1. What is ASTM A671 CJB115 Class 21 Steel Pipe?
Answer:
ASTM A671 CJB115 Class 21 is an electric-fusion-welded (EFW) carbon steel pipe designed for high-pressure and elevated-temperature industrial applications (typically above -20°F/-29°C). The "Class 21" designation indicates a minimum yield strength of 21 ksi (145 MPa), bridging the gap between standard and specialized high-pressure systems.
2. Key Specifications and Material Properties?
Answer:
Material Grade: CJB115 carbon steel (higher carbon than CJA grades).
Mechanical Properties:
Yield Strength: ≥21 ksi (145 MPa).
Tensile Strength: 75–95 ksi (517–655 MPa).
Impact Test: Optional (required if specified for low-temperature use).
Chemical Composition:
Carbon (C): ≤0.35%, Manganese (Mn): ≤1.35%, P/S ≤0.035%.
3. Typical Industrial Applications?
Answer:
High-pressure steam and process piping in power plants.
Oil and gas transmission systems with moderate thermal cycling.
Industrial boilers and heat exchangers.
4. How Does It Compare to Class 20 and Class 25?
Answer:
| Class | Yield Strength | Pressure Capability |
|---|---|---|
| Class 20 | 20 ksi (138 MPa) | Standard high-pressure |
| Class 21 | 21 ksi (145 MPa) | Enhanced high-pressure |
| Class 25 | 25 ksi (172 MPa) | Specialized high-pressure |
5. Fabrication and Quality Control Requirements?
Answer:
Welding: Preheat (250–350°F) mandatory for thickness >1" (25.4 mm).
Testing: Hydrostatic (1.5x design pressure) + optional UT/RT for critical joints.
Forming: Hot bending preferred for severe deformations.
Inspection: Full compliance with ASTM A671-26, including dimensional checks.
