1. What is ASTM A671 CC65 Class 71?
Answer:
ASTM A671 CC65 Class 71 specifies electric-fusion-welded carbon steel pipes for low-temperature service (down to -65°F/-54°C).
Grade CC65: Ensures controlled chemistry (e.g., carbon ≤0.30%, balanced Mn/Si).
Class 71: Denotes minimum yield strength of 71 ksi (490 MPa) and specific pressure/wall thickness ratings.
Standard: ASTM A671 (for atmospheric/cryogenic pressure vessels).
2. Key Applications of Class 71 Pipes?
Answer:
Used in critical低温infrastructure:
LNG Terminals: Cryogenic fluid transport.
Petrochemical Plants: Ethylene/ammonia pipelines.
Power Generation: Cold-climate cooling systems.
3. Material Properties & Testing Requirements?
Answer:
Impact Toughness: Charpy V-notch tested at -65°F (minimum energy absorption required).
Tensile Strength: 85–110 ksi (586–758 MPa).
Non-Destructive Testing (NDT): 100% radiography (RT) or ultrasonic (UT) per ASTM E164/E213.
4. How Does Class 71 Compare to Class 70?
Answer:
| Parameter | Class 71 | Class 70 |
|---|---|---|
| Yield Strength | 71 ksi (490 MPa) | 70 ksi (483 MPa) |
| Design Pressure | Slightly higher | Comparable |
| Cost | Marginally more expensive | Similar |
5. Fabrication Best Practices?
Answer:
Welding: Use low-hydrogen electrodes (e.g., AWS E7018) with preheat (200–300°F/93–149°C).
Post-Weld Heat Treatment (PWHT): Mandatory for stress relief (per ASME Sec VIII).
Coating: Apply epoxy or FBE coatings for corrosion resistance in harsh environments.
