Material selection of chemical valves
Corrosion has always been one of the most serious hazards of chemical equipment. A slight carelessness can damage the equipment, or cause an accident or even a disaster. In the selection of chemical valves, the first thing to pay attention to is the scientific nature 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 the medium and environmental conditions.
Here are some key points of material selection for some commonly used chemical media:
As one of the strong corrosive media, sulfuric acid is an important industrial raw material with a wide range of uses. Sulfuric acid of different concentrations and temperatures will relatively penetrate 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 better corrosion resistance, but it is not suitable for high-speed flowing sulfuric acid. It cannot be used as a material for pump valves; ordinary stainless steels such as 304 and 316 have limited use for sulfuric acid media. Therefore, the pump valve for transporting sulfuric acid is usually made of high-silicon cast iron (large defects in casting and machining) and high-alloy stainless steel (alloy 20). Fluoroplastics have better sulfate resistance, and fluorine-lined valves are a more economical choice.
Absolutely most metal materials are not resistant to hydrochloric acid corrosion (including various stainless steel materials), and high-silicon ferro-molybdenum can only be used with chlorine at 50°C and 30% below. Contrary to metal materials, non-metal materials can have good corrosion resistance to hydrochloric acid, so rubber valves and plastic valves (such as polypropylene, fluoroplastics, etc.) are the best choice for carbonization.
Most metals in general are rapidly corroded and destroyed 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) Ordinary stainless steel (such as 304, 321) with almost discontinuous corrosion resistance to nitrates, sometimes even worse. For high-temperature nitrates, titanium and titanium alloy materials are usually used.
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 demanding requirements such as high temperature and high concentration of acetic acid or containing other corrosive media, high alloy stainless steel valves or fluoroplastic valves can be selected.
Zhejiang Zhengfeng Valve Co., Ltd