Corrosion has always been one of the most headache hazards of chemical equipment. A little carelessness can damage the equipment, or cause an accident or even a disaster. According to relevant statistics, about 60% of the damage of chemical equipment is caused by corrosion. Therefore, the scientific nature of the material selection should be paid attention to when selecting the chemical valve. There is usually a misunderstanding that stainless steel is a "universal material". It is very dangerous to hold stainless steel valves regardless of the medium and environmental conditions.
Here are some key points of material selection for some commonly used 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. The corrosion of sulfuric acid with different concentrations and temperatures varies greatly. For concentrated sulfuric acid with a concentration above 80% and a temperature less than 80℃, carbon steel and cast iron have good corrosion resistance, but it is not suitable for high-speed flowing sulfuric acid. It is not suitable for use as a material for pump valves; ordinary stainless steels such as 304 (0Cr18Ni9) and 316 (0Cr18Ni12Mo2Ti) have limited use for sulfuric acid media. Therefore, pump valves for sulphuric acid are usually made of high-silicon cast iron (difficult to cast and process) and high-alloy stainless steel (alloy 20). Fluoroplastics have better resistance to sulfuric acid, and fluorine-lined valves are a more economical choice.
hydrochloric acid
Most metal materials are not resistant to hydrochloric acid corrosion (including various stainless steel materials), and high-silicon ferro-molybdenum can only be used in hydrochloric acid below 50°C and 30%. Contrary to metal materials, most non-metal materials have good corrosion resistance to hydrochloric acid, so rubber valves and plastic valves (such as polypropylene, fluoroplastics, etc.) are the best choice for transporting hydrochloric acid.
Nitric acid
Most metals are quickly corroded in nitric acid. Stainless steel is the most widely used nitric acid resistant material. It has good corrosion resistance to all concentrations of nitric acid at room temperature. It is worth mentioning that stainless steels containing molybdenum (such as 316, 316L) ) The corrosion resistance to nitric acid is not only not better than ordinary stainless steel (such as 304, 321), and sometimes even worse. For high temperature nitric acid, titanium and titanium alloy materials are usually used.
acetic acid
It is one of the most corrosive substances in organic acids. Ordinary steel will be severely corroded in acetic acid at all concentrations and temperatures. Stainless steel is an excellent acetic acid resistant material. 316 stainless steel containing molybdenum is also suitable for high temperature and dilute acetic acid vapor. . For harsh requirements such as high temperature and high concentration of acetic acid or other corrosive media, high alloy stainless steel valves or fluoroplastic valves can be selected.
