GB/T 1591 Q345A LSAW Pipe
GB/T 1591 Q345A LSAW Pipe: High Strength Low Alloy Structural Steel for Large Diameter Pipelines
Explore comprehensive material data for GB/T 1591 Q345A, a low alloy structural steel widely used in longitudinal submerged arc welded (LSAW) pipes. Includes chemical composition, mechanical and thermal properties, equivalent grades, and application guidance.
Hot rolling, normalizing, submerged arc welding (SAW), cold forming, shearing, bending, edge milling
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GB/T 1591 Q345A LSAW Pipe Introduction
Q345A is a low alloy high-strength structural steel specified in GB/T 1591-2008, primarily used in welded structures and large diameter pipes. Key characteristics:
- Minimum yield strength of 345 MPa, providing good strength-to-weight ratio
- Good weldability and formability, suitable for longitudinal submerged arc welding
- Cost-effective compared to quenched and tempered steels
- Widely applied in oil and gas transmission, water pipelines, and structural engineering
The grade is delivered in as-rolled or normalized condition, with no mandatory impact test (A quality). It can be made into hot-rolled plates and strips, which are further formed into LSAW pipes. Typical thickness range for LSAW pipe base material is 6-25 mm.
GB/T 1591 Q345A LSAW Pipe Chemical Composition
The chemical composition of Q345A according to GB/T 1591-2008 is optimized for good weldability and strength. All values are maximum limits (unless specified) for ladle analysis. Note: For LSAW pipe, the base metal composition may be further controlled by the pipe manufacturing standard (e.g., GB/T 9711 or API 5L equivalent), but the following reflects the material specification for steel plates used in such pipes.
| Chemical Element | Standard Value (wt%) | Remarks |
|---|---|---|
| Carbon (C) | ≤0.20 | Max, ensures weldability |
| Silicon (Si) | ≤0.50 | Max |
| Manganese (Mn) | ≤1.70 | Max, main strengthener |
| Phosphorus (P) | ≤0.035 | Max, impurity |
| Sulfur (S) | ≤0.035 | Max, impurity |
| Niobium (Nb) | ≤0.07 | Max, microalloying optional |
| Vanadium (V) | ≤0.15 | Max, microalloying optional |
| Titanium (Ti) | ≤0.20 | Max, microalloying optional |
| Chromium (Cr) | ≤0.30 | Max, residual |
| Nickel (Ni) | ≤0.30 | Max, residual |
| Copper (Cu) | ≤0.30 | Max, residual |
| Nitrogen (N) | ≤0.012 | Max, unless sufficient Ti present |
| Aluminium (Alt) | ≥0.015 | Min, for deoxidation and grain refinement if required |
GB/T 1591 Q345A LSAW Pipe Thermal and Electrical Physical Properties
Typical physical properties for Q345A steel at room temperature and moderate elevated temperatures. These values are not normatively specified in GB/T 1591 but are derived from engineering references for similar C-Mn structural steels. Variations may occur depending on exact composition and processing. Thermal conductivity decreases and specific heat increases with temperature.
| Property | Typical Value | Unit | Test Condition / Remarks |
|---|---|---|---|
| Density (ρ) | 7.85 | g/cm³ | At 20°C |
| Elastic Modulus (E) | 206 | GPa | At 20°C |
| Shear Modulus (G) | 79.3 | GPa | At 20°C |
| Poisson's Ratio (ν) | 0.30 | - | At 20°C |
| Thermal Expansion Coefficient (α) | 12.0 | 10⁻⁶/K | 20-100°C |
| Thermal Expansion Coefficient (α) | 12.5 | 10⁻⁶/K | 20-200°C |
| Thermal Expansion Coefficient (α) | 13.0 | 10⁻⁶/K | 20-300°C |
| Thermal Conductivity (λ) | 45 | W/(m·K) | At 100°C |
| Thermal Conductivity (λ) | 42 | W/(m·K) | At 200°C |
| Thermal Conductivity (λ) | 38 | W/(m·K) | At 300°C |
| Specific Heat Capacity | 470 | J/(kg·K) | 20-100°C |
| Electrical Resistivity (ρe) | 0.23 | µΩ·m | At 20°C |
GB/T 1591 Q345A LSAW Pipe Mechanical Properties
Mechanical properties of Q345A steel plate/coil as per GB/T 1591-2008. Values vary with thickness. For LSAW pipe, the pipe body properties are derived from the parent plate; however, the weld seam and heat-affected zone may have different properties. Impact test is not a mandatory requirement for grade A, typical Charpy V-notch energy at room temperature is not guaranteed. Testing is performed on longitudinal test pieces.
| Property | Standard Required Value | Unit | Test Condition / Remarks |
|---|---|---|---|
| Yield Strength (ReH/ReL) | ≥345 | MPa | Thickness ≤16 mm |
| Yield Strength (ReH/ReL) | ≥325 | MPa | Thickness 16-40 mm |
| Yield Strength (ReH/ReL) | ≥295 | MPa | Thickness 40-63 mm |
| Tensile Strength (Rm) | 470 - 630 | MPa | Thickness ≤100 mm |
| Elongation (A) | ≥21 | % | Thickness ≤16 mm, gauge length 5.65√S0 |
| Elongation (A) | ≥20 | % | Thickness 16-40 mm |
| Elongation (A) | ≥19 | % | Thickness 40-63 mm |
| Bending Test (180°) | d = 2a | - | Bend diameter for thickness ≤16 mm |
| Bending Test (180°) | d = 3a | - | Bend diameter for thickness 16-100 mm |
| Impact (KV) at 20°C | No requirement | J | Grade A does not guarantee impact toughness |
GB/T 1591 Q345A LSAW Pipe Completely Equivalent Material Standards & Alternative Grades
| Country/Region | Standard | Grade | Remarks |
|---|---|---|---|
| Europe | EN 10025-2:2004 | S355JR | Same strength level, but JR guarantees impact at room temperature (+20°C) |
| Japan | JIS G3106 | SM490A | Strength slightly higher (490 MPa min tensile), no impact guarantee |
| United States | ASTM A572/A572M | Grade 50 | Yield 345 MPa min, same strength basis, type 1 or 2 |
| International | ISO 630-2:2011 | S355E | E quality with higher toughness, S355 is the base designator |
| China (newer standard) | GB/T 1591-2018 | Q355B | Updated version of Q345, replaces Q345A in new projects |
GB/T 1591 Q345A LSAW Pipe Application Introduction
Q345A LSAW pipe combines moderate strength with excellent fabricability, making it a preferred choice for numerous infrastructural and industrial applications. The grade is suitable for welded structures that do not require low-temperature notch toughness. Typical uses include:
Product Applications: Longitudinally submerged arc welded (LSAW) pipes in large diameters (16-64 inch), Spiral submerged arc welded (SSAW) pipes, Hot-rolled structural sections (H-beams, I-beams, channels, angles), Pressure vessel shells (low severity), Wind turbine tower sections, Bridge bearing structural elements
Processed into products: Pipe fittings (elbows, tees, reducers, flanges), Piling pipe connectors and sleeves, Structural steel joints and gusset plates, Stiffeners, brackets, and base plates, Manhole covers and access hatches, Storage tank shell plates
Application industries: Oil and gas transmission (onshore and offshore), Water distribution and sewage treatment, Construction and civil engineering (steel structures, piling), Shipbuilding and marine engineering, Mining and slurry transportation, Chemical and petrochemical process piping
GB/T 1591 Q345A LSAW Pipe Similar / Alternative Materials with Comparable Performance
| Country/Region | Standard | Grade | Remarks |
|---|---|---|---|
| China | GB/T 1591-2008 | Q345B | Same strength, but requires impact test at +20°C (KV2 ≥ 34J) |
| China | GB/T 1591-2018 | Q355B | Newer standard, yield 355 MPa, slightly higher strength |
| Europe | EN 10025-2 | S355J0 | Impact at 0°C, cleaner composition, comparable weldability |
| Europe | EN 10210-1/EN 10219-1 | S355J2H | For hollow sections including pipes, good toughness |
| USA | API 5L | X52 | Pipeline steel, similar yield (359 MPa), widely used in LSAW pipes |
| USA | ASTM A709 | Grade 50 | For bridge construction, similar mechanicals |
Notes:
Special considerations for Q345A LSAW pipe:
- Welding consumables should match or overmatch the base metal strength (AWS E50XX / F7A0-EM12K for SAW).
- Pipe manufacturers may apply hydrostatic testing, ultrasonic inspection, and X-ray examination per tubular product standard.
- For services requiring low-temperature toughness (below -20°C), grades Q345C/D/E or normalized S355J2 are recommended.
- Coating and lining systems (FBE, 3LPE/PP, cement mortar) are commonly used for LSAW pipes in buried environments.
- The material is suitable for cold expansion (pipe sizing) up to 1.5% strain without significant property degradation.
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