Rotary Shaft Seals for Oil and Gas Industry | Advanced EMC Technologies
by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Sealing the Depths: Spring-Energized PTFE Seals for HPHT Downhole Tools

Oilfield environments often require PTFE seals for HPHT (High-Pressure, High-Temperature) downhole tools. And this should come as no surprise, because oilfield environments represent some of the harshest sealing conditions on Earth. Temperatures can exceed 200°C and pressures can easily surpass 20 ksi. There will be exposure to media, including hydrocarbons, hydrogen sulfide (H₂S), CO₂, and amines, which can quickly render traditional sealing solutions ineffective. In such unforgiving conditions, even minor seal failure can trigger catastrophic leaks, equipment damage, or non-productive time (NPT) costing thousands of dollars per hour. That’s where spring-energized PTFE seals come into play: they are engineered precisely for high-pressure, high-temperature (HPHT) downhole environments where traditional materials fall short.

In this blog post, we’ll explore the use of spring-energized PTFE seals for HPHT applications, as well as material selection and design considerations, followed by an overview of their applications in the oil and gas industry.

Why Consider Spring-Energized PTFE Seals for HPHT Oil & Gas Environments

Unlike elastomeric seals, which tend to soften, swell, or degrade when subjected to harsh fluids and heat, spring-energized PTFE seals combine the advantages of fluoropolymer chemistry with the power of metal energizers. The result is a hybrid sealing solution that can maintain a consistent sealing force in the most demanding oil & gas applications. This solution is able to compensate for thermal expansion and resist creep under sustained load. In the depths of oil wells or even in subsea installations, this hybrid spring-energized PTFE sealing solution can make the difference between failure and flawless performance.

The HPHT Challenge: Pressure, Temperature, and Chemistry

The deeper a system operates, the more intense the pressure and temperature gradients become. Under extreme differential pressure, soft polymers tend to extrude into clearance gaps between mating surfaces, especially in dynamic or reciprocating applications. At the same time, thermal cycling in HPHT environments causes differential expansion between metal housings and polymer elements. These dimensional shifts alter contact pressure and can lead to intermittent leakage or total seal failure.

Chemistry further complicates the situation. Aggressive fluids such as drilling muds, completion brines, and sour gases attack the molecular structure of conventional elastomers like NBR or FKM. When combined with vibration, mechanical shock, and pressure fluctuations, these factors cause compression set, abrasion, and fatigue cracking. In essence, a seal in a downhole environment must perform under a complex blend of mechanical, chemical, and thermal stress—often simultaneously and continuously.

Why Spring-Energized PTFE Seals Excel in HPHT Conditions

Spring-energized PTFE seals are capable of solving some of the weaknesses that are inherent in traditional designs. The PTFE jacket provides a low-friction, chemically inert sealing interface, while the internal metallic energizer (often a canted coil, V-spring, or helical design) applies a consistent load across the sealing surface. This ensures reliable contact pressure even when temperature or system pressure fluctuates dramatically.

As well pressure increases, the system itself reinforces the seal: fluid pressure energizes the PTFE jacket, pushing it against the mating hardware for a tighter, more reliable seal even in the presence of wide-ranging pressure changes and across wide temperature ranges. Filled PTFE jackets, such as those reinforced with glass, graphite, or carbon, can also minimize cold flow and enhance wear resistance, further extending service life in dynamic applications.

Because PTFE’s coefficient of friction is among the lowest of any solid material, it minimizes heat generation and stick-slip behavior in reciprocating or rotating motion. This self-lubricating, no stick quality is particularly useful when used with directional drilling motors and measurement-while-drilling (MWD) systems, where frictional heating can distort readings or damage sensitive components.

Material Selection for Downhole Sealing

Material selection defines the performance window of a seal. Virgin PTFE offers excellent chemical resistance and thermal stability, but has its limitations. PTFE’s natural creep resistance under prolonged load can be limited; this issue can be addressed through the use of fillers such as carbon, bronze, or glass are incorporated to increase the elastic modulus and wear resistance. These filled PTFE formulations combine durability with the chemical inertness essential for downhole fluids.

The choice of spring material is also critical. Inconel 718 and Elgiloy are common due to their superior strength, fatigue life, and corrosion resistance in sour environments. These two alloys in particular maintain a highly stable spring force even after extensive compression cycles. They aid the PTFE spring-energized seal in ensuring consistent sealing load over long service intervals.

Design Considerations for Spring-Energized PTFE Seals for HPHT Downhole Applications

Precision in design directly impacts seal life. Hardware surface finish must be carefully controlled (Ra values below 8 µin are typical for dynamic sealing surfaces) to prevent wear and micro-leakage. Extrusion gaps must be minimized, particularly when pressure exceeds 15 ksi. Where necessary, designers incorporate anti-extrusion rings or step-cut backup rings to maintain stability.

Thermal expansion is another major design consideration for downhole applications. PTFE expands significantly more than steel when heated, which can affect gland squeeze and frictional characteristics. Engineers must calculate clearances and tolerances to account for this mismatch.

Seal geometry also matters. Single-lip designs are suitable for rotary applications, while double-lip or pressure-balanced configurations are preferred in static or reciprocating systems to prevent fluid entrapment. Venting pathways behind seals may also be required to prevent trapped pressure differentials, which can cause extrusion or blowout during depressurization cycles.

Applications Across Oil and Gas Systems

Spring-energized PTFE seals have proven themselves across a wide range of oil and gas applications. In MWD (Measurement While Drilling) and LWD (Logging While Drilling)  systems, they protect internal electronics from drilling mud and hydrocarbon ingress while enduring continuous vibration and pressure pulsing. In completion tools, packers, and valves, these seals maintain long-term reliability under chemical attack and mechanical load.

Subsea valves, connectors, and actuators rely on spring-energized PRFE seals for high-pressure, high-temperature applications in oil & gas to maintain zero leakage across temperature extremes and under deep-water hydrostatic pressure. High-pressure pumps and reciprocating actuators use these seals to minimize downtime, extend maintenance intervals, and maintain consistent performance across thousands of operational cycles.

Performance that Endures Where Elastomers Fail

In HPHT downhole service, traditional elastomer seals simply can’t cope with the combined assault of heat, pressure, and chemistry. Spring-energized PTFE seals for high-pressure, high-temperature applicants bridge the gap between flexibility and endurance, offering predictable performance where failure is not an option. Their combination of low friction, corrosion resistance, and mechanical adaptability makes them indispensable in modern oilfield equipment.

As operators push deeper into the earth’s crust and toward higher-pressure, higher-temperature reserves, the demand for advanced sealing materials will continue to rise. Spring-energized PTFE seals—especially those engineered with filled PTFE and high-performance alloys—represent the next generation of reliability in extreme sealing applications.

If you are looking for a reliable sealing solution for HPHT download tools, contact Advanced EMC today. Our engineering team is ready to work with you to extend equipment life, enhance safety, and maintain uptime in some of the world’s most demanding operating environments.

by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Designing Polymer Seals for Dynamic Applications: Balancing Wear, Friction, and Thermal Expansion

Designing polymer seals for dynamic applications can be a challenging task. Polymer seals have proven vital in dynamic applications such as rotary shafts, reciprocating pistons, and oscillating systems. However, dynamic conditions can introduce challenges that are not found in static conditions. These challenges include continuous motion, heat buildup, wear mechanisms, and variable pressures.

This blog post examines three key challenges involved in dynamic sealing: wear, friction, and thermal expansion.

The Role of Polymers in Dynamic Seals

Engineering polymers such as PTFE and PEEK offer several advantages over both traditional metals and elastomeric seals in dynamic systems. Such benefits include outstanding performance even in operating environments that include extreme temperatures and require excellent chemical compatibility and extremely low friction. And engineers can further enhance the most desirable features of these polymers through the use of fillers and blends (e.g., graphite, carbon, bronze, glass, and even PTFE).  Polymer seals are also lightweight and ideal for compact systems where space is limited.

Balancing Wear Resistance

One of the most limiting factors in dynamic seal applications is wear. The three most common wear mechanisms involved are adhesion, abrasion, and fatigue. 

  • Adhesive wear happens when the seal momentarily sticks to the counterface, thus tearing material away from the surface and resulting in material transfer or scoring.
  • Abrasive wear occurs when hard (abrasive) particles or rough surfaces cut into the polymer, creating grooves and accelerating material loss.
  • Fatigue wear takes place when the seal is subject to repeated cyclic stresses that form micro-cracks, eventually leading to surface flaking or spalling.

Polymers can effectively address wear issues. PTFE effectively combines extremely low dynamic friction and excellent self-lubrication. This combination makes it well-suited for high-wear dynamic applications such as piston rings in gas compressors. Another example is the use of PEEK seals in aerospace actuators, where its high resistance and ability to maintain mechanical strength at high temperatures make it an excellent choice for applications involving cycling under high loads.

One of the most effective ways to further improve the wear resistance of PTFE and PEEK dynamic seals would be the use of filled composites, the use of appropriate surface finishes on countersurfaces, and wise design choices that minimize localized stresses.

Managing Friction

Friction is particularly problematic in dynamic seals, as it leads to heat generation, energy loss, and accelerated degradation. This problem leads to a trade-off between achieving an effective sealing force and maintaining low friction. 

PTFE is an excellent example of how low-friction engineering polymers can help achieve this balance. PTFE has the lowest coefficient of friction of any engineering polymer, and is far less than that of metal or elastomers. Its self-lubricating nature keeps friction very low at the shaft-seal interface, which will minimize heat buildup and lost energy. In fact, it can even reduce energy loss during dry running conditions. The strength and modulus of elasticity of PTFE can be modified through the use of fillers and hybrids.

Spring-energized seals, which use a metallic energizer to keep the seal lip in contact with the sealing surface and generate a predictable, consistent load to compensate for problems such as wear, thermal expansion, and pressure changes. As the load is kept within a predictable range, the friction is also kept at consistent levels over a well-distributed sealing force.

Thermal Expansion Considerations

Polymers indeed possess a higher coefficient of thermal expansion when compared to metals and most elastomers. Changes in dimensions can impact clearance, sealing performance, and contact pressure in dynamic sealing applications. In aerospace and automotive applications, for example,  there can be an abundance of extreme temperature cycling, which is going to be especially problematic in rotary shaft seal designs. 

There are several approaches to minimizing the impact of thermal expansion, starting with customized PTFE or PEEK polymer blends with materials that will lower the coefficient of thermal expansion without compromising wear resistance or friction.

The use of spring-energized seals allows the polymeric sealing lip to remain in contact with the sealing surface despite changes in geometry or alignment, whether they are due to wear, thermal expansion, or thermal contraction in the presence of extreme temperature cycling. 

Note that both of these approaches can be further enhanced through predictive modeling of how the seal will deform under thermal stress.

Polymer Seals for Dynamic Applications: Design Best Practices

Here are some straightforward design best practices related to dynamic sealing challenges:

  • Always match the seal geometry to motion type (i.e., rotary vs reciprocating).
  • Carefully consider the allowable surface roughness and hardness of mating surfaces.
  • Respect the PV limit (pressure × velocity) when selecting a polymer.
  • Remember the importance of predictive modeling (finite element analysis for thermal and tribological performance).
  • Always test under real-world operating conditions before full-scale deployment.

Conclusion

Dynamic sealing requires balancing wear, friction, and thermal expansion, with no single solution that fits all. Fortunately, advances in polymer science and composites make it possible to design seals that meet increasingly demanding requirements. However, engineers must still carefully match polymer formulations, energizers, and geometries to the unique conditions of each application.

If you need a dynamic seal for an application, contact the experts at Advanced EMC. Our engineers are very experienced and highly knowledgeable, able to take you all the way from seal design and material selection to testing.