Corrosion has always been one of the more serious hazar […]
Corrosion has always been one of the more serious hazards of chemical equipment. If it is slightly inadvertent, it will damage the equipment and cause accidents and even disasters. According to relevant statistics, about 60% of the destruction of chemical equipment is caused by corrosion. Therefore, in the selection of chemical valves, we must first pay attention to the scientific nature of material selection. There is usually a misunderstanding that stainless steel is a “universal material”. No matter what medium or environmental conditions, stainless steel valves are used. This is very dangerous. The following points should be discussed for some common chemical media:
As one of the strong corrosive media, sulfuric acid is an important industrial raw material with a wide range of uses. Different concentrations and temperatures of sulfuric acid have a great difference in corrosion of materials. For concentrated sulfuric acid with a concentration above 80% and temperature less than 80 °C, carbon steel and cast iron have good corrosion resistance, but it is not suitable for high-speed flowing sulfuric acid. Not suitable for pump valve materials; ordinary stainless steel such as 304 (0Cr18Ni9), 316 (0Cr18Ni12Mo2Ti) also has limited use of sulfuric acid media. Therefore, the pump valve for conveying sulfuric acid is usually made of high-silicon cast iron (difficult to cast and process) and high-alloy stainless steel (20 alloy). Fluoroplastics have better sulfuric acid resistance, and the use of fluorine-lined valves is a more economical option.
Most metal materials are not resistant to hydrochloric acid corrosion (including various stainless steel materials), and molybdenum-containing high-silicon iron can only be used for hydrochloric acid at 50 ° C and 30%. Contrary to metal materials, most non-metallic materials have good corrosion resistance to hydrochloric acid, so rubber valves and plastic valves (such as polypropylene, fluoroplastics, etc.) are the primary choice for conveying hydrochloric acid valves.
Generally, most metals are rapidly corroded and destroyed in nitric acid. Stainless steel is widely used as a nitric acid-resistant material. It has good corrosion resistance to all concentrations of nitric acid at normal temperature. It is worth mentioning that it contains molybdenum-containing stainless steel (such as 316 and 316L). The corrosion resistance to nitric acid is not only not superior to ordinary stainless steel (such as 304, 321), and sometimes even worse. For high temperature nitric acid, titanium and titanium alloy materials are usually used.
It is one of the most corrosive substances in organic acids. Ordinary steel is severely corroded in acetic acid of all concentrations and temperatures. Stainless steel is an excellent acetic acid resistant material. Molybdenum-containing 316 stainless steel can also be used for high temperature and dilute acetic acid vapor. . For high temperature, high concentration acetic acid or other corrosive media, high alloy stainless steel valves or fluoroplastic valves are available.
Know the performance of each material and the chemical properties of the corresponding media to better match and choose a more economical valve.