Here is a detailed introduction to the API 6A 6BX Figure 8 Blank Flange, covering pressure ratings, material options, performance requirements, and applicable standards:
API 6A: Specifies wellhead and Christmas tree equipment for the oil and gas industry, suitable for high-pressure and corrosive environments.
6BX Flange Connection:
Pressure Ratings: 2,000 PSI (13.8 MPa) to 20,000 PSI (138 MPa), common classes include 2K, 3K, 5K, 10K, 15K, 20K.
Sealing Type: Metal-to-metal seal (R-type groove), designed for high-pressure gas-tight applications.
Figure 8 Blank:
Function: Used for temporary pipeline isolation—one side is solid (blind), and the other side has an opening (flow path) for easy switching.
Construction: Fully forged to ensure structural integrity under high pressure.
API 6A 6BX Figure 8 Blank Flanges can be made from various materials, depending on pressure, corrosion resistance, and cost requirements:
| Material Type | Typical Grades | Applications | Characteristics |
|---|---|---|---|
| Carbon Steel | ASTM A105 | Low-pressure, non-corrosive environments (e.g., water, air) | Low cost, good weldability, but poor corrosion resistance. |
| Low-Alloy Steel | AISI 4130 / 4140 | High-pressure, high-temperature (e.g., wellheads) | High strength, excellent mechanical properties after heat treatment. |
| Stainless Steel | ASTM A182 F316 / F304 | Sour service (H₂S, CO₂ environments) | Corrosion-resistant but higher cost. |
| Duplex Stainless | ASTM A182 F51 / F53 | Highly corrosive environments (e.g., seawater, sour oil/gas) | High strength + corrosion resistance, but complex welding. |
| Nickel Alloys | Inconel 625 / 718 | Extreme HP/HT sour environments | Suitable for harsh conditions, but expensive. |
| Property | API 6A Requirement | Typical Value (Heat-Treated 4130) |
|---|---|---|
| Tensile Strength | ≥ 655 MPa (95,000 PSI) | 655-895 MPa (95,000-130,000 PSI) |
| Yield Strength | ≥ 517 MPa (75,000 PSI) | 517-758 MPa (75,000-110,000 PSI) |
| Elongation | ≥ 18% | 18-22% |
| Impact Toughness (Charpy V) | ≥ 27J @ -18°C | 40-60J @ -18°C (good low-temperature toughness) |
| Hardness | 190-230 HB | Compliant with NACE MR0175 (SSC resistance) |
Forging Process: Fully forged to avoid weld defects (unless customer permits segmented welding).
Heat Treatment: Normalizing + tempering or quenching + tempering for uniform material properties.
Non-Destructive Testing (NDT):
Ultrasonic Testing (UT): Detects internal flaws.
Magnetic Particle Testing (MT) or Liquid Penetrant Testing (PT): Checks for surface cracks.
Dimensional Standards: Strict compliance with API 6A and ASME B16.5 tolerances.
High-Pressure Oil & Gas Wells: Christmas trees, casing heads, manifolds.
Sour Service: Must comply with NACE MR0175/ISO 15156 (sulfide stress cracking resistance, SSC).
Offshore Platforms: Duplex stainless steel or nickel alloys for seawater corrosion resistance.
10K/15K High Pressure: Prefer AISI 4130/4140 (high strength + cost-effective).
Sour Service (H₂S): Choose F316/F51 duplex steel or Inconel 625.
Low-Temperature Service: Requires impact testing (e.g., -46°C).
Material Certification: MTC (Material Test Certificate), heat treatment reports, NDT reports.
Customization: Anti-corrosion coatings (e.g., nickel-phosphorus plating), non-standard sizes.
For detailed material chemical compositions or mechanical test data, refer to ASTM A105, ASTM A182, API 6A 21st Edition, or other relevant standards.
