Difference between Hot-dip Galvanized Steel Pipe and Cold-dip Galvanized Steel Pipe

Hot-dip galvanized steel pipe and cold-dip galvanized steel pipe

Hot-dip galvanized steel pipe involves first acid washing the steel components to remove the surface oxide layer, and then cleaning them through immersion in a tank containing ammonium chloride or zinc chloride water solution or a mixed solution of both. After that, the components are sent into a hot-dip galvanizing tank. The resulting coating is evenly distributed and highly adhesive, with a long service life and other advantages.

Although cold-dip galvanized steel pipes are rarely used on a large scale nowadays, we will provide an overview of the difference between the two. Cold-dip galvanized pipes, also known as electro-galvanized pipes, are coated with a layer of zinc on the surface of pre-manufactured pipes through an electroplating process. The pipes are first degreased and acid washed, and then placed in a solution composed of zinc salt. A zinc plate is placed opposite the pipe and connected to the positive electrode of an electroplating device, while the structural steel pipe is connected to the negative electrode. When a current flows from the positive electrode to the negative electrode, zinc will be deposited on the surface of the pipe. Therefore, cold-dip galvanized pipes are galvanized after the pipes have been processed.

The difference between hot-dip galvanized steel pipe and cold-dip galvanized steel pipe

  • Different construction techniques: hot dip galvanized steel pipe form an alloy layer through the reaction of molten metal and a steel base to combine the base and the coating. On the other hand, cold-dip galvanized steel pipes primarily use electrochemical principles to prevent corrosion through a layer of zinc coating.

  • Different equipment requirements: hot-dip galvanized steel pipes require acid washing equipment and draw-type annealing furnaces or hood-type annealing furnaces, whereas cold-dip galvanized steel pipes require electroplating equipment.

  • Different properties: Hot-dip galvanizing provides a durable, long-lasting corrosion resistance. The thickness of the standard galvanized layer ensures excellent durability, and the coating has strong toughness, allowing it to withstand mechanical damage during transport and use. Cold-dip galvanizing has excellent environmental protection properties. The solvents and diluents used in most cold-dip galvanizing processes do not contain large amounts of toxic organic solvents. The process also reduces the amount of organic solvent volatilization and drying energy consumption, making it beneficial for protecting the environment.

  • Different coating thickness: The zinc layer of a hot galvanized steel pipe is thicker (10um or more), producing a bright but rough surface and may result in zinc flowers. Conversely, the zinc layer of cold-dip galvanized steel pipe is much thinner, with a thickness of only 3-5um. Although the surface is smooth, it may have a dull appearance and can become dirty easily. Cold-dip galvanized steel pipes have good processing performance but inadequate corrosion resistance.

  • Different applications: Hot-dip galvanized steel pipes have excellent corrosion resistance and are widely used in power transmission towers, communication towers, railways, road protection, street lamp posts, ship components, building steel structural components, substation ancillary facilities, light industry, and other fields. Cold-dip galvanized steel pipes are a major development direction for heavy-duty corrosion-resistant coatings with an emphasis on environmental protection.

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