What valve can be suitable for various corrosive media working conditions?

The selection and selection of materials for chemical valves under various corrosive media conditions include sulfuric acid, hydrochloric acid, nitric acid, acetic acid, alkali (sodium hydroxide), ammonia (ammonia hydroxide), chlorine (liquid chlorine), saltwater (seawater), alcohols, ketones, esters, ethers, and other corrosive media conditions. Corrosion prevention is a key aspect of chemical equipment. If the correct metal materials for chemical valves cannot be selected, slight carelessness can damage the equipment, and serious accidents or even disasters. This article discusses the key points of valve material selection for commonly used chemical media, including the selection of chemical valves suitable for various corrosive media conditions

1. Sulfuric acid medium. As one of the strong corrosive media, sulfuric acid is an important industrial raw material with a wide range of uses. The corrosion of materials varies greatly with different concentrations and temperatures of sulfuric acid. For concentrated sulfuric acid with concentrations above 80% and temperatures below 80 ℃, 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 valve materials; Ordinary stainless steels such as 304 (0Cr18Ni9) and 316 (0Cr18Ni12Mo2Ti) also have limited applications in 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 (No. 20 alloy valve). Fluoroplastics have good sulfuric acid resistance, and using fluorine lined valves (F46) is a more economical choice. If the pressure is too high and the temperature rises, the use point of the plastic valve will be affected, so we can only choose a ceramic ball valve that is much more expensive than it.

2. Most metal materials (including various stainless steel materials) are not resistant to hydrochloric acid corrosion in hydrochloric acid medium, and high silicon iron containing molybdenum can only be used for hydrochloric acid below 50 ℃ and 30%. Contrary to metal materials, the vast majority of non-metallic materials have good corrosion resistance to hydrochloric acid, so lined rubber valves and plastic valves (such as polypropylene, fluoroplastics, etc.) are good choices for transporting hydrochloric acid. But if the temperature of such a medium exceeds 150 ℃ or the pressure is greater than PN16 kilograms, any plastic (including polypropylene, fluoroplastics, and even polytetrafluoroethylene) will not be able to handle it. Currently, there are no ideal valves on the market, but you can try the emerging ceramic ball valve. The advantages of this valve are self-lubricating, low torque force, non aging, and much longer lifespan than ordinary valves. Its disadvantage is that it is much more expensive than plastic valves.

3. Most metals in nitric acid medium are rapidly corroded and destroyed in nitric acid. Stainless steel is a widely used nitric acid resistant material, which has good corrosion resistance to all concentrations of nitric acid at room temperature. It is worth mentioning that stainless steel containing molybdenum (such as 316, 316L) not only does not have better corrosion resistance to nitric acid than ordinary stainless steel (such as 304, 321), but sometimes even worse. For high-temperature nitric acid, titanium ball valves and titanium alloy materials are usually used.

4. Acetic acid medium: Acetic acid is one of the highly corrosive substances in organic acids. Ordinary steel will suffer severe corrosion in all concentrations and temperatures of acetic acid. Stainless steel is an excellent acetic acid resistant material, and 316 stainless steel containing molybdenum can also be suitable for high temperatures and dilute acetic acid vapors. For high temperature and high concentration acetic acid or other corrosive media with strict requirements, high alloy stainless steel or fluoroplastic pumps can be selected.

5. Alkaline (sodium hydroxide) steel is widely used in sodium hydroxide solutions below 80 ℃ and within 30% concentration. Many petrochemical enterprises still use ordinary steel at temperatures below 100 ℃ and 75%. Although corrosion increases, it has good economic efficiency. Compared with cast iron, ordinary stainless steel does not have significant advantages in corrosion resistance to alkaline solution. As long as a small amount of iron is allowed to be added to the medium, stainless steel is not recommended. For high-temperature alkaline solutions, titanium gate valves and titanium alloy or high alloy stainless steel are commonly used.

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

7. Chlorine (liquid chlorine) Most metal valves have limited resistance to corrosion from chlorine gas, especially when chlorine gas carries water, including various alloy steel valves. In this case, PTFE lined valves are a good choice. However, chemical plants producing chlor alkali may find that if PTFE lined valves are used for a slightly longer period of time, the problems of torque and PTFE aging will become prominent, and the leakage that occurs in this situation is fatal. It is possible to consider replacing the original ordinary PTFE lined valve with a PTFE lined ceramic ball core, taking advantage of the self-lubricating properties of ceramics and the corrosion resistance of PTFE.

8. Salt water (seawater): Ordinary steel has a low corrosion rate in sodium chloride solution, seawater, and saline water, and generally requires coating protection; Various types of stainless steel also have a very low uniform corrosion rate, but may cause localized corrosion due to chloride ions. Generally, 316 stainless steel is preferred.

9. Alcohols, ketones, esters, and 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, butyl ether, etc. They are basically non corrosive and can be used with commonly used materials. When selecting, reasonable choices should also be made based on the properties and relevant requirements of the media. Additionally, it is worth noting that ketones, esters, and ethers have solubility in various types of rubber, so errors should be avoided when selecting sealing materials.