75x38mm Hot-Dip Galvanized Rectangular Hollow Steel Tube
Product Overview
Dimensions: 75mm (Width) × 38mm (Height)
Material Grades: Q235B, S235JR, S275JR, GR.B, GR.C, STK400, STK500.
Manufacturing Standards: EN 10219 / EN 10210 / ASTM A500 / ASTM A53 / ASTM A500 / JIS G3466 / BS 1387
This product is manufactured from high-quality hot-rolled steel strips, formed by cold roll forming and high-frequency electric resistance welding (ERW), followed by full-immersion hot-dip galvanizing. The rectangular cross-section offers a higher section modulus per unit weight compared to equal-angle steel, round tubes, or channels, making it an ideal lightweight alternative.
Detailed Core Process Advantages
Cold Forming & Welding
A continuous roll-forming line is applied, with progressive deformation minimizing internal stress concentration.
High-frequency welding (HFW) uses closed-loop control of temperature and power, producing smooth, crack-free seams. The weld bead is scraped internally and externally, with internal burr removal rate ≥95%, ensuring unobstructed fluid or wire passage.
Hot-Dip Galvanizing Process (Key Differentiator)
● Pre-treatment： Pickling → Water rinsing → Fluxing (zinc ammonium chloride solution) → Drying, for thorough rust and oil removal.
● Galvanizing temperature： Constant-temperature zinc bath at 445–465℃, with immersion time of 3–5 minutes, forming a composite structure of iron-zinc alloy layers and a pure zinc layer with exceptional adhesion.
● Passivation： Immediately after leaving the zinc bath, chromate or chromium-free passivation is applied to seal the pores of the zinc coating, further enhancing resistance to white rust.
● Coating uniformity inspection： Magnetic thickness gauges are used for batch sampling inspection to ensure the minimum thickness meets standard requirements.
Performance Parameters & Comparative Advantages
| Parameter | 75x38 Galvanized RHS | Same-size Black Tube (Uncoated) | Equal-weight Round Tube |
|---|---|---|---|
| Section Modulus (W) | Higher (rectangular advantage) | Same | Lower |
| Corrosion life (NSS test) | ≥1500h no red rust | ≤200h corrosion appears | Same (coating-dependent) |
| Annual corrosion rate (industrial) | ≤5μm/year | 50~100μm/year | Same |
| Secondary processing | Weldable, drillable, cuttable, minimal coating impact | Requires post-weld anti-corrosion | Requires post-weld anti-corrosion |
Service Life Comparison：
Under identical outdoor exposure conditions, this galvanized rectangular tube can achieve a service life of 25–30 years (before first major overhaul), while ordinary black tubes with paint coating require re-maintenance in just 5–8 years.
Cost-Effectiveness：
Although the initial purchase cost is about 30–40% higher than black tubes, the Life Cycle Cost (LCC) is reduced by more than 50%, saving labor and material costs from repetitive repainting and downtime replacements.
Detailed Application Scenarios
Building & Structural Engineering
◇ Light steel workshops： Used as roof purlins, wall horizontal bracing, and inter-column supports, with excellent wind pressure resistance.
◇ Residential framing： Secondary beams and joists in prefabricated steel-structured houses, reducing structural deadweight and foundation loads.
◇ Temporary prefab units： Quick to erect and dismantle, with high reusability.
Municipal & Transportation Infrastructure
◆ Highway guardrail posts： The 75x38 section fits standard corrugated panel connectors, offering notable impact energy absorption.
◆ Bridge maintenance walkway railings： High weatherability reduces elevated maintenance frequency.
◆ Bus shelters & light pole brackets： Square and aesthetic shape, convenient for fixing light boxes and billboards.
Modern Agriculture
◇ Smart greenhouse frames： Arches, longitudinal beams, and gutter supports, bearing snow loads and crop suspension loads.
◇ Vineyards & kiwifruit trellises： Flat cross-section for easy tying and netting.
New Energy & Industry
◆ PV mounting structures： Especially for ground-mounted distributed power stations – rectangular tubes offer better torsional resistance than C-channels, reducing tracking system deformation.
◆ Conveyor line supports & equipment platform guardrails： Clean, rust-free surfaces meet food-grade or electronic plant cleanliness requirements.
Decoration & Urban Furniture
◇ Landscape pergolas & outdoor signboard girders： The galvanized surface can be directly coated with fluorocarbon paint or wood-grain transfer, combining aesthetics with durability.
◇ Parking bumpers & bicycle racks： Low cost with high durability.
Quality Assurance & Service System
Raw material traceability： Each batch of steel strip comes with the mill test certificate, traceable to the heat number.
In-line inspection： Eddy Current Testing (ECT) continuously monitors weld defects, ensuring no cracks or lack of fusion.
Laboratory sampling tests：
Tensile test
Flattening test
Impact test
Bend test
Salt spray test
After-sales commitment： If coating peeling or geometrical dimension deviation is found due to manufacturing defects, we provide unconditional replacement and bear corresponding liability.
Why Choose Us?
20+ years of experience in hollow section production, with a monthly capacity of 12,000 tons, capable of handling both small and large orders.
End-to-end digital management with full tracking from order placement to logistics – customers can check progress anytime.
Free technical support： providing structural selection calculations, welding procedure specifications, and installation detail drawings.
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