Spiral-wound, camprofile and RTJ gaskets: when soft gaskets aren't enough

Spiral-wound gasket: springy metal strip plus soft filler

The spiral-wound gasket (SWG) is the most important semi-metallic type: a V-profile metal strip is wound spirally, with a soft filler between the layers. The springy V-profile maintains surface pressure even when temperature changes cause the bolt force to fluctuate - which is why the spiral-wound gasket is the first choice under thermal cycling and in hydrocarbon service. Standard winding metals are 1.4301/304 and 1.4404/316L (available up to titanium, Hastelloy or Inconel), the standard filler is graphite; PTFE takes over for aggressive chemistry, and special high-temperature fillers extend beyond the graphite limit.

Constructions: with and without rings

• With outer ring: standard for raised-face flanges - the ring centres the gasket on the bolts and stops compression before the winding is over-compressed (type designations vary by manufacturer, e.g. “CG” or type 10).
• With inner and outer ring: for medium to severe conditions (“CGI” or type 101). The inner ring prevents the winding from buckling inward and protects the filler from the medium and erosion. Rules of thumb: PTFE filler always with an inner ring; ASME B16.20 makes inner rings mandatory for large nominal sizes at high pressure classes.
• Wound body only (no rings, “R” or type 00) or with inner ring only (type 01): exclusively for confined flange forms (tongue/groove, male/female), where the confinement itself limits compression.

Marking: the colour code to ASME B16.20

Spiral-wound gaskets carry a standardised colour-code system on the outer ring: the solid colour of the ring edge identifies the winding metal, colour stripes at regular intervals identify the filler. In addition, mandatory stamping states manufacturer, materials, nominal size, pressure class and the standard reference. The most important codes:

The colour code is more than cosmetic: a common failure case is a spiral-wound gasket with an unsuitable inner-ring or winding material for the medium (e.g. carbon steel in chloride service). Before installation, check the colour code and stamping against the requirement - and always store spiral-wound gaskets flat in their original packaging, never hanging: a deformed winding no longer seals reliably even at the correct tightening torque.

Camprofile and metal-jacketed gaskets

The camprofile gasket consists of a solid metal core with a concentrically grooved surface, faced on both sides with thin soft layers - usually graphite. The groove peaks concentrate the bolt force onto narrow lines and generate high local pressures, while the facings provide the fine seal. The result is a practically over-compression-proof, very robust gasket for high pressures and temperatures - common on heat exchangers, in steam and heat-transfer systems, and as an alternative to the spiral-wound gasket at large nominal sizes, where the solid core makes handling easier.

The metal-jacketed gasket encloses a soft core in a thin metal jacket. It is the traditional solution for special heat-exchanger shapes with ribs and chambers, but in new plant it is increasingly replaced by camprofile and spiral-wound gaskets, which achieve higher tightness classes.

Ring-joint gaskets (RTJ): solid metal for the highest pressures

For the highest-pressure range - wellhead technology, oil and gas, high-pressure process plant - solid metal rings seal in the ring groove of dedicated RTJ flanges. The system to ASME B16.20 and API 6A:

• Type R (oval or octagonal cross-section): the classic design. The standardised ring numbers (R 11 to R 105) assign each ring unambiguously to a flange size and pressure class; oval and octagonal are interchangeable on modern octagonal grooves. Sealing is by bolt force alone, service up to around 10,000 psi.
• Type RX: a pressure-assisted development - internal pressure additionally presses the modified cross-section against the groove flanks. Fits the same groove as type R (a direct upgrade), service up to around 15,000 psi.
• Type BX: for API 6BX flanges up to 20,000 psi, with its own groove geometry and a pressure-equalising hole - not interchangeable with R/RX.

Two basic rules apply to all RTJ rings: the ring material must be softer than the flange material (typical grading from galvanised soft iron through low-carbon steel to 304/316 and nickel alloys, each with standardised maximum hardness values) - the plastic deformation is meant to happen in the replaceable ring, not in the flange groove. And: RTJ rings are single-use parts; they are replaced after each compression. The matching flange dimensions in the ASME system are shown on our page ASME B16.5 flange dimensions.

Which construction, when?

The same logic applies to selection as for all gaskets - medium, pressure/temperature, flange form and codes decide (see the gaskets overview). As a rule of thumb from practice: for hydrocarbons and cyclic operation, do not downgrade to a flat gasket for cost reasons - the spiral-wound gasket with graphite filler and inner ring is generally the right choice there, though the specific design remains application-dependent.

Frequently asked questions about metallic and composite gaskets