Complete reference chart for Ring Type Joint (RTJ) gasket ring numbers per ASME B16.20 — covering ASME B16.5 flanges (Class 150 to 2500) and ASME B16.47 Series A flanges. Nominal pipe sizes ½" to 36". Use this chart to identify the correct R-number for any RTJ-faced flange connection.
Ring Type Joint (RTJ) flanges use a precision-machined solid metal ring — seated in a trapezoidal or oval groove machined into the flange face — to achieve a metal-to-metal pressure seal. Unlike raised-face or flat-face flanges that rely on soft gasket materials, RTJ connections are specified for high-pressure, high-temperature, and critical service applications where absolutely no leakage is acceptable.
The ring designation numbers (R-11, R-12, R-13, etc.) are standardised by ASME B16.20 — Metallic Gaskets for Pipe Flanges. Each R-number defines a specific ring geometry (outer diameter, inner diameter, height, groove dimensions) that is identical across all manufacturers, ensuring full interchangeability. The chart below lists the correct R-number for every combination of nominal pipe size (NPS) and pressure class per ASME B16.5 and ASME B16.47 Series A.
| Nominal Pipe Size |
ASME B16.5 — Flanges up to 24" NPS | ASME B16.47 Series A — Large Diameter Flanges | ||||||
|---|---|---|---|---|---|---|---|---|
| Class 150 | Class 300 / 600 | Class 900 | Class 1500 | Class 2500 | Class 150 | Class 300 / 600 | Class 900 | |
| ½" (DN 15) | — | R-11 | R-12 | R-12 | R-13 | — | — | — |
| ¾" (DN 20) | — | R-13 | R-14 | R-14 | R-16 | — | — | — |
| 1" (DN 25) | R-15 | R-16 | R-16 | R-16 | R-18 | — | — | — |
| 1¼" (DN 32) | R-17 | R-18 | R-18 | R-18 | R-21 | — | — | — |
| 1½" (DN 40) | R-19 | R-20 | R-20 | R-20 | R-23 | — | — | — |
| 2" (DN 50) | R-22 | R-23 | R-24 | R-24 | R-26 | — | — | — |
| 2½" (DN 65) | R-25 | R-26 | R-27 | R-27 | R-28 | — | — | — |
| 3" (DN 80) | R-29 | R-31 | R-31 | R-35 | R-32 | — | — | — |
| 3½" (DN 90) | R-33 | R-34 | R-34 | — | — | — | — | — |
| 4" (DN 100) | R-36 | R-37 | R-37 | R-39 | R-38 | — | — | — |
| 5" (DN 125) | R-40 | R-41 | R-41 | R-44 | R-42 | — | — | — |
| 6" (DN 150) | R-43 | R-45 | R-45 | R-46 | R-47 | — | — | — |
| 8" (DN 200) | R-48 | R-49 | R-49 | R-50 | R-51 | — | — | — |
| 10" (DN 250) | R-52 | R-53 | R-53 | R-54 | R-55 | — | — | — |
| 12" (DN 300) | R-56 | R-57 | R-57 | R-58 | R-60 | — | R-57 | R-57 |
| 14" (DN 350) | R-59 | R-61 | R-62 | R-63 | — | — | R-61 | R-62 |
| 16" (DN 400) | R-64 | R-65 | R-66 | R-67 | — | — | R-65 | R-68 |
| 18" (DN 450) | R-68 | R-69 | R-70 | R-71 | — | — | R-69 | R-70 |
| 20" (DN 500) | R-72 | R-73 | R-74 | R-75 | — | — | R-73 | R-74 |
| 22" (DN 550) | — | — | — | — | — | R-80 | R-81 | — |
| 24" (DN 600) | R-76 | R-77 | R-78 | R-79 | — | — | R-77 | R-78 |
| 26" (DN 650) | — | — | — | — | — | — | R-93 | R-100 |
| 28" (DN 700) | — | — | — | — | — | — | R-94 | R-101 |
| 30" (DN 750) | — | — | — | — | — | — | R-95 | R-102 |
| 32" (DN 800) | — | — | — | — | — | — | R-96 | R-103 |
| 34" (DN 850) | — | — | — | — | — | — | R-97 | R-104 |
| 36" (DN 900) | — | — | — | — | — | — | R-98 | R-105 |
Source: ASME B16.20 — Metallic Gaskets for Pipe Flanges. — indicates combination not available in RTJ facing. Class 300 and 600 share the same ring number per ASME B16.20 (groove dimensions are identical for both classes).
A Ring Type Joint (RTJ) gasket is a precision-machined solid metal ring that creates a pressure-tight seal in flanged pipe connections. Unlike conventional gaskets that compress between flat or raised flange faces, RTJ rings seat into a trapezoidal groove machined directly into the flange face. When flange bolts are torqued, the ring plastically deforms into the groove flanks, creating a continuous metal-to-metal sealing line that is unaffected by pressure spikes, thermal cycling, or vibration.
RTJ joints are specified under ASME B16.20 (Metallic Gaskets for Pipe Flanges) and are the dominant seal choice in oil & gas, petrochemical, refinery, and offshore applications where Class 600 and above pressures are involved, or where zero-leakage of hazardous, flammable, or toxic process fluids is mandated by code or safety regulations.
The standard RTJ ring per ASME B16.20. Available in oval (circular cross-section) and octagonal (eight-sided cross-section) profiles. Octagonal rings provide greater seating area and higher bolt-load efficiency. Both fit the same groove. Used for Class 150 to 2500 flanges per ASME B16.5. Reusable if undamaged — re-seat in the groove on a new joint.
Interchangeable with Type R grooves but hollow-bevelled to become pressure-energised — internal pressure forces the ring harder into the groove, improving sealing at high pressure. Used in wellhead equipment, Christmas trees, and subsea connections. Suitable where Type R is specified but higher leak-tightness is required. Not interchangeable in reverse (an R ring cannot replace an RX).
Designed specifically for API 6A and ASME B16.47 Series B flanges in extreme-pressure service. BX rings have a unique profile that provides positive mechanical stop contact — preventing over-compression. Not interchangeable with R or RX grooves. Used in wellhead assemblies, BOPs, and high-pressure manifolds where API 6A specifies BX facing.
The fundamental rule for RTJ gaskets: the ring must be softer than the flange face material — typically by a minimum of 30 HRB. This ensures the ring deforms into the groove rather than the groove deforming into the ring, which would prevent proper seating on reassembly.
| Material | Hardness (max) | Typical Service | ASTM / Standard |
|---|---|---|---|
| Soft Iron | HRB 56 (max) | Low-pressure, non-corrosive service; carbon steel flanges | ASTM A576 Grade 1010 |
| Low Carbon Steel | HRB 68 (max) | General service; CS and low-alloy flanges, steam service | ASTM A108 Grade 1018 |
| 304 Stainless Steel | HRB 80 (max) | General corrosive service; food, pharmaceutical, chemical | ASTM A276 / A182 |
| 316 Stainless Steel | HRB 80 (max) | Chloride-containing environments, marine, acids | ASTM A276 / A182 |
| 410 Stainless Steel | HRB 75 (max) | High-temperature steam; alloy steel flanges | ASTM A276 |
| Monel 400 (UNS N04400) | HRB 70 (max) | Seawater, HF acid, reducing acids, alkalis | ASTM B164 |
| Inconel 625 (UNS N06625) | HRB 72 (max) | High-temperature oxidising environments, subsea | ASTM B446 |
| Titanium Grade 2 | HRB 73 (max) | Aggressive chemicals, brine, oxidising acids | ASTM B265 / B381 |
| Duplex (UNS S31803) | HRB 90 (max) | High-chloride, sour gas, offshore piping | ASTM A182 F51 |
A frequently asked question: why do Class 300 and Class 600 share the same RTJ ring number? Per ASME B16.5, the ring groove dimensions for Class 300 and Class 600 flanges of the same NPS are identical. The difference between these pressure classes lies in the flange body dimensions (hub height, bolt circle, etc.) — not the ring groove geometry. This means a single R-number ring serves both Class 300 and Class 600 RTJ connections at any given NPS, as reflected in the chart above.
| Factor | RTJ (Ring Type Joint) | Raised Face (RF) |
|---|---|---|
| Sealing Mechanism | Metal-to-metal — ring deforms into groove | Soft gasket compressed between raised faces |
| Pressure Range | Class 150 to 2500 (preferred from Class 600+) | Class 150 to 2500 (preferred up to Class 600) |
| Temperature Range | Unlimited — metal seal not temperature-limited | Limited by soft gasket material degradation |
| Hazardous Service | Preferred — zero-leak metal seal | Acceptable below Class 600 for non-critical fluids |
| Maintenance | Groove must be undamaged; ring replaced each disassembly | Gasket replaced each disassembly; face easy to resurface |
| Cost | Higher — grooved facing and precision rings | Lower — flat or raised face with soft gasket |
| API 6A / Wellhead | Mandatory | Not used |
| Typical Industry | Upstream oil & gas, refineries, offshore, petrochemical | General process, utilities, water, HVAC |
Weld neck, blind, socket weld, and slip-on flanges with RTJ facing — all materials, all pressure classes, ASME B16.5 and B16.47. Ready stock and custom orders exported to 65+ countries.