How to galvanize steel pipes?
Galvanizing of steel pipes is mainly divided into two processes: hot-dip galvanizing (hot-dip galvanizing) and electroplating galvanizing (cold galvanizing). Among them, hot-dip galvanizing is currently the most widely used method due to its thick coating, strong corrosion resistance, and long service life.
Mainstream process: hot-dip galvanizing
Hot dip galvanizing is the process of immersing pre treated steel pipes in molten zinc solution to induce metallurgical reactions on their surface, forming a firmly bonded and corrosion-resistant layer of zinc iron alloy.
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Raw material preparation and inspection |
Conduct appearance, size, and mechanical performance inspections on the incoming steel pipes to ensure that they meet the requirements of galvanizing processing. |
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Degreasing and degreasing |
Clean the surface of steel pipes with alkaline chemical solvents to remove oil and grease contamination during rolling and storage, ensuring that subsequent acid washing can evenly contact the steel substrate. |
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Acid pickling and rust removal |
Soak the steel pipe in acid solution (usually hydrochloric acid) to thoroughly dissolve the rust and black oxide scale on its surface, exposing a clean silver white metal surface. |
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Water washing |
Rinse off residual acid and iron salts on the surface of the steel pipe with flowing water to prevent contamination of subsequent plating aids. |
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Drying |
Send the coated steel pipe into a drying furnace to remove moisture and prevent the steel pipe with moisture from entering the high-temperature zinc solution and causing "zinc explosion" accidents (zinc liquid splashing), while also preheating the steel pipe. |
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Hot dip galvanizing |
Dip the dried steel pipe into molten zinc at a certain speed. Steel pipes stay in zinc solution for a period of time (usually a few minutes), and iron and zinc undergo diffusion reactions, forming a metallurgical bonded zinc iron alloy layer. When leaving the zinc pot, compressed air or steam will be used to quickly blow the inner and outer walls of the steel pipe to control the thickness and surface smoothness of the zinc layer, and prevent the accumulation of zinc liquid at the bottom to form "zinc nodules". |
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Cooling |
Place the galvanized steel pipe into a clean water tank and quickly cool it to fix the luster of the coating and terminate the excessive growth of the alloy layer. |
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Passivation |
Perform chromate passivation treatment on the cooled steel pipe. This can form a dense chemical conversion film on the surface of the zinc layer, preventing the formation of "white rust" due to moisture during storage and extending its appearance life. |
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Inspection and packaging |
Finally, the finished steel pipes are inspected for appearance, zinc layer thickness, adhesion, etc. After passing the inspection, they are coded and packaged for storage. |
Summary
Simply put, hot-dip galvanizing is a "chemical metallurgical combination" with thick, firm, and long-lasting coatings, making it the preferred choice for the vast majority of industrial and outdoor applications.
Electrogalvanizing, on the other hand, is a "physical electrochemical deposition" method with thin coating and good appearance, but poor corrosion resistance. It has basically withdrawn from the field of fluid transportation and is only used in specific occasions where anti-corrosion requirements are not high.
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