energized seals are preferable not only to elastomeric seals but to plated metal C-rings as well. The soft liner/jacketing of these seals is typically three to five times thicker than such plating, providing more range to fill flange imperfections and rougher machined surfaces while eliminating the potential adhesion problems platings have at elevated temperatures.

Oil and gas applications

As noted, spring-energized metal seals are used extensively by the oil and gas industry. In North Sea operations they are used on the flanges of all equipment, where the seals provide longevity in the face of extreme temperatures and pressures. They also are used to protect subsea and downhole electronics that measure, log and transmit data while drilling. The seals can withstand typical operating temperatures from cryogenic to more than 538 C (1,000 F) and are subjected to pressures of up to 35,000 psi in a highly corrosive environment.

Another application for these seals is subsea valving systems, or christmas trees, where they prevent pressures of up to 15,000 psi from blowing out pipes and creating leaks. These also eliminate the potential for explosive decompression, which results in environmental issues and loss of production.

Valves are critical to subsea systems, yet some producers still use polytetrafluoroethylene and other elastomeric materials, which expand and contract drastically with changes in temperature and pose problems above 177 C (350 F). A better solution is to use spring-energized metal seals, which have the resilience to tolerate most operating temperature gradients.

Spring-energized seals are designed on a case-by-case basis. Like most metal seals, they have been used primarily in static applications, where movement due to thermal expansion, pressure cycling and flange deflection is not an issue. Due to the nature of recent oil and gas activity, traditional static applications are few and far between. It is not uncommon to see spring-energized seals in standard dynamic applications such as globe, ball and butterfly valves, where they serve as seat-sealing components. Designs of this type take time to develop.

Notwithstanding the difficulty of understanding flange dynamics and simulating actual operating conditions, semidynamic seals are continuously under development to accommodate greater flange movement. Helpful in this regard is a mnemonic acronym, STAMPS, that defines the basic criteria of seal design and selection, namely size, temperature, application, media, pressure and speed.

Spring-energized metal seals can be designed for a 30- year life while providing low leak rates with zero visible leakage over time. The seals can be manufactured using materials that meet the requirements of the U.S. National Association of Corrosion Engineers.

Another critical condition in oil and gas equipment is abrupt change in the axial direction of pressure, which can cause flanges, piping and seals to flex and shuttle. This can be an issue for some spring-energized seals, which must be specially designed to tolerate extreme bidirectional on/off pressures. It should be noted that bidirectional sealing capability is not a requirement for radial flange seal configurations.

Spring-energized metal seals are the sealing solution of choice for many oil and gas industry applications. The seals not only provide greater chemical compatibility and longevity than elastomeric seals but also the structural integrity that comes from metal-to-metal contact. In addition, they can offer more resilience and lower compressive loads than other types of metal seals.

picture of spring-energized metal sealCapable of handling extremes of temperature and pressure, the corrosion-resistant seals are particularly well suited for subsea applications, where they protect critical equipment and systems from harsh operating conditions. Their ability to absorb the flexing that accompanies temperature and pressure changes also protects piping systems in which the seals are installed.

Spring-energized metal seals meet both U.S. and other countries’ industry standards, helping assure compliance with applicable safety and environmental regulations. New versions are being developed for semidynamic and bidirectional applications, further expanding the capabilities of metal seals.


The original article was written by Jacob Young and Kevin Lamb at Technetics Group. Find the article on their website here.

For more information about spring-energized seals, contact Gallagher Fluid Seals today.

Spring Types and Materials in Sealing Systems

Springs are an integral part of all sealing systems. A simple air cylinder has O-rings to seal in the air, and the O-ring exhibits spring-like qualities to ensure a good seal over a broad temperature range.

But what are the different types of springs and materials in sealing systems? And how do you choose the best for your application?

image of metal spring types

Metal Springs

Metal springs, such as the Cantilever and Canted Coil spring, are used to energize polymers such as Teflon and ultra high molecular weight polyethylene (UHMW) to allow sealing in a wide range of temperatures. Selecting the correct spring material is critical to the life of the seal.

Metal energized seals are often subjected to a wide variety of fluids and temperature ranges, which then requires the correct material choice for the life of the seal in the application.

One of the earliest metal springs was the flat band or marcel expander, often made from common materials like 300 series Stainless Steel or heat treated 17-7 Stainless Steel.

These materials are often chosen for their tensile strength. But due to the cost to manufacture and the high volumes of spring required, these two expanders were often relegated to industrial or aerospace hydraulic systems.

If system fluids were not compatible with Stainless Steel, customers generally went to a different sealing system to avoid the high cost of short runs in these styles of energizers.

O-Rings cover a wide range of temperatures, and fluids, but generally not both. If there are multiple fluids involved, O-Rings often fail to provide compatibility over a range of fluids.

The use of Cantilever, Canted Coil or Helical coiled spring allowed for long runs and lower costs. The most common spring material is Stainless Steel, but these styles of spring lend themselves to materials that have a wide range of chemical and temperature range while maintaining tensile strength.

Alternative Spring Materials

Some of the more common alternative materials are Hastelloy and Elgiloy. While 17-7 is available, it’s seldom used because Elgiloy (while more expensive per pound) is often run at a higher volume, bringing the overall cost down making 17-7 less attractive due to cost.

Another style metal spring for polymers is the Garter spring. Garter springs are normally run on a per job basis, but because it’s made from wire, it can easily be wound from any material like Elgiloy or Stainless.

Garter springs are often used in rubber style lip seals, but we often find them coupled with polymer-style seals.

Mechanical Seals

Mechanical face seals typically marry a material with the fluids the seal will be running in. Mechanical seals have the overall body and internal springs made from specific materials capable of handling variations in temperature and fluids.

PEEK in Seals

Polymers are thought of as seal materials, but PEEK has been used as a spring in polymer-style seals. PEEK can be wound into helical style springs, and also formed into cantilever springs. As a Helical style, it can be wound into a diameter to energize Teflon or rubber lip seals.

If you consider radiation service, a PEEK spring makes an excellent choice keeping metals out of the seal.

How to Choose the Right Spring Material

While there are a variety of metals, often economics determine the practicality of specialty metals.

A consideration is reviewing the hardware used in the application as to what spring material is acceptable in an application. We often review what the customer is using in the rest of the service for determining a spring material.

Temperature is often a key factor in determining materials for spring. Elgiloy tends to do an excellent job in maintaining tensile strength at elevated temperatures.


The original article can be found on Eclipse Engineering’s website and was written by Cliff Goldstein.

Gallagher Fluid Seals is an authorized distributor of Eclipse engineering. For more information about choosing the right spring material for your application, contact our engineering department today.

Case Study: Replacing U-Cups with PTFE Spring Energized Seals in High Temperature Applications

Being commodity items, U-Cups are readily available in a number of materials and can be found on-the-shelf from multiple distributors and manufacturers in many standard sizes.

Named for the shape of their cross-section, a U-Cup’s design will be pressure energized increasing sealing effectiveness when compared to a standard O-Ring.

This means as pressure increases, the sealing lips are continually forced into the mating hardware surface, ensuring good contact at all times.

The simple and easily moldable design is an effective sealing solution to many systems in both hydraulic and pneumatic applications. Modifications in lip thickness and inclusion of an O-Ring Energizer can tailor sealing loads and wear life to specific situations.Spring Seal and U Cup

A key advantage to an elastomeric U-Cup is the relatively small and simple hardware space needed. Because of their flexible compounds, most U-Cups can be installed in a solid gland configuration.

A basic ID or OD groove is all you need for proper seal retention. Plus, no special tools or considerations need to be taken for correct installation.

U-Cups are available in many of the same compounds as standard O-Rings such as Nitrile, Fluorocarbon, and EPDM, but polyurethanes may be the most common material.

Urethane provides a good combination of elasticity/pliability and toughness. Therefore, it exhibits good sealing characteristics as well as, durability and wear resistance.

These desirable qualities make U-Cups an optimal solution for many sealing systems across multiple industries and they can be found in countless standard products. But Eclipse is approached many times a year with customers pushing the limits of standard U-Cups and in need of better solutions.

The Client’s Issue

Eclipse was approached by a leading pneumatic cylinder manufacturing seeking a sealing solution for a unique application.

While U-Cups typically provide optimal sealing performance in pneumatic cylinders, this application presented a difficult challenge.

The air cylinder was to be used as an actuator for a latch on a large industrial oven. While pressures, speeds, and cycle times were nothing out of the ordinary, the temperature at which it had to operate at was — a continuous 500°F.

Continue reading Case Study: Replacing U-Cups with PTFE Spring Energized Seals in High Temperature Applications

Preliminary Considerations for Spring-Energized Seals

springsealsToday we’ll continue our look at spring-energized seals by exploring some of the preliminary considerations to made when working with these seals.

A spring energized PTFE seal is selected to fit an exact set of service conditions found in your application.

Gallagher Fluid Seals recommends conducting a review of the entire sealing environment. You should use the Engineering Action Request (EAR) form before selecting a seal design.

Continue reading Preliminary Considerations for Spring-Energized Seals

New Video: Spring Energized Seals


 

Gallagher Fluid Seals is happy to introduce its latest video, which deals with spring-energized seals.

In the clip above, Gallagher Engineering Manager Craig Beil discusses these seals and the tools and materials used to manufacture them. Gallagher can meet your requirements for PTFE sealing in most, if not all, environments and operating conditions.

Be sure to watch our previous videos on GORE expanded PTFE seals and static seal gaskets to learn more about our products.

And don’t hesitate to contact Gallagher with any questions, whether they’re about spring energized seals or any other product or service. We’ll be happy to hear from you.

What is a Spring Energized PTFE Seal?

spring

Spring energized PTFE seals perform reliably in a variety of applications where conventional elastomeric seals fail due to chemical attack, extreme heat or cold, friction, extrusion or compression set.

PTFE seals have three basic design elements:

  • A pressure-actuated U-shaped jacket
  • A metal spring loading device
  • High performance polymeric seal materials

So what is a spring energized PTFE seal? It’s a spring-energized U-cup that uses a variety of jacket profiles, spring types and materials in rod and piston, face and rotary seal configurations. They are used when elastomeric seals fail to meet temperature range, chemical resistance or friction requirements.

Jacket profiles are made from PTFE and other high performance polymers. Spring types are available in corrosion-resistant alloys, including stainless steel, Elgiloy and Hastelloy.

Continue reading What is a Spring Energized PTFE Seal?