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Help CenterSteel Pipe & Galvanized Pipe，Tube & A53 Gr.B、S235JR、STK400、SS400
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1. Basic Definition
Ordinary carbon steel pipes are coated with a zinc layer for anti-corrosion treatment, divided into hot-dipped galvanized steel pipe (universal compliant type for engineering) and cold galvanized (electro-galvanized, eliminated by housing and construction authorities, prohibited for water supply and fire protection systems).
The base material is mostly ERW straight seam welded pipe. Domestic standard: GB/T3091-2024 Welded Steel Pipes for Low-Pressure Fluid Delivery. Foreign trade equivalent standards: ASTM A53 Grade B, BS1387, JIS G3444.
2. Core Differences: Hot-Dipped vs Cold Galvanized Pipe
| Comparison Item | Hot-Dipped Galvanized Steel Pipe (Recommended) | Cold/Electro-Galvanized Pipe (Forbidden for Fluid Pressure Pipelines) |
|---|---|---|
| Production Process | Immersed in molten zinc liquid at 450~480℃, forming metallurgical bond between zinc and iron | Electroplated at room temperature, zinc layer only physically attached |
| Zinc Coating Thickness | 50~100μm, zinc coating weight ≥600g/㎡ | 5~20μm, only 10~50g/㎡ |
| Adhesion Performance | Excellent adhesion; zinc layer does not peel off massively after cutting and threading | Poor adhesion; zinc layer peels and rusts easily upon collision or dampness |
| Service Life | 10~15 years outdoor, 5~8 years buried underground | Less than 3 years for dry indoor use; rusts within 1 year in humid environment |
| Application Scenarios | Fire protection, water supply & drainage, gas transportation, greenhouse frames, scaffolding, municipal guardrails | Only for short-term dry indoor decoration; strictly banned for fluid delivery in new construction and municipal water supply projects |
| Policy Requirements | Mandatory for building and fire protection projects | Eliminated for new residential buildings and municipal water supply systems |
3. Common Specification Parameters
(1) Nominal Diameter DN (General for Water & Gas Pipelines)
DN15(1/2"), DN20(3/4"), DN25(1"), DN32(1-1/4"), DN40(1-1/2"), DN50(2"), DN65(2-1/2"), DN80(3"), DN100(4"), DN150(6") Fixed outer diameters: DN15=21.3mm, DN50=60.3mm, DN100=114.3mm
(2) Wall Thickness Grades
Standard pipe SCH40 (for conventional pressure bearing)
Extra heavy pipe SCH80 (for high pressure and underground burial) Conventional wall thickness: 2.0/2.5/2.75/3.0/3.25/3.5/4.0mm
(3) Fixed Length
Domestic standard: 6 meters; Common foreign trade lengths: 5.8m, 11.8m, 12m. Custom lengths of 3–12m available for non-standard orders.
(4) Material Grades
Domestic: Q195, Q215, Q235B (mainstream grade), Q345B
Foreign trade equivalent: A53 Gr.B, S235JR, STK400, SS400
(5) National Standard Requirements for Zinc Coating
Average zinc coating thickness ≥65μm, minimum single-point thickness ≥55μm. Qualified standard: no red rust after 5 copper sulfate immersion tests.
4. Main Application Scenarios
Building Fire Protection: Sprinkler pipes, main standpipes for fire hydrants, fire water supply (hot-dipped galvanized pipe mandatory for project acceptance)
Water Supply, Drainage & Gas: Municipal reclaimed water, factory tap water, low-pressure gas transportation
Scaffolding Works: Φ48×3.0 special galvanized scaffolding pipes
Agricultural Greenhouses: Greenhouse frames, breeding sheds, farm irrigation pipes
Municipal Steel Structures: Road guardrails, street lamp poles, bridge supports
Electrical Cable Conduits: Cable protection sleeves with anti-corrosion and leakage-proof performance
5. Connection Methods
Threaded Connection: Small diameters DN15–DN100, threading after galvanization, matched with malleable iron pipe fittings
Flanged Connection: Large diameters above DN100 and high-pressure pipelines
Welded Connection: Structural supports; supplementary zinc-rich paint anti-corrosion treatment required after welding
6. Advantages & Disadvantages
Advantages
Sacrificial anode protection by zinc layer, excellent rust and corrosion resistance, low maintenance frequency for outdoor use
High mechanical strength, good machinability for welding and threading
Higher cost performance than stainless steel, suitable for mass engineering procurement
Recyclable and eco-friendly
Disadvantages
Trace zinc may precipitate when transporting drinking water for a long time; lined plastic galvanized pipe is recommended for direct drinking water pipelines
Accelerated corrosion under strong acid and strong alkali environments; not applicable for pipelines carrying highly corrosive chemical media
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