Seamless Alloy 31 tube
Distinguished by a high Pitting Resistance Equivalent Number (PREN ≥ 48), our Alloy 31 tubing excels in aggressive environments containing hot concentrated phosphoric acid, sulfuric acid, and high-chloride media. With mechanical strength significantly surpassing standard austenitic steels, these tubes are indispensable for mission-critical applications in flue gas desulfurization (FGD), chemical reactors, and fine chemical processing. Through advanced cold-drawing and specialized solution annealing, we ensures every tube maintains a uniform microstructure and maximum durability for the most demanding industrial conditions.
PREN = %Cr + 3.3X(%Mo + 0.5X%W) + 16X%N≥ 48
What Is a Seamless Alloy 31 tube?
Seamless Alloy 31 Tube is a high-performance, cylindrical tube made from a solid billet of a nickel-chromium-molybdenum alloy. Unlike welded tubes, it is manufactured without a weld joint, ensuring superior structural integrity and reliability, especially under high-stress, high-temperature, and extremely corrosive conditions. The"Alloy 31"designation refers to a specific grade known for its outstanding resistance to a wide range of corrosive media. Its unique composition, which includes high levels of chromium, nickel, and molybdenum, provides excellent resistance to pitting, crevice corrosion, and stress-corrosion cracking. This makes it a top choice for demanding applications in harsh chemical processing and marine environments.
Key Features and Advantages
Alloy 31 seamless tube offer a unique combination of benefits that make them invaluable in the most demanding industries:
Exceptional Corrosion Resistance: It provides outstanding resistance to pitting, crevice corrosion, and stress-corrosion cracking, particularly in sulfuric acid and chloride-containing environments. Its PREN (Pitting Resistance Equivalent Number) value is very high, indicating its superior performance in these conditions.
High Strength: It maintains high tensile and yield strength at both room and elevated temperatures, providing reliable performance in high-stress and high-pressure applications.
High Pressure and Temperature Tolerance: The seamless construction and robust material allow the tube to safely handle high internal pressures and extreme temperatures.
Superior Weldability: The alloy can be welded using standard methods without the risk of post-weld corrosion, a key advantage for complex fabrications.
Cost-Effectiveness: It provides a good balance of performance and cost, offering a high-performance alternative to more expensive nickel alloys for certain applications.
Product Specifications and Data
To provide a comprehensive overview of this high-performance material, here are the detailed technical specifications and performance data for Alloy 31.
Table 1: Chemical Composition of Alloy 31
The composition of Alloy 31 is carefully balanced to achieve its superior corrosion resistance and high strength.
| Cr | Ni | Mo | Cu | N | Mn | Si | Fe | C |
| 26.00 - 28.00 | 30.00 - 32.00 | 6.00- 7.00 | 1.00 - 1.50 | 0.15 - 0.25 | ≤ 2.00 | ≤ 1.00 | Bal | ≤ 0.02 |
Table 2: Typical Mechanical Properties of Alloy 31
Alloy 31 is specifically designed to maintain its strength and shape in high-stress, corrosive environments.
| Property | Value (Annealed) |
| Tensile Strength | ≥ 650 MPa |
| Yield Strength | ≥ 310 MPa |
| Elongation | ≥ 30% |
| Hardness | ≤ 240 HBW |
| Brinell Hardness | ≤ 217 HB |
Table 3: Typical Physical Properties of Alloy 31
These physical properties highlight the material's ability to perform reliably under a wide range of conditions.
| Property | Value |
| Density | 8.16 g/cm³ |
| Melting Point | 1350 - 1400 °C approx. |
| Thermal Expansion | 13.5 µm/m·°C (20-100°C) |
| Thermal Conductivity | 11.5 W/m·K (20°C) |
| Modulus of Elasticity | 205 GPa |
| Electrical Resistivity | 1.05 x 10⁻⁶ Ω·m (20°C) |
Table 4: The Standard of Stainless Steel Seamless Tube Size Tolerance Size Chart :
| Standard | OD(D) | Tolerance（MM) | Thickness(S) | Tolerance(MM) | Length | Tolerance | |
| MM | Common | High | MM | MM | |||
| EN 10216-5 HFD | 30≤D≤219.1（D2) | ±1.0% or ±0.5mm, whicever is the greater(取较大者) | T1, T≤4 | ±15% or ±0.6mm, whicever is the greater(取较大者) | L≤6M | +5/0 | |
| T2 | ±12.5% or ±0.4mm, whicever is the greater(取较大者) | ||||||
| 219.1≤D≤610 (D1) | ±1.5% or ±0.75mm, whicever is the greater (取较大者) | T≤0.05D | +22.5%/-15% | 6 | +10/0 | ||
| T1, 0.05D | ±15% or ±0.6mm, whicever is the greater(取较大者) | ||||||
| T2, T>0.09D | ±12.5% or ±0.4mm, whicever is the greater(取较大者) | L>12 | +by agreement/0 | ||||
| EN 10216-5 CFD | D3(D≤219.1) | ±0.75% or ±0.3mm, whicever is the greater(取较大者) | T3 | ±10% or ±0.2mm, whicever is the greater(取较大者) | |||
| D4(D≤219.1) | ±0.5% or ±0.mm, whicever is the greater(取较大者) | T4 | ±7.5% or ±0.15mm, whicever is the greater(取较大者) | ||||
| ASTM A213 HFD | D≤100 | +0.4/-0.8 | D<100,S≤2.4 | +40%/0 | HFD, all size | +5.0/0 | |
| +0.4/-1.2 | D<100,2.4 | +35%/0 | |||||
| +0.4/-1.6 | D<100,3.8 | +33%/0 | |||||
| D<100,S>4.6 | +28%/0 | ||||||
| 100 | +0.4/-1.2 | D>100, 2.4 | +35%/0 | ||||
| 200 | +0.4/-1.6 | D>100,3.8 | +33%/0 | ||||
| D>100,S>4.6 | +28%/0 | ||||||
| ASTM A213 CFD | D<25 | ±0.10 | D≤38.1 | +20%/0 | CFD, D<50.8 | +3.0/0 | |
| 25≤D≤40 | ±0.15 | ||||||
| 40 | ±0.20 | ||||||
| 50≤D<65 | ±0.25 | ||||||
| 65≤D<75 | ±0.30 | D>38.1 | +22%/0 | CFD, D≥50.8 | +5.0/0 | ||
| 75≤D≤100 | ±0.38 | ||||||
| 100 | +0.38/-0.64 | ||||||
| 200 | +0.38/-1.14 | ||||||
| ASTM A269 | D≤13 | ±0.13 | D≤13 | ±15% | D<38 | +3.2/0 | |
| 13 | ±0.13 | 13 | ±10% | ||||
| 38≤D<89 | ±0.25 | D>38 | +4.8/0 | ||||
| 89≤D<140 | ±0.38 | ||||||
| 140≤D<203 | ±0.76 | ||||||
| 203≤D<305 | ±1.01 | ||||||
| 305≤D<356 | ±1.26 | ||||||
| ASTM A270 | D<25 | ±0.13 | For weld pipe all size | ±12.5% | +3.0/0 | ||
| 25-50 | ±0.20 | ||||||
| 50-75 | ±0.25 | ||||||
| 75-100 | ±0.38 | For CD SMLS pipe D≤38.1 | +20%/0 | ||||
| 100-140 | ±0.38 | +5.0/0 | |||||
| 140-200 | ±0.75 | For CD SMLS pipe D>38.1 | +22%/0 | ||||
| 200-300 | ±1.25 | ||||||
Common Applications
The combination of high strength and exceptional corrosion resistance of seamless Alloy 31 tubes makes them a preferred choice for:
Chemical Processing: Used in reactors, heat exchangers, and piping for handling sulfuric, phosphoric, and other aggressive acids.
Marine Engineering: In seawater applications and components where resistance to saltwater corrosion is critical.
Pulp and Paper Industry: In bleaching and other processes where corrosive media are present.
Pharmaceuticals: In the production of pharmaceutical goods where high purity and corrosion resistance are critical.
Manufacturing Process
The manufacturing of a Seamless Alloy 31 Tube is a precise, multi-step process:
- Heating: A solid billet of Alloy 31 is heated to a high temperature.
- Piercing: A piercing mill pushes a mandrel through the center of the heated billet to form a hollow shell.
- Drawing and Sizing: The hollow shell is then rolled and drawn to reduce its diameter and wall thickness to the desired dimensions.
- Heat Treatment: The tube is solution annealed to achieve its specified metallurgical properties and to ensure optimal performance and corrosion resistance.
- Finishing: The tube is cut to length, straightened, and subjected to rigorous non-destructive testing to verify its integrity before final inspection and packaging. This meticulous process ensures that every seamless Alloy 31 tube is built to withstand the most demanding applications
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