1. What is ASTM A671 CD80 Class 31 Steel Pipe?
Answer:
ASTM A671 CD80 Class 31 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 ensure cryogenic toughness.
Class 31: Minimum yield strength of 31 ksi (214 MPa), engineered for moderate-to-high-pressure cryogenic applications (e.g., LNG processing, liquid hydrogen transfer, industrial gas storage).
2. What are the manufacturing and certification requirements?
Answer:
Welding: EFW process with low-sulfur filler metal, 100% radiography (RT) + ultrasonic testing (UT) for weld integrity.
Heat Treatment: Normalized or quenched & tempered for cryogenic stability.
Certification: Mill test reports (MTRs) must include:
Chemical composition (e.g., C ≤ 0.25%, Mn ≤ 1.65%, microalloyed with Nb/V).
Mechanical properties (yield strength ≥ 31 ksi, tensile strength 80–100 ksi).
Impact test results at -80°F (minimum 32 ft-lb average energy absorption).
3. How does Class 31 compare to other ASTM A671 classes?
Answer:
| Parameter | CD80 Class 31 | CD80 Class 20 | CD80 Class 60 |
|---|---|---|---|
| Yield Strength | 31 ksi (214 MPa) | 20 ksi (138 MPa) | 60 ksi (414 MPa) |
| Application | Moderate-high pressure | Moderate-pressure | High-pressure cryogenic |
| Cost | Mid-to-high | Mid-range | Premium |
4. What are standard dimensions and tolerances?
Answer:
Diameter: 16"–144" OD (for industrial and energy projects).
Wall Thickness: Tolerance ±10% nominal thickness (per ASTM A671).
Length: Typically 40ft (12.2m), customizable up to 80ft for reduced field welds.
5. How to ensure corrosion protection and longevity?
Answer:
External:
3LPE/3LPP coating for buried or submerged service.
Cathodic protection for corrosive environments (e.g., coastal/offshore).
Internal:
FBE or polyurethane linings for chemical resistance (e.g., H₂S/CO₂ in LNG).
Maintenance:
Annual smart pigging with MFL/EC sensors for defect detection.
