Specialty RTJ Gaskets

Oval ring gaskets

The original ring joint shape. The rounded cross-section seals along a narrow line where it meets the groove walls, which makes it a good fit for older flanges with round-bottom grooves. Oval rings also fit the modern flat-bottom groove.

Octagonal ring gaskets

Octagonal rings have four angled flats that bear against the walls of a flat-bottom groove. The wider contact area makes the octagonal ring the common choice for new flanges. Both oval and octagonal rings are made to the R ring numbers in ASME B16.20, which tie each ring to a flange size, pressure class and flange standard.

Lens rings

Lens rings have curved, spherical sealing faces that seat on matching conical faces machined into the flanges. They are covered by DIN 2696 for high-pressure piping, and ASME flanges can be modified to take them. Lens rings work-harden in service, so they are generally replaced rather than re-used.

Octagonal kammprofile rings with graphite facing

A standard octagonal ring with concentric serrations machined into its sealing flats and a flexible graphite facing over them. See the next section for how they work.

A kammprofile RTJ gasket starts as an octagonal ring made to the same dimensions as a standard ring for the groove. We then machine fine, concentric serrations into its four angled sealing faces, and the faces are covered with a thin layer of oxidation-inhibited flexible graphite.

• Lower seating load. The soft graphite seals before the metal ring has to deform into the groove, so the joint can seal at a lower bolt load than a plain ring.
• Gentler on the groove. The graphite fills small scratches and imperfections and reduces friction and wear between the ring and the groove.
• Common uses. Flanges with worn or previously damaged grooves, heat exchangers and joints that see temperature cycling.

The ring fits the same groove as a standard octagonal ring, so no flange changes are needed.

A ring gasket must be softer than the flange groove it seals in, so the ring deforms and the groove does not. ASME B16.20 sets a maximum hardness for each ring material and a marking that goes on the ring with the ring number (for example, R51 S316). The customer selects the ring material for the service.

We also machine rings in other alloys to your specification. Compare alloys in our Fastener Materials Matrix.

To quote specialty RTJ gaskets, tell us:

• Ring type: oval, octagonal, lens ring or octagonal kammprofile with graphite facing.
• Ring number (for example, R24), or the flange size, pressure class and flange standard.
• Material and any hardness limit for your flanges.
• Drawing for lens rings and non-standard sizes.
• Quantity and the date you need them.

If you send a drawing, we make the rings to it.

What is an RTJ gasket?

An RTJ (ring type joint) gasket is a solid metal ring that sits in a machined groove in the faces of two flanges. When the bolts are tightened, the ring is pressed into the groove and forms a metal-to-metal seal. RTJ gaskets are used on high-pressure and high-temperature flanged joints in oil and gas, refining and petrochemical service.

What is the difference between oval and octagonal ring gaskets?

Oval rings have a rounded cross-section that seals along a narrow line of contact with the groove walls. Octagonal rings have flat, angled faces that bear against the groove walls over a wider area. Both fit the standard flat-bottom groove, while older round-bottom grooves take oval rings only.

What is a lens ring?

A lens ring is a metal ring with curved (spherical) sealing faces that seat against matching conical faces machined into the flanges. Lens rings are covered by DIN 2696 and are used on high-pressure piping. Flanges can also be modified to accept them.

What is a kammprofile RTJ gasket?

It is an octagonal ring gasket with fine concentric grooves machined into its angled sealing faces, which are then covered with a thin layer of flexible graphite. The graphite flows into small imperfections in the flange groove, so the ring can seal at a lower bolt load than a plain metal ring and is gentler on the groove.

Why must the ring be softer than the flange groove?

A ring gasket seals by deforming slightly into the groove. If the ring is softer than the flange, the ring takes that deformation and the groove is not damaged. ASME B16.20 lists a maximum hardness for each ring material for this reason.

Who makes these rings?

Patriot Bolt CNC machines the rings, including the kammprofile serrations, in Humble, Texas, and supplies them complete with the flexible graphite facing.