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Help CenterSteel Pipe & Tube & Galvanized Steel Pipe，Q195, Q215A/B, Q235B, Q355B
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1. Product Overview
Galvanized steel pipe is a composite anti-corrosion pipe made of low-carbon ERW seamless steel pipe as substrate, with a dense zinc-iron alloy anti-corrosion layer formed on both inner and outer walls through the hot-dip galvanizing process. It delivers dual anti-corrosion protection via physical isolation of zinc coating and sacrificial anode, greatly improving the rust resistance, moisture resistance and soil corrosion resistance of steel pipes. It is a general anti-corrosion pipe widely used in fire protection, municipal engineering, construction, fluid transportation and steel structure projects.
Cold galvanized (electro-galvanized) pipes feature thin zinc coating that easily peels off with poor anti-corrosion performance. They have been officially prohibited for water supply, fire protection and gas pipelines in China. Our factory only supplies compliant hot-dipped galvanized steel pipes.
2. Product Classification
2.1 By Substrate Forming Process
Hot-Dipped Galvanized ERW Steel Pipe (Mainstream Product)Raw material: Q195/Q215/Q235B steel strip formed by high-frequency welding. It features low cost and complete specifications, suitable for low-pressure fluid transportation, scaffolding and guardrails.Executive Standard: GB/T 3091-2025 Welded Steel Pipes for Low-Pressure Fluid Delivery
Hot-Dipped Galvanized Seamless Steel PipeFormed by hot rolling and piercing steel billets without welding seams, it boasts higher pressure resistance for high-pressure oil & gas and chemical hydraulic pipelines.Executive Standards: GB/T 8162, GB/T 8163
2.2 By Cross-Section Shape
Hot-dipped galvanized round pipe (main material for fire protection, water supply & drainage, gas delivery and scaffolding)
Hot-dipped galvanized square & rectangular pipe (steel structure supports, guardrails, greenhouses and curtain walls)
2.3 By Application Scenario
Low-pressure fluid delivery pipe (water, gas, air, heating steam, working pressure ≤1.6MPa)
Structural support pipe (scaffolding, pipe piles, steel structure columns and road guardrails)
Electrical conduit, agricultural irrigation pipe and chemical anti-corrosion pipeline
3. Substrate Material & Mechanical Properties
3.1 Common Steel Grades
Q195, Q215A/B, Q235B (standard for civil engineering); Q355B (high-strength load-bearing structures)
3.2 Mechanical Indicators (Q235B)
Yield strength ≥235MPa, tensile strength ≥375MPa, elongation ≥21%, with excellent performance in welding, bending and cutting processing.Carbon content ≤0.2%. Low-carbon material adapts well to high-temperature hot-dip galvanizing without coating peeling defects.
4. Complete Hot-Dip Galvanizing Production Process (HDG)
Degreasing & oil removal → Pickling & rust removal (hydrochloric acid to eliminate iron oxide scale) → Flux activation (ammonium chloride & zinc chloride solution) → Preheating & drying → Hot dipping in molten zinc at 450℃±5℃ for 1–2 minutes → Air cooling & water quenching → Passivation & sealing treatment → Hydraulic pressure test / appearance inspection / zinc coating thickness test → Fixed length bundling & deliveryCoating structure: inner zinc-iron alloy layer + outer pure zinc layer, metallurgically bonded to steel substrate with strong adhesion, resistant to peeling upon collision.
5. Technical Standards for Zinc Coating (GB/T 13912)
Standard zinc coating: single-side zinc coating weight ≥300g/㎡, average thickness ≥80μm, local minimum thickness ≥70μm
Custom heavy-duty anti-corrosion coating: zinc coating ≥500g/㎡, thickness 100–140μm, applicable to coastal high salt-fog areas and underground pipelines in heavily corrosive soil
Neutral salt spray test: standard zinc coating withstands 720 hours without red rust; heavy-duty coating lasts over 1200 hours
6. Specification Parameters System
6.1 Nominal Diameter DN Series (General for Fluid Pipelines)
DN15(1/2"), DN20(3/4"), DN25(1"), DN32(1-1/4"), DN40(1-1/2"), DN50(2"), DN65, DN80, DN100, DN125, DN150, DN200, DN250, DN300
6.2 Outer Diameter × Wall Thickness Marking
Outer diameter range: 21.3mm–630mm; standard wall thickness 2.0mm–12.0mm, divided into standard wall thickness and reinforced wall thickness
6.3 Fixed Length
Standard national specification: 6 meters per piece, tolerance ±10mm; customized lengths of 3m, 9m, 12m available, cutting service supported
6.4 Weight Calculation
Theoretical weight of galvanized pipe = weight of black steel pipe × galvanizing weight gain coefficient (coefficient 1.064~1.028 for wall thickness 2.0–4.5mm)
7. Connection & Installation Methods
Threaded Connection: small caliber DN15–DN80 water supply, drainage and gas pipelines, pipe ends threaded with matching galvanized pipe fittings
Grooved Clamp Connection: DN65 and above fire sprinkler & main fire pipes, featuring fast construction
Flange Connection: large-diameter, high-pressure fluid and equipment interfaces with stable sealing performance
Welded Connection: steel structures and scaffolding supports; zinc-rich paint shall be sprayed to repair coating after welding
8. Core Product Advantages
Long-term anti-corrosion performance: zinc coating provides sacrificial anode protection, preventing rust even if local coating is damaged. Service life reaches 20–30 years under ordinary outdoor environments; 40–50 years for underground or coastal pipes with heavy zinc coating
High cost performance: much lower procurement cost than stainless steel pipes with minimal regular anti-rust maintenance in later stage
Balanced mechanical performance: excellent compression, bending and impact resistance, meeting safety standards for scaffolding and load-bearing structures
Wide application compatibility: usable for indoor, outdoor, underground, humid workshop and mildly acidic & alkaline industrial environments
Convenient processing: support cutting, threading, bending and welding with complete matching pipe fittings
Environmentally friendly & recyclable: both zinc and steel materials can be recycled for secondary use
9. Product Limitations & Operation Notes
Not resistant to long-term immersion in strong acid, alkali or high-concentration chemical agents. Lined plastic pipe or stainless steel pipe is recommended for severely corrosive chemical media
Long-term service temperature shall not exceed 200℃; high temperature accelerates oxidation loss of zinc coating
Old cold galvanized pipes are forbidden to purchase, with anti-corrosion service life less than 1–3 years and risks of pipeline rust and water leakage
Galvanized pipes easily generate scale for long-term domestic cold water supply. PPR pipes are widely adopted for new residential cold water pipes, while galvanized pipes are prioritized for fire protection, hot water, gas and structural projects
10. Main Application Fields
Fire Protection Engineering (Largest Application Scenario)Main fire hydrant pipes, sprinkler pipelines and pump house pipelines, designated pipes passing fire acceptance for all buildings
Municipal InfrastructureCommunity gas transmission, factory water supply & drainage, road guardrails, bridge pipe piles and street lamp supports
Construction WorksConstruction scaffolding, steel factory columns, curtain wall keels and balcony protective railings
Agriculture, Forestry & Water ConservancyFarmland irrigation pipelines, greenhouse frames and breeding shed steel structures
Industrial ElectromechanicsWorkshop compressed air pipelines, electrical conduits, light equipment supports and ventilation pipes
Oil & Gas TransportationLow-pressure crude oil and natural gas branch pipelines (galvanized seamless steel pipes)
11. Factory Inspection Items
Each batch undergoes mandatory factory inspection with material certificate and galvanizing test report attached:
Substrate material spectrum test & tensile mechanical test
Hydraulic pressure resistance test (DN10–168.3 withstands 3MPa; DN177.8–323.9 withstands 5MPa)
Zinc coating thickness & zinc coating weight test
Visual appearance inspection: no missing galvanizing, peeling, pits or accumulated zinc nodules
Retest of dimensional tolerance, wall thickness, outer diameter and length
Coating adhesion impact test
12. Packaging & Delivery Instructions
Small-caliber pipes bundled with steel strips; each bundle labeled with specification, material and furnace batch number
Plastic dust plugs installed at pipe ends to avoid collision damage and sediment entering during transportation
Standard spot goods with 6m fixed length, full specifications DN15–DN300 in stock
Delivery cycle: spot goods loaded within 5–7 days
Shipping ports: Tianjin Port, Qingdao Port. Support full container export for foreign trade, English material certificates and inspection certificates available
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