1. What is A671/CG100 Class 70 Steel Pipe?
Answer:
A671/CG100 Class 70 is an electric-fusion-welded (EFW) steel pipe conforming to ASTM A671 standards, designed for high-pressure and low-temperature service. The "CG100" denotes carbon steel material, while "Class 70" indicates its pressure class (higher than Class 22/32) and stringent testing requirements (e.g., 100% radiography).
Key Features:
Pressure Rating: Suited for systems requiring ≥70 MPa design pressure.
Temperature Range: Optimized for cryogenic conditions (down to -46°C/-50°F).
Construction: Longitudinal seams welded with full penetration, often post-weld heat-treated (PWHT).
2. Where is Class 70 Typically Used?
Answer:
Primary applications include:
Oil & Gas: High-pressure transmission lines, LNG terminals.
Power Generation: Boiler feedwater, steam lines.
Chemical Plants: Handling aggressive fluids at low temperatures.
Note: Class 70 is selected for critical systems where leak integrity and burst resistance are paramount.
3. How Does Class 70 Differ from Lower Classes (e.g., Class 22)?
Answer:
| Parameter | Class 70 | Class 22 |
|---|---|---|
| Pressure Rating | Higher (≥70 MPa) | Moderate (lower than Class 70) |
| Radiography | 100% RT + UT (Ultrasonic Testing) | 100% RT only |
| Material Toughness | Enhanced impact testing at -46°C | Standard low-temp testing |
Key Difference: Class 70 undergoes more rigorous testing and uses thicker walls/higher-grade materials.
4. What Are the Material and Mechanical Specifications?
Answer:
ASTM A671 Compliance: Mandates chemical composition control (e.g., C≤0.30%, P/S≤0.025%).
Mechanical Properties:
Tensile Strength: ≥485 MPa
Yield Strength: ≥275 MPa
Charpy V-notch: ≥20J at -46°C (for toughness verification).
Dimensions: Typically supplied in sizes 6" to 48" OD, with wall thicknesses per ASME B36.10.
5. What Are the Fabrication and Quality Control Requirements?
Answer:
Welding: SAW (Submerged Arc Welding) or similar, with 100% radiographic (RT) and ultrasonic (UT) inspection.
Testing:
Hydrostatic test at 1.5x design pressure.
Hardness testing to avoid HAZ (Heat-Affected Zone) cracking.
Certification: Mill test reports (MTRs) must include chemical, mechanical, and NDE results.
Note: Compliance with ASME B31.3 (Process Piping) and API 5L (if applicable) is common.
