ASTM A671 CF70 Class 72 steel pipes

1. What is ASTM A671 CF70 Class 72?

Answer:
ASTM A671 covers electric-fusion-welded steel pipes for low-temperature and high-pressure services. The CF70 Class 72 designation specifies:

Material: Carbon steel with a minimum yield strength of 72 ksi (496 MPa).

Manufacturing: Pipes are fabricated from plates/sheets via longitudinal welding.

Temperature Range: Designed for cryogenic service down to -50°F (-45°C).
Note: Class 72 is a less common variant; Class 70/71 are more frequently used.

2. Chemical Composition Requirements for CF70 Class 72?

Answer:
Key chemical limits (weight % max, unless stated):

Carbon (C): ≤0.30%

Manganese (Mn): ≤1.20%

Phosphorus (P): ≤0.035%

Sulfur (S): ≤0.035%

Silicon (Si): 0.10–0.35% (improves weldability and toughness).
Similar to Class 70/71 but with adjusted mechanical properties.

3. Mechanical Properties of CF70 Class 72 Pipes?

Answer:

Tensile Strength: 80–100 ksi (550–690 MPa).

Yield Strength: ≥72 ksi (496 MPa) (key difference from Class 70/71).

Elongation: ≥18% (dependent on wall thickness).

Impact Testing: Mandatory Charpy V-notch test at -50°F (-45°C).

4. Typical Applications of ASTM A671 CF70 Class 72?

Answer:
Used in demanding low-temperature environments:

LNG (liquefied natural gas) pipelines and storage tanks.

Cryogenic processing units in petrochemical plants.

Power plant coolant systems requiring high-pressure resistance.
Advantage: Optimized balance of strength and ductility for sub-zero conditions.

5. How Does CF70 Class 72 Compare to Other ASTM/API Standards?

Comparison Table:

Additional Notes:

Testing: Requires hydrostatic testing (per ASTM A671 Section 12) and NDE (e.g., radiography or ultrasonic).

Procurement: Class 72 may require custom orders; confirm availability with suppliers.