GB/T 1591-2009 Grade B steel is a common and widely used material grade for manufacturing Longitudinal Submerged Arc Welded (LSAW) pipes. This corresponds to the Q345B steel grade, which is a low-alloy high-strength structural steel extensively used in construction, engineering structures, and low-pressure fluid transmission applications .
The key specifications are summarized in the following table:
Key Specifications
| Attribute | Description |
|---|---|
| Product Type | Longitudinal Submerged Arc Welded (LSAW) Pipe, manufactured using JCOE, UOE, or similar forming processes . |
| Material Standard | GB/T 1591-2008: Hot-rolled low-alloy structural steels (Note: the standard number shows 2008 in the source, though 2009 is mentioned in your query) . |
| Common Steel Grade | Q345B. The "Q" stands for Yield Strength, "345" indicates the minimum yield strength in MPa, and "B" denotes the quality grade with specified impact requirements at room temperature (+20°C) . |
| Chemical Composition (Ladle Analysis, max %) | |
| Carbon (C): ≤ 0.20 | |
| Silicon (Si): ≤ 0.55 | |
| Manganese (Mn): 1.00-1.60 | |
| Phosphorus (P): ≤ 0.040 | |
| Sulfur (S): ≤ 0.040 | |
| Vanadium (V): 0.02-0.15 | |
| Niobium (Nb): 0.015-0.060 | |
| Titanium (Ti): 0.02-0.20 | |
| Mechanical Properties (min) | |
| Yield Strength (t ≤ 16mm): ≥ 345 MPa | |
| Yield Strength (16mm < t ≤ 35mm): ≥ 325 MPa | |
| Yield Strength (35mm < t ≤ 50mm): ≥ 295 MPa | |
| Yield Strength (50mm < t ≤ 100mm): ≥ 275 MPa | |
| Tensile Strength: 470-630 MPa | |
| Elongation: ≥ 21% | |
| Impact Energy (Charpy V-notch): ≥ 34 Joules at +20°C . | |
| Typical Size Range | |
| Outside Diameter: 20 mm to 610 mm (larger sizes may be available from some manufacturers) | |
| Wall Thickness: 4 mm to 70 mm | |
| Length: 4 m to 12 m (customizable) | |
| Manufacturing Process | 1. Steel plate selection and edge milling. 2. Forming using JCOE or UOE processes. 3. Internal and external submerged arc welding. 4. Mechanical expanding (for UOE/JCOE). 5. Non-destructive testing. 6. Hydrostatic testing. 7. End facing and beveling. |
| Common Applications | Low-pressure fluid transmission (water, gas, oil); structural components in construction; bridge components; machinery manufacturing; transportation of low-pressure fluids; general engineering structures. |
| Certification | Mill Test Certificate typically provided as per EN 10204 / 3.1 or project requirements. |
📊 Q345 Grade Comparison
The Q345 family has multiple quality grades with progressively stricter controls and impact requirements :
| Grade | Impact Test Temperature | Key Application |
|---|---|---|
| Q345A | Not required | General structures, non-critical, indoor applications |
| Q345B | +20°C (34J min) | General construction, mild climate applications |
| Q345C | 0°C (27-34J) | Colder climates, outdoor structures |
| Q345D | -20°C (27-34J) | Severe cold environments |
| Q345E | -40°C (27J) | Extreme cold, critical infrastructure |
Grade B is the most commonly specified grade in the Q345 family, offering a good balance of strength, weldability, and cost with guaranteed impact toughness at room temperature (+20°C) .
🔍 Key Points to Understand
Meaning of "Grade B": In GB/T 1591-2008, the letter B indicates a quality grade that requires Charpy V-notch impact testing at +20°C with a minimum energy absorption of 34 Joules. This makes it suitable for general construction applications where some impact resistance is needed .
Relationship to Q355: Note that GB/T 1591-2008 has been superseded by GB/T 1591-2018, which replaced Q345 with Q355 (minimum yield strength adjusted to 355 MPa). However, Q345B remains widely referenced in industry and is still produced for projects based on the older standard.
Micro-alloying Elements: Q345B contains small additions of vanadium, niobium, and titanium (0.02-0.20%) which contribute to grain refinement and improved mechanical properties .
Weldability: Q345B has good weldability due to its controlled chemistry, making it suitable for common welding methods including submerged arc welding (SAW), which is the process used for LSAW pipe manufacturing .
💡 When to Choose Q345B Grade
Select GB/T 1591-2008 Grade B (Q345B) LSAW pipe when:
The application requires guaranteed impact toughness at room temperature (+20°C)
General construction and engineering projects in mild climate conditions
Low-pressure fluid transmission lines requiring higher strength than carbon steel
Structural components subject to moderate dynamic loads
Cost-sensitive projects needing a balance of performance and economy
For most general construction and engineering applications, Grade B (Q345B) provides the optimal combination of strength, toughness, and cost-effectiveness . For applications requiring guaranteed low-temperature performance, higher grades such as Q345C, D, or E should be specified.
In summary, GB/T 1591-2008 Grade B (Q345B) LSAW pipe is the most commonly specified grade in the Q345 family, offering reliable strength and guaranteed room-temperature impact toughness for a wide range of structural and fluid transmission applications .
