Tag Archives: spring energized seal

Metal Seals for Critical Valve Applications

picture of metal seals

In a typical oil refinery or chemical processing plant, 60% of fugitive emissions are attributable to leaking valves. Of these, nearly 80% are released at valve stems. Also contributing to valve failures, are leaks at the bonnet, flanges and seats. As operating conditions in these and other industries continue to subject valves to ever more extreme temperatures and pressures, sealing them effectively poses a challenge that cannot be met with traditional materials and methods. Soft, compressible elastomers provide good sealing performance, but they are porous and cannot withstand temperatures in excess of 482°F (250°C). They also become hard and brittle in cryogenic service. Metal seals have much greater temperature capabilities, high mechanical properties, lack of porosity and long shelf life. Ductility and elasticity are typically the limiting factors.

Today more resilient, metal-to-metal seals are available and being used in valves operating under extreme conditions. Spring- and pressure-energized metal seals function much like a gasket between two flanges with little or no relative motion between them.

picture of c-ring metal seals
C-Ring Metal Seals

The sealing principle of spring-energized seals is based on plastic deformation of a jacket that is more ductile than the mating surface. This deformation occurs between the sealing face and an elastic core composed of a closely wound helical spring. The spring provides specific resistance to compression, during which the resulting pressure forces the jacket to yield and fill flange imperfections. Each coil of the helical spring acts independently, allowing the seal to conform to any surface irregularities. This combination of elasticity and plasticity provides an extremely effective seal even under the decompression cycles. Continue reading Metal Seals for Critical Valve Applications

Why an Extrusion Gap is Important

“How much pressure can this seal handle?”

The answer to this question depends on a number of parameters and conditions. But the principle limiting factor in the pressure handling of any seal system is the extrusion gap.

Commonly referred to as the “E-Gap,” the extrusion gap is one of the most critical design aspects in any high-pressure application. Seal design, type, and material are all influenced by the extrusion gap and the desired pressure handling capability.

What exactly is an extrusion gap, and why is it so important in the successful design of a sealing system? Let’s find out.

The Basics: What is an Extrusion Gap?

In terms of sealing systems, the extrusion gap is defined as the clearance between the hardware components.

In a piston configuration, this would be the clearance between the piston and bore. In a rod configuration, this is the clearance between the rod and housing it’s passing through.

The extrusion gap can be expressed in terms of radial or diametral clearance, which can lead to some confusion. Our partners at Eclipse define the E-Gap by stating it as the radial clearance. The radial clearance is equal to the diametral clearance divided by two.

 

It’s important to note that while hardware components might be machined to have a specified clearance, this gap might not be perfectly realized or maintained. Continue reading Why an Extrusion Gap is Important

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.

The Manufacturing Challenges of Tiny Spring Energized Seals

tiny spring energized sealEclipse Engineering has in-house capabilities to manufacture seals up to 55 inches in diameter, and over 100 inches through production partners.

While seals with huge diameters certainly grant their own significant levels of intricacy, here we’ll look at the other end of the spectrum: the micro-sized seals.

We won’t just look at a simple seal ring, but an inherently more complicated and geometrically detailed spring energized seal. As we’ll see, very small diameters make multiple manufacturing aspects more involved and challenging.

The Client’s Issue

A sealing solution in a customer’s epoxy dispensing equipment. They needed an effective seal for the reciprocating rod responsible for the flow-control and metering of the epoxy while being dispensed.

Operating Conditions:

  • Reciprocating Rod Seal
  • Epoxy Dispensing Head
  • Rod Diameter: 1.2mm [0.047”]
  • Stroke Length: 6mm [0.236”]
  • Cycle Rate: 15 per min
  • Media: Epoxy
  • Operating Pressure: 1,500 PSI
  • Temperature: 70° to 150°F

In general terms, most viscous media sealing solutions have three things in common:

  1. A variant of UHMW for the seal jacket,
  2. heavy spring loading, and
  3. multiple point contacts with increased interference.

In most cases, multiple nested V-Springs are incorporated to provide optimal load and energize the compound contact points on the seal. With this formula, we’ve had great success sealing media like epoxy, urethane, silicones and acrylics.

The heavy loading is necessary to effectively wipe the reciprocating rod. This is balanced with the correct material and design geometry to provide long wear life of the seal, which has the potential to be compromised under such loading.

The challenge in this case was to incorporate these same proven principles in a micro-sized seal.

The Eclipse Solution

Continue reading The Manufacturing Challenges of Tiny Spring Energized Seals

Angled Spring Grooves for Custom Spring Energized Ball Seats

A ball valve is a simple and robust valve used in applications and industries across the spectrum. It consists of a ball with a hole through the center that can be rotated 90°.

custom spring energized ball seat

The hole is either aligned with flow and open, or perpendicular to flow and closed. The straightforward, quarter-turn action is fast and simple to operate, and the position of the handle provides a clear indicator of whether the valve is open or closed.

Most ball valves are typically used as a shut-off valve. Many households likely use ball valves at some point in the water supply plumbing.

Not relegated to common plumbing, many industries use ball valves for critical control applications including aerospace and cryogenics. Their reliable operation and high-pressure handling ability make them an attractive solution for many specialty operations.

Seals Inside a Ball Valve

The seals inside the ball valve play an important role in their performance and reliability. There are two main seals in a common ball valve, which are referred to as seats.

The seats are typically machined or molded to match the diameter of the ball and are mechanically compressed against the ball face. Seat material varies by application needs, but virgin PTFE is frequently used for this application.

The Client’s Issue

The customer wanted a very specialized ball seat: utilizing a spring energizer in the seat. While easy to suggest, this would create a significant challenge in how the seal is manufactured.

The customer was looking for a sealing solution for a ball valve in their industrial gas processing plant. The ball valve would serve as a critical shut-off point in the system. The valve would be actuated by an electric motor, and could therefore be operated remotely.

The customer was looking for an improvement in the overall wear life of the ball seats, while still providing consistent and predictable actuation torque. Being motor activated, the torque required to move the ball open or closed was limited—so the friction generated by the ball seats would need to be carefully controlled.

Operating Conditions:

  • Ball Valve Seat
  • Ball Diameter: Ø2.500”
  • Media: Petroleum Processing Gases
  • Pressure: 100 PSI
  • Temperature: -40° to 175°F

The Challenge

Continue reading Angled Spring Grooves for Custom Spring Energized Ball Seats

Sealing Solutions for Subsea Systems in the North Sea

Innovative Subsea Processing Technologies

The Aasgard oil and gas field in the North Sea has been operating since 1999. Innovative subsea processing technologies were used to compress the oil and gas on the site’s seabed to improve recovery rates as the field ages and as equipment begins to draw from increasingly deeper subsea reservoirs. The operator required seals for the lid and body of the control power distribution unit in order to protect its vital electronics in the harsh, unforgiving subsea environment.

As a globally trusted source for engineered components, seals, assemblies, and sub-systems for demanding environments, Technetics was uniquely positioned to evaluate and specify a sealing solution for this application. The system designer and Technetics engineers subsequently underwent a two-year testing phase to examine the performance of a variety of sealing options.

Demanding Subsea Environment

Due to the extremely demanding environment in which the subsea Subsea Techneticspressure vessel would be operating, finding a sealing solution that would meet both the operator’s and governmental requirements turned out to be lengthy and complex. Specifically, the operator noted that the seal needed to meet high-pressure requirements with a strict leak rate of 10-11 cc/sec He for a period in excess of 10 years.

Based on the extensive testing results, Technetics identified a HELICOFLEX® spring energized metal seal as the ideal sealing solution. The HELICOFLEX® seal consists of a close-wound helical spring core and outer jacket material that provides a highly ductile and plastic sealing surface. This combination of materials allows it to provide consistent and reliable sealing performance under uneven flange pressures and imperfections in the flange surface. Benefits of the HELICOFLEX® seal include helium tightness, long seal life, and excellent corrosion resistance.

This solution not only secured the electronic equipment inside the vessel, but it also alleviated any environmental and safety concerns from potential leakage and failure of the system. Thus, the installation of the HELICOFLEX® spring energized metal seal provided the required sealing integrity.

To learn more about the HELICOFLEX® seal, download the HELICOFLEX® seal PDF.


The original article can be found on Technetics’ website.

To learn more about Technetics products, speak to a Gallagher representative today by calling 1-800-822-4063