Last updated: April 2026
An RTJ gasket (ring-joint gasket, or ring-type joint) is a solid metal sealing ring that sits in a machined groove on a ring-joint flange. It seals by metal-to-metal line contact under high bolt load, and is the standard gasket for Class 600 and above — wellheads, high-pressure hydrocarbon pipelines, and API 6A flanged connections.
GritGasket machines octagonal and oval RTJ gaskets to ASME B16.20 and API 6A in soft iron, 304SS, 316SS, Monel, Inconel, and other alloys. Standard ring numbers R11 through R105, plus BX and RX profiles for API flanges. Made in Sydney, shipped across Australia and New Zealand.
What Is an RTJ Gasket?
"RTJ" stands for ring-type joint — a machined metal ring that seats inside a trapezoidal groove cut into the face of a ring-joint flange. When the flange bolts are tightened, the ring crushes slightly along two narrow contact bands, forming a metal-to-metal seal. The ring material is selected to be softer than the flange so the ring yields first, protecting the flange groove from damage.
RTJ gaskets come in three profile families:
- Type R — Octagonal — flat-topped eight-sided profile. The standard for ASME B16.5 Class 300–2500 ring-joint flanges.
- Type R — Oval — rounded profile. Older, less common, still used on legacy flanges; seals on a curved contact band.
- Type RX / BX — pressure-energised profiles for API 6A wellhead and subsea flanges at Class 900 through 20,000 psi. BX is for API 6BX flanges only.
Is an RTJ Gasket the Same as a Ring Joint Gasket?
Yes — "RTJ gasket" and "ring joint gasket" are the same product. "RTJ" is the abbreviation used in piping spec sheets; "ring joint" is the long form. Both refer to a solid metal ring that seats in a grooved flange.
Material Selection
The ring must be softer than the flange groove (the rule of thumb is 30–40 HB softer). API 6A sets maximum hardness limits for each material — exceeding them risks galling and flange damage.
| Material | Max hardness | Typical service |
|---|---|---|
| Soft iron | ≤72 HB (90 HRB) | General HP hydrocarbon, steam, water |
| Low-carbon steel (F5) | ≤130 HB | Moderate temp steam, HP oil & gas |
| 304 stainless | ≤160 HB | Corrosive, food, general SS flanges |
| 316 stainless | ≤160 HB | Chloride exposure, sour gas (with NACE) |
| Monel 400 | ≤150 HB | Hydrofluoric acid, seawater |
| Inconel 625 / 825 | ≤160 HB | Sour gas, cryogenic, very high temp |
For sour-service (H₂S) duties, rings must also meet NACE MR0175 / ISO 15156 for sulphide stress cracking resistance — we stock NACE-compliant 316SS, Inconel 625, and Monel 400 to ring numbers R20 through R85.
Octagonal vs Oval — Which Do I Need?
Nearly every new installation uses the octagonal (Type R) profile — it seals on two flat contact bands which distribute load evenly and are more forgiving on minor groove imperfections. Oval rings are kept for retrofit service on legacy flanges that were machined to the older oval groove geometry. If in doubt, check the flange groove cross-section: a trapezoidal groove with flat sides fits either profile, but the sealing behaviour differs.
Pressure and Temperature
| Profile | Class range | Max pressure (cold) | Typical temp range |
|---|---|---|---|
| Type R Octagonal | 150 – 2500 | 420 bar (Class 2500) | Material dep. |
| Type R Oval | 150 – 2500 | 420 bar | Material dep. |
| Type RX | API 6A, 2000 – 15,000 psi | 1034 bar | Wellhead, up to 345 °C |
| Type BX | API 6BX, 5000 – 20,000 psi | 1380 bar | Wellhead / subsea |
Where Are RTJ Gaskets Used?
- Oil & gas wellheads — API 6A Christmas tree, BOP, and master valve flanges.
- HP pipelines — Class 600+ hydrocarbon, steam, and high-pressure water.
- Refinery hot service — FCC units, coker drums, high-pressure separators.
- Subsea & offshore — BX rings on compact flanges, Inconel-clad for sour service.
- Power generation — superheated steam headers, HP turbine extraction.
Installation Notes
RTJ gaskets are single-use — remove and discard after any disassembly; do not reuse. Inspect the flange groove for nicks, dents, or corrosion before assembly, and clean thoroughly. Assembly stress is high (metal-to-metal seal), so bolting is critical: follow ASME PCC-1 four-pass cross-pattern with calibrated tension or torque. Our bolt torque calculator sizes the bolt preload for standard ring numbers.
Stocked Ring-Joint Gaskets
RTJ-R-OCT-SI
RTJ-R-OCT-316
Frequently Asked Questions
An RTJ (ring-type joint) gasket is a solid metal sealing ring machined to sit in a grooved flange face. It seals by metal-to-metal line contact under high bolt load and is the standard gasket for Class 600 and above — wellheads, HP hydrocarbon pipelines, and API 6A flanges. Made from soft iron, stainless steel, Monel, or Inconel depending on service.
Yes — "RTJ" and "ring joint" are the same product. RTJ is the abbreviation used in piping spec sheets; "ring joint gasket" is the long form. Both refer to a machined metal ring (octagonal or oval, Type R, RX, or BX) that seats in a grooved flange to form a metal-to-metal seal.
Octagonal (Type R) is the default for any new installation — it seals on two flat contact bands, distributes load evenly, and is more forgiving on minor groove imperfections. Oval rings are kept for retrofit service on legacy flanges originally machined to the older oval geometry. When in doubt, match what came out of the flange.
No — RTJ gaskets are single-use. Once bolted up, the ring yields to conform to the flange groove; disassembly deforms it permanently. Reuse almost always causes leaks and can damage the flange groove. Always install a new ring on reassembly and inspect the groove for nicks or corrosion first.
API 6A specifies maximum hardness limits by material: soft iron ≤72 HB, low-carbon steel (F5) ≤130 HB, 304/316 stainless ≤160 HB, Monel and Inconel ≤150–160 HB. The ring must be softer than the flange groove (typically 30–40 HB softer) so it yields first without damaging the groove. Hardness certificates are supplied with every ring.
Related Products
- Spiral wound gaskets — for raised-face ASME B16.5 flanges below Class 900
- Kammprofile gaskets — severe-service alternative for raised-face flanges
- Graphite gaskets — for lower-class flange service
Learn More
Sources
- ASME B16.20 — Metallic Gaskets for Pipe Flanges: Ring-Joint, Spiral-Wound, and Jacketed
- API 6A — Specification for Wellhead and Christmas Tree Equipment
- NACE MR0175 / ISO 15156 — Materials for use in H₂S-containing environments
- ASME PCC-1 — Guidelines for Pressure Boundary Bolted Flange Joint Assembly