Products Description
Hot Dip Galvanized Iron Pipe (GI Pipe) is manufactured by immersing high-quality low-carbon steel strip or pipe into molten zinc (approx. 445–465°C) after pickling and fluxing. This process creates a metallurgically bonded zinc-iron alloy layer and a pure zinc coating on both inner and outer surfaces, providing barrier protection + sacrificial anode protection. It is the most widely used type of welded steel pipe for low-pressure fluid transmission and light structural applications.
Detailed Performance Advantages
| Property | Description |
|---|---|
| Corrosion life | Average zinc coating ≥ 300g/m² → first rust >15–20 years in general atmosphere; >30 years in dry indoor environments. |
| Coating adhesion | Zinc-iron alloy layer metallurgically bonded; no peeling or cracking after 90° cold bend, flattening, or hammering tests. |
| Fluid resistance | Inner surface roughness (Ra) ≤12.5μm – low head loss, less scaling and bacterial growth. |
| Temperature range | Suitable for –20°C to +200°C medium (long‑term recommended ≤120°C to avoid zinc discoloration). |
Key Manufacturing Process Control Points
Base material: Q235B hot-rolled/cold-rolled strip; C ≤0.20%, P/S ≤0.035% to ensure weldability and galvanizing quality.
HFW welding: Weld zone microstructure matching base metal.
Internal/external burr removal: Fully automatic scrapers.
Pre-treatment before galvanizing: Alkaline degreasing → HCl (15–20%) pickling → rinsing → fluxing (ZnCl₂+NH₄Cl) → drying.
Zinc bath: Temperature 445–465°C; immersion 30–90 sec (depending on wall thickness); zinc consumption ≤8%.
Cooling & passivation: Water cooling + low‑chromium or chromium‑free eco‑passivation to prevent white rust.
Typical Engineering Applications
| Industry | Specific Use |
|---|---|
| Construction & municipal | Indoor fire sprinkler risers, building water supply risers, heating branch pipes, scaffolding tubes, fence posts, temporary barriers |
| Industrial & energy | Compressed air lines, low-pressure steam return lines, cable tray supports, factory conduit |
| Agriculture & horticulture | Multi‑span greenhouse main frames, livestock water lines, sprinkler risers |
| Transport & public works | Lamp post foundation tubes, traffic sign supports, bus shelter columns, waste transfer station structures |
| Furniture & display | Shelving uprights, display racks, sports equipment frames, clothesline main poles |
Why GI Pipe over Other Anti-Corrosion Methods?
| Parameter | Hot Dip GI | Electro‑galvanized | Black paint / Epoxy |
|---|---|---|---|
| Protection mechanism | Alloy layer + sacrificial | Pure thin zinc | Physical barrier |
| Coating thickness | 40–150μm | 5–15μm | - |
| Neutral salt spray resistance | ≥120h | ≤24h | Coating‑dependent |
| Mechanical damage resistance | High (hard alloy layer) | Low | Poor (fails if scratched) |
| Lifecycle cost | Low | High (frequent maintenance) | Medium (needs repainting) |
Certificates available: Mill test certificate (EN 10204 3.1 or 3.2), third‑party inspection report (SGS, BV, Intertek)
Packaging & Shipping Recommendations
Rust protection for export: Shrink film + moisture‑proof paper + plastic end caps
Bundling: Hexagonal or rectangular bundling with steel straps to avoid pipe‑to‑pipe abrasion
Marking: Inkjet coding on each pipe (spec/grade/heat no./batch no.) + hanging tag
Storage & handling: Store off the ground to avoid standing water; no dropping or rough handling to protect coating
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