1. What is A671/CG100 Class 71 Steel Pipe?
Answer:
A671/CG100 Class 71 is an electric-fusion-welded (EFW) carbon steel pipe per ASTM A671, designed for ultra-high-pressure and cryogenic service. The "CG100" indicates carbon steel material, while "Class 71" denotes its exceptional pressure rating (≥71 MPa) and 100% radiographic testing (RT).
Key Features:
Pressure Class: Higher than Class 70, suitable for extreme conditions.
Temperature Range: Certified for -46°C to 200°C (-50°F to 392°F).
Construction: Longitudinal seams with full penetration welds, often post-weld heat-treated (PWHT).
2. Typical Applications of Class 71 Pipes
Answer:
Used in critical industries requiring leak-proof integrity:
Oil & Gas: Offshore platforms, high-pressure gas transmission.
Power Plants: Supercritical steam lines, nuclear coolant systems.
Chemical Processing: Handling corrosive fluids at high pressures.
Note: Class 71 is chosen for safety-critical systems where failure risks are unacceptable.
3. How Does Class 71 Differ from Class 70?
Answer:
| Parameter | Class 71 | Class 70 |
|---|---|---|
| Pressure Rating | ≥71 MPa (higher) | ≥70 MPa |
| Testing | 100% RT + UT + stricter impact tests | 100% RT + UT |
| Material Grade | Enhanced carbon steel (lower S/P content) | Standard CG100 |
Key Difference: Class 71 has tighter tolerances and additional quality checks.
4. Material and Mechanical Specifications
Answer:
Chemical Composition:
Carbon: ≤0.25%, Sulfur/Phosphorus: ≤0.020% (improved weldability).
Mechanical Properties:
Tensile Strength: ≥515 MPa
Yield Strength: ≥315 MPa
Charpy V-notch: ≥27J at -46°C (superior low-temp toughness).
Dimensions: Common sizes 8" to 60" OD, wall thickness per ASME B36.10.
5. Fabrication and Quality Assurance
Answer:
Welding: SAW (Submerged Arc Welding) with 100% RT/UT and PWHT.
Testing:
Hydrostatic test at 1.8x design pressure (exceeds Class 70).
Hardness mapping to prevent stress corrosion cracking (SCC).
Certification: Full traceability with MTRs (Mill Test Reports) and third-party inspection.
Standards Compliance: ASME B31.3, API 5L (supplementary), and ISO 3183.
