RTJ Ring Gasket Reference

How RTJ Sealing Works

A ring-type joint flange has a precision-machined groove in the flange face. The ring gasket (a solid metal ring with a specific cross-section profile) sits in the groove. When the mating flanges are bolted together, the bolt-up force compresses the ring against the groove walls until the metal deforms slightly and creates a continuous line contact seal around the entire flange. The result is a metal-to-metal seal with no soft sealing material - critical for high-temperature service where elastomers fail and for high-pressure service where extrusion of soft gasket material is a leak path.

R-Series Rings

R-series ring gaskets are designated R-x where x is a numeric size identifier. Common sizes run from R-11 (small bore) through R-94 (24 inch). R-series rings come in oval and octagonal cross-section. Oval was the original profile; octagonal is the modern preference because it seats more reliably under varying bolt-up torque and groove tolerance.

R-series rings mate to ASME B16.5 RTJ flanges Class 150 through 2500 and API 6A 6B class flanges (2M, 3M, 5M). The flange order should specify the ring groove designation (R-x), and the ring order should match.

BX-Series Rings

BX-series ring gaskets are designated BX-x where x is a numeric size identifier. Common sizes include BX-150 through BX-303. BX rings have a rectangular cross-section with relieved corners and a deliberate angle on the contact face that causes the ring to self-energize: internal pressure pushes the ring outward against the groove wall, increasing seal force as pressure rises.

BX rings mate to API 6BX class flanges (10M, 15M, 20M, 25M). They are not interchangeable with R-series rings. The flange groove geometry is different, and mating an R ring to a BX groove (or vice versa) is a service failure mode.

Ring Materials

• Soft iron / low-carbon steel: standard for sweet service. Most common ring material.
• F5 chrome-moly: moderate elevated temperature service.
• F304 / F316 stainless: corrosion service and standby applications.
• Inconel 718 / Inconel 625: severe sour service and HPHT applications.
• Monel 400: seawater and hydrofluoric acid service.

Ring material is matched to service environment and to the mating flange material. The flange + ring assembly is ordered together to ensure compatibility.