How to choose valves in chemical industry

When selecting chemical valves, we should first pay attention to the scientificity of material selection. There is usually a misunderstanding that stainless steel is a "universal material". It is very dangerous to hold stainless steel valves regardless of medium and environmental conditions. The following editor will introduce the key points of material selection for some common chemical media:

Sulfuric acid: 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 great differences in the corrosion of materials. For concentrated sulfuric acid with a concentration of more than 80% and a temperature of less than 80 ℃, carbon steel and cast iron have good corrosion resistance, but it is not suitable for high-speed flowing sulfuric acid and is not suitable for pump valve materials; Ordinary stainless steels such as 304 (0Cr18Ni9) and 316 (0Cr18Ni12Mo2Ti) are also limited to sulfuric acid medium. Therefore, the pump valve for transporting sulfuric acid is usually made of high silicon cast iron (difficult to cast and process) and high alloy stainless steel (No. 20 alloy). Fluoroplastics have good resistance to sulfuric acid, so using fluorine lined valve is a more economical choice.

Hydrochloric acid: 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 below 50 ℃ and 30%. In contrast to metal materials, most non-metallic materials have good corrosion resistance to hydrochloric acid, so lined rubber valves and plastic valves (such as polypropylene, fluoroplastics, etc.) are better choices for transporting hydrochloric acid.

Nitric acid: most general metals are rapidly corroded and damaged in nitric acid. Stainless steel is a more widely used nitric acid resistant material and has good corrosion resistance to all concentrations of nitric acid at room temperature. It is worth mentioning that the corrosion resistance of molybdenum containing stainless steel (such as 316 and 316L) to nitric acid is not only better than that of ordinary stainless steel (such as 304 and 321), but sometimes even worse. For high temperature nitric acid, titanium and titanium alloy materials are usually used.

Acetic acid: it is one of the more corrosive substances in organic acids. Ordinary steel will be seriously corroded in acetic acid at all concentrations and temperatures. Stainless steel is an excellent acetic acid resistant material. 316 stainless steel containing molybdenum can also be used for high temperature and dilute acetic acid steam. For high temperature and high concentration acetic acid or other corrosive media, high alloy stainless steel valve or fluoroplastic valve can be selected.