1.Why is galvanized steel coil the preferred material for underground utility tunnel supports?
High humidity: Poor air circulation within the utility tunnel, groundwater infiltration, and air condensation can lead to prolonged high humidity.
Condensation: Temperature variations can cause condensation to form on supports and pipe surfaces.
Stray currents (in some areas): If there are electric railways or high-voltage cables within the utility tunnel, electrochemical corrosion may occur.
Chemical substances: Potentially present wastewater, exhaust gases, etc.
2.What are the advantages of galvanized coils (which are typically processed into galvanized steel strips or profiles) in response to these challenges?
Excellent corrosion resistance: The zinc coating provides a reliable physical barrier and cathodic protection (sacrificial anode) for the steel, effectively resisting corrosion from humid environments and condensation.
High cost-effectiveness: Compared to high-grade materials such as stainless steel, hot-dip galvanized steel is significantly cheaper, effectively controlling total project investment while ensuring long-term safety.
High strength and long service life: Supports made from galvanized coils possess sufficient strength and load-bearing capacity, with a design life typically exceeding 20-30 years, matching the design life of the pipe gallery.
Mature technology: The galvanizing process is highly mature, ensuring stable quality and facilitating large-scale production and processing.
3.What are the challenges and key points that must be considered?
Zinc Coating Thickness is Crucial
Underground utility tunnels are long-term, critical infrastructure with extremely high corrosion protection requirements. It is essential to select galvanized coils with a sufficiently thick zinc coating. High-heat galvanized products are generally recommended, with a zinc coating weight of Z200 (200g/m²) or higher, and even better, Z275 (275g/m²). Ordinary, thinner electroplated zinc (such as SECC) is completely unsuitable.
Corrosion Protection of Cut and Drilled Sections – The Most Easily Overlooked Aspect!
This is the biggest weak point of galvanized supports. When you cut, punch, or weld galvanized coils, the zinc coating at these points is damaged, exposing the steel substrate.
Without treatment, corrosion will begin at these sections and gradually spread inwards.
The Correct Approach: "Zinc patching" should be applied to all machined sections. Common methods include:
Spraying with zinc-rich paint: This is the most common and effective method.
Using zinc-based repair paste.
Ensure the coating thickness is sufficient to cover the cross-section.
4.What are the post-hot-dip galvanizing steps?
Using ordinary steel strips or profiles (such as Q235B), the components are first processed, cut, and welded into a complete bracket.
Then, the entire bracket is subjected to "overall hot-dip galvanizing."
Advantages: The zinc layer completely covers every corner, section, and weld point, forming a seamless, continuous protective layer with optimal corrosion resistance.
5.How to process galvanized coil/sheet raw materials and apply zinc to the cross-section?
Purchase galvanized coils/sheets with a high zinc coating weight directly as raw materials.
Perform cold working, cutting, and punching according to the drawings (avoiding on-site welding as much as possible).
Carefully spray all cut edges and the inner walls of drilled holes with zinc-rich paint.