1. What is ASTM A671 CD80 Class 21 Steel Pipe?
Answer:
ASTM A671 CD80 Class 21 is an electric-fusion-welded (EFW) carbon steel pipe designed for low-temperature service (down to -80°F/-62°C). Key specifications:
CD80: Material grade requiring Charpy V-notch impact testing at -80°F to validate cryogenic toughness.
Class 21: Minimum yield strength of 21 ksi (145 MPa), suitable for moderate-pressure cryogenic applications (e.g., LNG transfer lines, industrial gas distribution).
2. What are the manufacturing and certification requirements?
Answer:
Welding: EFW process with filler metal, 100% radiography (RT) or ultrasonic testing (UT) for weld integrity.
Heat Treatment: Stress-relieved or normalized to enhance low-temperature ductility.
Certification: Mill test reports (MTRs) must include:
Chemical composition (e.g., C ≤ 0.30%, Mn ≤ 1.45%).
Mechanical properties (yield strength ≥ 21 ksi, tensile strength 60–80 ksi).
Impact test results at -80°F (minimum 22 ft-lb average energy absorption).
3. How does Class 21 compare to other ASTM A671 classes?
Answer:
| Parameter | CD80 Class 21 | CD80 Class 10 | CD80 Class 60 |
|---|---|---|---|
| Yield Strength | 21 ksi (145 MPa) | 10 ksi (69 MPa) | 60 ksi (414 MPa) |
| Application | Moderate-pressure cryogenic | Low-pressure | High-pressure cryogenic |
| Cost | Mid-range | Low | Premium |
4. What are standard dimensions and tolerances?
Answer:
Diameter: 16"–120" OD (standard for industrial pipelines).
Wall Thickness: Tolerance ±10% nominal thickness (per ASTM A671).
Length: Typically 40ft (12.2m), customizable up to 60ft.
5. How to ensure corrosion protection and longevity?
Answer:
External:
3LPE coating (3-layer polyethylene) for buried pipelines.
Cathodic protection for corrosive environments.
Internal:
FBE lining for chemical resistance (e.g., LNG/BOG compatibility).
Maintenance: Biannual inspections for coating and weld integrity.
