GB/T 700-2006 Grade B steel is a very common and widely available material grade for manufacturing Longitudinal Submerged Arc Welded (LSAW) pipes. This typically corresponds to the Q235B steel grade, which is one of the most frequently used carbon structural steels in China for general construction, structural supports, and low-pressure fluid transmission applications [citation:2, citation:4].
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 [citation:1, citation:3, citation:4]. |
| Material Standard | GB/T 700-2006: Carbon Structural Steels [citation:1, citation:2, citation:4]. |
| Common Steel Grade | Q235B. The "Q" stands for Yield Strength, "235" indicates the minimum yield strength in MPa, and "B" denotes the quality grade with specified impact requirements at room temperature (+20°C) [citation:2, citation:3, citation:4]. |
| Chemical Composition (Ladle Analysis, max %) [citation:1, citation:2, citation:3, citation:4] | |
| Carbon (C): 0.20 | |
| Silicon (Si): 0.35 | |
| Manganese (Mn): 1.40 | |
| Phosphorus (P): 0.045 | |
| Sulfur (S): 0.045 | |
| Mechanical Properties (min) [citation:2, citation:3, citation:4] | |
| Yield Strength: ≥ 235 MPa (for thickness ≤ 16mm) | |
| Tensile Strength: 370-500 MPa | |
| Elongation: ≥ 26% | |
| Impact Energy (Charpy V-notch): ≥ 27 Joules at +20°C | |
| Typical Size Range [citation:2, citation:3, citation:4] | |
| Outside Diameter: 219 mm to 2500 mm+ (approx. 8" to 100"+) | |
| Wall Thickness: 5 mm to 25.4 mm+ | |
| Length: 3 m to 18 m (customizable) | |
| Manufacturing Process [citation:3, citation:4] | 1. Steel plate or coil selection and edge milling. 2. Edge crimping and forming using JCOE or UOE processes. 3. Internal and external submerged arc welding (for LSAW). 4. Mechanical expanding (for UOE/JCOE). 5. Non-destructive testing (Ultrasonic, X-ray). 6. Hydrostatic testing (typically 6 MPa hold). 7. End facing and beveling. |
| Common Applications [citation:2, citation:3, citation:4] | Low-pressure fluid transmission (water, gas, air, ≤1.6 MPa); building structural supports and columns; bridge components; piling foundations; general engineering structures; machinery manufacturing. |
| Certification | Mill Test Certificate typically provided as per EN 10204 / 3.1 or project requirements. |
💡 Key Points to Understand
Meaning of "Grade B": In the GB/T 700-2006 standard, the letter B indicates a specific quality grade. The key difference from Grade A is that Grade B guarantees a minimum impact energy of 27 Joules at room temperature (+20°C) , making it more suitable for applications subject to dynamic loads or where some toughness is required [citation:3, citation:4].
Standard Update: GB/T 700-2006 has been superseded by GB/T 700-2019. It is good practice to confirm which version year is required for your project .
Weldability: Q235B has excellent weldability due to its low carbon equivalent (<0.3%), typically not requiring preheating under normal conditions, which reduces fabrication costs [citation:3, citation:4].
Operating Limits: For pressure applications, it is generally recommended to keep working pressure ≤1.6 MPa and operating temperature between -20°C and 300°C. For sustained low-temperature service below -20°C, higher grades like Q235D are recommended [citation:3, citation:4].
In summary, GB/T 700-2006 Grade B (Q235B) LSAW pipe is a reliable, cost-effective, and widely manufactured product for general structural and low-pressure applications, offering the important advantage of guaranteed room-temperature impact toughness compared to Grade A.
