Q345B Low Alloy Structural Steel for LSAW Pipe
Q345B Low Alloy Structural Steel for LSAW Pipe - GB/T 1591 Standard
Comprehensive technical data for Q345B steel as per GB/T 1591, including chemical composition, mechanical and physical properties, international equivalents, and application guidelines for LSAW pipes.
The base material is processable by hot rolling, cold forming, welding (SAW, GMAW), gas cutting, and machining. For LSAW pipe production, plates are formed by UOE, JCOE, or roll bending and joined by submerged arc welding.
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Q345B Low Alloy Structural Steel for LSAW Pipe Introduction
Q345B is a low-alloy high-strength structural steel specified in Chinese standard GB/T 1591. With a minimum yield strength of 345 MPa, it offers excellent weldability, toughness, and cold-forming ability. The material is widely used in structural applications and is a common choice for longitudinal submerged arc welded (LSAW) pipes. Its balanced chemical composition, including controlled microalloying elements such as niobium and vanadium, ensures reliable performance under static and dynamic loads. Q345B is suitable for ambient temperature service and can be supplied in various delivery conditions.
Q345B Low Alloy Structural Steel for LSAW Pipe Chemical Composition of Q345B
This table lists the specified chemical elements and their permissible ranges as per GB/T 1591-2008. The composition is designed to achieve a balance of strength, weldability, and toughness. Microalloying elements like Nb and V are used for grain refinement and precipitation strengthening. Residual elements are controlled to ensure consistent mechanical properties.
| Element | Specified Value (wt%) | Remarks |
|---|---|---|
| Carbon (C) | ≤0.20 | Key element for strength; higher content may affect weldability |
| Silicon (Si) | ≤0.50 | Deoxidizer; improves strength without significantly reducing ductility |
| Manganese (Mn) | ≤1.70 | Enhances hardenability and strength; upper limit for weldability |
| Phosphorus (P) | ≤0.035 | Residual element; limited to maintain toughness |
| Sulfur (S) | ≤0.035 | Residual element; kept low to avoid hot shortness |
| Niobium (Nb) | ≤0.07 | Grain refiner and precipitation strengthening element |
| Vanadium (V) | ≤0.15 | Contributes to precipitation hardening and grain refinement |
| Titanium (Ti) | ≤0.20 | Forms stable carbides and nitrides for grain size control |
| Aluminium (Als) | ≥0.015 | Acid-soluble Al ensures sufficient deoxidation and grain refinement |
Q345B Low Alloy Structural Steel for LSAW Pipe Thermal and Electrical Physical Properties of Q345B
The physical properties are typical values for low-alloy steels and may vary with temperature and production conditions. These data are useful for heat transfer and stress analysis in LSAW pipe applications.
| Property | Typical Value | Unit | Test Condition / Remarks |
|---|---|---|---|
| Density (ρ) | 7850 | kg/m³ | At room temperature |
| Modulus of Elasticity (E) | 206 | GPa | At room temperature, typical for carbon/low-alloy steel |
| Shear Modulus (G) | 79.3 | GPa | Calculated from E and Poisson's ratio |
| Poisson's Ratio (ν) | 0.30 | – | Typical value at ambient temperature |
| Thermal Expansion Coefficient (α) | 12.0 | 10⁻⁶/K | 20–100°C range |
| Thermal Conductivity (λ) | 45 | W/(m·K) | At room temperature |
| Specific Heat Capacity | 460 | J/(kg·K) | At room temperature |
| Electrical Resistivity (ρₑ) | 0.22 | µΩ·m | At 20°C, approximate |
Q345B Low Alloy Structural Steel for LSAW Pipe Mechanical Properties of Q345B
The mechanical properties are based on GB/T 1591 and apply to hot-rolled plates. Values vary with thickness. The yield strength, tensile strength, and elongation are measured at room temperature. Impact test is performed on Charpy V-notch specimens. For LSAW pipe manufacturing, the base plate properties are critical for pipe strength and toughness.
| Property | Specified Value | Unit | Test Condition |
|---|---|---|---|
| Yield Strength (ReH) | ≥345 | MPa | Plate thickness ≤16 mm |
| Yield Strength (ReH) | ≥335 | MPa | Plate thickness 16–40 mm |
| Yield Strength (ReH) | ≥325 | MPa | Plate thickness 40–63 mm |
| Tensile Strength (Rm) | 470–630 | MPa | All thicknesses |
| Elongation (A) | ≥20 | % | Gauge length 5.65√S₀, thickness ≤40 mm |
| Elongation (A) | ≥19 | % | Gauge length 5.65√S₀, thickness 40–63 mm |
| Impact Energy (KV₂) | ≥34 | J | At 20°C, longitudinal specimens |
Q345B Low Alloy Structural Steel for LSAW Pipe Exact Equivalent Material Standards and Replaceable Grades
| Country/Region | Standard | Grade | Remarks |
|---|---|---|---|
| European Union | EN 10025-2:2004 | S355JR | Equivalent in chemical and mechanical requirements; widely used for structural purposes |
| International | ISO 4950-2:1995 | S355JR | Same as EN S355JR, high compatibility |
| Japan | JIS G3106:2015 | SM490A | Comparable yield and tensile properties; typical for welded structures |
| USA | ASTM A572/A572M-18 | Grade 50 | Yield strength 345 MPa (50 ksi); closest match in US standards |
Q345B Low Alloy Structural Steel for LSAW Pipe Application Introduction
Q345B is a reliable material for welded structural pipes, especially LSAW pipes for oil, gas, and water transmission. It can be used in static and dynamic loading structures due to its good combination of strength and toughness. Key applications include:
- Line pipe for long-distance transmission of hydrocarbons
- Structural tubular members for bridges, offshore platforms, and buildings
- Fluid transportation in water supply and sewage systems
Product Applications: LSAW (Longitudinal Submerged Arc Welded) pipes in diameters from 406 mm to 1626 mm, Steel pipe piles for foundation structures, Tubular columns and trusses for large-span buildings, High-pressure transmission pipelines, Penstocks and industrial piping systems
Processed into products: Pipe body (plate forming and welding), Flanges and end connections (machined from plates), Pipe supports and saddles, Nozzles and reinforcement pads, Expansion joints (using formed sections)
Application industries: Oil and gas transportation, Water supply and sewage infrastructure, Structural engineering and construction, Offshore and marine engineering, Machinery and equipment manufacturing
Q345B Low Alloy Structural Steel for LSAW Pipe Similar and Alternative Material Recommendations
| Country/Region | Standard | Grade | Remarks |
|---|---|---|---|
| China | GB/T 1591-2018 | Q355B | Updated version from 2018 replaces Q345B; minimum yield 355 MPa, slightly higher strength |
| China | GB/T 700-2006 | Q235B | Lower strength (235 MPa yield) but similar carbon content; used where higher strength is not required |
| European Union | EN 10025-2:2004 | S275JR | Lower yield strength (275 MPa) but similar weldability and toughness; suitable for less demanding structures |
| Japan | JIS G3106:2015 | SM490B | Similar to SM490A but with guaranteed impact properties; slightly higher tensile strength |
Notes:
Additional Information:
- For LSAW pipe production, the base Q345B plates shall meet GB/T 1591, and the pipes may be supplied according to standards such as API 5L PSL1/PSL2, GB/T 9711, or equivalent project specifications.
- The pipe weld seam must be qualified by procedure, and mechanical testing including tensile and impact tests across the weld is required.
- The material is not intended for prolonged exposure above 400°C due to potential degradation of mechanical properties.
- Weldability: Carbon equivalent (CEV) is typically below 0.45%; preheating may be required for thicker sections.
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