What Is API 6A Flange? Wellhead Equipment
API 6A flanges are flanged connections designed specifically for wellhead and christmas tree equipment in upstream oil and gas. Governed by API Specification 6A (ISO 10423), these flanges use a different rating system (2,000-20,000 psi working pressure), different seal technology (BX-type metal ring gaskets), and different material requirements than standard ASME B16.5 piping flanges. API 6A flanges are rated for the extreme pressures, temperatures, and corrosive conditions found at the wellhead.
API 6A Pressure Ratings
| API 6A Rating | Working Pressure (psi) | Working Pressure (barg) | Common Name |
|---|---|---|---|
| 2,000 | 2,000 | 138 | 2K |
| 3,000 | 3,000 | 207 | 3K |
| 5,000 | 5,000 | 345 | 5K |
| 10,000 | 10,000 | 690 | 10K |
| 15,000 | 15,000 | 1,034 | 15K |
| 20,000 | 20,000 | 1,379 | 20K |
Working pressure at rated temperature per API 6A. Higher ratings (up to 30K) exist in API 17D for subsea applications.
Key Specifications
| Property | Detail |
|---|---|
| Standard | API 6A (ISO 10423) |
| Size range | 1-13/16 in to 21-1/4 in (nominal bore) |
| Size designation | Bore diameter (not NPS) |
| Gasket | BX-type metal ring gasket (pressure-energized) |
| Material classes | AA, BB, CC, DD, EE, FF, HH (defines body, trim, and seal materials) |
| Temperature class | K (-60degC), L (-46degC), P (-29degC), S (-18degC), T (ambient), U (121degC), V (180degC) |
| Performance requirement | PR1, PR2 (fire and gas tested) |
| Product specification level | PSL 1 through PSL 4 |
| Traceability | Full material traceability required (PSL 3 and 4) |
Material Classes
| Material Class | Body Material | Typical Application |
|---|---|---|
| AA | Carbon/low-alloy steel | Standard wellhead service |
| BB | Carbon/low-alloy steel (higher strength) | Standard to intermediate |
| CC | Stainless steel (overlay or solid) | Corrosive well fluids |
| DD | Austenitic stainless | High-corrosion service |
| EE | Duplex stainless (CRA) | Sour gas, high chloride |
| FF | Nickel alloy (Inconel, Monel) | Extreme corrosion |
| HH | Case-by-case | Special application |
BX Ring Gaskets
API 6A flanges exclusively use BX-type ring gaskets—pressure-energized metal rings with a vent hole. Unlike standard RTJ rings (R, RX), BX rings have a square cross-section with a through-hole that allows pressure to energize the seal from the inside. Each BX ring number corresponds to a specific flange size and rating.
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