Q345B Fluid Seamless Pipe (GB/T 8163) Low-Alloy Steel
Q345B Fluid Seamless Pipe (GB/T 8163): High-Strength Low-Alloy Steel for Fluid Transport
Complete material datasheet for Q345B fluid seamless pipe under GB/T 8163 standard, covering chemical composition, mechanical properties, physical properties, international equivalents, and application guidance.
Hot-rolled, cold-drawn, normalized, or as agreed
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Q345B Fluid Seamless Pipe Low-Alloy Steel Introduction
Q345B is a low-alloy high-strength structural steel grade widely used for manufacturing seamless pipes for fluid transportation according to GB/T 8163. Key features include high yield and tensile strength, good notch toughness, excellent weldability, and satisfactory corrosion resistance in mild environments. It is suitable for transporting water, oil, gas, steam, and other fluids at medium pressures. The material is typically delivered in hot-rolled, cold-drawn, or normalized condition and finds extensive use in industries such as petrochemical, power generation, boiler and heat exchanger manufacturing, and offshore engineering.
Q345B Fluid Seamless Pipe Low-Alloy Steel Chemical Composition
The chemical composition of Q345B for fluid seamless pipes complies with GB/T 8163-2018, which references the limits of GB/T 1591 for Q345B. Key elements include controlled carbon and manganese for strength, microalloying elements such as vanadium, niobium, and titanium for grain refinement, and low sulfur and phosphorus for toughness. A minimum total aluminum content ensures fine grain practice.
| Element | Specified Value | Remark |
|---|---|---|
| C | ≤0.20 | Ladle analysis |
| Si | ≤0.50 | Ladle analysis |
| Mn | ≤1.70 | Ladle analysis |
| P | ≤0.035 | Ladle analysis |
| S | ≤0.035 | Ladle analysis |
| Cr | ≤0.30 | Ladle analysis, residual element |
| Ni | ≤0.50 | Ladle analysis, residual element |
| Cu | ≤0.20 | Ladle analysis, residual element |
| Mo | ≤0.10 | Ladle analysis, residual element |
| V | ≤0.15 | Ladle analysis, microalloying |
| Nb | ≤0.07 | Ladle analysis, microalloying |
| Ti | ≤0.20 | Ladle analysis, microalloying |
| Alt | ≥0.015 | Total aluminum for grain refinement |
Q345B Fluid Seamless Pipe Low-Alloy Steel Thermal and Electrical Physical Properties
Physical properties are typical values for Q345B/low-alloy carbon-manganese steel at ambient temperature, unless otherwise noted. These properties are not mandatory in GB/T 8163 but are useful for design calculations. Properties such as thermal expansion, thermal conductivity, and electrical resistivity can vary with temperature and exact composition.
| Property | Typical Value | Unit | Test Condition |
|---|---|---|---|
| Density (ρ) | 7850 | kg/m³ | At 20°C |
| Modulus of elasticity (E) | 206 | GPa | At 20°C |
| Shear modulus (G) | 79.3 | GPa | At 20°C |
| Poisson's ratio (ν) | 0.3 | - | At room temperature |
| Thermal expansion coefficient (α) | 10.0 ~ 12.0 ×10⁻⁶ | K⁻¹ | 20°C to 300°C |
| Thermal conductivity (λ) | ~45 | W/(m·K) | At 100°C |
| Specific heat capacity (c) | ~460 | J/(kg·K) | At 20°C |
| Electrical resistivity (ρ_e) | ~0.25 ×10⁻⁶ | Ω·m | At 20°C |
Q345B Fluid Seamless Pipe Low-Alloy Steel Mechanical Properties
Mechanical properties of Q345B seamless pipes are tested in accordance with GB/T 8163-2018. Requirements depend on wall thickness. Yield and tensile strength values apply to delivery condition. Impact test is optional and performed only when specified by the purchaser; typical acceptance at 0°C. Elongation is measured on longitudinal full-section specimens or strip specimens.
| Property | Required Value | Unit | Test Condition |
|---|---|---|---|
| Yield strength (ReH) | ≥345 | MPa | Wall thickness ≤16 mm |
| Yield strength (ReH) | ≥325 | MPa | Wall thickness >16 mm to ≤30 mm |
| Tensile strength (Rm) | 470 ~ 630 | MPa | All thicknesses |
| Elongation (A) | ≥20 | % | Wall thickness ≤16 mm, longitudinal |
| Elongation (A) | ≥19 | % | Wall thickness >16 mm, longitudinal |
| Impact energy (KV2) | ≥34 | J | Temperature 0°C, optional on request, V-notch, longitudinal |
Q345B Fluid Seamless Pipe Low-Alloy Steel Fully Equivalent Material Standards and Alternative Designations
| Country/Region | Standard | Designation | Remark |
|---|---|---|---|
| China | GB/T 8163 | Q345B | Original standard and grade |
| Europe | EN 10216-2 | P355N | Seamless steel tubes for pressure purposes; close match in strength and chemistry; suitable for fluid service |
Q345B Fluid Seamless Pipe Low-Alloy Steel Application Introduction
Q345B seamless pipes are extensively used in fluid transport systems where a combination of high strength, good weldability, and moderate cost is required. Typical industries include:
- Oil and gas transmission pipelines
- Petrochemical and chemical processing plants
- Power generation (boiler tubes, economizers, steam lines)
- Heat exchangers and condensers
- Pressure vessels and piping
- Offshore and marine engineering
- Structural and mechanical hollow sections
The grade can be fabricated into various components by bending, flanging, and welding with proper preheat and interpass control.
Product Applications: Long-distance oil and gas pipelines, Process piping for refineries and chemical plants, Boiler tubes and superheater elements, Heat exchanger tube bundles, Pressure pipe spools and headers, Structural support hollow sections (when ordered to GB/T 8163 for fluid service)
Processed into products: Pipe elbows (45° and 90°), Tees (equal and reducing), Reducers and caps, Flanges (weld neck, slip-on), Pipe fittings (couplings, unions), Bent pipe segments for layout
Application industries: Oil & gas pipeline and distribution, Petrochemical and refining, Chemical processing, Power generation (boilers, steam piping), Heat exchanger and condenser manufacturing, Offshore platform piping, Pressure vessel and tank construction, Building and structural mechanical systems
Q345B Fluid Seamless Pipe Low-Alloy Steel Similar or Comparable Alternative Materials
| Country/Region | Standard | Designation | Remark |
|---|---|---|---|
| Europe | EN 10216-2 | P355NH | Higher min. tensile strength, normalized delivery, suitable as close alternative |
| USA | ASTM A106 | Grade B | Lower strength (yield ≥240 MPa), higher carbon; limited substitution for high-pressure Q345B |
| USA | API 5L | X52 (L360) | Pipelines; comparable yield (~360 MPa) but different chemistry requirements; suitable for piping |
| Japan | JIS G3454 | STPG410 | Carbon steel pipes for pressure service; tensile strength ≥410 MPa, lower yield (~245 MPa); not direct substitute but common commercial equivalent |
| International | ISO 9329-2 | P355N | Seamless steel tubes for pressure purposes; similar philosophy to EN 10216-2 |
Notes:
Welding: Q345B has good weldability but low preheat (typically 50-150°C) may be required for thicker sections (>25 mm) to avoid hydrogen cracking. Low-hydrogen welding processes are recommended. Corrosion: The steel offers moderate atmospheric corrosion resistance; for aggressive fluids, coatings or linings should be considered. Testing: Additional non-destructive testing (ultrasonic, eddy current) is often specified by purchasers for critical pipe applications. Certification: Mill test certificates (EN 10204 type 3.1) are standard.
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