Metal C-Rings
Metal C-rings, also known as metal C-seals or metallic C-rings, are high-performance static sealing solutions designed for high-temperature, high-pressure, vacuum and demanding industrial applications where conventional elastomeric seals may not provide the required performance. The characteristic C-shaped cross-section provides controlled resilience under compression, allowing the seal to generate contact load against the mating surfaces and to recover (or spring back) if the flanges separate in service. In pressure-energised applications, system pressure can act within the open section of the C-ring to increase sealing force as operating pressure rises.
International Seal supplies standard and custom metal C-ring seals in stainless steels, nickel-based superalloys and specialist metals. Seals can be supplied to customer drawings, existing specifications or application requirements, with a range of materials, dimensions and surface coatings available.
Metal C-Ring Specifications
Metal C-rings are designed for critical static sealing applications involving elevated temperatures, high pressures, vacuum conditions, aggressive media or repeated thermal and pressure cycling.
- Pressure-Energised Metal C-Ring Design
- Standard & Custom Diameters Available
- High-Temperature & High-Pressure Applications
- Vacuum & High-Vacuum Applications
- Surface Platings & Coatings Available
- Supplied to Drawings or Application Requirements
Materials & Surface Coatings
Metal C-rings are available in a range of stainless steels, nickel-based superalloys and specialist materials. Material selection should consider operating temperature, pressure, process media, corrosion resistance, thermal cycling and the mechanical requirements of the sealing system.
A range of surface platings and coatings can be applied to metal C-rings to improve sealing performance, surface conformity and corrosion resistance.
Depending on the application, options include silver, gold, copper, nickel, tin, PTFE-based coatings and specialist plating combinations. Coating selection should consider the base alloy, operating temperature, pressure, available seating load, flange surface finish and required leakage performance.
For further information, see our Metal Seal Platings and Coatings section.
Material Condition and Heat Treatment
The condition a C-ring alloy is supplied in work hardened, age hardened or annealed affects its strength and spring characteristics, and therefore the seating load the seal requires and the springback it retains. Two C-rings of identical profile, diameter and alloy can behave differently if supplied in different conditions. Where a drawing or existing specification calls for a particular condition, include it with your enquiry.
Typical Applications
Metal C-rings are commonly used where conventional elastomeric or polymer seals may be unsuitable because of extreme temperatures, high pressures, vacuum conditions or aggressive operating environments.
Their pressure-energised design makes them particularly suitable for critical static joints where sealing performance must be maintained through changes in pressure and temperature.
- Aerospace & Defence Equipment
- High-Pressure Flanges & Connections
- High-Temperature Process Equipment
- Vacuum & High-Vacuum Systems
- Turbines, Engines & Exhaust Systems
- Valves, Pumps & Compressors
- Chemical & Petrochemical Processing
- Power Generation & Energy Systems
- Pressure Vessels & Critical Static Joints
The correct metal C-ring material, orientation, section geometry and surface coating should be selected according to the pressure direction, operating temperature, flange design, surface finish, process media and required leakage performance.
Metal C-Rings vs Metal O-Rings
Metal C-rings and metal O-rings are often considered for the same joint, and the decision usually comes down to three things: the load the joint can apply, how much the joint moves, and whether system pressure can be used to help seal.
- Seating load. The open C-section deflects more readily than a closed ring of comparable size, so a C-ring will generally seat at a lower load than a metal O-ring. Where flange load is limited, that can be decisive.
- Springback. A C-ring retains more elastic recovery after compression than a metal O-ring, so it can follow a greater amount of flange separation before sealing contact is lost. Joints that move under thermal or pressure cycling tend to favour a C-ring.
- Pressure energisation. Both profiles can be pressure-energised, but the C-ring's open section is inherently suited to it — system pressure acts directly within the C. Metal O-rings require venting to achieve the same effect.
- Pressure direction. Because the C-section is open on one side, orientation is part of the specification for a C-ring in a way it is not for a plain compressed O-ring.
- Sealing interface. A metal O-ring presents a narrower contact band, which for a given load can produce a higher contact stress. Where the tightest interface is the priority and load is available, that can favour an O-ring.
Where a joint moves significantly, or where clamping load is restricted, a C-ring is often the better starting point. Where load is plentiful and the joint is stable, a metal O-ring may be simpler and more economical. For joints with substantial flange movement, a metal E-ring offers greater springback again.
These are general relationships rather than fixed rules. Actual performance depends on diameter, section size, wall thickness, alloy, material condition, surface coating and the design and condition of the groove. Send us the joint details and operating conditions and we will advise on the appropriate profile.
Groove and Flange Considerations
A metal C-ring seals by controlled deformation against the mating faces, so the joint is part of the sealing system. When specifying or replacing a C-ring, the following should be established:
- Pressure direction – internal or external to the sealed cavity. This determines the orientation of the open section and, for internal pressure designs, means the groove outside diameter is normally the reference dimension; for external pressure designs, the groove inside diameter.
- Groove depth – which sets the compression applied to the seal and therefore the load and sealing interface achieved.
- Groove width – which must allow the C-section to deflect without being constrained.
- Available clamping load – at the joint. A flange that cannot deliver the seating load will not seal.
- Mating surface finish and condition – The tighter the leakage requirement, the more the finish of the groove and flange faces governs the outcome.
- Plating thickness – which adds to the effective section. Confirm whether drawing dimensions are before or after plating.
- Expected flange movement – in service, which determines how much springback the seal needs.
Where seals are supplied to a drawing we work to the dimensions and tolerances specified. Where a new joint is being designed, send the operating conditions, available space and flange arrangement and we will advise on what can be supplied and what the seal will require of the groove.
Metal C-Ring Configurations
Metal C-rings can be manufactured in different orientations depending on the direction of system pressure and the design of the sealing joint.
Spring-Energised Metal C-Rings
Where a joint cannot rely on system pressure to energise the seal, because pressure is low, variable, or because sealing must be maintained during start-up and shutdown a metallic spring element can be fitted inside the C-section.
The spring provides sealing load independently of system pressure and helps maintain contact as the joint moves through thermal and pressure cycles. Spring-energised C-rings are typically specified where a higher and more consistent sealing load is required than the C-section alone would deliver, and they are available in both internal and external pressure configurations.
The trade-off is that a spring-energised design generally requires a higher seating load and offers less recovery than the equivalent pressure-energised C-ring, so the choice should be made against the clamping load available at the joint. See Spring-Energised Metal Seals for the wider range of spring-energised metallic designs.
Internal Pressure Metal C-Rings
Internal pressure C-rings are orientated so that system pressure acts within the open section of the seal. As pressure increases, the C-ring is energised against the mating surfaces, increasing contact load and helping maintain sealing performance under demanding operating conditions.
These designs are commonly used in high-pressure vessels, flanges, valves, aerospace assemblies and other internally pressurised systems.
External Pressure Metal C-Rings
External pressure C-rings are configured for applications where pressure acts from outside the sealed joint. The seal orientation allows external pressure to energise the C-section and increase sealing force against the mating surfaces.
External pressure designs can be used in vacuum systems, specialised pressure equipment and applications where the pressure differential acts from outside the sealed cavity.
Custom Metal C-Rings
Custom metal C-rings can be supplied for applications requiring specific diameters, cross-sections, materials, wall thicknesses or surface treatments.
International Seal can support requirements based on new applications, customer drawings, existing seal specifications and replacement components.
Metal C-Ring FAQs
What is a metal C-ring?
A metal C-ring is a static sealing ring with an open, C-shaped cross-section, compressed between two mating faces to seal a joint. The open section allows system pressure to act within the seal, energising it against the mating surfaces as pressure rises, and gives the seal useful recovery if the flanges separate in service.
What is the difference between a metal C-ring and a metal C-seal?
There is no difference — the terms describe the same component and are used interchangeably. You may also see metallic C-ring, C-ring seal or metal face C-seal used for the same product.
What is the difference between a metal C-ring and a metal O-ring?
A C-ring’s open section generally seats at a lower load and retains more springback than a metal O-ring, which makes it well suited to joints with limited clamping load or significant movement. A metal O-ring presents a narrower contact band and can produce a higher contact stress where load is available. See our comparison above.
What is an internal pressure C-ring?
One orientated so that system pressure acts inside the open section of the seal, pushing the sealing faces outwards against the mating surfaces. As pressure rises the seal is energised further. Internal pressure designs are used in pressure vessels, flanges, valves and other internally pressurised systems.
What is an external pressure C-ring?
One configured for pressure acting from outside the sealed joint, including vacuum service where the differential runs inwards. The open section faces outwards so that external pressure energises the seal. Orientation matters: an internal pressure C-ring fitted in an external pressure joint will not energise correctly.
What is a spring-energised metal C-ring?
A C-ring with a metallic spring element fitted inside the C-section, providing sealing load independently of system pressure. It is specified where pressure is low or variable but a consistent sealing load is required, at the cost of a higher seating load and less recovery than the equivalent pressure-energised design.
Can metal C-rings be used in vacuum applications?
Yes. Metal C-rings are used in vacuum and high-vacuum equipment, where they avoid the outgassing and permeation associated with elastomers. In vacuum the seal must be configured as an external pressure design, and mating surface finish becomes more important as the required leak performance tightens.
What are metal C-rings made from?
Metal C-rings are commonly manufactured from stainless steels, including 304 and 316, and nickel-based alloys such as Inconel X-750, Alloy 718 and Hastelloy. Surface finishes can include silver, gold, copper, nickel, tin and PTFE-based coatings, depending on the application.
Material condition, including work-hardened, age-hardened or annealed states, also influences seal strength, seating load and springback characteristics.
Can you supply metal C-rings to a drawing or part number?
Yes. Metal C-rings can be manufactured to customer drawings, dimensions or application requirements across a range of diameters, cross-sections, alloys, wall thicknesses and surface treatments. Existing drawings, manufacturer part numbers and physical samples can be reviewed where a replacement or alternative supply route is needed.
Need a Metal C-Ring Quote?
Send us the seal or groove dimensions, direction of pressure, operating temperature and pressure, process media and quantity where known, and we will confirm the configuration, alloy, material condition and surface coating that suit the joint.
If you are replacing an existing seal, a drawing, manufacturer part number, photograph or physical sample is usually enough to work from. Alternative alloys and coatings can be reviewed where the original specification is unavailable or no longer economical, and prototype or small-quantity requirements can be discussed alongside production volumes.