ASTM A333 Grade 6 alloy pipe
Dec 05, 2025
What is ASTM A333 Grade 6 Low Temperature Steel Pipe
The A333 Grade 6 steel pipe is based on carbon steel, with small amounts of alloying elements added to improve low-temperature toughness. Its chemical composition mainly includes carbon, manganese, silicon, phosphorus, and sulfur, with strictly controlled phosphorus and sulfur content to ensure the material's impact toughness at low temperatures. In terms of mechanical properties, the steel pipe has a tensile strength of no less than 415 MPa, a yield strength of no less than 240 MPa, and maintains an elongation of over 30%. These characteristics make it resistant to brittle fracture in low-temperature environments, ensuring structural integrity.
ASTM A333 Grade 6 carbon steel pipe specification
| Crade | The lowest temperature for strike test | |
| ℉ | ℃ | |
| ASTM A333 Grade 6 | -50 | -45 |
| Grade | Tensile Strength (MPa) | Yield Point (MPa) | Elongation (%) | |
| Y | X | |||
| Grade 6 | ≥415 | ≥240 | ≥30 | ≥16.5 |
| Grade | Chemical Composition (%) | ||||||||||
| C | Si | Mn | P | S | Cr | Ni | Cu | Mo | V | Al | |
| Grade 6 | ≤0.30 | ≥0.10 | 0.29-1.06 | ≤0.025 | ≤0.025 | ||||||
Processing and Welding Precautions
Welding:
Recommended to use low-hydrogen electrodes (e.g., E7016-G) with a preheat temperature of ≥100°C.
Post-weld stress relief heat treatment (600-650°C) can improve the toughness of the welded joints.
Cold Bending and Forming:
When the ambient temperature is below -10°C, preheating (≥15°C) is required to avoid cold cracking.
The bending radius should be ≥3 times the pipe diameter to minimize work hardening.
Impact Energy (Low-Temperature Toughness Index)
Standard Requirement:
Charpy V-notch impact test: At -46°C (-50°F), the average impact energy of three specimens shall be ≥20J, with no single specimen below 16J.
Actual Performance:
Using fine-grained killed steel process, actual impact energy can typically reach 40-60J (-46°C), far exceeding standard requirements. The addition of nickel elements maintains high toughness in the alloy at -100°C (impact energy ≈30J).
Influencing Factors:
Grain Size: Controlled grain refinement via Al deoxygenation (ASTM 5 or higher level) to improve toughness.
Heat Treatment: Normalizing or normalizing + tempering treatment eliminates stress and homogenizes microstructure.
Low-Temperature Parameters:
Ductile-to-Brittle Transition Temperature (DBTT):
The DBTT for A333 GR6 is approximately -70°C to -80°C (depends on composition and heat treatment), i.e., below this temperature, the material transitions from ductile to brittle fracture.
Allowable Stress:
ASME BPVC Section II Part D specifies an allowable stress of 138MPa at -46°C (similar to room temperature), indicating no significant strength reduction at low temperatures.
Thermal Expansion Coefficient:
Approximately 11.2×10⁻⁶/℃ (20-100°C), similar to carbon steel, suitable for thermal matching in low-temperature piping systems.
Packaging and shipping
