According to authoritative statistics, chemical equipment damage caused by corrosion accounts for more than 60%. Therefore, the chemical industry should select scientific materials when choosing vacuum pumps, and do not fall into the misunderstanding that stainless steel is a "universal material". Today, I will introduce the material selection of vacuum pump in combination with the key points of chemical medium.

1、 The chemical medium is sulfuric acid

Sulfuric acid is an important industrial raw material with a wide range of uses. The corrosion resistance of carbon steel and cast iron is good for concentrated sulfuric acid with concentration above 80% and temperature less than 80 ℃, but it is not suitable for high-speed flow of sulfuric acid, and it is not suitable for pump valve material; ordinary stainless steel such as 304 (0Cr18Ni9) and 316 (0Cr18Ni12Mo2Ti) are also limited in the use of sulfuric acid medium. Therefore, high silicon cast iron (casting and processing is difficult), high alloy stainless steel (alloy 20), fluoroplastics and fluorine lining (F46) are usually used for the pump valve conveying sulfuric acid.

2、 The fluid contains acetic acid

Acetic acid is one of the most corrosive substances in organic acids. Ordinary steel will be seriously 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 steam. For high temperature and high concentration acetic acid or containing other corrosive media, vacuum pump made of high alloy stainless steel or fluoroplastics can be selected.

3、 Medium containing hydrochloric acid

Most metal materials are not resistant to hydrochloric acid corrosion (including all kinds of stainless steel materials), and high silicon iron containing molybdenum can only be used in hydrochloric acid below 50 ℃ and 30%. On the contrary, most nonmetal materials have good corrosion resistance to hydrochloric acid. Therefore, lined rubber pump and plastic pump (such as polypropylene, fluoroplastics, etc.) are the best choice for transporting hydrochloric acid.

4、 Most metals in nitric acid 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 the corrosion resistance of stainless steel containing molybdenum (such as 316, 316L) to nitric acid is not better than that of ordinary stainless steel (such as 304, 321), sometimes even worse. For high temperature nitric acid, titanium and titanium alloy are usually used.