overview of Q345 LSAW Steel Pipe& International Equivalents
Q345 LSAW Steel Pipe (Longitudinal Submerged Arc Welded Steel Pipe) is a high-performance large-diameter welded pipe manufactured from Q345 low-alloy high-strength structural steel plate. The pipe is formed into a cylindrical shape through the JCOE (J-forming, C-forming, O-forming, Expansion) or UOE (U-forming, O-forming, Expansion) process, then welded along a single longitudinal seam using the double-sided submerged arc welding (DSAW) method. This manufacturing approach delivers superior weld integrity, uniform mechanical properties, and tight dimensional tolerances that make it the preferred choice for demanding industrial applications.
Q345 is a low-alloy high-strength structural steel defined under GB/T 1591-2008. The "Q" denotes yield strength, and "345" indicates a minimum yield strength of 345 MPa for plate thickness ≤ 16 mm. It is widely recognized internationally with the following equivalents：
| Region | Standard | Equivalent Grade |
|---|---|---|
| USA | ASTM | A572 Grade 50 |
| Europe | EN 10025 | S355JR / S355J2 |
| Japan | JIS | SM490 |
Typical Supply specification
| Parameter | Typical Range |
|---|---|
| Outside diameter | 400-1626 mm (LSAW; smaller by agreement) |
| Wall thickness | 8-60 mm or per design |
| Length | 6-12.5 m |
| Tolerances (example) | OD +/-1%; WT +12.5%/-10% (per standard) |
| Surface | Black or coated |
Chemical Composition (GB/T 1591)
Based on ladle (heat) analysis per GB/T 1591 requirements：
| Element | Q345A | Q345B | Q345C | Q345D | Q345E |
|---|---|---|---|---|---|
| C ≤ | 0.20% | 0.20% | 0.20% | 0.18% | 0.18% |
| Si ≤ | 0.55% | 0.55% | 0.55% | 0.50% | 0.50% |
| Mn | 1.00-1.60% | 1.70% | 1.60% | ≤1.70% | ≤1.70% |
| P ≤ | 0.045% | 0.040% | 0.035% | 0.030% | 0.025% |
| S ≤ | 0.045% | 0.040% | 0.035% | 0.025% | 0.020% |
| V | 0.02-0.15% | 0.15% | 0.15% | 0.02-0.15% | 0.02-0.15% |
| Nb | 0.015-0.060% | 0.060% | 0.060% | 0.015-0.060% | 0.015-0.060% |
| Ti | 0.02-0.20% | 0.20% | 0.20% | 0.02-0.20% | 0.02-0.20% |
| Al ≥ | - | - | 0.015% | 0.015% | 0.015% |
| Cr ≤ | 0.30% | 0.30% | 0.30% | 0.30% | 0.30% |
| Mo ≤ | 0.10% | 0.10% | 0.10% | 0.10% | 0.10% |
The total alloying content is less than 3%. Grades B through E contain micro-alloying elements (Nb, V, Ti) for grain refinement and precipitation strengthening.
Quality Assurance & Testing
Every Q345 LSAW pipe undergoes comprehensive quality verification：
| Test | Purpose |
|---|---|
| 100% Ultrasonic Testing (UT) | Weld seam and HAZ defect detection |
| X-ray Radiographic Inspection (RT) | Internal weld defects (porosity, slag, lack of fusion) |
| Hydrostatic Pressure Test | ≥ 85% of SMYS – verifies leak-tight integrity |
| Mechanical Property Testing | Tensile, Charpy V-notch impact, flattening, guided bend |
Advantages of LSAW
LSAW (Longitudinal Submerged Arc Welded) pipes are manufactured by forming and welding a single steel plate along a longitudinal seam-. The key advantages over ERW and SSAW alternatives include:
Highest pressure-bearing capacity – straight seam eliminates helical stress concentration
Shortest weld seam per unit length – fewer potential defect sites
Optimal conditions for full-length NDT – straight seams enable 100% automated ultrasonic and radiographic inspection
Superior geometric consistency – better roundness and straightness facilitate on-site girth welding
Submerged arc welding is a method in which the arc burns under the flux layer for welding. Its advantages are stable welding quality, high welding productivity, no arc light and little smoke. Therefore, Q345 longitudinal submerged arc welded steel pipe can ensure high welding quality and production efficiency during the manufacturing process, while having lower pollution emissions and complying with environmental protection requirements.
Application
Q345 LSAW pipes are engineered primarily for large-diameter, thick-wall, high-pressure applications：
| Industry | Applications |
| Oil & Gas | Long-distance transmission pipelines, offshore subsea flowlines, high-pressure gas transport |
| Structural Engineering | Bridge piling, high-rise building foundations, port structures |
| Petrochemical | Process piping systems, pressure vessels |
| Power Engineering | Hydropower station penstocks, cooling water systems |
| Water Infrastructure | Municipal water transmission mains, cooling water systems |
Packaging & Shipping
Packaging:
End caps (steel or plastic) protect bevels. Steel strapping with hardwood dunnage secures bundles; VCI film and waterproof tarpaulin prevent corrosion.
Shipping:
Containers for OD ≤ 20"; break‑bulk for larger diameters (up to 64") and wall thicknesses up to 50 mm. Shipping marks: PO#, grade, OD×WT×length, heat number, bundle count. Documentation: commercial invoice, packing list and certificate.
FAQ
1. What is the difference between Q345 and Q355?
Q355 is the successor grade under GB/T 1591-2018. The mechanical properties are essentially equivalent; Q355 has slightly tightened yield strength requirements for thinner plates.
2. What is LSAW steel pipe?
LSAW (Longitudinal Submerged Arc Welded) pipe is formed by rolling a steel plate into a cylindrical shape and welding the longitudinal seam with the submerged arc welding process. It is typically used for large-diameter, thick-wall applications.
3. What is the difference between LSAW and SSAW?
LSAW has a straight longitudinal weld seam, offering more uniform stress distribution and better dimensional accuracy. SSAW (Spiral Submerged Arc Welded) has a helical weld, which is more economical for large diameters but has more complex weld stress.
4. What are the typical applications of Q345 LSAW steel pipe?
Q345 LSAW steel pipes are primarily used for high-pressure, long-distance oil, gas, and water transmission, as well as high-strength structural support and piling in large-scale infrastructure projects.
