Analysis Of Corrosion Resistance Of Sanitary Rotary Vane Pumps

Corrosion has always been one of the most troublesome hazards for Sanitary Rotary Lobe Pump. If you are not careful, it may damage the equipment at the least, or cause accidents or even disasters at the worst. According to relevant statistics, about 60% of the damage to sanitary rotary vane pumps is caused by corrosion. Therefore, when selecting sanitary rotary vane pumps, you should first pay attention to the scientific selection of materials. There is usually a misunderstanding that stainless steel is a "universal material" and it is very dangerous to use stainless steel regardless of the medium and environmental conditions. The following is a discussion of the key points of material selection for some commonly used chemical media:

1. Sulfuric acid is one of the highly corrosive media and is an important industrial raw material with a wide range of uses. Sulfuric acid of different concentrations and temperatures has a large difference 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 and is not suitable for use as pump and valve materials; ordinary stainless steel such as 304 (0Cr18Ni9) and 316 (0Cr18Ni12Mo2Ti) are also limited in use for sulfuric acid media. Therefore, sanitary rotary vane pumps for conveying sulfuric acid are usually made of high-silicon cast iron (difficult to cast and process) and high-alloy stainless steel (No. 20 alloy). Fluoroplastics have good resistance to sulfuric acid, and the use of fluorine-lined pumps (F46) is a more economical choice.

2. Hydrochloric acid Most metal materials are not resistant to hydrochloric acid corrosion (including various stainless steel materials), and molybdenum-containing high-silicon iron can only be used for hydrochloric acid below 50°C and 30%. In contrast to metal materials, most non-metallic materials have good corrosion resistance to hydrochloric acid, so lined rubber pumps and sanitary rotary vane pumps (such as polypropylene, fluoroplastics, etc.) are the best choices for conveying hydrochloric acid.

3. Nitric acid Most general metals are quickly 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 not better than that of ordinary stainless steel (such as 304, 321), but sometimes even worse. Sanitary rotary vane pumps are usually made of titanium and titanium alloys for high-temperature nitric acid.

4. Acetic acid is one of the most corrosive substances among organic acids. Ordinary steel will be severely 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 vapor. For demanding requirements such as high temperature and high concentration acetic acid or other corrosive media, high alloy stainless steel or sanitary rotary vane pumps can be selected.

5. Alkali (sodium hydroxide) steel is widely used in sodium hydroxide solutions below 80°C and within 30% concentration. Many factories still use ordinary steel at 100°C and below 75%. Although corrosion increases, it is economical. Ordinary stainless steel has no obvious advantage over cast iron in corrosion resistance to alkali solution. As long as a small amount of iron is allowed to be added to the medium, stainless steel is not recommended for sanitary rotary vane pumps. Titanium and titanium alloys or high alloy stainless steel are often used for high-temperature alkali solutions.

6. Ammonia (ammonia hydroxide) Most metals and non-metals are slightly corroded in liquid ammonia and ammonia water (ammonia hydroxide). Only copper and copper alloys are not suitable for sanitary rotary vane pumps.

7. Salt water (seawater) The corrosion rate of ordinary steel in sodium chloride solution, seawater and salt water is not very high, and coating protection is generally required; various types of stainless steel for sanitary rotary vane pumps also have a very low uniform corrosion rate, but may cause local corrosion due to chloride ions, and 316 stainless steel is usually 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 esters, ethyl esters, etc., ether media include methyl ether, ethyl ether, butyl ether, etc., they are basically non-corrosive, and commonly used materials can be applied. When selecting sanitary rotary vane pumps, reasonable choices should be made based on the properties of the media and related requirements.