I. Introduction to Stainless Steel:
All metals react with oxygen in the atmosphere, forming an oxide film on the surface. Unfortunately, the iron oxide that forms on ordinary carbon steel continues to oxidize, causing rust to spread continuously and eventually forming holes.
It is possible to protect the surface of carbon steel using paint or by electroplating with corrosion-resistant metals (such as zinc, nickel, and chromium), but as is well known, this type of protection is only a thin film. If the protective layer is damaged, the underlying steel begins to rust.
Steel that resists corrosion by weak corrosive media such as air, steam, water, and chemical corrosive media such as acids, alkalis, and salts is called stainless steel, also known as stainless acid-resistant steel. In practical applications, steel that resists corrosion by weak corrosive media is commonly referred to as stainless steel, while steel that resists chemical media corrosion is called acid-resistant steel.
Due to differences in chemical composition, the former is not necessarily resistant to chemical media corrosion, while the latter generally has stainless properties. The corrosion resistance of stainless steel depends on the alloy elements contained in the steel. Chromium is the basic element that gives stainless steel its corrosion resistance. 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 (passivation film) on the surface of the steel, which can prevent further corrosion of the steel substrate.
In addition to chromium, other common alloy elements include nickel, molybdenum, titanium, niobium, copper, nitrogen, etc., to meet the requirements of various uses for stainless steel structure and performance.
II. Classification of Stainless Steel
Stainless steel is usually classified according to the matrix structure into:
Ferritic stainless steel. Contains 12% to 30% chromium. Its corrosion resistance, toughness, and weldability increase with the increase of chromium content, and its resistance to chloride stress corrosion is better than other types of stainless steel.
Austenitic stainless steel. Contains more than 18% chromium, about 8% nickel, and a small amount of molybdenum, titanium, nitrogen, and other elements. It has good comprehensive properties and can resist corrosion by various media.
Austenitic-ferritic duplex stainless steel. It has the advantages of both austenitic and ferritic stainless steels and possesses superplasticity.
Martensitic stainless steel. It has high strength but poor plasticity and weldability.
The main material for making stainless steel filter elements is stainless steel, which can greatly reduce the occurrence of corrosion.
The main material for making marine stainless steel filter elements is stainless steel, which can greatly reduce the occurrence of corrosion.
When a stainless steel filter has not been used for a long time, it is necessary to drain the filter liquid inside the filter, then take out the filter element, and carry out a cleaning and drying process. After completing this series of operations, place the product in a clean plastic bag and seal it to ensure that the filter element product is not contaminated. Finally, wipe the stainless steel filter clean and store it in a dry place.
Generally, the replaced filter element should be soaked in a strong acidic wash solution for about twenty-four hours, and remember to keep the temperature of the acidic liquid between 25-50 degrees Celsius!!! During the soaking process, it is recommended that the proportion of acid to alkali in the liquid should be controlled within twenty percent to avoid damage and contamination to the internal structure of the filter element product. Generally speaking, wash liquid products with high protein content are the best, both in terms of cleanliness and economy, the effect is very good! Therefore, enzyme solutions with high protein content should be used for cleaning. After cleaning, be sure to perform a secondary cleaning and use steam for overall disinfection. This process is the most important for the maintenance of the filter.
