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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.
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.
The ring number is the central sizing reference for ring joint gaskets. The three main families are R, RX, and BX.
| 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 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.
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 HB maximum | General oil and gas, standard ASME flanges |
| Low carbon steel | 1010 or similar | 120 HB maximum | Higher strength than soft iron |
| 304 stainless steel | UNS S30400 | 160 HB maximum | Corrosive service and high temperature oxidation |
| 316 stainless steel | UNS S31600 | 160 HB maximum | Chloride or chemical exposure |
| Duplex stainless steel | UNS S31803 or S32205 | Agreed case by case | High strength and improved chloride resistance |
| Inconel 625 or Incoloy 825 | UNS N06625 or N08825 | Agreed case by case | High temperature and sour or corrosive service |
Temperature limits for ring joint gaskets depend on the selected metal and the flange material. Soft iron works for many standard oil and gas temperatures, while 304 stainless, 316 stainless, Inconel 625, and Incoloy 825 are used when oxidation or corrosion resistance is required. Include the operating temperature and fluid in the quote request.
For sour service, include H2S partial pressure, pH, temperature, and chloride content in the inquiry. The gasket material must be reviewed against NACE MR0175 or ISO 15156 if the flange and sealing system are in sour gas or sour oil service.
Never select a ring joint gasket by nominal pipe size alone. A 2 inch Class 600 flange can use a different ring number than a 2 inch Class 900 flange, and the ring number also changes with the flange standard. Read the ring number stamped on the flange face or take it from the flange drawing.
If the ring number is not marked, send the groove outside diameter, groove width, groove depth, pitch diameter, flange standard, pressure class, and a clear photograph of the flange face. A used gasket measurement can help, but a deformed used ring is not a reliable sizing source.
Standard ring numbers cover most ASME and API flanges. For nonstandard grooves, custom ring joint gaskets can be quoted from groove dimensions or flange drawings.
Before installing a ring joint gasket, clean the flange groove and inspect the surface finish. Remove rust, old gasket particles, oil, grease, and scale. The groove must be free of scratches and dents because damage can prevent a full metal-to-metal seal.
Install the new gasket straight into the groove. Do not reuse a ring joint gasket. The ring deforms during the first bolting sequence and cannot recover its original shape. Reusing a deformed RTJ gasket can cause leakage and flange damage.
If the flange does not have a ring groove, do not force an RTJ gasket onto a raised face or flat face flange. For raised face ASME flanges, check spiral wound gaskets or kammprofile gaskets. For low pressure or nonmetallic service, compare PTFE gaskets and graphite gaskets.
1. What is the difference between R, RX, and BX ring joint gaskets?
R rings follow ASME B16.20 and fit ASME ring joint flanges. RX and BX rings follow API 6A and fit API 6A flanges. RX rings are common for 6B flanges, and BX rings are common for 6BX high pressure flanges.
2. Can I replace an oval ring joint gasket with an octagonal ring joint gasket?
In many ASME B16.20 grooves the same ring number can accept both cross sections. Check the flange drawing before changing the cross section because the contact stress and bolt load can differ.
3. What material should I use for a sour gas ring joint gasket?
Material selection depends on H2S partial pressure, pH, temperature, chloride content, and the flange specification. Send the full service conditions so the gasket material can be checked against NACE MR0175 or ISO 15156.
4. How do I measure a ring joint gasket?
Measure the outside diameter, height, width, and cross section shape. Compare the measurements to the ring number table. A used gasket is not a reliable substitution for the flange drawing because the ring deforms after installation.
5. What information is needed to quote a ring joint gasket?
Send the flange standard, ring number, gasket type, material, pressure class, fluid, temperature, and quantity. If the ring number is unknown, send the groove dimensions and flange photograph.
Request a ring joint gasket quote. Send us the flange standard, ring number, gasket type, material, pressure class, fluid, temperature, and required quantity. If the ring number is not marked, send the groove dimensions, flange drawing, and existing gasket photo. For sour service, include H2S partial pressure, pH, temperature, and chloride content.
