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Corrosion has always been one of the most troublesome hazards of chemical equipment. If you are not careful, it may damage the equipment, or cause accidents or even disasters. According to relevant statistics, about 60% of the damage to chemical equipment is caused by corrosion. Therefore, when selecting a chemical pump, you must first pay attention to the scientific nature of material selection. There is usually a misunderstanding that stainless steel is a "universal material". It is very dangerous to use stainless steel pumps regardless of the medium and environmental conditions. Let’s talk about the key points of chemical pump material selection for some commonly used chemical media.: 1. Sulfuric acid is one of the highly corrosive media. Sulfuric acid is an important industrial raw material with a wide range of uses. The corrosion of materials by sulfuric acid at different concentrations and temperatures is quite different. For concentrated sulfuric acid with a concentration above 80% and a temperature less than 80°C, carbon steel and cast iron have good corrosion resistance, but they are not suitable for high-speed flowing sulfuric acid and are not suitable as materials for pump valves. ； Ordinary stainless steels such as 304 (0Cr18Ni9) and 316 (0Cr18Ni12Mo2Ti) also have limited use in sulfuric acid media. Therefore, pump valves for transporting sulfuric acid are usually made of high-silicon cast iron (which is difficult to cast and process) and high-alloy stainless steel (No. 20 alloy). Fluorine plastic has good sulfuric acid resistance, and using a fluorine-lined pump (F46) is a more economical choice. 2. Hydrochloric acid rule Most metal materials are not resistant to hydrochloric acid corrosion (including various stainless steel materials), and molybdenum-containing high-silicon ferrosilicon can only be used in hydrochloric acid below 50°C and 30%. Contrary to metal materials, most non-metallic materials have good corrosion resistance to hydrochloric acid, so rubber-lined pumps and plastic pumps (such as polypropylene, fluoroplastics, etc.) are the best choices for transporting hydrochloric acid. 3. Nitric acid. Most general metals are rapidly corroded and destroyed in nitric acid. Stainless steel is the most 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, 316L) to nitric acid is not only no better than that of ordinary stainless steel (such as 304, 321), but sometimes even worse. For high-temperature nitric acid, titanium and titanium alloy materials are usually used. 4. Acetic acid is one of the most corrosive substances among 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 can also be used at high temperatures and dilute acetic acid vapor. For demanding requirements such as high temperature, high concentration acetic acid or other corrosive media, high alloy stainless steel pumps or fluoroplastic pumps can be selected. 5. Alkali (sodium hydroxide) steel is widely used in sodium hydroxide solutions below 80°C with a concentration of 30%. There are also many factories that still use ordinary steel at temperatures below 100°C and 75%. Although corrosion increases, the economy is good. The corrosion resistance of ordinary stainless steel to alkali liquid has no obvious advantage compared with cast iron. As long as a small amount of iron is allowed to be incorporated into the medium, stainless steel is not recommended. For high-temperature alkaline solutions, titanium and titanium alloys or high-alloy stainless steel are often used. 6. Ammonia (ammonium hydroxide) Most metals and non-metals corrode very slightly in liquid ammonia and ammonia water (ammonia hydroxide). Only copper and copper alloys are not suitable for use. 7. Salt water (sea water) The corrosion rate of ordinary steel in sodium chloride solution, sea water, and salt water is not very high, and it generally needs to be protected by paint. ； Various types of stainless steel also have very low uniform corrosion rates, but may cause localized corrosion due to chloride ions. Generally, 316 stainless steel is better. 8. Alcohols, similar media, esters, ethers. Common alcohol media include methanol, ethanol, ethylene glycol, propanol, etc. Similar media include propylene glycol and butylene glycol, etc., ester media include various methyl esters, ethyl esters, etc., and ether media include methyl ether, ethyl ether, butyl ether, etc. They are basically non-corrosive and can be used with commonly used materials. Reasonable selection should be made based on the properties of the medium and related requirements. It is also worth noting that homologs, esters, and ethers are soluble in a variety of rubbers, so avoid mistakes when selecting sealing materials.