Plate Heat Exchanger Plate Material

Stainless Steel: Refers to steel that is resistant to weak corrosive media such as air, steam, and water, as well as chemically corrosive media like acids, alkalis, and salts. It is also known as acid-resistant stainless steel. In practical applications, steel resistant to weak corrosive media is often called stainless steel, while steel resistant to chemical media is referred to as acid-resistant steel. There are certain differences in chemical composition between the two; the former may not necessarily resist chemical media corrosion, while the latter generally possesses stainless properties. The corrosion resistance of stainless steel depends on the alloying elements it contains.

Corrosion Resistance Mechanism: Chromium is the fundamental element that imparts corrosion resistance to stainless steel. When the chromium content in the steel reaches about 12%, chromium reacts with oxygen in the corrosive medium to form a very thin oxide film (a self-passivating film, Cr?O?) on the steel surface. This film is highly insoluble in water and further prevents oxygen from causing iron corrosion. Similarly, damaging the passivating film Cr?O? means compromising its resistance to oxygen corrosion.

Additionally, halogen elements in the corrosive medium (such as chloride ions commonly found in water) can, under certain conditions, replace chromium. Therefore, stainless steel can also rust under specific conditions and can be corroded in media containing acids, alkalis, or salts. Thus, the corrosion resistance of stainless steel varies depending on its chemical composition, processing state, conditions of use, and the type of environmental medium. Corrosion of stainless steel in water is primarily caused by chloride ions.

Other added elements in stainless steel also play various roles. For example, molybdenum (Mo) can, to some extent, counteract corrosion caused by chloride ions, but this effect is limited to a certain range.

Common Stainless Steels: 304 and 316 belong to austenitic stainless steels. Their grades are abbreviated from foreign designations (generally imported) and belong to the 300 series. The American grade is designated by the American Iron and Steel Institute.