Gasket Dimensions: ASME B16.20 Ring Joint
Ring joint gaskets (RTJ) are metallic gaskets that seat in machined grooves on RTJ-type flanges. They provide a high-integrity, metal-to-metal seal for high-pressure and high-temperature services. ASME B16.20 defines the dimensions, tolerances, and materials for ring joint gaskets used with ASME B16.5 flanges.
When Ring Joint Gaskets Are Used
RTJ gaskets are specified for:
- High-pressure applications (typically Class 600 and above, though available for Class 150/300)
- High-temperature services where spiral wound gaskets may not provide adequate sealing
- Critical services requiring zero-leakage joints (subsea, sour gas, high-pressure steam)
- Wellhead and Christmas tree connections per API 6A
Ring Gasket Dimensions (ASME B16.20)
| R-Number | NPS | Class | OD (mm) | ID (mm) | Height (mm) | Width (mm) | Groove Depth (mm) |
|---|---|---|---|---|---|---|---|
| R-11 | 1/2 | 2500 | 28.7 | 22.1 | 9.5 | 3.3 | 5.6 |
| R-13 | 3/4 | 2500 | 34.1 | 26.9 | 9.5 | 3.6 | 5.6 |
| R-16 | 1 | 2500 | 41.1 | 33.0 | 11.2 | 4.1 | 6.4 |
| R-20 | 1-1/2 | 2500 | 54.8 | 44.5 | 11.2 | 5.2 | 6.4 |
| R-23 | 2 | 600-2500 | 66.5 | 55.6 | 11.2 | 5.6 | 6.4 |
| R-26 | 2-1/2 | 600-2500 | 74.6 | 63.5 | 11.2 | 5.6 | 6.4 |
| R-31 | 3 | 600-2500 | 90.5 | 77.8 | 11.2 | 6.4 | 6.4 |
| R-37 | 4 | 600-2500 | 114.3 | 100.0 | 13.5 | 7.1 | 7.9 |
| R-41 | 5 | 600-2500 | 136.7 | 122.2 | 13.5 | 7.1 | 7.9 |
| R-45 | 6 | 600-2500 | 163.6 | 147.6 | 15.7 | 7.9 | 9.5 |
| R-49 | 8 | 600-2500 | 211.1 | 193.8 | 15.7 | 8.7 | 9.5 |
| R-53 | 10 | 600-2500 | 260.4 | 241.3 | 17.5 | 9.5 | 11.2 |
| R-57 | 12 | 600-2500 | 313.9 | 292.1 | 17.5 | 11.2 | 11.2 |
| R-61 | 14 | 600-2500 | 346.1 | 323.9 | 17.5 | 11.2 | 11.2 |
| R-65 | 16 | 600-2500 | 393.7 | 371.6 | 17.5 | 11.2 | 11.2 |
| R-69 | 18 | 600-2500 | 447.5 | 422.4 | 20.6 | 12.7 | 12.7 |
| R-73 | 20 | 600-2500 | 498.3 | 473.1 | 20.6 | 12.7 | 12.7 |
| R-77 | 24 | 600-2500 | 596.9 | 571.5 | 20.6 | 12.7 | 12.7 |
Dimensions are for octagonal cross-section rings per ASME B16.20. Oval rings have slightly different cross-section geometry but identical OD, ID, and groove dimensions.
Oval vs Octagonal Ring Gaskets
| Feature | Oval (Type R) | Octagonal (Type R) |
|---|---|---|
| Cross-section shape | Elliptical | Eight-sided |
| Sealing mechanism | Line contact (inner and outer radii) | Face contact (flat surfaces) |
| Groove fit | Fits both oval and octagonal grooves | Fits only octagonal grooves |
| Sealing pressure | Lower bolt load required | Higher bolt load required |
| Reusability | Single use only | Single use only |
| Common application | Older installations, API 6A | Standard for new construction |
| Interchangeability | Fits in octagonal grooves | Does NOT fit in oval grooves |
Octagonal rings are preferred for new construction because the flat contact surfaces provide a better seal and are easier to manufacture to tight tolerances. Oval rings are used for legacy grooves and specific API 6A wellhead applications.
Ring Gasket Materials
| Material | ASME Designation | Application |
|---|---|---|
| Soft iron | - | Low-pressure, low-temperature |
| Low-carbon steel | - | General service, moderate P/T |
| 304 Stainless Steel | F304 | Corrosion-resistant services |
| 316 Stainless Steel | F316 | Marine, chemical services |
| Alloy 625 (Inconel) | - | High-temperature, sour gas |
| Monel 400 | - | Seawater, HF acid |
The ring material must be softer than the flange groove material to ensure the ring deforms into the groove surfaces and creates a seal. Hardness is verified per ASME B16.20 requirements.
For a comparison of RTJ vs spiral wound gaskets and guidance on gasket selection, see the full reference guide.
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