What Is RX Ring Gasket? API 6BX Standard
The RX design bridges the gap between conventional R-type RTJ gaskets and the higher-pressure BX ring gaskets. RX rings fit into existing R-type flange grooves, making them a direct upgrade path for operators who want pressure-energized sealing without replacing flanges.
Pressure-Energized Sealing Mechanism
The RX ring cross-section is machined with an internal cavity (hollow section). Under bolt load, the ring initially seals like a standard R-type gasket through metal-to-metal deformation. As bore pressure acts on the hollow interior, the ring expands outward against the groove walls, tightening the seal.
| Feature | R-Type (Standard) | RX (Pressure-Energized) | BX |
|---|---|---|---|
| Sealing source | Bolt load only | Bolt load + pressure | Bolt load + pressure (via hole) |
| Groove type | R-groove | R-groove (compatible) | BX-groove only |
| Cross-section | Solid oval or octagonal | Hollow octagonal | Octagonal with pressure hole |
| Max working pressure | 10,000 psi | 15,000 psi | 20,000 psi |
| Reusability | No | No | No |
RX Ring Dimensions (API 6A)
RX ring numbers correspond to standard R-ring numbers, allowing direct replacement in API 6B flanges with R-type grooves:
| RX Ring Number | Bore Size (in) | Pressure Rating (psi) | OD (mm) | ID (mm) | Height (mm) |
|---|---|---|---|---|---|
| RX-20 | 1-13/16 | 2,000-5,000 | 44.45 | 33.32 | 7.92 |
| RX-23 | 2-1/16 | 2,000-5,000 | 50.80 | 38.10 | 9.52 |
| RX-24 | 2-1/16 | 5,000-10,000 | 55.56 | 41.28 | 11.13 |
| RX-26 | 2-9/16 | 2,000-5,000 | 63.50 | 49.21 | 9.52 |
| RX-27 | 2-9/16 | 5,000-10,000 | 66.68 | 52.37 | 11.13 |
| RX-31 | 3-1/8 | 2,000-5,000 | 73.02 | 57.15 | 11.13 |
| RX-35 | 4-1/16 | 2,000-5,000 | 87.31 | 69.85 | 11.13 |
| RX-39 | 4-1/16 | 5,000-10,000 | 95.25 | 74.61 | 12.70 |
The groove dimensions for RX rings match R-ring grooves, which means existing API 6B flanges machined for R-type gaskets can accept RX rings without modification.
Material Grades
| Material | Hardness (max) | Typical Service |
|---|---|---|
| Low-carbon steel (AISI 1018) | 56 HRB | Non-corrosive, low-pressure |
| AISI 4130 | 22 HRc | Standard wellhead service |
| SS 304 | 160 HB | Corrosive service, moderate temperature |
| SS 316 | 160 HB | Marine, chemical service |
| Incoloy 825 | 25 HRc | Sour gas (H2S) per NACE MR0175 |
| Inconel 625 | 30 HRc | Subsea, severe corrosion |
The RX ring must always be softer than the groove material, consistent with all RTJ gasket practice.
When to Specify RX Over R-Type
- Pressure surges: wellhead systems subject to kick pressures and water hammer
- Thermal cycling: the hollow section absorbs thermal expansion better than solid R-type
- Upgrade existing flanges: swap R-type for RX without re-machining grooves
- API 6A compliance: some operators mandate pressure-energized gaskets for all upstream flanged connections above 5,000 psi
Apply bolt load per the API 6A flange assembly procedure using calibrated tensioning tools and stud bolts meeting the equipment specification.
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