1. What is ASTM A671 CF70 Class 70?
Answer:
ASTM A671 is a standard for electric-fusion-welded steel pipes designed for atmospheric and low-temperature service. The CF70 Class 70 designation indicates:
Material Grade: Carbon steel with a minimum yield strength of 70 ksi (483 MPa).
Manufacturing: Pipes are fabricated from plate/sheet and longitudinally welded.
Application: Used in low-temperature environments (down to -50°F/-45°C).
2. What are the chemical requirements for CF70 Class 70?
Answer:
Key composition limits (wt.% max, unless specified):
Carbon (C): 0.30%
Manganese (Mn): 1.20%
Phosphorus (P): 0.035%
Sulfur (S): 0.035%
Silicon (Si): 0.10–0.35%
Note: Higher Mn/C ratio improves low-temperature toughness.
3. What are the mechanical properties of CF70 Class 70 pipes?
Answer:
Tensile Strength: 80–100 ksi (550–690 MPa)
Yield Strength: ≥70 ksi (483 MPa)
Elongation: ≥18% (varies with wall thickness)
Impact Testing: Required for Class 70 (e.g., Charpy V-notch at -50°F/-45°C).
4. What are common applications of these pipes?
Answer:
Typical uses include:
Low-temperature pressure vessels (e.g., LNG storage).
Cryogenic pipelines in petrochemical plants.
Power plants and refrigeration systems.
Key advantage: Weldability and toughness at sub-zero temperatures.
5. How does ASTM A671 CF70 differ from API 5L or ASTM A106 pipes?
Answer:
| Feature | ASTM A671 CF70 | API 5L/A106 |
|---|---|---|
| Manufacturing | Electric-fusion-welded | Seamless/welded |
| Temperature | Low-temperature service | High-temperature (A106) |
| Application | Cryogenic/pressure | Oil/gas pipelines (API) |
Bonus Note: ASTM A671 pipes require hydrostatic testing and non-destructive examination (NDE) per the standard. For exact dimensions/tolerances, refer to ASTM A671 Table 3.
