API 6A Flanges (Wellhead & Christmas Tree Equipment)
API 6A Flanges are the critical connection components used in high-pressure wellhead and christmas tree equipment. Unlike standard piping flanges (ASME B16.5), API 6A flanges are engineered to withstand extreme pressures and harsh drilling environments.
At Sunhy, we manufacture API 6A flanges strictly in accordance with API Spec 6A (ISO 10423). Our flanges are designed for high-pressure service ranging from 2,000 PSI (13.8 MPa) to 20,000 PSI (138 MPa), ensuring safety and reliability in oil & gas extraction.
Types of API 6A Flanges We Supply
Stainless Steel Flanges
By Design Type
By Standard & Class
Advanced Materials
API 6A Flange Material & Manufacturing Quality
High-pressure environments allow for zero margin of error. Our manufacturing process ensures integrity:
Raw Material: We use premium Forged Alloy Steel (typically AISI 4130 or 4140) for standard service. For sour gas service ($H_2S$ environments), we provide materials compliant with NACE MR0175.
Heat Treatment: Normalized and tempered to achieve the required Yield Strength (e.g., 45K, 60K, 75K) and impact toughness.
Testing (PSL Level Verification):
Tensile & Impact Testing.
Hardness Testing (Brinell/Rockwell).
Ultrasonic Testing (UT) and Magnetic Particle Inspection (MPI).
Note: All our API 6A flanges come with full MTR (Material Test Reports) traceable to the heat number.
What is API 6A Flange?
An API 6A flange is a ring-type pressure-containing connector defined by the API 6A standard for upstream oil and gas equipment, especially wellheads and Christmas trees. It is engineered for very demanding service, with working pressures up to 20,000 psi and resistance to temperature cycling and corrosive fluids such as H₂S, so it is much more robust than typical ASME B16.5 industrial flanges.
In practice, API 6A flanges are selected together with defined material classes, temperature classes and PSL/PR levels, and should be manufactured and pressure-tested strictly in line with the API 6A specification to ensure reliable sealing in high-pressure, sour-gas service.
Technical Specifications & Parameters
| Parameter | Specification Details |
| Standard | API Spec 6A / ISO 10423 |
| Flange Types | Type 6B, Type 6BX, Weld Neck, Blind, Threaded, Target Flange, Test Flange |
| Pressure Ratings | 2000, 3000, 5000, 10000, 15000, 20000 PSI |
| Material Classes | AA, BB, CC, DD, EE, FF, HH (Carbon Steel, Low Alloy Steel, Stainless Steel, Duplex) |
| Product Specification Level | PSL 1, PSL 2, PSL 3, PSL 3G, PSL 4 |
| Temperature Ratings | K, L, P, R, S, T, U, V (-60°C to 121°C) |
API 6A Flange Dimensions & Weights
We provide comprehensive API 6A flange charts for engineers and procurement teams to verify sizes.
Need a complete data sheet? Includes detailed bolt sizes, ring gasket numbers, and weight charts.
*”Data is for reference only. Always consult the specific project engineering requirements.”
| Nominal Size (Bore) |
Flange OD (O) |
Total Thickness (T) |
Bolt Circle (BC) |
Bolt Hole (Qty x Dia) |
|---|---|---|---|---|
| 2-1/16″ | 8.50″ (215 mm) | 1.81″ (46.1 mm) | 6.50″ (165.1 mm) | 8 x 7/8″ |
| 2-9/16″ | 9.62″ (245 mm) | 1.94″ (49.3 mm) | 7.50″ (190.5 mm) | 8 x 1″ |
| 3-1/8″ | 10.50″ (265 mm) | 2.19″ (55.6 mm) | 8.00″ (203.2 mm) | 8 x 1-1/8″ |
| 4-1/16″ | 12.25″ (310 mm) | 2.44″ (62.0 mm) | 9.50″ (241.3 mm) | 8 x 1-1/4″ |
| 5-1/8″ | 14.75″ (375 mm) | 3.19″ (81.0 mm) | 11.50″ (292.1 mm) | 8 x 1-1/2″ |
| 7-1/16″ | 15.50″ (395 mm) | 3.62″ (92.1 mm) | 12.50″ (317.5 mm) | 12 x 1-1/2″ |
| 9″ | 19.00″ (485 mm) | 4.06″ (103.2 mm) | 15.50″ (393.7 mm) | 12 x 1-7/8″ |
| 11″ | 23.00″ (585 mm) | 4.69″ (119.1 mm) | 19.00″ (482.6 mm) | 12 x 2″ |
* Dimensions for API 6A Type 6B 5000 PSI Flanges. For 2000 or 3000 PSI, please contact us.
| Nominal Size (Bore) |
Flange OD (O) |
Total Thickness (T) |
Bolt Circle (BC) |
Ring Gasket (BX) |
|---|---|---|---|---|
| 1-13/16″ | 7.38″ (185 mm) | 1.66″ (42.1 mm) | 5.75″ (146.1 mm) | BX-151 |
| 2-1/16″ | 7.88″ (200 mm) | 1.73″ (44.1 mm) | 6.25″ (158.8 mm) | BX-152 |
| 2-9/16″ | 9.12″ (230 mm) | 2.02″ (51.2 mm) | 7.25″ (184.2 mm) | BX-153 |
| 3-1/16″ | 10.62″ (270 mm) | 2.30″ (58.4 mm) | 8.50″ (215.9 mm) | BX-154 |
| 4-1/16″ | 12.44″ (315 mm) | 2.77″ (70.3 mm) | 10.19″ (258.8 mm) | BX-155 |
| 5-1/8″ | 14.06″ (360 mm) | 3.12″ (79.4 mm) | 11.81″ (300.0 mm) | BX-169 |
| 7-1/16″ | 18.88″ (480 mm) | 4.06″ (103.2 mm) | 15.88″ (403.2 mm) | BX-156 |
| 9″ | 21.75″ (550 mm) | 4.88″ (123.9 mm) | 18.75″ (476.3 mm) | BX-157 |
| 11″ | 25.75″ (655 mm) | 5.56″ (141.3 mm) | 22.25″ (565.2 mm) | BX-158 |
| 13-5/8″ | 30.25″ (770 mm) | 6.62″ (168.3 mm) | 26.50″ (673.1 mm) | BX-159 |
* Standard Dimensions for API Spec 6A Type 6BX 10000 PSI Flanges.
Difference Between API 6A and ASME B16.5
While both standards cover flanges, they are distinct:
API 6A focuses on wellhead equipment with much higher pressure ratings (up to 20,000 PSI).
ASME B16.5 focuses on pipeline systems (up to Class 2500, roughly 6,000 PSI).
Interchangeability: They are generally not interchangeable due to different dimensions and material requirements.
For standard pipeline applications, please refer to our ASME B16.5 Flanges page.
Detailed Classification: Type 6B vs. Type 6BX
Understanding the design differences is crucial for safe installation:
Type 6B Flanges (2,000 – 5,000 PSI):
Designed for lower pressure ranges within the API standard.
Sealing: Uses R or RX ring gaskets.
Design Feature: These are not designed for face-to-face contact. The bolting tension acts on the ring gasket seal, maintaining a standoff gap between the flange faces.
Common Uses: Standard wellhead connections, older systems.
Type 6BX Flanges (2,000 – 20,000 PSI):
Designed for high-pressure applications (up to 20K PSI).
Sealing: Uses BX pressure-energized ring gaskets.
Design Feature: Designed for face-to-face contact. This ensures the flange bolts are not subjected to additional bending stresses, making them ideal for ultra-high pressure environments.
Common Uses: Deepwater drilling, high-pressure gas flanges, hydrogen service.
Custom High Pressure Flange Solutions
Beyond standard dimensions, we offer OEM high pressure flange services:
Companion Flanges: Threaded explicitly to match casing or tubing threads.
Blind Flanges: For closing off wellhead outlets during testing.
Test Flanges: Specialized flanges with ports for pressure testing.
Adapter Flanges: For connecting different sizes or pressure ratings safely.
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FAQ
What is the main difference between API 6A and ASME B16.5 flanges?
The primary difference lies in their design application and pressure containment capabilities.
Application: API 6A flanges are engineered specifically for upstream wellhead and Christmas tree equipment, designed to withstand extreme pressure fluctuations, shock loads, and untreated corrosive fluids (e.g., H2S, CO2). ASME B16.5 flanges are intended for general industrial and downstream piping systems with relatively stable conditions.
Pressure Ratings: API 6A flanges possess significantly higher pressure ratings than ASME B16.5 flanges of comparable physical dimensions. For example, a flange that appears dimensionally similar may be rated for 5,000 psi under API 6A, but only equivalent to ~3,705 psi (Class 1500) under ASME standards. They are not interchangeable, and mixing them poses a severe safety risk.
What is the difference between Type 6B and Type 6BX flanges?
These types represent distinct design philosophies for different pressure ranges:
Type 6B: Designed for low-to-medium pressures (2,000 – 5,000 psi). They utilize R or RX style gaskets. A key design feature is the standoff, meaning the flange faces are not designed to touch when fully bolted; the bolt load acts primarily on the gasket.
Type 6BX: Designed for high pressures (10,000 – 20,000 psi). They strictly use BX style gaskets. 6BX flanges feature a Raised Face and are designed to allow face-to-face contact (though not strictly required for sealing). This contact provides overload protection for the gasket and increases the connection’s structural rigidity.
Which gasket should be used for high-pressure API 6A flanges?
For high-pressure applications (10,000 psi and above, i.e., Type 6BX flanges), BX Ring Gaskets are mandatory.
Technical Features: BX gaskets are pressure-energized and incorporate a unique pressure balance hole to prevent pressure locking in the groove or dangerous gas entrapment during decompression.
Medium Pressure: For Type 6B flanges (up to 5,000 psi), RX gaskets are recommended over standard R gaskets for critical applications as they also utilize internal fluid pressure to enhance the seal (pressure-energized).
What materials are API 6A flanges made from?
API 6A flanges are typically manufactured from high-strength low-alloy steel forgings (e.g., AISI 4130, 4140, or 8630 modified) to achieve high yield strengths (e.g., 60K or 75K psi).
Corrosion Resistance: Material selection depends on the “Material Class” (AA through HH).
Sour Service: For environments containing Hydrogen Sulfide (H2S), materials (Classes DD, EE, FF, HH) must comply with NACE MR0175 / ISO 15156 standards. This involves strict hardness controls (typically < 22 HRC) to prevent Sulfide Stress Cracking (SSC). Extremely corrosive environments (HH Class) may require Corrosion Resistant Alloy (CRA) cladding, such as Inconel 625.
Do you provide API 6A flange bolt torque charts?
Yes, however, torque charts must be used with extreme caution regarding the coefficient of friction (f).
The Friction Variable: Standard torque values often assume a friction coefficient of f = 0.13 (light oil). However, if bolts are coated (e.g., Teflon/Xylan) or used with specific lubricants (e.g., Moly paste), the coefficient may drop to f = 0.07. Applying “dry” torque values to lubricated bolts can result in bolt yield or failure.
Recommendation: For large diameters (> 1-1/2″) or high-pressure connections, hydraulic tensioning is strongly recommended over torqueing. Tensioning applies direct load, eliminating friction variables and ensuring accurate preload.