This article presents complete standard specifications for low-pressure fluid transmission welded galvanized steel pipes complying with GB/T 3091-2015, including dimensions from DN15 to DN300, outer diameter, wall thickness, theoretical weight, pressure ratings and common applications.
Case Details
1. Applicable Standard & Scope
- National Standard: GB/T 3091-2015 (replaces GB/T 3091-2008)
- Application: Water supply, gas delivery, heating, fire protection, municipal water distribution and other low-pressure fluid conveying systems. Working temperature ≤ 200°C, working pressure ≤ 1.6 MPa.
- Exclusion: Not suitable for high-pressure, high-temperature pipelines or pipelines conveying corrosive chemical media. Seamless galvanized pipes or stainless steel pipes are recommended for such scenarios.
2. Main Specification Chart (DN15 - DN300, Standard & Reinforced Wall)
All pipes are supplied in 6-meter fixed lengths (hot-dip galvanized). The theoretical weight is calculated based on steel density of 7.85 g/cm³.
| Nominal Diameter DN |
Inch Size |
Outer Diameter (mm) |
Standard Wall Thickness (mm) |
Reinforced Wall Thickness (mm) |
Theoretical Weight (kg/m, Standard) |
Theoretical Weight (kg/m, Reinforced) |
| DN15 |
1/2" |
21.3 |
2.75 |
3.25 |
1.36 |
1.50 |
| DN20 |
3/4" |
26.9 |
2.75 |
3.50 |
1.73 |
2.01 |
| DN25 |
1" |
33.7 |
3.25 |
4.00 |
2.41 |
2.91 |
| DN32 |
1¼" |
42.4 |
3.25 |
4.00 |
3.14 |
3.77 |
| DN40 |
1½" |
48.3 |
3.50 |
4.25 |
3.86 |
4.58 |
| DN50 |
2" |
60.3 |
3.80 |
4.50 |
5.29 |
6.19 |
| DN65 |
2½" |
76.1 |
4.00 |
4.75 |
7.11 |
8.32 |
| DN80 |
3" |
88.9 |
4.00 |
4.75 |
8.38 |
9.81 |
| DN100 |
4" |
114.3 |
4.00 |
5.00 |
10.85 |
13.44 |
| DN125 |
5" |
140.0 |
4.50 |
5.50 |
15.04 |
18.24 |
| DN150 |
6" |
168.3 |
4.50 |
6.00 |
18.18 |
23.72 |
| DN200 |
8" |
219.1 |
6.00 |
7.00 |
31.45 |
36.60 |
| DN250 |
10" |
273.0 |
6.50 |
8.00 |
42.42 |
51.54 |
| DN300 |
12" |
323.9 |
7.50 |
9.00 |
57.28 |
68.54 |
Data Source: GB/T 3091-2015 and factory standards of mainstream galvanized pipe manufacturers.
2.1 Allowable Deviation for Wall Thickness
- Standard wall thickness: +12% / -15%
- Reinforced wall thickness: +10% / -12%
2.2 Allowable Deviation for Outer Diameter
- DN ≤ 100: ±0.4 mm
- DN ＞ 100: ±1% of outer diameter
2.3 Zinc Coating Thickness (Hot-dip Galvanized)
- Regular requirement: ≥70 μm (DN15-DN50); ≥85 μm (DN65-DN150)
- Heavy anti-corrosion requirement: ≥100 μm (for outdoor, municipal and general chemical environments)
3. Inch and Metric Conversion Reference
- 1/2 inch (4 points) = DN15, OD 21.3 mm
- 3/4 inch (6 points) = DN20, OD 26.9 mm
- 1 inch = DN25, OD 33.7 mm
- 1 1/4 inch = DN32, OD 42.4 mm
- 1 1/2 inch = DN40, OD 48.3 mm
- 2 inch = DN50, OD 60.3 mm
4. Theoretical Weight Calculation Formulas
4.1 Round Galvanized Steel Pipe
Weight per meter (kg/m) = (Outer Diameter - Wall Thickness) × Wall Thickness × 0.02466 × 1.0599
The coefficient 1.0599 accounts for the extra weight of galvanized coating.
Example: DN50 pipe (OD 60.3 mm, wall thickness 3.8 mm)
Calculation result is 5.29 kg/m, which is consistent with standard data.
4.2 Galvanized Square Steel Pipe
Weight per meter (kg/m) = 4 × Wall Thickness × (Side Length - Wall Thickness) × 7.85 ÷ 1000
5. Specification Selection by Application
5.1 Residential Water Supply
- DN15 (1/2"): Branch pipes and faucet connections
- DN20 (3/4"): Main pipes for kitchen and bathroom
- DN25 (1"): Main water inlet of the whole building
5.2 Fire Protection Systems (Compliant with GB50974-2014)
- DN65 - DN125: Minimum wall thickness 4.0 mm
- DN150: Minimum wall thickness 4.5 mm
- DN200: Minimum wall thickness 6.0 mm. Hydrostatic test pressure: 1.2 - 1.5 MPa
5.3 Low-pressure Gas Pipelines (Working pressure ≤ 0.4 MPa)
- DN15 - DN50: Standard wall thickness, threaded connection
- DN65 and above: Reinforced wall thickness, flange connection
5.4 Scaffolding & Structural Support
Common specifications: DN40 and DN50. Features high structural strength and easy installation.
6. Key Points for Procurement & Inspection
- Verify production standard: Adopt pipes manufactured in accordance with GB/T 3091-2015, reject non-standard products.
- Check outer diameter strictly to avoid leakage caused by dimensional errors.
- Measure wall thickness with caliper, ensure the value is not lower than the minimum allowable limit.
- Inspect galvanized layer: Uniform surface without missing plating, peeling or cracks. Choose thickened zinc coating for outdoor use.
- Conduct hydrostatic test: Apply 1.5 times of working pressure and keep pressure for 30 minutes, no leakage is allowed.
7. Summary
This guide covers full set of standard dimensions of galvanized steel pipes per GB/T 3091-2015, including outer diameter, wall thickness, theoretical weight, unit conversion, calculation formulas and practical selection & inspection tips. It is a practical reference for engineering design, construction and procurement.
