Redefining The Limits Of Sealing Performance In Fluid Handling

TL;DR: Metal spring energised seals offer reliable long-life sealing in extreme pressure temperature and chemically aggressive environments where elastomeric seals fail. Their ability to perform in cryogenic LNG systems high-pressure oil and gas wells and chemical processing applications makes them a robust alternative for critical fluid handling equipment.

In industries where performance under pressure is non-negotiable, selecting a seal is a critical decision. For decades, elastomeric seals have been the default choice: flexible, cost-effective and easy to install.

But as operational environments grow more extreme, from cryogenic Liquid Natural Gas (LNG) systems to high-pressure oil and gas wells, elastomers are often pushed beyond their capabilities.

Enter metal spring-energised seals (MSEs): an innovative and versatile solution engineered to redefine the limits of sealing performance. In these demanding environments, MSEs offer a robust solution for these applications.

Why Choose Metal Spring-Energised Seals?

First developed in the 1950s, MSEs have a proven track record in critical service applications.  They deliver exceptional reliability and long service life, particularly in environments with maintenance challenges, such as valves installed deep within a deepwater oil & gas well. With extensive customisation options for jacket materials, spring types and geometries, MSEs can be installed in both static and dynamic applications.

A key factor in the longevity of the MSE is its ability to resist chemical attack. This makes metal spring energised seals indispensable in oil and gas chemical processing and industrial manufacturing environments where exposure to aggressive fluids is common.

Variations in MSE jacket geometry may also include additional features, such as debris exclusion in abrasive applications, or lubrication grooves for applications sensitive to friction increases.

Where Metal Spring Energised Seals Are Used

The adaptability of MSEs means metal spring energised seals are utilised across a wide range of demanding industrial applications. Examples of where MSEs can be used include:

• Oil & Gas: used in safety valves in Completions tools where requirements for 25-year lifetime combine with operational conditions like rapid gas decompression, exposure to abrasives in drilling muds and temperature create challenging conditions
• Chemical Processing: Exposure to multiple fluids with cryogenic conditions makes the MSE an ideal candidate for use in pumps, compressors and valves
• Industrial Applications: Ability to customise jacket configurations and sizes allow MSEs to be used in fluid dispensing systems and other specialised equipment.

How Metal Spring Energised Seals Work

“Metal spring-energised seals deliver unmatched reliability and versatility in environments where elastomeric seals meet their limits.”

An MSE, which can also be considered a type of “lip seal”, combines a thermoplastic jacket with an internal metal spring. The cavity of the seal must face the media being sealed because the MSE does not generate sealing force on its own. Instead, it relies on two mechanisms:

• Spring Deflection: The internal spring is installed with an initial compression or squeeze, providing initial sealing force and enabling performance at low pressures
• System Pressure: As pressure rises, it acts outward through the seal cavity, pushing the jacket lips outward and dramatically increasing sealing force.

Spring deflection and system pressure work in tandem to form a robust seal. As system pressure increases, the lips deform further, expanding the sealing footprint. Eventually, system pressure becomes the dominant contributor to sealing force.

However, the constant spring force remains, providing a continuous lower level of sealing force even in situations with rapid removal of or drops in system pressure. This is what makes MSEs strong performers in pressure cycling situations when compared to elastomeric solutions

When to Use MSEs

“A key factor in the longevity of the MSE is its ability to resist chemical attack.”

MSEs outperform elastomeric seals in scenarios such as:

• Cryogenic temperatures: The low temperature capabilities of an MSE make the seal a preferred choice in equipment such as valves in LNG processing systems where sealing temperatures can fall well below -60°F (-52°C), a temperature where elastomers start to become hard and brittle.
• High-pressure environments: Capable of withstanding pressures up to 19,000 PSI and with certain designs, up to 30,000 PSI, MSEs are ideal for sealing safety valves installed in high pressure oil and gas wells.
• Exposure to multiple fluids: PTFE jackets and stainless-steel springs resist chemical attack, reducing premature failure, especially in chemical processing applications where equipment may have exposure to multiple fluids.
• Dynamic applications: Low friction properties make MSEs suitable for moving parts.
• Rapid gas decompression resistance: Thermoplastic jackets resist gas absorption, while springs maintain sealing force through pressure cycles.
• Hard to access installation: Long-life reliability minimises costly or impractical replacements, such as in downhole completion tools requiring more than 25 years of service.

In some cases, MSEs can replace O-rings in the same gland, though open or two-piece glands are generally recommended for ease of installation.

Materials and Design Options for Metal Spring Energised Seals

MSEs can be engineered to provide optimal performance in specific applications. This process includes selecting the jacket and spring materials as well as the type of spring that will be installed in the MSE.

MSE jackets are typically made from thermoplastic materials including PTFE. PTFE (Polytetrafluoroethylene) is the one of the most common choices for MSE jackets due to its chemical inertness, low friction and wide temperature range. Fillers can enhance creep resistance, high-temperature performance and wear characteristics.

“Spring deflection and system pressure work in tandem to form a robust seal.”

When it comes to the springs, there are quite a few options available for the material. Common metals offered include stainless steel, Hastelloy, Elgiloy and Inconel with configurations such as finger coil, canted coil, or standard coil. Each type offers unique energising characteristics for optimal performance.

Designs can be tailored for specific needs, for example, scraper lips for non-lubricated applications with abrasive media, preventing contamination and reducing wear. An extended heel in either rod or piston configuration might be selected for a high temperature, high pressure application, while a face seal may be the appropriate choice for a static application.

Providing full details of an application, including temperature conditions, pressure variables, fluid exposure and gland details will allow engineers to select the appropriate jacket and spring materials and design a solution that works best in that equipment.

The Bottom Line

Metal spring-energised seals deliver unmatched reliability and versatility in environments where elastomeric seals meet their limits. MSEs’ ability to withstand extreme temperatures, pressures and chemical exposure should make them a strong candidate for applications pushing the boundaries of temperature, pressure and chemical exposure.

Whether it’s a 25-year downhole installation or a compressor in a chemical plant subject to rapid gas decompression conditions, MSEs mitigate the possibility that a piece of equipment will experience unplanned downtime and provide a viable solution when an elastomeric seal won’t work.

FAQs

What are metal spring energised seals?
Metal spring energised seals are high-performance sealing solutions that use a thermoplastic jacket and internal metal spring to maintain sealing force under extreme conditions.

Why choose metal spring energised seals over elastomer seals?
Metal spring energised seals outperform elastomers in high pressure cryogenic temperature chemical exposure and pressure cycling applications.

Where are metal spring energised seals commonly used?
They are widely used in oil and gas chemical processing LNG systems compressors pumps and critical valve applications.

How do metal spring energised seals work?
They rely on spring deflection for initial sealing force and system pressure to increase sealing effectiveness as pressure rises.

Can metal spring energised seals be customised?
Yes metal spring energised seals can be customised through jacket materials spring types geometries and design features to suit specific applications.