1. What is ASTM A671 CC70 Class 50 Steel Pipe?
Answer:
ASTM A671 CC70 Class 50 is an electric-fusion-welded (EFW) carbon steel pipe designed for ultra-low-temperature service (down to -70°F/-57°C). Key specifications:
CC70: Material grade requiring Charpy V-notch impact testing at -70°F to ensure cryogenic fracture resistance.
Class 50: Minimum yield strength of 50 ksi (345 MPa), suitable for high-pressure cryogenic applications (e.g., LNG export terminals, high-pressure ethylene pipelines).
2. How is it manufactured and certified?
Answer:
Welding: EFW process with filler metal, 100% radiography (RT) or ultrasonic testing (UT) for weld integrity.
Heat Treatment: Stress-relieved or normalized to meet low-temperature ductility requirements.
Certification: Mill test reports (MTRs) include:
Chemical analysis (e.g., C ≤ 0.25%, Mn ≤ 1.35%).
Mechanical properties (yield/tensile strength, elongation).
Impact test results at -70°F.
3. How does Class 50 compare to other ASTM A671 classes?
Answer:
| Parameter | CC70 Class 50 | CC70 Class 22 | CC65 Class 72 |
|---|---|---|---|
| Yield Strength | 50 ksi (345 MPa) | 22 ksi (152 MPa) | 72 ksi (500 MPa) |
| Application | High-pressure cryogenic | Low-pressure storage | Extreme-strength cryogenic |
| Cost | High (premium performance) | Budget-friendly | Highest (specialized) |
4. What are standard dimensions and tolerances?
Answer:
Diameter: 16"–120" OD (standard for large-diameter cryogenic pipelines).
Wall Thickness: Tolerance ±10% nominal thickness (per ASTM A671).
Length: Typically 40ft (12.2m), with custom lengths up to 60ft available.
5. How to ensure corrosion protection and operational safety?
Answer:
External:
3LPE coating (3-layer polyethylene) for buried/offshore pipelines.
Cathodic protection in corrosive environments (e.g., seawater exposure).
Internal:
Epoxy/FBE linings for chemical resistance (e.g., acidic LNG contaminants).
Maintenance:
Annual inspections of welds and coatings, especially in thermal/pressure cycling.
