I. Overview of LSAW Carbon Steel Structural Pipes
LSAW carbon steel structural pipes are steel pipe products manufactured using the longitudinal submerged arc welding process. They are made from carbon steel or low-alloy structural steel plates through processes such as forming, internal and external submerged arc welding, expanding, and multiple inspections.
These steel pipes have stable weld quality, high dimensional accuracy, and possess good load-bearing capacity and structural stability, making them widely used in various load-bearing engineering structures.
II. Comparison of Differences between LSAW / ERW / SSAW Structural Pipes
i. Core Process and Structural Differences
| Comparison Item | LSAW Structural Pipe | ERW Structural Pipe | SSAW Structural Pipe |
|---|---|---|---|
| Welding Method | Longitudinal Submerged Arc Welding (Inner + Outer Weld) | High-Frequency Resistance Welding | Spiral Submerged Arc Welding |
| Weld Seam Type | Straight | Straight | Spiral |
| Weld Seam Length | Shortest | Shortest | Longest |
| Weld Stress Distribution | Uniform | Relatively Uniform | Non-uniform |
| Forming Method | UOE / JCOE | Continuous Roll Forming | Spiral Rolling |
ii. Comparison of dimensions and wall thickness capabilities
| Item | LSAW | ERW | SSAW |
|---|---|---|---|
| Outside Diameter Range | Large (219–1420+ mm) | Small to Medium (≤660 mm) | Medium to Large (219–3000 mm) |
| Wall Thickness Capability | Thick (10–50 mm) | Thin to Medium (1.5–12 mm) | Medium (6–25 mm) |
| Suitability for Extra-Thick Walls | Optimal | Not Suitable | Limited |
| Roundness & Dimensional Accuracy | High | High | Moderate |
iii. Load-bearing capacity and structural safety
| Comparison Point | LSAW | ERW | SSAW |
|---|---|---|---|
| Single-Pipe Load-Bearing Capacity | Highest | Medium | Medium to Low |
| Suitability for Main Load-Bearing Structures | Very Suitable | Not Recommended | Conditionally Usable |
| Fatigue and Dynamic Load Performance | Excellent | Average | Poor |
| Weld Inspection Controllability | Best (100% UT feasible) | Good | More Difficult |
iv. Difficulty in quality control and testing
| Item | LSAW | ERW | SSAW |
|---|---|---|---|
| Weld Inspection Difficulty | Low | Low | High |
| Feasibility of 100% UT | High | High | Low |
| Weld Repair Risk | Low | Medium | High |
| Quality Stability | High | Medium | Highly Variable |
v. Typical application scenarios
| Engineering / Application | Recommended Pipe Type | Reason |
|---|---|---|
| Bridge Main Beams / Columns | LSAW | High load-bearing capacity and high safety level |
| Pile Foundations / Pipe Piles | LSAW | Reliable welds and uniform stress distribution |
| Building Steel Structures | ERW / LSAW | ERW suitable for medium to small loads |
| Industrial Equipment Supports | LSAW | Designed for long-term heavy loads |
| Pipe Racks / Structural Supports | ERW / LSAW | Depends on load requirements |
| Temporary or Non-Critical Structures | SSAW | Lower cost but higher risk |
III. LSAW Carbon Steel Structural Pipe Selection Guide
i. Selection Principles
- Load-Bearing Capacity Determines Pipe Type
- High load-bearing, primary structural elements → LSAW thick-walled pipes
- Secondary load-bearing or auxiliary structures → ERW pipes
- Non-load-bearing or temporary structures → SSAW pipes
- Wall Thickness and Outer Diameter Selection
- Bridges, pile foundations, and other critical structures: Wall thickness ≥16 mm, outer diameter ≥219 mm
- Medium load-bearing industrial structures: Wall thickness 10–30 mm
- Non-critical structures: Wall thickness 6–12 mm, ERW or SSAW pipes are optional
- Weld and Inspection Requirements
- High load-bearing structures: 100% UT + RT as needed
- Secondary load-bearing structures: Random inspection or visual inspection
- Ultra-thick-walled pipes (≥40 mm): Heat treatment + full inspection recommended
- Environmental and Corrosion Protection Requirements
- Outdoor/seaside/humid environments → Anti-corrosion coating or hot-dip galvanizing
- High or low temperature environments → Material grade and heat treatment must be matched
- Standard Compliance
- Domestic projects: GB/T 1591 / GB/T 9711
- Export or international projects: ASTM / API / EN
ii. Quick Selection Reference Table
| Load / Risk Level | Recommended Pipe Type | OD / Wall Thickness | Weld Inspection | Reason |
|---|---|---|---|---|
| High Load / Bridges, Pile Foundations, Columns | LSAW Thick-Wall Pipe | ≥219 mm / 16–50 mm | 100% UT | High load capacity, uniform welds, safe and reliable |
| Medium-High Load / Industrial Building Main Beams | LSAW / ERW | 168–508 mm / 10–30 mm | LSAW 100% UT, ERW spot check | LSAW preferred for load-bearing structures |
| Secondary Load / Building Secondary Beams, Pipe Racks | ERW Pipe | 60–323 mm / 4–12 mm | Spot check UT | Low cost, easy construction |
| Non-Load-Bearing / Temporary Supports, Canopies | SSAW Pipe | 219–3000 mm / 6–25 mm | Visual Inspection | Non-critical structures, cost-priority |
| Extra-Thick Wall / High-Fatigue Structures | LSAW + Heat Treatment | ≥40 mm | 100% UT + RT | Eliminates residual stress, improves fatigue resistance |
IV. List of Real Engineering Risks Caused by Incorrect Material Selection
- Incorrect selection of ERW or SSAW for main load-bearing structures
- Risk: Weld fatigue cracking, insufficient load-bearing capacity
- Consequences: Rework, project delays, and even safety accidents
- Prevention: Main load-bearing components must use LSAW thick-walled pipes, with 100% UT inspection.
- Considering only nominal wall thickness, neglecting negative tolerance
- Risk: Insufficient effective cross-section, reduced strength
- Consequences: Failure to pass acceptance testing, inability to assign responsibility later
- Prevention: Clearly define allowable wall thickness tolerances and require 100% ultrasonic thickness measurement.
- Insufficient weld inspection ratio
- Risk: Undetected internal defects, localized stress concentration
- Consequences: Cracks during operation, structural failure
- Prevention: High-load-bearing structures must undergo 100% UT inspection, and RT inspection when necessary.
- Using SSAW for load-bearing structures
- Risk: Helical welds, uneven stress distribution
- Consequences: Early failure under dynamic or alternating loads
- Prevention: SSAW should only be used for non-critical structures.
- Failure to differentiate between structural and conveying pipe standards
- Risk: Insufficient mechanical properties and dimensional tolerances
- Consequences: Appears compliant on the surface, but lacks sufficient structural load-bearing capacity
- Prevention: Strictly adhere to structural pipe standards (GB/T, ASTM, API, EN)
- Failure to heat treat extra-thick-walled pipes
- Risk: High residual stress in welds, poor fatigue resistance
- Consequences: Microcracks develop during long-term use, shortening lifespan
- Prevention: Heat treatment is recommended for wall thicknesses ≥40 mm
- Neglecting environmental corrosion factors
- Risk: Pipe body corrosion reduces wall thickness
- Consequences: Reduced load-bearing capacity, shortened lifespan
- Prevention: Anti-corrosion treatment is mandatory for outdoor or corrosive environments
- Failure to specify testing requirements in procurement documents
- Risk: No complete test report, unclear responsibility
- Consequences: Problems must be borne at one’s own risk
- Prevention: Require EN 10204 3.1 / 3.2 testing documents and a complete report
