What Is a Stainless Steel Tank?
A stainless steel tank is a tank made of stainless steel. If there is no specification, steel tanks are used for cost effectiveness, but stainless steel tanks are used when rust prevention is important. There are also different types of stainless steel tanks, and they should be used according to the specific application and budget.
Stainless steel tanks are mainly used for mixing materials in a tank with an agitator. Stainless steel tanks are also used for the temporary storage of hazardous materials.
Uses of Stainless Steel Tanks
Stainless steel tanks are often used in rust-prone situations because of their rust resistance. However, even stainless steel tanks can rust. It is important to remember that stainless steel tanks are rust-resistant, not rust-proof.
Stainless steel is indicated by SUS (Stainless Steel) followed by a number. To decrease chemical resistance, SUS430, SUS304, SUS316, and SUS316L are used.
SUS304 is commonly used for applications other than tanks. When handling chemicals or seawater, SUS316, which has even higher chemical resistance, is used. SUS316L is used for pharmaceuticals and cosmetics.
Principle of Stainless Steel Tanks
The following explains why stainless steel is resistant to rust. Rust is caused by iron reacting with oxygen in the air to form iron oxide. Stainless steel, therefore, contains chromium inside, which combines with oxygen in the air before iron does, thereby preventing rust. When the chromium oxidizes, it forms a passive film of several nanometers on the surface. The passive film serves to prevent oxygen from bonding with iron because it is difficult to change chemically. When stainless steel is scratched, the passive film may peel off, but the chromium will soon oxidize to form a new passive film.
SUS304 contains 18% chromium and 8% nickel, also known as 18-8 stainless steel. Nickel further facilitates the formation of an immobile film. SUS316 is stainless steel with an additional nickel content and molybdenum. A stronger version of SUS316 is SUS316L. The reduced carbon content reduces the corrosiveness of welds.