1. What is ASTM A671 CH115 Class 33 Steel Pipe?
Answer:
ASTM A671 CH115 Class 33 is the most advanced specification in the A671 standard, designed for ultra-extreme conditions combining cryogenic temperatures (-150°F/-101°C) and ultra-high pressure (1,500 psi hydrostatic test).
Material: Micro-alloyed C-Mn-Si steel (CH115) with Ni/Cr additions for enhanced low-temperature ductility.
Key Features:
Triple NDE: 100% radiography (RT) + phased-array UT (PAUT) + magnetic particle testing (MT).
Thermomechanical processing: Accelerated cooling + tempering for grain refinement.
Impact Testing: Charpy V-notch at -150°F (-101°C) with ≥35 ft-lb (47 J) requirement.
2. Material Specifications & Mechanical Properties
Answer:
| Property | Specification |
|---|---|
| Chemical Composition | C≤0.22%, Mn:1.20-1.80%, Si:0.20-0.50%, Ni≤0.50% |
| Tensile Strength | ≥85 ksi (586 MPa) |
| Yield Strength | ≥55 ksi (379 MPa) |
| Elongation | ≥22% (longitudinal) |
| Hardness | ≤22 HRC (to prevent H₂ embrittlement) |
3. Applications
Answer:
Energy:
LNG terminals (-260°F/-162°C storage).
Subsea pipelines in Arctic environments.
Aerospace: Cryogenic fuel lines for reusable launch vehicles.
Nuclear: Gen IV reactor primary coolant systems.
Industrial: High-pressure hydrogen transport (≥10,000 psi).
4. Comparison with Lower Classes
Answer:
| Class | Test Pressure | Min. Temp. | Key Advancement |
|---|---|---|---|
| 33 | 1,500 psi | -150°F (-101°C) | Ni-alloyed, PAUT, -101°C toughness |
| 32 | 1,200 psi | -100°F (-73°C) | Standard AUT, no Ni addition |
| 31 | 900 psi | -75°F (-60°C) | Basic UT, higher thickness range |
5. Standards & Procurement Requirements
Answer:
Primary Standard: ASTM A671 + Supplementary Requirement S12 (Class 33-specific).
Testing Protocols:
ASTM E1820: Fracture toughness (J-integral) testing.
ISO 15614: Welding procedure qualification for cryogenic service.
Certifications:
NACE MR0175 Level VI (for severe sour service).
ASME Section III Div. 3 (nuclear containment).
Procurement Notes:
Mandatory: Batch-specific Charpy curves from -196°C to 20°C.
Optional: Hydrogen compatibility tests per ISO 11114-4.
Delivery Condition: Normalized + tempered with hardness report.
