GB/T 1591 Q345E Low Alloy Structural Steel for LSAW Pipe
Q345E Low Alloy Structural Steel for LSAW Pipe per GB/T 1591
Comprehensive data sheet for Q345E steel including chemical composition, mechanical/physical properties, equivalents, and application guidance for longitudinal submerged arc welded pipes.
Hot rolling, controlled rolling, normalizing, normalizing rolling, welding (especially for pipe fabrication)
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GB/T 1591 Q345E Low Alloy Structural Steel for LSAW Pipe Introduction
Q345E is a Chinese standard low alloy high-strength structural steel grade defined in GB/T 1591-2008 (now superseded by GB/T 1591-2018 with grade Q355NE). It features a minimum yield strength of 345 MPa, excellent low-temperature impact toughness (≥34 J at -40°C), good weldability, and is widely used in welded pipes such as LSAW (Longitudinal Submerged Arc Welded) pipes. The 'E' suffix indicates quality level with the strictest impact requirements. It is delivered in normalized or controlled rolled condition, suitable for structural applications in bridges, buildings, offshore platforms, and pressure vessels operating at low temperatures.
GB/T 1591 Q345E Low Alloy Structural Steel for LSAW Pipe Chemical Composition
Typical ladle analysis according to GB/T 1591-2008. For Q345E, phosphorus and sulfur are strictly limited to achieve low-temperature toughness. All values are maximum unless a range is indicated. Fine grain elements (Nb, V, Ti) may be added singly or in combination.
| Element | Specification Value (%) | Remark |
|---|---|---|
| C | ≤ 0.18 | Carbon |
| Si | ≤ 0.50 | Silicon |
| Mn | ≤ 1.70 | Manganese |
| P | ≤ 0.020 | Phosphorus |
| S | ≤ 0.020 | Sulfur |
| Nb | ≤ 0.07 | Niobium |
| V | ≤ 0.15 | Vanadium |
| Ti | ≤ 0.20 | Titanium |
| Cr | ≤ 0.30 | Chromium |
| Ni | ≤ 0.50 | Nickel |
| Cu | ≤ 0.30 | Copper |
| Mo | ≤ 0.10 | Molybdenum |
| N | ≤ 0.012 | Nitrogen |
| Als | ≥ 0.015 | Total Aluminum (acid soluble), if added as grain refiner |
GB/T 1591 Q345E Low Alloy Structural Steel for LSAW Pipe Thermal and Electrical Physical Properties
Physical properties at room temperature unless noted. These are typical values for low-carbon low-alloy steel. They may vary slightly with manufacturing route. Data sourced from published engineering tables.
| Property | Typical Value | Unit | Test Condition |
|---|---|---|---|
| Density (ρ) | 7.85 | g/cm³ | 20°C |
| Young's Modulus (E) | 206 | GPa | 20°C |
| Shear Modulus (G) | 79.3 | GPa | 20°C |
| Poisson's Ratio (ν) | 0.30 | – | 20°C |
| Thermal Expansion Coeff. (α) | 12.0 | 10⁻⁶/K | 20–100°C |
| Thermal Expansion Coeff. (α) | 13.5 | 10⁻⁶/K | 20–300°C |
| Thermal Conductivity (λ) | 53 | W/(m·K) | 20°C |
| Specific Heat Capacity | 486 | J/(kg·K) | 20°C |
| Electrical Resistivity (ρe) | 0.13 | 10⁻⁶ Ω·m | 20°C |
GB/T 1591 Q345E Low Alloy Structural Steel for LSAW Pipe Mechanical Properties
Tensile testing according to GB/T 228.1. Specimens are taken from plate/pipe in transverse direction. Values for thickness ≤ 16 mm, unless otherwise noted. Impact test is carried out at -40°C with a minimum average value of 34 J (longitudinal).
| Property | Specification Requirement | Unit | Test Condition |
|---|---|---|---|
| Yield Strength (ReH) | ≥ 345 | MPa | t ≤ 16 mm |
| Yield Strength (ReH) | ≥ 335 | MPa | 16 < t ≤ 40 mm |
| Tensile Strength (Rm) | 470 – 630 | MPa | t ≤ 40 mm |
| Elongation (A) | ≥ 20 | % | Gauge length 5.65√So, t ≤ 40 mm |
| Bend Test (d = bend diameter) | No cracks – d = 2a | – | 180° bending, a = specimen thickness |
| Impact Energy (KV2) | ≥ 34 (average); ≥ 27 (individual) | J | -40°C, V-notch longitudinal |
| Hardness | Not specified (approx. 150 HBW) | HBW | Typical for reference |
GB/T 1591 Q345E Low Alloy Structural Steel for LSAW Pipe Exact Equivalent Material Standards and Replaceable Grades
| Country/Region | Standard | Grade | Remark |
|---|---|---|---|
| China | GB/T 1591-2018 | Q355NE | New designation directly replacing Q345E |
| European Union | EN 10025-2 | S355J2 | Equivalent strength grade, -20°C impact |
| European Union | EN 10025-3 | S355NL | Normalized, -50°C impact, closest overall properties |
| United States | ASTM A572/A572M | Grade 50 | 50 ksi (345 MPa) yield, general structural |
| Japan | JIS G3106 | SM490YB | 490 MPa tensile class, impact test available |
| International | ISO 4950-2 | S355 | High yield strength flat products |
GB/T 1591 Q345E Low Alloy Structural Steel for LSAW Pipe Application Introduction
Q345E steel is engineered for demanding welded structures requiring high strength, excellent low-temperature toughness, and reliable weldability. The LSAW pipe form is particularly suited for long-distance transportation of oil, gas, water, and slurries under high pressure and low ambient temperatures. The material is often selected for critical infrastructure where safety margins and resistance to brittle fracture are paramount.
Product Applications: LSAW steel pipes (API 5L PSL2 compatible grades X52/X56 equivalent), Spiral welded pipes for piling and water lines, Hot-rolled plates for storage tank shells and roofs, Wide flange beams and structural sections, Pressure vessel shells (when certified per GB 150), Welded tubular sections for offshore jackets and decks
Processed into products: Main pipeline segments and fittings (elbows, tees, reducers), Transition pieces between different wall thicknesses, Pile sleeves and connectors for offshore foundations, Stiffening rings and support saddles for pressure vessels, Bridge girders welded from plate, Anchor flanges and blind flanges for high-pressure piping
Application industries: Oil & gas transmission (onshore and offshore), Petrochemical plant piping and pressure vessels, Bridge and building construction in cold regions, Wind turbine towers and foundations, Shipbuilding and marine structures, Hydraulic engineering and penstocks, Railway car and heavy machinery frames
GB/T 1591 Q345E Low Alloy Structural Steel for LSAW Pipe Similar / Near-Equivalent Replacement Material Recommendations
| Country/Region | Standard | Grade | Remark |
|---|---|---|---|
| China | GB/T 1591-2008 | Q345D | Same strength, impact at -20°C instead of -40°C |
| China | GB/T 1591-2008 | Q345E (Q355NE) | Designation update, direct substitute |
| European Union | EN 10025-2 | S355K2 | -20°C impact, higher toughness than S355J2 |
| European Union | EN 10025-4 | S355M/ML | Thermomechanical rolled, good weldability |
| United States | ASTM A709/A709M | Grade 50W | Weathering option, similar strength |
| India | IS 2062 | E350 | Yield 350 MPa, C ≤0.20%, similar weldable structural steel |
Notes:
- Q345E is often specified for LSAW pipes complying with GB/T 9711 (PSL2) or API Spec 5L (up to grade X56).
- For thickness above 40 mm, higher alloy content or normalizing may be required to achieve the Charpy impact guarantee.
- Welding consumables should match the strength and low-temperature toughness; preheat and post-weld heat treatment may be needed depending on thickness and local codes.
- In GB/T 1591-2018, the equivalent grade Q355NE has similar composition with slight adjustments (e.g., Mn ≤ 1.65, C ≤ 0.20).
- When used in sour service, supplementary HIC/SSC tests should be performed per NACE MR0175/ISO 15156.
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