GB/T 700-2006 Grade C steel is a recognized material grade for manufacturing Longitudinal Submerged Arc Welded (LSAW) pipes. This corresponds to the Q235C steel grade, which offers enhanced low-temperature performance compared to Grades A and B, making it suitable for more demanding structural applications in colder environments .
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 700-2006: Carbon Structural Steels . |
| Common Steel Grade | Q235C. The "Q" stands for Yield Strength, "235" indicates the minimum yield strength in MPa, and "C" denotes the quality grade with specified impact requirements at 0°C . |
| Chemical Composition (Ladle Analysis, max %) | |
| Carbon (C): 0.17 | |
| Silicon (Si): 0.35 | |
| Manganese (Mn): 1.40 | |
| Phosphorus (P): 0.040 | |
| Sulfur (S): 0.040 | |
| Mechanical Properties (min) | |
| Yield Strength: ≥ 235 MPa (for thickness ≤ 16mm) | |
| Tensile Strength: 370-500 MPa | |
| Impact Energy (Charpy V-notch): ≥ 27 Joules at 0°C | |
| Typical Size Range | |
| Outside Diameter: 219 mm to 2500 mm+ (approx. 8" to 100"+) | |
| Wall Thickness: 5 mm to 25 mm+ | |
| Length: 3 m to 18 m (customizable) | |
| Manufacturing Process | 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 | Structural supports in colder climates; building components requiring guaranteed 0°C impact toughness; bridge components; general engineering structures exposed to low ambient temperatures. |
| Certification | Mill Test Certificate typically provided as per project requirements. |
🔍 Key Points to Understand
Meaning of "Grade C": In the GB/T 700-2006 standard, the letter C indicates a specific quality grade with stricter controls on phosphorus and sulfur compared to Grades A and B. The defining characteristic of Grade C is that it guarantees a minimum impact energy of 27 Joules at 0°C, making it the appropriate choice for applications in colder environments where Grade B's room-temperature impact guarantee (+20°C) is insufficient .
Comparison of Q235 Grades:
| Grade | Impact Test Temperature | Key Application |
|---|---|---|
| Q235A | Not guaranteed | General structures, low-pressure fluids, non-critical applications |
| Q235B | +20°C (27J min) | General construction, mild climate applications |
| Q235C | 0°C (27J min) | Colder climates, outdoor structures exposed to low temperatures |
| Q235D | -20°C (27J min) | Severe cold environments, demanding applications |
Standard Update: GB/T 700-2006 has been superseded by GB/T 700-2019. It is recommended to confirm which version year is required for your project.
Weldability: Q235C maintains excellent weldability due to its low carbon content (0.17% max), typically not requiring preheating under normal conditions, which reduces fabrication costs.
💡 When to Choose Grade C
Select GB/T 700-2006 Grade C (Q235C) LSAW pipe when:
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 in regions with cold winters
For most general construction in mild climates, Grade B (Q235B) is sufficient and more economical. For severe cold environments below -20°C, Grade D (Q235D) would be required.
In summary, GB/T 700-2006 Grade C (Q235C) 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.
