1. Raw Material Preparation
Steel Coil/Strip Selection:
Typically uses low-carbon steel (grades like Q195, Q235 or ASTM A36)
Width and thickness determined by final pipe dimensions
Surface must be clean and free of rust/contaminants
2. Pipe Forming
Uncoiling: Steel coil is fed into production line
Leveling: Passed through leveling rollers to remove coil curvature
Forming: Progressive shaping through roll forming stands into circular cross-section
Welding:
High-frequency induction welding (HFIW) most common
Welds at 1000-1300°C without filler metal
Weld seam is immediately heat-treated to normalize structure
3. Sizing & Cutting
Sizing Rolls: Precisely calibrate pipe diameter (typical tolerance ±0.5mm)
Cutting:
Flying saw cuts pipes to required lengths (usually 6m standard)
Can produce custom lengths as required
4. Surface Preparation for Galvanizing
Degreasing: Alkaline bath removes oils
Pickling: Hydrochloric/sulfuric acid bath (15-20% concentration) removes oxides
Fluxing: Zinc ammonium chloride application to prevent re-oxidation
5. Hot-Dip Galvanizing
Galvanizing Bath:
Molten zinc at 445-465°C (pure zinc or Zn-0.2%Al alloy)
Immersion time 30-60 seconds depending on thickness
Air Knife:
High-pressure air jets control zinc coating thickness
Typical coating: 50-600 g/m² (Z60-Z600)
6. Post-Treatment
Cooling: Water quenching or air cooling
Passivation: Chromate or non-chromate treatment to prevent white rust
Inspection: Coating thickness measurement (magnetic gauge) and visual checks
7. Finishing Operations
Straightening: Rotary straightener ensures dimensional accuracy
Hydrostatic Testing: Pressure test for leak-proof verification
End Facing: Square-cut or beveled ends as required
Threading: For threaded pipes (optional)
8. Quality Control & Packaging
Testing:
Coating adherence (hammer test)
Zinc thickness (magnetic induction)
Dimensional checks
Mechanical properties (tensile, flattening tests)
Marking: Stamped with size, grade, standard
Packaging: Bundled with steel straps, plastic caps on ends
Key Standards
ASTM A53: Standard specification for galvanized pipe
BS 1387: British standard for threaded pipes
EN 10240: European standard for hot-dip galvanizing
JIS G3442: Japanese industrial standard
Production Capacity
Typical line speed: 20-60 m/min
Common diameters: 1/2" to 8" (15-200mm)
Wall thickness: 1.0-6.0mm
Applications
Construction scaffolding
Fencing and handrails
Water/gas distribution
Electrical conduits
Agricultural equipment