1. What is ASTM A671 CF65 Class 71 Pipe?
Answer:
ASTM A671 CF65 Class 71 is an electric-fusion-welded (EFW) carbon steel pipe designed for low-temperature and high-pressure service (rated for -65°F/-54°C).
Standard: ASTM A671 (EFW pipes for cryogenic/pressure vessel use).
Grade: CF65 denotes carbon steel with enhanced impact resistance.
Class 71: Minimum yield strength of 71 ksi (490 MPa).
Key Applications: LNG pipelines, cryogenic storage tanks, and petrochemical plants.
2. Material Properties & Testing Requirements
Answer:
Chemistry: Low-carbon steel (e.g., C ≤ 0.30%, Mn ≤ 1.20%) with strict control of sulfur/phosphorus (≤0.025%).
Impact Testing: Mandatory Charpy V-notch testing at -65°F (minimum energy absorption specified).
Welding: Longitudinal seam welded via submerged arc welding (SAW), often with PWHT for stress relief.
3. How Does It Differ from Other ASTM A671 Classes?
| Feature | CF65 Class 71 | CF65 Class 70 | CC65 Class 72 |
|---|---|---|---|
| Yield Strength | 71 ksi (490 MPa) | 70 ksi (483 MPa) | 72 ksi (500 MPa) |
| Temp Range | -65°F to +650°F | -65°F to +650°F | -65°F to +650°F |
| Common Use | High-pressure cryogenic | General cryogenic | High-strength cryogenic |
4. Dimensions & Manufacturing Tolerances
Answer:
Size Range: 16" to 120" OD (common for large-diameter pipelines).
Wall Thickness: 0.3" to 2.5" (varies with design pressure; Class 71 often uses thicker walls).
Tolerances: Complies with ASTM A671 Annex A:
OD: ±1%
Wall thickness: ±10%
Straightness: ≤0.1% of length.
5. Typical Applications & Industry Standards
Answer:
Primary Uses:
LNG Export Terminals (transporting liquefied natural gas at -260°F).
Refineries (low-temperature alkylation units).
Power Plants (ammonia/CO₂ handling systems).
Compliance: Meets ASME B31.3 (Process Piping) and API 5L (supplementary requirements).
