Galvanizing is a plating technique that applies a surface finish to metal to protect it from corrosion. This often involves coating the metal in a layer of molten zinc. While other metals like aluminium or zinc-aluminium alloy can be used in the process, the term "galvanizing" generally refers specifically to the application of a zinc coating.

A surface treatment is a process that gives a material a new function or property. The specific effects include decorative properties that make things look more attractive, corrosion resistance that protects materials from rust, and wear resistance that prevents damage or wear and tear.

Galvanizing is mainly used for corrosion resistance, known as "sacrificial corrosion," in which zinc protects the steel by corroding itself to prevent rust from forming. It is widely used as a coating for steel materials.

While commonly called hot-dipping, galvanizing methods vary depending on whether the molten zinc is applied before or after the steel is fabricated into its final shape.

Hot-dipping mainly refers to the process of formed steel or products made of steel being dipped in a galvanizing bath containing molten zinc at high temperatures. The entire surface can be covered since the product is galvanized after forming, processing, or assembly. With hot-dipping, however, the immersion time for applying the zinc dipping takes tens of seconds to several minutes, which allows the alloy layer to develop and grow, increasing the risk of oxidation from the excessive iron contained in the layer. It is also prone to cracking or peeling of the zinc coating.

Hot-dipping involves immersing steel products in a bath of molten zinc at high temperatures. This allows for a complete and even coating, including on complex shapes, as the process occurs after the product has been formed and processed. The immersion time in the zinc bath typically ranges from tens of seconds to several minutes, allowing a zinc-iron alloy layer to develop on the steel's surface. A thicker alloy layer provides better corrosion resistance but can also be more prone to cracking or peeling.

In contrast, pre-galvanizing, also known as in-line galvanizing (ILG), is a highly efficient process that involves plating the steel before forming the product, which takes place in a continuous production line, ensuring a streamlined operation. 

This particular galvanizing method also makes a difference in our steel-pipe making at DSTI and STI, o2OG umbrella companies. ILG requires less time to galvanize the steel sheet, so the alloy layer, a mixture of iron and zinc, grows slower while the pure zinc layer becomes thicker. The outer surface is coated by galvanizing after forming steel sheets into pipes. 

ILG is a key process in our steel-pipe manufacturing at DSTI and STI, both companies under the o2OG umbrella. ILG allows for faster galvanization of the steel sheet, resulting in a thinner alloy layer (a mixture of iron and zinc). This method involves forming the steel sheets, galvanizing them, and forming them into pipes.

This process integrates the entire pipe production sequence, from sheet cutting and galvanizing to pipe forming, allowing for a highly efficient workflow. A key advantage of ILG is its scalability. Because the tube-making equipment is relatively inexpensive, production lines can be easily expanded or adapted to meet varying demands, including high-mix, low-volume production.

Since the welding process used to form the steel pipe removes the zinc coating, thermal spraying is applied to the outer weld as a post-treatment. While the inner welds are not galvanized, the products are designed to protect the inner surfaces by utilizing the sacrificial corrosion effect of the zinc coating elsewhere in the pipe. ILG allows for efficient production and significantly reduces zinc consumption, thus supporting DSTI's slogan, ‘Let’s provide eco-friendly steel tubes from Tochigi to the world.