Galvanized Steel Pipes

Tianjin Lefin Industrial Co., Ltd is one of the most experienced manufacturers and suppliers of galvanized steel pipes in China. Please feel free to buy high quality galvanized steel pipes from our factory. Good service and reasonable price are available.

For engineering pressure-bearing, outdoor, and buried applications, all should use hot-dip galvanization (hot-dip galvanizing); electro-galvanizing (cold galvanizing) has a very thin zinc layer and is only suitable for dry indoor light-load decoration. It is strictly prohibited for use in pressure pipelines, outdoor, and buried locations.

✅ Hot-dip Galvanized Steel Pipes (HDG)
Zinc layer: 45–100 μm +, zinc-iron alloy layer + pure zinc layer. It has cathodic protection and the zinc layer can still protect the steel substrate even if scratched

1. Building fire protection pipes (most common): indoor sprinkler, fire hydrant network; GB50974 requires hot-dip galvanizing, indoor conventional ≥ 55 μm; buried fire pipes are recommended ≥ 85 μm, and additional anti-corrosion coating is recommended when necessary
2. Building water supply, HVAC: indoor domestic water supply (old standards), air conditioning condensation, low-pressure fluid heating; indoor dry/ordinary damp select 45–55 μm
3. Municipal pipelines: outdoor water supply, street lamp supports, guardrails, conduit; urban open-air C3 environment, recommended ≥ 55 μm
4. Agriculture: greenhouse frame, farmland irrigation pipe; outdoor high humidity, ≥ 55 μm, coastal greenhouse upgrade ≥ 85 μm
5. Buried pipes: buried water supply, cable protection steel pipes; soil corrosion fluctuation is large, ≥ 85 μm, strong corrosive soil recommend galvanized + epoxy coating (Duplex double-layer anti-corrosion)
6. Coastal/chemical factory areas (C4/C5 high corrosion): ports, salt spray, sulfur dioxide-containing factory areas; ≥ 85 μm, prefer double-layer anti-corrosion
7. Steel structures, scaffolding: outdoor supports, temporary scaffolding; ordinary urban outdoor ≥ 55 μm

✅ Electro-galvanized (cold galvanized) steel pipes
Zinc layer is only 5–15 μm, with only physical isolation, and the zinc layer will rust quickly after damage
- Applicable: dry indoor decoration supports, indoor lightweight conduit, furniture pipe materials; non-pressure, no rain, no burial

Simple conversion of zinc layer weight: 300g/m² ≈ 45 μm; 400g/m² ≈ 55 μm; 600g/m² ≈ 85 μm

Supplementary GB/T13912-2020: The thickness of the base steel is different, the minimum requirements for the galvanized layer are also different

• Steel pipe substrate ≤ 3mm: average ≥ 45μm
• 3–6mm substrate: average ≥ 55μm
• > 6mm substrate: average ≥ 70μm

1. Pipe wall thickness ≠ Zinc layer thickness
The pipe wall thickness is the pressure-bearing parameter; the zinc layer is the anti-corrosion coating, two independent indicators. Fire protection pipes must meet both the pipe wall thickness and the zinc layer requirements.
2. Thread cutting risk
The galvanized pipe threading will damage the zinc layer. After installation, the threaded part must be re-coated with zinc-rich paint; otherwise, the threaded part will be corroded first, even if the zinc layer is very thick.
3. Cost balance
The thicker the zinc layer, the higher the unit price; for C3 environment, it is not necessary to blindly use 85μm; it will increase the procurement cost; for buried, coastal areas, do not omit the zinc layer, the maintenance cost will be extremely high in the future.
4. Galvanized pipe inner coating
Fluid conveying pipes (water supply, fire protection) must confirm the inner and outer wall hot-dip galvanizing; many low-price products only galvanize the outer surface, the inner wall will soon rust and clog.
5. Export standard distinction
- GB/T3091: domestic welded pipe hot-dip galvanizing; GB/T13912: general hot-dip zinc layer;
- ASTM A123/A153: US standard hot-dip zinc; ISO1461: European standard, commonly used in Middle East/Australia projects.

• Indoor fire protection, indoor water supply: ≥55μm inner and outer hot galvanizing
• Urban open-air, greenhouse: ≥55μm
• Buried, coastal salt spray: ≥85μm inner and outer hot galvanizing
• Strong corrosion chemical industry: ≥85μm + external epoxy coating
• Dry indoor decoration light frame: can choose electro-galvanized (not used for fluid pressure pipes)