Metal Seals & Spring‑Energized Seals: When to Replace Elastomer O‑Rings for Extreme Conditions

Elastomeric O‑rings are the workhorses of industrial sealing. Their simple, torus‑shaped geometry and low cost make them ubiquitous in pumps, valves, compressors and countless other components. When compressed between two surfaces, an O‑ring creates a barrier that prevents liquids or gases from escaping. At moderate pressures this compression actually improves the seal, but there is a limit. As pressure continues to rise or motion becomes dynamic, the elastomer can deform beyond its elastic limit and can extrude from its groove, leading to leaks. Repeated cycling also wears down the material; Depending on the material used, O‑rings can eventually harden, crack or swell and must be replaced. Even high‑performance elastomers like FKM (Viton®) and AFLAS® have finite temperature and chemical limits - AFLAS maintains its properties up to about 232 °C (450 °F) and Viton up to 225 °C (437 °F). For applications that venture beyond these boundaries - extreme heat, cryogenic temperatures, high pressures, aggressive chemicals, intense radiation or deep vacuum - the best solution may be to replace the elastomer entirely. This article explains when to make that transition and introduces two robust alternatives: metal seals and spring‑energized seals.

Why elastomer O‑rings have limits

O‑rings seal by deforming elastomeric material. When two mating surfaces squeeze the ring, the rubber flows and fills micro‑irregularities to block passageways. The more internal pressure applied to the joint, the more the O‑ring is distorted in its groove; at first this increases sealing force, but beyond a certain pressure or under dynamic loads the material can extrude or tear. Other factors that hasten failure include:

• Extreme temperatures. Most rubber compounds degrade above ~205 °C and become brittle below -50 °C. Even advanced elastomers like FKM and AFLAS are rated to ~225-235 °C. Cryogenic temperatures can cause glass‑transition embrittlement, leading to leaks.
• High pressures and explosive decompression. Rapid gas decompression forces trapped gas to expand within the elastomer, creating blisters or cracks. Canyon’s own blog on low‑temperature FKM and AED‑resistant materials stresses how explosive decompression requires special compounds and testing.
• Aggressive chemicals and sour gases. Hydrogen sulfide, amines, super‑critical CO₂ and other media attack elastomers. The AFLAS vs. Viton article notes that AFLAS resists bases, acids and solvents better than Viton yet still requires careful selection depending on H₂S concentration.
• Vacuum and radiation. Elastomers outgas under high vacuum and can be damaged by ionizing radiation. Vacuum applications often use vacuum‑baked O‑rings or replace elastomers with metal seals for ultra‑clean environments.

Because these factors often coincide in aerospace, nuclear, semiconductor and oil‑and‑gas systems, engineers need sealing solutions that go beyond elastomer technology. There are many options available, but in this post we will focus on two families: metal seals and spring‑energized seals, which offer the durability and performance needed in extreme service.

Metal seal basics

A metal seal replaces the polymer with a thin‑walled ring of stainless steel, Inconel or other high‑performance alloy. During installation the seal deforms plastically and elastically to create a tight interface. Notes that metal seals come many formats, but we will focus on these three energization types: self‑energized C‑rings, spring‑energized seals and pressure‑energized designs. Metal C‑rings are self‑energizing; their C‑shaped profile springs back after compression, allowing them to seal internal, external and axial pressures without an additional energizer. Pressure‑energized designs use system pressure to generate a hydrostatic load, enabling metal seals to withstand applications exceeding 25,000 psi.

Types of metal seals

Three primary metal seal styles and their preferred applications:

• Metal C‑rings. These versatile seals handle moderate to high pressures and adapt to pressure and temperature fluctuations. Their cross‑section is open on one side, giving the ring resilience and allowing it to flex under load.
• Metal O‑rings. A fully enclosed circular tube provides a reliable seal across a broad temperature range, making metal O‑rings a classic choice for static or slow‑dynamic applications. They are often selected for simplicity and cost‑effectiveness.
• Spring‑energized metal C‑rings. A helical or canted coil spring inside the C‑ring exerts constant radial force. This design maintains contact under extreme pressure fluctuations or axial movement, preventing leakage even when mating surfaces shift.

Metal seals can be tailored for internal or external pressure service, and designers adjust wall thickness, cross‑section and material hardness to meet specific load requirements. To further improve sealing, manufacturers plate or coat the sealing surface with gold, silver, tin or PTFE. These coatings create a malleable outer layer that reduces friction and allows the metal to bed into microscopic surface imperfections. High‑performance alloys such as Inconel, Hastelloy and stainless steel 321 offer exceptional corrosion resistance and comply with industry standards (NORSOK M‑710, NACE TM0297, ISO 23936‑2, etc.).

Pros and cons of metal seals

Metal seals excel when operating conditions exceed the capability of polymers:

• Temperature extremes. Some metal seals handle continuous service above 300 °C and short excursions to over 1,200 °C (≈2,200 °F). They also remain leak‑tight in cryogenic conditions.
• High pressures. Metal seals can withstand vacuums and pressures well above 7,000 psi, with pressure‑energized designs rated to tens of thousands of psi.
• Chemical and radiation resistance. Metallic alloys are inert to most chemicals and immune to radiation damage, making them ideal for nuclear, deep‑space and corrosive process environments.
• Low outgassing. Unlike elastomers, metal seals do not release volatiles in vacuum systems.

However, there are trade‑offs. Metal O‑rings are generally more cost‑effective but may require more frequent replacement under severe thermal cycling. Metal C‑rings offer durability and reliable performance but can be expensive. Spring‑energized C‑rings provide unmatched reliability with minimal maintenance but have the highest initial cost. Installation and groove design are also more complex than with elastomers, and the rigid metal can damage mating surfaces if not carefully plated or coated.

Spring‑energized polymer seals

Spring‑energized seals bridge the gap between elastomers and metal by combining a high‑performance polymer jacket (usually PTFE) with an internal metal spring. The use of PTFE and other advanced polymers allows these seals to operate from -436 °F to 575 °F (≈ -260 °C to 302 °C). The integrated spring exerts continuous radial force, ensuring a reliable seal even as the polymer wears or deforms. Key advantages include:

• Low friction and wide temperature range. PTFE’s intrinsic lubricity minimizes wear and energy loss. This makes spring‑energized seals ideal for dynamic applications like shafts and actuators.
• Enhanced durability. The spring maintains contact pressure throughout the seal’s life, allowing longer maintenance intervals and reducing downtime.
• Chemical compatibility. PTFE and reinforced blends resist aggressive chemicals, solvents and gases. Reinforcements such as carbon or glass fibers improve wear resistance.
• Extreme pressure capability. These seals handle pressures over 60,000 psi and temperatures from -436 °F to 575 °F. Canyon Components’ own Spring Energized Seal (SES) page notes that some SES are rated for pressures over 60,000 psi and temperatures ranging from cryogenic -450 °F up to 300 °C.

Spring‑energized seals are available with different spring designs. Cantilever springs provide moderate load and are suited to dynamic applications requiring wiping action. Slantcoil springs offer a wide deflection range and constant load for precision instruments. Helical springs deliver high unit load for static or slow‑dynamic high‑pressure service. These seals excel in static, reciprocating and rotary service: they seal flanges, valve bodies and hydraulic cylinders. Material options include virgin PTFE, carbon‑filled PTFE, glass‑filled PTFE, UHMW‑PE, PEEK and FDA‑compliant blends; spring materials include various stainless steels and Hastelloy.

When to replace elastomer O‑rings with metal or spring‑energized seals

Selecting the right seal depends on balancing operating conditions, material capabilities and cost. The following guidelines help determine when an elastomeric O‑ring is no longer sufficient:

• Temperatures beyond elastomer limits. If continuous operating temperatures exceed roughly 200 °C or fall below -50 °C, certain elastomers may harden or soften. While specialty elastomers may solve some of the challenges of a given application, sometimes elastomers will not be satisfactory. Metal seals and spring‑energized PTFE seals maintain integrity from cryogenic conditions up to 300 °C or more.
• High pressures and extrusion risk. Conventional elastomeric seals are typically limited to about 1,500-10,000 psi depending on groove design, hardness, and use of backup rings; at higher pressures they can extrude from the groove and fail. Metal seals handle tens of thousands of psi and spring‑energized PTFE seals can reach over 30,000-60,000 psi.
• Rapid gas decompression. Explosive decompression in high‑pressure gas systems can rupture elastomers. Anti‑explosive decompression grades of FKM exist (see Canyon’s article on low‑temperature FKM), but for the highest safety margins metal or SES solutions are preferred.
• Aggressive chemicals and sour fluids. If the medium attacks conventional elastomers - strong acids/bases, solvents, aromatic hydrocarbons or sour gas -spring‑energized PTFE seals offer chemical inertness. Metal seals made from Inconel or Hastelloy also withstand harsh chemicals.
• Vacuum or radiation exposure. In ultra‑high vacuum or radiation environments, outgassing and radiation degradation make elastomers unsuitable. Metal seals provide hermetic sealing and do not outgas, while PTFE SES offer very low permeation.
• Safety‑critical and mission‑critical systems. Aerospace, nuclear and semiconductor equipment often specify metal or SES solutions because failures can be catastrophic and maintenance access is limited. Metal seals are used when polymer seals cannot meet extreme requirements such as high temperatures, pressures, radiation or cryogenic conditions.

Key selection factors

Once the decision is made to move beyond elastomers, choosing the right metal or SES requires careful engineering. Consider the following factors:

1. Pressure and temperature ratings. Select a design rated above the maximum anticipated pressure and within the expected temperature range. Metal seals typically handle higher pressure but may require thicker cross‑sections; SES handle a broader temperature span.
2. Material compatibility. Match the seal material to the media and environment. Stainless steel, Inconel and Hastelloy provide corrosion resistance for metal seals. PTFE blends offer different wear and chemical resistance profiles.
3. Seal design. Choose between C‑rings, O‑rings, gaskets or SES. C‑rings provide lower load and easier compression; O‑rings supply uniform contact; SES offer continuous spring force for dynamic or high‑pressure applications.
4. Coatings and platings. Apply coatings such as gold, silver or PTFE to reduce friction and galling and to improve sealing against rough surfaces.
5. Installation and hardware. Proper groove design, surface finish and hardness are critical. Canyon recommends fine surface finishes (8-16 µin Ra) and hardness of 44-72 RC for mating surfaces. Installation procedures must avoid twisting or contamination to prevent leaks.

Canyon Components solutions

Canyon Components supplies a full spectrum of sealing solutions, from standard elastomeric O‑rings to custom metal and polymer‑hybrid seals. For moderate extreme conditions, our FFKM perfluoroelastomers offer chemical resistance and continuous service up to 335 °C (e.g., CP75BK20). For sour‑gas or high‑temperature oil and gas applications, we supply low‑temperature and anti‑explosive‑decompression FKM formulations. When conditions exceed elastomer capabilities, our Spring Energized Seals (SES) provide reliable service from -260 °C to 300 °C and pressures above 60,000 psi. SES are available in diverse jacket and spring materials and can be custom‑designed for static, reciprocating or rotary service. For the most extreme environments - nuclear reactors, rocket engines, subsea oil wells - we engineer metal C‑rings, O‑rings and spring‑energized metal seals using alloys like Inconel and stainless steel and apply appropriate coatings to ensure hermetic sealing.

Our engineering team can help you evaluate when to transition from elastomer O‑rings to metal or SES solutions. If your application involves temperatures above 200 °C, pressures above 1,500 psi, rapid gas decompression, aggressive chemicals or mission‑critical reliability, we invite you to contact our product consultants or request a quote. We also encourage you to explore our educational resources, such as our guide comparing AFLAS and Viton in hydrogen sulfide environments, our deep dive on low‑temperature and anti‑explosive‑decompression FKM, and our comprehensive overview of Spring‑Energized Seals.

By understanding the capabilities and limitations of each sealing technology, you can ensure that your equipment operates safely and efficiently - even in the harshest conditions.