Low-Temperature Seamless Pipes are primarily used in the production of ethylene, propylene, urea, synthetic ammonia, N-P-K compound fertilizers, and in the pharmaceutical industry for washing, purification, desulfurization, and degreasing, among other processes.
They are also used in the manufacture of cryogenic equipment, ultra-low temperature cold storage, pipelines for transporting ultra-low temperature liquefied gases, and their associated pipe components. Internationally, the low-temperature seamless pipe system is represented by the ASTM A333/A333M—2011 standard, which is suitable for low-temperature environments as low as -196°C.
Among the 9 grades of low-temperature pipes in the ASTM A333/A333M standard, Gr.6 is widely used in the petrochemical industry and fluid transport in low-temperature, high-altitude regions. The chemical composition of Gr.6 in the 2010 version of the standard includes only five common elements—C, Si, Mn, P, and S—while the 2011 version adds alloying elements such as Cr, Ni, Mo, Cu, V, and Nb. Since the implementation of the 2011 standard, Gr.6 has fully complied with the new specifications and is now classified as a low-alloy steel system for low-temperature pipes.
From the perspective of low-temperature toughness, elements such as C, Si, P, S, and N are considered harmful, with P being the most detrimental, while Mn and Ni are beneficial elements. The old standard primarily relied on Mn to improve low-temperature performance, whereas the new standard enhances low-temperature properties further by adding Ni, V, Nb, and other alloying elements.
Statistical data show that for every 1% increase in Ni, the brittle transition temperature can decrease by about 20°C, although this increases the cost.
Comparison of Chemical Composition
Element | 2010 Version (Old) Composition | 2011 Version (New) Composition |
Carbon (C) | Max 0.30% | Max 0.30% |
Silicon (Si) | Max 0.15% | Max 0.15% |
Manganese (Mn) | 0.90% – 1.35% | 0.90% – 1.35% |
Phosphorus (P) | Max 0.03% | Max 0.03% |
Sulfur (S) | Max 0.03% | Max 0.03% |
Chromium (Cr) | / | Max 0.30% |
Nickel (Ni) | / | Max 0.50% |
Molybdenum (Mo) | / | Max 0.12% |
Copper (Cu) | / | Max 0.35% |
Vanadium (V) | / | Max 0.08% |
Niobium (Nb) | / | Max 0.05% |
Reasons and Impacts of Element Content Changes
The addition of elements such as Chromium (Cr), Nickel (Ni), Molybdenum (Mo), Copper (Cu), Vanadium (V), and Niobium (Nb) aims to improve the low-temperature performance and resistance to brittleness of the pipe, enhancing its toughness and strength in low-temperature environments.
The 2010 version (Old) mainly relied on elements like C, Si, Mn, P, and S, with Mn used to improve low-temperature performance.
The 2011 version (New) introduced additional alloying elements (such as Cr, Ni, Mo, Cu, V, and Nb), which help enhance the pipe’s toughness and strength, particularly in low-temperature environments.
The inclusion of these alloying elements contributes to improving the pipe’s low-temperature impact resistance, reducing the brittle transition temperature, and significantly enhancing material stability, especially in ultra-low-temperature environments (e.g., -196°C).
Mechanical Properties Comparison
Property | 2010 Version (Old) | 2011 Version (New) |
Yield Strength (YS) | Min 415 MPa | Min 415 MPa |
Tensile Strength (TS) | 515 – 690 MPa | 515 – 690 MPa |
Elongation (El) | Min 20% | Min 20% |
Hardness (HRB) | Min 95 | Min 95 |
Yield Strength (YS) and Tensile Strength (TS) remain consistent between the 2010 and 2011 versions, ensuring that the material meets the pressure-bearing requirements for low-temperature pipelines.
Elongation and Hardness also remain unchanged, indicating that the material’s ductility and resistance to deformation are not significantly affected.
Low-Temperature Toughness Comparison
Property | 2010 Version (Old) | 2011 Version (New) |
Impact Toughness | Min 27 J (-46°C) | Min 27 J (-46°C) |
Brittle Transition Temperature | -46°C | -50°C |
Low-Temperature Impact Resistance | Weaker | Stronger |
The Brittle Transition Temperature decreases in the 2011 version (from -46°C to -50°C), meaning the material remains tougher at lower temperatures.
The Low-Temperature Impact Toughness is enhanced in the 2011 version, as the addition of Ni, V, Nb, and other alloying elements further improves the pipe’s ability to resist brittleness at extremely low temperatures.
Physical Properties Comparison
Property | 2010 Version (Old) | 2011 Version (New) |
Density | 7.85 g/cm³ | 7.85 g/cm³ |
Elastic Modulus | 210 GPa | 210 GPa |
Thermal Conductivity | 46 W/m·K | 46 W/m·K |
Density, Elastic Modulus, and Thermal Conductivity do not exhibit significant changes between the two versions, suggesting that the basic physical properties of the material are essentially the same.
These properties are critical for determining the pipe’s thermal expansion and compressive strength, but the enhancement of low-temperature performance primarily depends on the improvements in chemical composition.
Conclusion
Chemical Composition: The 2011 version introduces more alloying elements (like Ni, V, Nb), significantly improving the material’s low-temperature performance.
Mechanical Properties: The yield strength, tensile strength, and elongation remain consistent between the two versions, ensuring their suitability for low-temperature applications.
Physical Properties: Density, elastic modulus, and thermal conductivity are unchanged, with improvements primarily coming from the chemical composition changes.
Low-Temperature Toughness: The 2011 version exhibits better toughness, especially in extremely low temperatures, due to the addition of beneficial alloying elements.
Therefore, the 2011 version of ASTM A333 GR6 provides enhanced low-temperature performance and toughness compared to the 2010 version, making it more suitable for extreme low-temperature conditions.
More resources:
ASTM A333 Pipe