GB/T 1591-2009 Grade C Longitudinal Submerged Arc Welding (LSAW) Pipe
Yes, GB/T 1591-2009 Grade C steel is a recognized material grade for manufacturing Longitudinal Submerged Arc Welded (LSAW) pipes. This corresponds to the Q345C steel grade, which offers enhanced low-temperature performance with guaranteed impact toughness at 0°C, making it suitable for structural applications in colder environments [citation:2, citation:7].
Key Specifications
| Attribute | Description |
|---|---|
| Product Type | Longitudinal Submerged Arc Welded (LSAW) Pipe, manufactured using JCOE, UOE, or similar forming processes [citation:2, citation:3, citation:5]. |
| Material Standard | GB/T 1591-2009: Hot-rolled low-alloy structural steels. |
| Common Steel Grade | Q345C. The "Q" stands for Yield Strength, "345" indicates the minimum yield strength in MPa, and "C" denotes the quality grade with specified impact requirements at 0°C [citation:2, citation:7]. |
| **Chemical Composition (Ladle Analysis, max %) ** | |
| Carbon (C): ≤ 0.20 | |
| Silicon (Si): ≤ 0.50-0.55 | |
| Manganese (Mn): 1.00-1.70 | |
| Phosphorus (P): ≤ 0.035 | |
| Sulfur (S): ≤ 0.035 | |
| **Mechanical Properties (min) ** | |
| Yield Strength (t ≤ 16mm): ≥ 345 MPa | |
| Yield Strength (16mm < t ≤ 35mm): ≥ 325 MPa | |
| Tensile Strength: 470-630 MPa | |
| Elongation: ≥ 21% | |
| Impact Energy (Charpy V-notch): ≥ 34 Joules at 0°C | |
| Typical Size Range [citation:5, citation:9] | |
| Outside Diameter: 325 mm to 1820 mm (approx. 12" to 72") | |
| Wall Thickness: 5 mm to 50 mm (thicker walls available on request) | |
| Length: 3 m to 18 m (customizable) | |
| Manufacturing Process [citation:3, citation:5] | 1. Steel plate selection and edge milling. 2. Edge crimping and forming using JCOE or UOE processes. 3. Internal and external submerged arc welding. 4. Mechanical expanding (for UOE/JCOE). 5. Non-destructive testing (Ultrasonic, X-ray). 6. Hydrostatic testing. 7. End facing and beveling. |
| Common Applications [citation:2, citation:5, citation:7] | Structural supports in colder climates; bridge construction; offshore platforms; piling foundations; low-pressure fluid transmission; machinery manufacturing; applications requiring guaranteed 0°C impact toughness. |
| Certification | Mill Test Certificate typically provided as per EN 10204 / 3.1 or project requirements [citation:5, citation:9]. |
📊 Q345 Grade Comparison
The Q345 family has five quality grades with progressively stricter controls and impact requirements [citation:2, citation:7]:
| Grade | Impact Test Temperature | P max (%) | S max (%) | Key Application |
|---|---|---|---|---|
| Q345A | Not required | 0.045 | 0.045 | General structures, non-critical, indoor applications |
| Q345B | +20°C (34J min) | 0.040 | 0.040 | General construction, mild climate applications |
| Q345C | 0°C (34J min) | 0.035 | 0.035 | Colder climates, outdoor structures |
| Q345D | -20°C (34J min) | 0.030 | 0.030 | Severe cold environments |
| Q345E | -40°C (27J min) | 0.025 | 0.025 | Extreme cold, critical infrastructure |
Grade C occupies the intermediate position in the Q345 family, offering guaranteed impact toughness at 0°C with stricter phosphorus and sulfur controls (0.035% max each) compared to Grades A and B [citation:2, citation:7].
🔍 Key Points to Understand
Meaning of "Grade C": In GB/T 1591-2009, the letter C indicates a quality grade that requires Charpy V-notch impact testing at 0°C with a minimum energy absorption of 34 Joules. This makes it suitable for outdoor structures and applications in colder climates where Grade B's room-temperature impact guarantee (+20°C) is insufficient [citation:2, citation:7].
Relationship to Q355: Note that GB/T 1591-2009 has been superseded by GB/T 1591-2018, which replaced Q345 with Q355 (minimum yield strength adjusted to 355 MPa). However, Q345C remains widely referenced in industry and is still produced for projects based on the older standard.
Chemical Composition: Grade C has stricter phosphorus and sulfur limits (≤0.035% each) compared to Grade A (≤0.045%) and Grade B (≤0.040%), contributing to improved toughness and weldability .
Weldability: Q345C has excellent weldability due to its controlled chemistry and low carbon equivalent, making it suitable for common welding methods including submerged arc welding (SAW), which is the process used for LSAW pipe manufacturing [citation:3, citation:5].
💡 When to Choose Q345C Grade
Select GB/T 1591-2009 Grade C (Q345C) LSAW pipe when [citation:2, citation:7]:
The structure will be exposed to temperatures around or below freezing (0°C)
The application requires guaranteed impact toughness at 0°C
Projects in temperate to cold climates where Grade B's room-temperature guarantee is inadequate
Outdoor structures, bridges, and infrastructure in regions with cold winters
Piling foundations in areas subject to low ambient temperatures
Applications requiring better toughness than Grade B without the cost of Grade D or E
For most general construction in mild climates, Grade B (Q345B) is sufficient and more economical . For severe cold environments below -20°C, Grade D or E would be required [citation:2, citation:7].
⚙️ Manufacturing & Availability
Production Standards: Q345C LSAW pipes are typically manufactured to product standards such as GB/T 3091 (for low-pressure fluid transmission), GB/T 9711 (for pipeline applications), or API 5L [citation:2, citation:5, citation:9].
Size Availability: LSAW pipes in Q345C are available in a wide range of diameters (325 mm to 1820 mm) and wall thicknesses (5 mm to 50 mm), with some manufacturers offering larger sizes on request [citation:5, citation:9].
Quality Control: The JCOE and UOE forming processes provide precise dimensional accuracy with out-of-roundness tolerance of ±1% and straightness deviation ≤0.2% . Non-destructive testing (ultrasonic, X-ray) and hydrostatic testing are standard quality assurance measures .
📝 Standard Update Note
GB/T 1591-2009 has been superseded by GB/T 1591-2018, which introduced Q355 as the replacement for Q345 with a minimum yield strength of 355 MPa. It is recommended to confirm which version year is required for your project. Current production of Q345C LSAW pipes may still reference the 2009 standard, but the material properties remain consistent with the established Q345 specifications .
In summary, GB/T 1591-2009 Grade C (Q345C) LSAW pipe is a reliable choice for structural applications requiring guaranteed impact toughness at 0°C, offering an intermediate option between general-purpose Grade B and cold-weather Grade D with enhanced low-temperature performance [citation:2, citation:7].
