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What should be paid attention to when selecting materials for chemical pumps

2021-08-13

The chemical industry has always been facing the problem of equipment corrosion, which is the most headache. Once corrosion occurs, it can damage the equipment, or cause accidents or even disasters. According to relevant statistics, about 60% of the damage of chemical equipment is caused by corrosion. Therefore, when selecting a chemical pump, it is necessary to pay attention to the scientific nature of the material selection. 



Today, we will talk about some common chemical mediums to pay attention to the selection of chemical pump materials:

1. 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°C, carbon steel and cast iron have good corrosion resistance, but it is not suitable for high-speed flowing sulfuric acid. Not suitable for use as a material for pump valves;

Ordinary stainless steels such as 304 (0Cr18Ni9) and 316 (0Cr18Ni12Mo2Ti) also have limited uses for sulfuric acid media. Therefore, pump valves for transporting sulfuric acid are usually made of high-silicon cast iron (difficult to cast and process) and high-alloy stainless steel (alloy 20). Fluoroplastics have good resistance to sulfuric acid, and fluorine-lined pumps (F46) are a more economical choice.

2. Hydrochloric acid

Most metal materials are not resistant to hydrochloric acid corrosion (including various stainless steel materials), and ferrosilicon containing molybdenum can only be used for hydrochloric acid below 50°C and 30%. Contrary to metal materials, most non-metal materials have good corrosion resistance to hydrochloric acid, so rubber pumps and plastic pumps (such as polypropylene, fluoroplastics, etc.) are the best choice for transporting hydrochloric acid.

3. Nitric acid

Most metals 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) ) 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.

4. 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 demanding requirements such as high temperature and high concentration of acetic acid or other corrosive media, high alloy stainless steel or fluoroplastic pumps can be used.

5. Alkali (sodium hydroxide)

Steel is widely used in sodium hydroxide solution below 80°C and 30% concentration. There are also many factories that still use ordinary steel when the temperature is below 100°C and 75%. Although corrosion increases, it is economical. The corrosion resistance of ordinary stainless steel to lye has no obvious advantages compared with cast iron. As long as a small amount of iron is allowed to be mixed in the medium, stainless steel is not recommended. For high-temperature lye, titanium and titanium alloy or high-alloy stainless steel are mostly used.

6. Ammonia (Ammonia Hydroxide)

Most metals and non-metals have slight corrosion in liquid ammonia and ammonia (ammonium hydroxide), and only copper and copper alloys are not suitable for use.

7. Salt water (sea water)

Ordinary steel has a low corrosion rate in sodium chloride solution, sea water and salt water, and generally must be protected by paint; all kinds of stainless steel also have a very low uniform corrosion rate, but may cause local corrosion due to chloride ions, usually 316 stainless steel better.

8. Alcohols, ketones, esters, ethers

Common alcohol media include methanol, ethanol, ethylene glycol, propanol, etc., ketone media include acetone, butanone, etc., ester media include various methyl and ethyl esters, and ether media include methyl ether, ethyl ether, etc. Butyl ether, etc., they are basically non-corrosive, and common materials can be applied. When selecting, a reasonable choice should be made according to the properties of the medium and related requirements. It is also worth noting that ketones, esters, and ethers are soluble in a variety of rubbers, so errors should be avoided when selecting sealing materials.