【2025 Standards】Key Updates in GB/T 3091-2015 VS GB/T 3091-2025: Welded Steel Tubes for Low-Pressure Fluid Transport
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GB/T 3091-2025 \"Welded steel pipes for low-pressure fluid transport\" – this standard applies to straight-seam welded steel pipes (ungalvanized/hot-dip galvanized) used for transporting low-pressure fluids such as water, air, gas, and steam, and it replaces the GB/T 3091-2015 version. The following is a detailed technical analysis, summarizing the standard updates, key parameters, and key points for engineering applications.
I. Key Points of Standard Updates (2025 Version vs 2015 Version)
II. Core Parameters and Technical Specifications 1. Steel pipe specifications and mechanical properties
2. Performance of the zinc coating (hot-dip galvanized pipes): Coating type: pure zinc coating (traditional) or zinc-aluminum alloy coating (new)； Coating weight: ≥500 g/m² (average), ≥480 g/m² locally ； Salt spray resistance test: No red rust for ≥72 hours (zinc-aluminum alloy coating: ≥120 hours).
3. Process requirements: Weld quality – to be inspected by ultrasonic testing (UT); defect level ≤ Grade B as per GB/T 11345-2013； Bending test: Steel pipes with DN≤50mm must pass an 180° cold bending test (d=3a, no cracks).
III. Precautions for Engineering Applications 1. Selection Recommendations: Ordinary fluids (water, air): Ungalvanized Q235B pipes (DN≤300mm, pressure≤1.6MPa)； Corrosive environments (gas, seawater): Q355B hot-dip galvanized pipe + zinc-aluminum alloy coating ； Low-temperature areas (-40°C): Q420D grade steel pipes, ensuring an impact energy of ≥27J at -40°C.
2. Construction and acceptance: Cutting and welding: Oxygen-acetylene cutting is prohibited; mechanical cutting or plasma cutting is recommended； Welding of galvanized pipes: Zinc-rich paint must be reapplied after welding (no reaplication is required for the zinc-aluminum alloy layer) ； Pressure test: Hydrostatic test pressure = 1.5 × design pressure (GB/T 3087-2022).
3. Environmental compliance: The Pb content in zinc-aluminum alloy coatings shall be ≤0.1%, and the Cd content shall be ≤0.01% (GB 38400-2019).