1. What is ASTM A671 CF65 Class 21 Steel Pipe?
Answer:
ASTM A671 CF65 Class 21 is an electric-fusion-welded (EFW) carbon steel pipe designed for low-temperature service (down to -65°F/-54°C). Key specifications:
CF65: Material grade requiring Charpy V-notch impact testing at -65°F to ensure cryogenic toughness.
Class 21: Minimum yield strength of 21 ksi (145 MPa), engineered for moderate-to-high-pressure cryogenic systems (e.g., LNG terminals, industrial gas processing, and chemical pipelines).
2. What are the manufacturing and certification requirements?
Answer:
Welding: EFW with controlled sulfur filler metal, 100% visual inspection + 50% RT (radiographic testing).
Heat Treatment: Stress-relieved (mandatory for thickness > 0.375 inches).
Certification: MTRs must include:
Composition (e.g., C ≤ 0.16%, Mn ≤ 0.85%, P/S ≤ 0.010%).
Mechanical properties (yield ≥ 21 ksi, tensile 90–115 ksi).
Impact tests at -65°F (min 45 ft-lb avg., 35 ft-lb individual).
3. How does Class 21 compare to other ASTM A671 classes?
Answer:
| Parameter | CF65 Class 21 | CF65 Class 10 | CF65 Class 60 |
|---|---|---|---|
| Yield Strength | 21 ksi (145 MPa) | 10 ksi (69 MPa) | 60 ksi (414 MPa) |
| Application | High-pressure cryogenics | Low-pressure | Ultra-high-pressure |
| Cost | Mid-to-high | Economical | Premium |
4. What are standard dimensions and tolerances?
Answer:
Diameter: 16"–144" OD (standard industrial range).
Wall Thickness: Tolerance ±10% nominal thickness (per ASTM A671).
Length: Typically 40ft (12.2m), extendable to 120ft (36.6m) for project needs.
5. How to ensure corrosion protection and longevity?
Answer:
External:
3LPE coating (3-layer polyethylene) for corrosive environments.
Cathodic protection for buried pipelines.
Internal:
FBE or polyurethane lining for chemical/abrasion resistance.
Maintenance:
Annual ultrasonic thickness testing (UT) + coating integrity checks.
