GB/T 700-2006 Grade A Double-Sided Submerged Arc Welding (DSAW) Steel Pipe
✅ Basic Overview
GB/T 700-2006 Grade A (Q235A) Double-Sided Submerged Arc Welding (DSAW) steel pipe is a standard carbon structural steel pipe manufactured to the Chinese national standard. The "Grade A" designation is the most basic quality level in the GB/T 700 series, with no guaranteed impact toughness requirements, making it the most economical choice for general structural and low-pressure applications .
The DSAW (also known as LSAW - Longitudinal Submerged Arc Welding) process is a high-integrity welding method where both inside and outside welds are applied, typically in separate processes, forming a single high-quality weld nugget. This process is particularly well-suited for large-diameter, thick-wall pipes used in structural, piling, and low-pressure fluid applications .
📋 Name Explanation
| Part | Meaning |
|---|---|
| GB/T | Chinese national standard (Guobiao/Tuijian) |
| 700-2006 | Standard number for Carbon Structural Steels (2006 edition) |
| Grade A | The most basic quality grade – no impact testing required; highest allowable phosphorus (0.045%) and sulfur (0.050%) |
| DSAW | Double-Sided Submerged Arc Welding – both inside and outside welds are applied; the welding arc is submerged in granular flux during welding |
🔧 Key Specifications
| Attribute | Description |
|---|---|
| Material Standard | GB/T 700-2006 – Carbon Structural Steels (current version; GB/T 700-2019 is newer) |
| Steel Grade | Q235A – Minimum yield strength 235 MPa (for thickness ≤ 16mm) |
| Quality Level | Grade A – Most basic; no guaranteed impact toughness; highest S and P allowances |
| Manufacturing Process | DSAW (Double-Sided Submerged Arc Welding) / LSAW (Longitudinal Submerged Arc Welding) |
| Forming Methods | JCOE (progressive J-C-O forming) or UOE (U-ing, O-ing, Expanding) |
| Size Range | 219 mm to 1829 mm (8" to 72") OD – typical for DSAW |
| Wall Thickness | 5 mm to 40 mm (up to 50 mm for piling applications) |
| Length | 6 m to 12.3 m standard; up to 18 m available |
🔬 Chemical Composition (GB/T 700-2006 Grade A)
| Element | Maximum % | Notes |
|---|---|---|
| Carbon (C) | 0.22% | Low carbon for good weldability |
| Manganese (Mn) | Not specified | Typically ≤ 1.40% |
| Silicon (Si) | 0.35% | Deoxidizer |
| Phosphorus (P) | 0.045% | Highest among Q235 grades (A > B > C > D) |
| Sulfur (S) | 0.050% | Highest among Q235 grades (A > B > C > D) |
Note: Grade A has no mandatory aluminum or nitrogen requirements, and does not require impact testing .
📊 Q235 Grade Comparison (Quality Levels)
| Grade | Impact Test Temperature | P max (%) | S max (%) | Key Feature |
|---|---|---|---|---|
| Q235A | Not guaranteed | 0.045 | 0.050 | Most economical; general structures |
| Q235B | +20°C (27J min) | 0.045 | 0.045 | General construction, mild climates |
| Q235C | 0°C (27J min) | 0.040 | 0.040 | Colder climates, outdoor structures |
| Q235D | -20°C (27J min) | 0.035 | 0.035 | Severe cold environments |
Grade A is the only Q235 grade that does not guarantee impact toughness .
📊 Mechanical Properties (GB/T 700-2006)
| Property | Q235A Requirement | Condition |
|---|---|---|
| Yield Strength (min) | 235 MPa | Thickness ≤ 16mm |
| 225 MPa | 16mm < t ≤ 40mm | |
| 215 MPa | 40mm < t ≤ 60mm | |
| 205 MPa | 60mm < t ≤ 100mm | |
| 195 MPa | 100mm < t ≤ 150mm | |
| 185 MPa | t > 150mm | |
| Tensile Strength | 370-500 MPa | All thicknesses |
| Elongation (min) | 25% | Thickness ≤ 40mm |
| 24% | Thickness > 40mm to 60mm | |
| 23% | Thickness > 60mm to 100mm | |
| 22% | Thickness > 100mm to 150mm | |
| 21% | Thickness > 150mm | |
| Charpy Impact | Not required | Grade A has no impact testing |
| Hardness | ≤ 185 HB | Typical |
📏 Dimensional Specifications
| Parameter | Range / Tolerance |
|---|---|
| Outside Diameter | 219 mm to 1829 mm (8" to 72") – typical DSAW range |
| Wall Thickness | 5 mm to 40 mm (up to 50 mm for piling) |
| Diameter Tolerance | ±0.75% of specified OD (typical) |
| Wall Thickness Tolerance | +15% / -12.5% of nominal (typical) |
| Length | 6 m to 12.3 m standard; up to 18 m available |
🔧 DSAW/LSAW Manufacturing Process
Double-Sided Submerged Arc Welding (DSAW), also known as Longitudinal Submerged Arc Welding (LSAW), is a high-efficiency process used primarily for large-diameter steel pipes :
Process Description
Welding arc is submerged in granular flux during welding, protecting the weld from atmospheric contamination
Both inside and outside welds are required, usually accomplished in separate processes
The separate welds consume a portion of the other, resulting in a single high-quality weld nugget
Forming Methods
| Method | Description | Typical Diameters |
|---|---|---|
| JCOE | Progressive J-C-O forming steps (J-shape → C-shape → O-shape), expanded after welding | 406-1626 mm (16"-64") |
| UOE | Plate pressed into U-shape, then O-shape, expanded after welding | 508-1118 mm (20"-44") |
Process Steps
Plate Selection – Steel plates meeting GB/T 700 Q235A requirements
Edge Preparation – Edges are beveled to create a V-shaped groove
Forming – Steel plates are formed into cylindrical shapes using JCOE or UOE presses
Tack Welding – Formed plates are tack-welded to maintain shape
Double Submerged Arc Welding – Pipe seam welded on both interior and exterior surfaces
Cold Expansion – Pipe may be expanded up to 1.5% to achieve final OD dimension
Ultrasonic Inspection – Seam inspected by continuous ultrasonic automatic flaw detection
Hydrostatic Pressure Test – Each pipe undergoes hydrostatic pressure testing
Finishing – End processing, beveling, coating, and marking
🧪 Testing & Inspection Requirements
| Test Type | Requirement | Notes |
|---|---|---|
| Chemical Analysis | Per heat lot | Verifies composition limits per GB/T 700 |
| Tensile Test | Per lot | Verifies yield and tensile strength |
| Flattening Test | Required | Checks ductility and weld integrity |
| Bend Test | Required | Verifies weld integrity |
| Charpy Impact Test | Not required for Grade A | Only Grades B, C, D require impact testing |
| Hydrostatic Test | Each pipe | Pressure integrity verification |
| Ultrasonic Inspection | 100% of weld seam | Continuous automatic flaw detection |
| X-ray Inspection | For "T" joints | Where strip butt welds intersect spiral seams |
| Dimensional Inspection | 100% | Per standard tolerances |
| Mill Test Certificate | Provided | With full test results |
🏭 Common Applications
| Application | Description |
|---|---|
| General Structural Engineering | Building frames, columns, trusses for industrial plants, stadiums |
| Piling Foundations | Light to medium load-bearing piles for buildings and structures |
| Low-Pressure Fluid Transmission | Water, gas, and oil pipelines (non-critical) |
| Temporary Structures | Construction supports, scaffolding, temporary bridges |
| Mechanical Manufacturing | Equipment frames, machinery bases, low-stress components |
| Infrastructure Projects | Tunnel supports, retaining walls, highway structures |
| Agricultural Applications | Irrigation systems, livestock equipment frames |
📊 Q235A vs. Higher Grades (Q235B/C/D) Comparison
| Feature | Q235A | Q235B | Q235C | Q235D |
|---|---|---|---|---|
| Impact Testing | Not required | 27J at +20°C | 27J at 0°C | 27J at -20°C |
| Phosphorus (P) max | 0.045% | 0.045% | 0.040% | 0.035% |
| Sulfur (S) max | 0.050% | 0.045% | 0.040% | 0.035% |
| Typical Application | Most economical, indoor/non-critical | General construction, mild climates | Colder climates, outdoor structures | Severe cold environments |
Grade A is the most economical but lacks guaranteed low-temperature toughness .
🛡️ Coating Options
Q235A DSAW pipe can be supplied with various coatings for corrosion protection:
| Coating Type | Best For | Key Features |
|---|---|---|
| 3LPE (3-layer polyethylene) | Buried pipelines | Most common; excellent corrosion protection, high impact resistance |
| FBE (Fusion Bonded Epoxy) | Oil & gas pipelines | Strong adhesion, chemical resistance |
| Epoxy Powder Coating | Corrosive environments | Good protection, smooth surface |
| Varnish / Anti-rust oil | Temporary protection | Short-term corrosion protection during transport |
| Bitumen Coating | Buried service | Cost-effective protection |
| Black Oil Coating | Standard mill finish | Temporary protection |
📝 End Finishes
Available end treatments include:
Plain ends (PE) – standard for most applications
Beveled ends (BE) – for field welding (30° bevel angle)
Threaded ends – for mechanical connections
🌍 International Equivalents
| Standard | Equivalent Grade | Notes |
|---|---|---|
| ASTM | A36 (similar) | 250 MPa yield vs. 235 MPa |
| EN 10025 | S235JR | 235 MPa yield, 27J at +20°C |
| JIS G3101 | SS400 | 245 MPa yield |
| DIN | ST37-2 | Historical German equivalent |
| BS | Grade 43A | Historical British standard |
✅ Key Advantages
| Advantage | Description |
|---|---|
| Most Economical | Lowest cost among Q235 grades; no impact testing required |
| Excellent Weldability | Low carbon content (≤0.22%) allows welding with minimal preheat (100-150°C) |
| Good Cold Forming | Suitable for cold bending, flanging, and shaping without cracking |
| Large Diameter Capability | DSAW produces pipes from 8" to 72" OD – ideal for large-diameter applications |
| High Weld Integrity | Double-sided welding creates a single high-quality weld nugget with 100% UT inspection |
| Wide Availability | Commonly stocked by Chinese manufacturers |
| Versatile Applications | Suitable for structural, piling, and low-pressure fluid applications |
📝 Important Considerations
1. Grade A vs. Higher Grades
Grade A is the most economical but lacks guaranteed impact toughness
For outdoor applications in cold climates, specify Q235B (0°C), Q235C (-20°C), or Q235D (-40°C)
Grade A is best suited for indoor or non-critical applications
2. Standard Version Note
GB/T 700-2006 has been superseded by GB/T 700-2019
When ordering, specify the required version year to ensure compliance
Most manufacturers still produce to the 2006 standard specifications
3. Product Standard
While GB/T 700 defines the material grade, the finished DSAW pipe product is typically manufactured to product standards such as:
GB/T 3091 – Welded steel pipes for low-pressure fluid transmission
GB/T 9711 – Petroleum and natural gas industries line pipe
SY/T 5037 – Spiral submerged arc welded pipe for low-pressure fluid service
4. Pressure Limitations
Q235A is suitable for low-pressure applications only (typically ≤ 1.6 MPa)
For higher pressure requirements, consider Q345 or Q355 grades
5. Temperature Limitations
Maximum recommended service temperature: 350°C (662°F)
Short-term exposure up to 450°C possible
No guaranteed low-temperature toughness – not suitable for sub-zero applications
6. Coating for Corrosion Protection
For buried applications, specify 3LPE or FBE coating
For temporary protection, varnish or anti-rust oil is sufficient
7. Third-Party Inspection
Available inspection services include SGS, BV, Lloyds
8. Weldability
Preheat temperature: 100-150°C recommended
No post-weld heat treatment required for most thicknesses
Excellent for field welding
📝 Summary
GB/T 700-2006 Grade A (Q235A) Double-Sided Submerged Arc Welded (DSAW) steel pipe is the most economical carbon structural steel pipe for large-diameter applications. With minimum yield strength of 235 MPa (34,000 psi) and tensile strength of 370-500 MPa, this material is suitable for general structural engineering, piling foundations, and low-pressure fluid transmission where guaranteed low-temperature toughness is not required .
Key features:
Material standard: GB/T 700-2006 Q235A
Grade A is the most basic quality level – no impact testing required
DSAW manufacturing produces pipes from 8" to 72" OD with wall thickness up to 40 mm
Double-sided welding creates a single high-quality weld nugget
JCOE or UOE forming methods ensure precise dimensional accuracy
100% ultrasonic inspection of weld seam ensures quality
Most economical choice among Q235 grades
Excellent weldability with low carbon content (≤0.22%)
Good cold forming capabilities
Common applications include:
General structural engineering (building frames, columns, trusses)
Piling foundations for light to medium loads
Low-pressure fluid transmission (water, gas, oil)
Temporary structures and mechanical manufacturing
Infrastructure projects
When ordering, specify: GB/T 700-2006, Grade Q235A, DSAW (Double-Sided Submerged Arc Welded), Size (OD x WT), Length, End Finish (plain/beveled), Coating Requirements, and Mill Test Certificate.
For applications requiring guaranteed low-temperature toughness, specify Q235B (0°C), Q235C (-20°C), or Q235D (-40°C) instead .
