Galvanized Square & Rectangular Tubes

• ​Introduction

Galvanized square and rectangular tubes are steel tubes with square or rectangular cross-sections that have undergone a galvanization process. This process involves coating the surface of the steel tubes with a layer of zinc, which forms a protective barrier against corrosion. These tubes are widely used in various industries due to their combination of structural strength, corrosion resistance, and versatile shapes.

• ​Main Functions

Structural Support: Provide stable load-bearing capacity in buildings, bridges, and frames, ensuring structural integrity.

Corrosion Resistance: The galvanized layer acts as a protective barrier, preventing the base steel from rusting and extending service life in humid or harsh environments.

Conveyance: Used in low-pressure fluid transportation systems (e.g., water, gas) due to their sealed hollow structure.

Aesthetic Decoration: Applied in architectural decoration, such as handrails and facades, thanks to the smooth and uniform galvanized surface.

• ​Tubing Standards

ASTM A500；

EN 10210-1,EN 10219；

GB/T 3094，GB/T 6728.

• ​Material & Performance

Base Material:

ASTM A500: Grade B、C、D； EN 10210-1: S235JR、S275J0H、S275J2H、S355J0H、S355J2H、S355K2H, EN 10219:S235JRH、S275J0H、S275J2H、S355J0H、S355J2H、S355K2H； GB/T 3094: 10#、20#、Q215A/B、Q235A/B、Q355B、Q390、Q420, GB/T 6728: Q235B、Q355B、Q390、Q420；

Zinc coating:

Hot-dip galvanizing coating – Formed by immersing cleaned steel pipes in a molten zinc bath (temperature ~450°C). The high temperature triggers a chemical reaction between iron (from the steel) and zinc, forming a multi-layer structure.

Thickness – Typically 35~200μm , with thicker coatings for harsher environments (e.g., coastal areas with high salinity).

Performance :

Corrosion Resistance – The zinc coating protects the steel from rust and extends its service life. High Strength – Maintains structural integrity under high pressure and mechanical stress. Weldability – Suitable for welding processes like arc welding and resistance welding without damaging the galvanized layer significantly.

• ​Manufacturing Process

Steel Pipe Formation：Produced via seamless or welded (ERW, LSAW) methods.

Surface Preparation: The steel pipe is cleaned to remove rust, oil, and debris through processes like pickling (using hydrochloric or sulfuric acid) and rinsing.

Fluxing: The cleaned pipe is dipped in a flux solution (e.g., zinc ammonium chloride) to prevent re-oxidation of the steel surface before galvanizing.

Hot-Dip Galvanizing: The pipe is immersed in a molten zinc bath (temperature around 450°C), where the zinc reacts with the steel to form a zinc-iron alloy layer, followed by a pure zinc layer on top.

Post-Treatment： Cooling – Remove galvanized pipes from the zinc bath and immediately cool them with cold water spraying or immersion to rapidly solidify the zinc layer, reducing uneven thickness caused by zinc flow. Zinc Layer Trimming – Remove excess zinc nodules and dross from pipe ends and inner walls using mechanical brushing to ensure dimensional accuracy and smooth inner walls.

Quality Inspection: Check zinc layer thickness (with a magnetic thickness gauge), uniformity (inspecting for bare spots or bubbles), and adhesion (using cross-cut or bending tests). Unqualified products are reprocessed.

• Specifications