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Ring Joint Gasket Guide: R, RX, BX Types, Materials, and Ring Number Selection
Quick Answer: A ring joint gasket is a metallic gasket that seals by being compressed into a matching groove on an RTJ flange. To select the correct ring joint gasket, confirm the flange standard, ring number, cross section, material, and pressure class. Always send the flange drawing or ring number with your inquiry.
CORASEALS is an industrial sealing supplier. We supply ring joint gaskets, RTJ gaskets, and other flange gaskets for ASME B16.5, ASME B16.47, and API 6A connections. The ring joint gasket family includes R, RX, and BX types in oval and octagonal cross sections.
What Is a Ring Joint Gasket?
A ring joint gasket is also called an RTJ gasket or ring type joint gasket. The gasket is a metal ring that fits into a precision machined groove in a flange face. When flange bolts are tightened, the ring deforms into the groove and forms a metal-to-metal seal.
Ring joint gaskets are used where pressure, temperature, or fluid hazard is too high for soft gaskets. Typical applications include wellhead equipment, Christmas tree connections, choke and kill manifolds, high pressure pipelines, refinery hydroprocessing units, and chemical plant flanges with ring joint grooves.
R, RX, and BX Ring Joint Gasket Types
The ring number is the central sizing reference for ring joint gaskets. The three main families are R, RX, and BX.
- R ring joint gaskets. R rings follow ASME B16.20 and fit ASME B16.5 and ASME B16.47 ring joint flanges. They are made in oval and octagonal cross sections.
- RX ring joint gaskets. RX rings are used on API 6A flanges. The RX cross section is pressure energized, which means the seal contact improves as internal pressure increases.
- BX ring joint gaskets. BX rings are used on API 6A type 6BX flanges. They are common in high pressure wellhead and choke connections from 5,000 psi through 20,000 psi.
| Type | Standard | Flange system | Cross section | Typical pressure class or service | Common ring number examples |
|---|---|---|---|---|---|
| R | ASME B16.20 | ASME B16.5 and ASME B16.47 | Oval and octagonal | Class 150 through 2500 | R20, R24, R31, R37, R45, R49, R53, R57, R63, R71, R73, R75, R78, R93, R95, R99 |
| RX | API 6A | API 6A type 6B | Octagonal | 2,000 psi through 5,000 psi | RX20, RX24, RX31, RX37, RX44, RX46, RX50, RX54, RX57, RX65, RX69, RX70, RX73, RX82 |
| BX | API 6A | API 6A type 6BX | Octagonal | 5,000 psi through 20,000 psi | BX150, BX151, BX152, BX153, BX154, BX155, BX156, BX157, BX158, BX159 |
Oval and Octagonal Cross Sections
Oval ring joint gaskets contact the flange groove along a curved surface. Octagonal ring joint gaskets contact the groove along flat surfaces and are common for modern pipe flanges and many API connections.
In many ASME B16.20 flange grooves, oval and octagonal R rings share the same ring number and groove dimensions. However, do not change the cross section without checking the flange drawing. The bolt load and contact stress can be different, and an incorrect cross section can damage the groove.
Ring Joint Gasket Material Selection
The gasket material must be softer than the flange groove material. The ring deforms during bolting and protects the flange from plastic damage. A harder ring can destroy the groove and require flange re-machining or replacement.
| Material | Common grade | Typical hardness limit | Common application |
|---|---|---|---|
| Soft iron | Armco or equivalent | 90 |