Q355 steel pipe is a type of Chinese low-alloy, high-strength structural tubing that succeeds the earlier Q345 grade. It has a material density of 7.85 g/cm³. Under the GB/T 1591-2018 standard, the Q355 series includes three quality classes: Q355B, Q355C, and Q355D.
The "Q" refers to the yield point of the material, while "355" represents its minimum yield strength. This steel is engineered for welded structural components designed to withstand heavy stress and load-bearing environments.
Features of Q355 Steel Pipe
Q355 steel pipe delivers a minimum yield strength of 345 MPa and a tensile strength of around 450 MPa. Known for its excellent forming performance and strong compressive ability, it can be used for fabricating medium to high-pressure gas vessels under 500 liters. The steel also forms a natural protective layer that enhances its resistance to atmospheric corrosion.
Applications of Q355 Steel Pipe
Due to its superior mechanical properties, weldability, and moderate corrosion resistance, Q355 steel pipe is widely adopted across multiple industries. Typical uses include the construction of petroleum storage facilities, pressure vessels, power boilers, marine structures, and other components subjected to substantial mechanical loads.
Available Sizes
Outer diameter: 34 mm – 610 mm
Wall thickness: 3.5 mm – 50 mm
Shape: Round
Production method: Hot rolled or hot expanded
Length: SRL/DRL or custom lengths up to 12 m
Chemical Composition (%)
Q355 Series
| Steel Grade | C (≤) | Si (≤) | Mn (≤) | P (≤) | S (≤) | Cr (≤) | Ni (≤) | Cu (≤) | N (≤) |
|---|---|---|---|---|---|---|---|---|---|
| Q355B | 0.24 | 0.55 | 1.6 | 0.035 | 0.035 | 0.3 | 0.3 | 0.4 | 0.012 |
| Q355C | 0.20 | – | – | 0.03 | 0.03 | – | – | – | 0.012 |
| Q355D | 0.20 | – | – | 0.025 | 0.025 | – | – | – | – |
Mechanical Properties
Yield Strength (≥ N/mm²)
(Values vary depending on thickness/diameter)
Q355B: 355 → 275 MPa (d ≤ 400 mm)
Q355D: 265 MPa (selected ranges)
Tensile Strength (N/mm²)
Q355B: 470–630 (≤100 mm) / 450–600 (above 100 mm)
Q355D: 450–600
Elongation (%)
Ranges from 17–22% depending on sample direction and diameter.
Impact Performance
| Quality | Test Temp | Longitudinal (≥J) | Transverse (≥J) |
|---|---|---|---|
| Q355B | +20°C | 34 | 27 |
| Q355C | 0°C | 34 | 27 |
| Q355D | –20°C | 34* | 27* |
*For thickness ≥ 250 mm.
Equivalent Grades
| Region | Standard | Grade |
|---|---|---|
| China | GB/T 1591-2018 | Q355B/C/D |
| ISO | ISO 630-2 | S355B/C/D |
| EU | EN 10025-2 | S355JR / S355J0 / S355J2 |
Production Processes
Straightening
After annealing, the pipe undergoes seven-roller straightening for dimensional accuracy.
Eddy Current Testing
Each tube is inspected for surface defects; only defect-free tubes proceed to shipment.
Finishing
Products are either oiled or varnished per customer requirement. Plastic caps are applied to protect pipe ends, and all markings are added before packaging.
Industry Applications
Q355 hot-rolled seamless steel pipes are widely used in sectors requiring a combination of high strength and corrosion resistance:
Nuclear engineering components
Gas transmission pipelines
Petrochemical equipment
Shipbuilding structures
Boiler and pressure vessel manufacturing