GB/T 3091 Q235B ERW Welded Steel Pipe 8 Inch 4.5mm Thickness Pre-galvanized

Our GB/T 3091 Q235B Pre-galvanized ERW Steel Pipe is a highly cost-effective, corrosion-resistant welded steel tube designed for low-pressure fluid transportation and structural applications. Featuring an 8-inch nominal size and a 4.5mm wall thickness, this pipe is manufactured using premium pre-galvanized steel strips. The steel strip is cold-formed and longitudinally welded using high-frequency Electric Resistance Welding (ERW) technology.
Compliant with the recognized Chinese National Standard GB/T 3091, the pre-galvanized surface coating provides uniform, clean zinc protection that eliminates the need for post-fabrication dipping. It is a dependable choice for agricultural greenhouses, fire sprinkler systems, water supply utilities, and HVAC ducting networks.

Product Features & Advantages

Uniform Pre-galvanized Finish: Manufactured directly from continuous zinc-coated steel coils, ensuring a highly smooth, aesthetic bright surface with excellent and uniform zinc layer adhesion.

Cost-Effective Corrosion Resistance: Provides reliable atmospheric rust protection suitable for indoor, outdoor, and agricultural environments at a more budget-friendly price point than hot-dipped galvanized pipes.

High-Frequency ERW Seam Reliability: Utilizing advanced HF-ERW technology, the longitudinal weld seam is structurally sound, and the external weld bead is systematically zinc – repaired to restore continuous corrosion defense.

Excellent Formability & Workability: The Q235B carbon steel grade offers a perfect balance of moderate tensile strength and superb ductility, allowing hassle-free threading, grooving, bending, and light welding on project sites.

Strict Dimensional Accuracy: Produced under rigorous quality control guidelines to ensure consistent 4.5mm wall thickness and accurate 8-inch outer diameter matching for standard industrial pipe fittings.

Technical Specifications

Specification Item	Details / Technical Standards
Manufacturing Standard	GB/T 3091 (Welded steel pipes for low pressure liquid delivery)
Steel Grade	Q235B (Q: Yield strength; 235: Min. 235 MPa; B: Grade B quality classification)
Nominal Diameter	8 inch / DN200
Outer Diameter (OD)	Approx. 219.1 mm (8.626 inches)
Wall Thickness (WT)	4.5 mm
Theoretical Weight	Approx. 23.82 kg/m
Zinc Coating Mass	Standard 40 - 120 g/m² (Customizable upon project requirements)
End Finishing	Plain Ends (Square Cut), Beveled Ends, Threaded & Coupled (NPT/BSPT), or Grooved
Length Profiles	Standard 5.8m / 6m (Optimized for 20ft/40ft shipping containers)

Product Applications

This 8-inch, 4.5mm pre-galvanized pipe is highly versatile, striking a perfect balance between mechanical layout rigidity and light dead-weight:

Agricultural Greenhouses: Serves as high-strength structural framing, roof purlins, and support pillars for large-scale multi-span modern agricultural greenhouses.

Low-Pressure Fluid Utilities: Used in non-potable water systems, agricultural irrigation pipelines, and drainage distribution networks.

HVAC & Air Ducting Systems: Installed as chilled water circulation lines, low-pressure ventilation duct piping, and cooling tower conduits in commercial structures.

Fire Protection Piping: Deployed in indoor fire sprinkler mainlines where moderate pressure containment and neat appearance are valued.

Light Structural Frameworks: Utilized for protective handrails, indoor scaffolding, decorative architectural supports, fencing, and storage racking systems.

Rigorous Quality Control & Manufacturing Process

To ensure structural integrity and long-term durability, our pre-galvanized pipes undergo strict quality control:

Weld Seam Zinc-Spraying Repair: During the high-frequency ERW welding process, the zinc coating at the seam is burned off. Our production line automatically sprays a high-purity molten zinc layer onto the external weld seam while the pipe is still hot, fully restoring the anti-corrosion barrier.

Dimensional Tolerance Checks: Continuous monitoring of outer diameter (approx. 219.1mm) and wall thickness (4.5mm) to ensure precise fitting compatibility.

Mechanical Property Testing: Standard testing to verify the minimum yield strength of 235 MPa and appropriate elongation values.

Mill Certification: Every batch is supplied with complete documentation verifying the chemical heat analysis and mechanical test values.

Frequently Asked Questions (FAQ)

Q: What is the exact difference between “Pre-galvanized” and “Hot-Dipped Galvanized (HDG)” steel pipes?

A: The primary difference is the manufacturing sequence and zinc thickness:
Pre-galvanized pipes are formed from steel strips that are already galvanized in a continuous zinc bath at the steel mill. They have a smoother, shinier finish and are more economical, with a standard zinc coating of 40 – 120 g/m².
HDG pipes are welded from black carbon steel first, and then the entire finished pipe is dipped into a molten zinc kettle. HDG has a thicker, rougher zinc layer (300 – 500 g/m”) and offers
higher heavy-duty protection for underground or marine applications, but comes at a higher cost.

Q: Is the weld seam of a pre-galvanized pipe prone to rusting?

A: No, because we apply a weld seam zinc-spraying repair system. During the high-frequency ERW welding process, the zinc coating at the seam is burned off. Our production line automatically sprays a high-purity molten zinc layer onto the external weld seam while the pipe is still hot. This restores continuous, uniform corrosion protection across the entire outer circumference of the pipe tube.

Q: What is the equivalent of GB/T 3091 Q235B in international standards?

A: The standard GB/T 3091 Q235B is highly recognized globally and functionally equivalent to the following standards for low-pressure and structural services:
European Standard:EN 10219/ EN10255Steel GradeS235JR
American Standard:ASTMA53GradeA/ASTMA500GradeB
International Standard: ISO 65 Carbon Steel Tubes.