Gasket Dimensions: American Standard 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. American Standard B16.20 defines the dimensions, tolerances, and materials for ring joint gaskets used with American Standard 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 (American Standard 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 American Standard 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 | American Standard 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 American Standard 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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