Galvanized Steel Round Pipe Production Process
1. Steel Strip Preparation
Cold-rolled steel coils are used as the base material.
The strip is uncoiled, leveled, and trimmed to the required width.
2. Pipe Forming (Roll Forming or ERW Process)
High-Frequency Electric Resistance Welding (ERW):
The steel strip is passed through forming rolls to shape it into a round profile.
The edges are welded together using high-frequency induction or contact welding.
Seamless Pipe Alternative (Less Common for GI Pipes):
Hot extrusion or piercing is used for seamless pipes before galvanizing.
3. Weld Seam Treatment (For ERW Pipes)
The welded seam is heat-treated to normalize the metal structure.
Excess weld material is removed (inside & outside flash trimming).
4. Cleaning & Surface Preparation
Degreasing: Removes oils and dirt.
Pickling: Acid bath (HCl or H₂SO₄) removes rust and scale.
Fluxing: Dipped in zinc-ammonium chloride to ensure proper zinc adhesion.
5. Hot-Dip Galvanizing
Galvanizing Bath: The pipe is immersed in molten zinc (~450°C/842°F).
Air Knife Wiping: Controls zinc coating thickness by blowing off excess zinc.
Quenching: The pipe is cooled in water or air.
6. Post-Galvanizing Treatments
Passivation: Chromate or non-chromate solution improves corrosion resistance.
Drying: Ensures no moisture remains.
7. Inspection & Testing
Coating Thickness: Measured with a magnetic gauge or spectrometer.
Adhesion Test: Bent or hammered to check zinc bonding.
Hydrostatic Test (Optional): Checks weld integrity for pressurized applications.
8. Cutting & Finishing
Pipes are cut to specified lengths (e.g., 6m standard).
Threading or grooving (for construction pipes).
9. Packaging & Shipping
Bundled with protective caps on ends and wrapped in plastic or steel straps.
Key Features of Galvanized Round Pipes
Corrosion Resistance: Zinc layer protects against rust.
High Strength: Suitable for structural and fluid transport.
Applications: Fencing, scaffolding, water/gas pipelines, and construction.