I. Definition of welded steel pipes for construction
Welded steel pipes for construction are one of the indispensable structural materials in modern construction projects and are widely used in factories, residential buildings, Bridges, municipal engineering and other fields. Welded steel pipes play a significant role in building structures due to their high strength, excellent welding performance and ease of construction.
II. Materials and standards for welded steel pipes used in construction
Welded steel pipes used in construction usually select low alloy structural steels such as Q235B or Q345B.
Q235B: Yield strength ≥ 235 MPa, suitable for general building structures, with good plasticity and excellent weldability.
Q345B: Yield strength ≥ 345 MPa, with higher strength, suitable for building structures and bridge projects with higher load-bearing requirements.
Common standards include:
GB/T 3091-2008: Standard for Low-pressure Fluid Welded Steel pipes.
GB/T 8162-2018: Standard for Seamless steel tubes for structural purposes.
GB/T 8163-2018: Standard for Seamless steel tubes for Fluid Conveyance.
III. Specifications and dimensions of welded steel pipes for construction
| Outer Diameter (mm) | Wall Thickness (mm) | Nominal Length (m) | Application Notes |
|---|---|---|---|
| 21.3 | 2.0–3.0 | 6 / 12 | Short-span light structures |
| 25 | 2.0–4.0 | 6 / 12 | Small-scale building supports |
| 32 | 2.0–4.5 | 6 / 12 | Light indoor framing |
| 38 | 2.5–5.0 | 6 / 12 | Medium-size structural supports |
| 42 | 2.5–5.5 | 6 / 12 | Industrial building beams & columns |
| 48 | 3.0–6.0 | 6 / 12 | Medium-load-bearing structures |
| 50 | 3.0–6.5 | 6 / 12 | Trusses & bracing frames |
| 57 | 3.0–7.0 | 6 / 12 | Bridge structures or plant frames |
| 60 | 3.5–7.0 | 6 / 12 | Heavy-load-bearing structures |
| 76 | 3.5–8.0 | 6 / 12 | Large-span workshop supports |
| 89 | 4.0–8.5 | 6 / 12 | High-capacity beams & columns |
| 102 | 4.0–9.0 | 6 / 12 | Bridge & floor load-bearing supports |
| 108 | 4.5–9.5 | 6 / 12 | Industrial load-bearing structures |
| 114 | 4.5–10.0 | 6 / 12 | High-rise building supports |
| 127 | 5.0–10.5 | 6 / 12 | Long-span beams & columns |
| 133 | 5.0–11.0 | 6 / 12 | Heavy structural supports |
| 140 | 5.5–11.5 | 6 / 12 | Bridge supports & large workshops |
| 159 | 6.0–12.0 | 6 / 12 | Special load-bearing structures |
| 168 | 6.0–12.5 | 6 / 12 | Heavy-industry supports |
| 219 | 6.5–16.0 | 6 / 12 | Main beams & columns for bridges and plants |
IV. Load-bearing capacity and safety factor
(1) Load-bearing capacity
The load-bearing capacity of welded steel pipes used in construction is mainly determined by the material, outer diameter, wall thickness and length.
For example:
Q235B steel pipe: Yield strength ≥235 MPa, suitable for medium and low-rise buildings or light structures.
Q345B steel pipe: Yield strength ≥345 MPa, suitable for high-rise buildings, large-span factories and Bridges and other structures with high load-bearing requirements.
(2) Safety factor
Architectural design typically requires a safety factor of ≥1.5-2, meaning that the actual bearing capacity should be at least 50% – 100% higher than the designed load.
The safety factor takes into account: pipe strength, construction errors, material aging and sudden loads.
(3) Material selection suggestions
For high-rise buildings or large-span structures, Q345B or higher strength steel pipes should be given priority.
For key components such as load-bearing beams and trusses, steel pipes with larger wall thickness and thicker diameter should be selected, and combined with calculated load and force analysis.
(4) Construction precautions
Welding and connection must be strictly carried out in accordance with construction specifications, and the strength of the weld seam should be greater than or equal to that of the base material.
During the installation of pipes, excessive bending or collision should be avoided to prevent affecting the load-bearing capacity.
V. Anti-corrosion treatment of welded steel pipes for construction
i. The importance of anti-corrosion treatment
Steel pipes are prone to rust when exposed to air, moisture or chemical environments for a long time in building structures, which reduces their load-bearing capacity and service life.
Anti-corrosion treatment can effectively extend the service life of pipes, enhance structural durability and reduce maintenance costs.
ii. Common anti-corrosion methods
| Anti-corrosion Method | Characteristics | Applicable Environment |
|---|---|---|
| Hot-dip galvanizing | Uniform zinc coating, good corrosion resistance, easy application | Outdoor, humid, mildly acidic/alkaline environments |
| Epoxy coating / FBE | Powder or liquid epoxy covering, excellent anti-corrosion, water & chemical resistant | Outdoor, underground, utility tunnels, humid environments |
| Painting or anti-rust oil | Simple application, effective short-term protection | Indoor, dry environments or temporary protection |
| 3PE / 2PE coating | Polyethylene layer plus anti-corrosion primer, strong corrosion resistance | Buried pipelines, corrosive environments |
iii. Construction precautions
The surface of the pipe must be clean, dry, free of oil stains and oxide scale.
The coating thickness should comply with the standard requirements, for example, FBE single layer 150-250 μm, 3PE approximately 0.3-0.5 mm.
Avoid scratches or peeling during transportation and installation. Damaged areas should be repaired in a timely manner.
iv. Maintenance suggestions
Regularly inspect the surface of the pipe body. Repair any rust spots or coating damage found in a timely manner.
For pipes that are used outdoors for a long time, anti-rust oil can be sprayed regularly or local coating reinforcement can be carried out.
VI. Advantages of installing welded steel pipes for construction
(1) Convenient for construction
The pipe specifications are standardized. The length, diameter and wall thickness can be selected according to the design requirements, which is convenient for on-site measurement and cutting.
(2) Good welding performance
Q235B and Q345B steel pipes have good weldability, and the strength of the weld seam can reach the strength of the base material, ensuring structural safety.
(3) It can be bent and processed
The pipe can be bent or cut on site, adapting to various building structure layouts. The bending radius is ≥3D and it is not easy to crack.
(4) Easy to handle
Each piece has a moderate weight and can be transported with lifting gear or forklifts, ensuring safe and efficient on-site stacking.
(5) Strong adaptability
It is applicable to various construction scenarios such as factories, residential buildings, Bridges and municipal engineering, with high construction flexibility.
(6) Easy to maintain
After installation, check the welds, straightness and anti-corrosion coating. The later maintenance is simple and ensures a long service life.
