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Help CenterSteel Pipe & Tube & Hot Dipped Galvanized Steel Pipe，Q235B、 Q215B、Q345B、20#
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1. Product Overview
Hot-dipped galvanized steel pipe, fully named hot-dipped galvanized electric resistance welded pipe (HDG ERW Pipe), is manufactured with Q235B high-quality carbon steel strip or steel billet as base material. After forming via high-frequency welding, the whole pipe is immersed in molten zinc bath at 445–455°C to complete internal and external double-sided hot-dip galvanizing. Metallurgical reaction occurs between steel substrate and zinc coating to form composite protective zinc-iron alloy layer. It is completely different from electro-galvanized (cold galvanized) pipes with thin coating only on outer wall. This product is the anti-corrosion pipe specified for municipal, fire protection and outdoor projects.
2. Applicable Standards
Domestic Standards
GB/T 3091-2025 Welded Steel Pipes for Low-Pressure Fluid Delivery (universal for water supply, gas and fire protection)
GB/T 13793 Straight Resistance Welded Steel Tubes
GB/T 24701 Technical Requirements for Coatings of Hot-Dipped Galvanized Steel Pipes
International Export Standards
ASTM A53 Gr.B, BS 1387, EN 39, ISO 9001, CE certification. SGS coating inspection reports can be provided.
3. Base Material & Grade
Main grade: Q235B (general engineering use); optional grades Q215B, Q345B, seamless base pipe 20#.
Mechanical Properties:
Yield strength ≥235MPa
Tensile strength: 375–500MPa
Elongation ≥26%, excellent performance in welding, threading and bending processing.
4. Complete Production Process
Base pipe inspection → Degreasing & oil removal → Clean water rinsing → Hydrochloric acid pickling to remove oxide scale → Flux soaking (ammonium chloride + zinc chloride) → Preheating & drying → Hot-dip galvanizing at 450°C for 3–5 minutes → High-pressure internal air blowing to remove residual zinc → Water cooling & passivation → Finished product inspection → Marking, bundling & warehousing.
Internal and external walls are coated synchronously in the whole process without missing plating or uneven thin zinc layer.
5. Core Technical Parameters
5.1 Specification Range (Round Pipe)
Nominal diameter: DN15–DN300 (1/2"–12")Outer diameter: 21.3mm–323.9mmWall thickness: 2.0mm–8.0mm, including standard SCH40 and extra-thick SCH80 series.
Standard fixed length: 6 meters per piece; customized non-standard lengths of 3m, 9m and 12m are acceptable.
5.2 Galvanized Coating Indicators (National Standard Mandatory)
Average zinc coating thickness ≥70μm; ≥85μm for underground buried dedicated type
Zinc coating weight ≥610g/㎡
Adhesion: 30N/mm²; zinc coating no peeling or falling off after hammering and cutting
Salt spray resistance test ≥1000 hours, long-term anti-corrosion in saline-alkali and coastal high-humidity environments.
5.3 Pressure Bearing Performance
DN15–DN168.3: Hydrostatic test pressure 3.0MPaDN177.8–DN323.9: Hydrostatic test pressure 5.0MPa, meeting pressure requirements of low-pressure fluid delivery standards.
5.4 Theoretical Weight Calculation Formula
W=C×[0.02466×(D−S)×S]W = weight per meter (kg/m); D = outer diameter; S = wall thickness; C = galvanizing weight gain coefficient (1.028–1.064)
6. Core Product Advantages
Full internal & external anti-corrosion, ultra-long service lifeDouble protection of zinc-iron alloy layer and pure zinc layer. Zinc provides electrochemical protection preferentially when coating is damaged. Normal service life reaches 20–40 years for open-air and buried installation, far longer than 2–3 years of cold galvanized pipes.
Strong adhesion, anti-collision and wear resistanceMetallurgically bonded coating will not peel off in large areas after cutting, welding and threading, bringing high construction tolerance.
Excellent processing compatibilitySupport four mainstream connection methods: threading, grooved clamp connection, flange connection and welding. Matching complete series of galvanized pipe fittings in same specifications are available.
Smooth inner wall for unobstructed flow and less scalingUniform smooth inner wall reduces resistance for water and gas transportation, effectively avoiding rust blockage.
High cost performanceOne-time investment with zero post-maintenance cost, greatly cutting project cost compared with stainless steel pipes.
7. Key Differences between Hot-Dipped Galvanized Pipe and Cold (Electro) Galvanized Pipe
| Comparison Item | Hot-Dipped Galvanized Steel Pipe (Engineering Special) | Cold Galvanized Pipe (Only Indoor Short-Decoration Use) |
|---|---|---|
| Coating Thickness | 70–200μm, fully covered inside and outside | 5–25μm, almost no zinc coating on inner wall |
| Adhesion | Metallurgical bonding, impact resistant | Physical adsorption, coating peels easily with slight friction |
| Applicable Environment | Open-air, buried, fire protection, coastal saline land | Indoor dry temporary supports, prohibited for fire protection and buried use |
| Service Life | 20–40 years | Rust penetration within 2–3 years |
8. Main Application Fields
Fire Protection Engineering: Indoor and outdoor fire sprinkler & fire hydrant pipelines (hot-dipped galvanized pipe is mandatory for fire acceptance)
Municipal Fluid Transportation: Tap water supply, low-pressure natural gas and liquefied gas transmission pipelines
Steel Structure Engineering: Construction scaffolding, factory frames, photovoltaic brackets, guardrails and iron fences
Agricultural Irrigation: Greenhouse frames and farmland water pipelines, resistant to acid and alkali soil corrosion
Electrical Power Industry: Cable protection conduits with anti-mechanical damage and rust insulation performance
HVAC & Chemical Industry: Factory ventilation, low-pressure oil transportation and underground coal mine ventilation pipelines
9. Quality Inspection Standards
Full visual inspection: No missing plating, black spots, burrs, zinc tumors or cracks; uniform matte silver-gray zinc flower on surface.
Dimensional sampling inspection: Outer diameter, wall thickness and length tolerance strictly controlled within national standard allowable range.
Coating inspection: Zinc thickness test by magnetic thickness gauge, coating adhesion hammer test.
Hydrostatic burst test: Sampling pressure test per batch without leakage or deformation.
Material spectrum re-inspection: Guarantee Q235B material compliance.
10. Packaging & Delivery
Packaging: Bundled with steel strips, 6–12 pieces per bundle; plastic caps at pipe ends to prevent collision and sediment entry.
Marking: Specification, material grade, applicable standard, factory logo and production date sprayed on pipe surface.
Delivery: Container loading at Tianjin Port, delivery within 5–7 days. Full truck bulk cargo, 20GP / 40HQ container export available.
Supporting Products: Complete matching pipe fittings including galvanized elbows, tees, flanges, couplings and pipe clamps can be supplied together.
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