About various corrosive media conditions of chemical control valve selection selection in the sulfuric acid, hydrochloric acid, nitric acid, acetic acid, alkali (sodium hydroxide), ammonia (ammonia hydroxide), chlorine (liquid chlorine), salt water Corrosion of alcohols, ketones, esters, ethers and other media under the conditions of the valve, anti-corrosion is the most critical chemical equipment, if you can not choose the correct chemical valve metal material, a little careless, ranging from damage to equipment , While causing accidents and even lead to disaster. In this paper, some common chemical media to talk about the main points of the valve selection: 1. Sulfuric acid sulfuric acid as one of the strong corrosive media, sulfuric acid is an important use of a wide range of industrial raw materials. Different concentrations and temperatures of sulfuric acid on the corrosion of materials vary greatly, for the concentration of more than 80%, the temperature is less than 80 ℃ of concentrated sulfuric acid, carbon steel and cast iron has good corrosion resistance, but it is not suitable for high-speed flow of sulfuric acid, Not suitable for the valve material; ordinary stainless steel, such as 304 (0Cr18Ni9), 316 (0Cr18Ni12Mo2Ti) sulfuric acid medium is also limited use. Therefore, the delivery of sulfuric acid pump valve is usually used high silicon cast iron (casting and machining difficult), high alloy stainless steel (20 alloy valve) manufacturing. Fluorine plastic has good resistance to sulfuric acid performance, the use of fluorine-fined valve (F46) is a more economical choice. If the pressure is too large, the temperature rises, the plastic valve's point of use has been the impact, we can only choose more than its more expensive ceramic ball valve. 2. Hydrochloric acid solution Most metal materials (including a variety of stainless steel materials) are not resistant to hydrochloric acid corrosion, molybdenum high ferrosilicon can only be used for 50 ℃, 30% hydrochloric acid. In contrast to metallic 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, fluoroplastic, etc.) are the best choice for the delivery of hydrochloric acid. However, if the temperature of this medium exceeds 150 ° C, or if the pressure exceeds PN16 kg, any plastic (including polypropylene, fluoroplastic or even PTFE) will not be able to do so and there is no ideal valve on the market , But you can try now emerging ceramic ball valve, the advantages of this valve is self-lubricating, torque is small, not aging, life expectancy much longer than the average valve, its disadvantage is that the price is much higher than plastic valves . 3. Nitric acid medium Most metals are mostly corrosive nitric acid corrosion damage, stainless steel is the most widely used nitric acid-resistant materials, all concentrations of nitric acid at room temperature have good corrosion resistance, it is worth mentioning that the stainless steel containing molybdenum ( Such as 316,316L) nitric acid corrosion resistance not only not superior to ordinary stainless steel (such as 304,321), sometimes even worse. For high temperature nitric acid, titanium ball valve and titanium alloy materials are usually used. 4. Acetic acid medium Acetic acid is one of the most corrosive substances in organic acids. Ordinary steel will be seriously corroded in all concentrations and temperatures of acetic acid. Stainless steel is an excellent acetic acid-resistant material. Molybdenum-containing 316 stainless steel is also suitable for high temperature And dilute acetic acid steam. For high temperature and high concentration of acetic acid or other corrosive media containing harsh requirements, the choice of high-alloy stainless steel or fluorine plastic pump. 5. Alkali (sodium hydroxide) steel is widely used in sodium hydroxide solution below 80 ℃, 30% concentration, there are many petrochemical companies at 100 ℃, 75% below the ordinary steel is still used, although the corrosion increases, but the economy it is good. Ordinary stainless steel lye corrosion resistance compared with no obvious advantages, as long as the medium allows a small amount of iron mixed, stainless steel is not recommended. For high temperature alkaline use of titanium gate valves and titanium or high alloy stainless steel. 6. Ammonia (ammonia hydroxide) Most metals and non-metals in liquid ammonia and ammonia (ammonia hydroxide) corrosion are minor, only copper and copper alloy should not be used. 7. Chlorine (liquid chlorine) Most metal valves are very resistant to chlorine gas corrosion, especially in the case of chlorine gas, including a variety of alloy steel valves, in this case, lining PTFE valve is a very good Choice, but the production of chlor-alkali chemical plant will find: lined PTFE valve with a slightly longer time, increased torque, the problem of aging PTFE will be highlighted, in which case the leak is fatal. You can consider the lining of PTFE ceramic ball core replaced the original ordinary PTFE valve, the use of self-lubricating ceramic and PTFE corrosion will have the perfect effect. 8. alcohols, ketones, esters, ethers Common alcohol mediums are methanol, ethanol, ethylene glycol, propanol, ketones have acetone, butanone and so on, the ester medium has a variety of methyl esters, Ethyl ether, ethers medium ether, butyl ether, etc. They are basically non-corrosive, common materials are applicable, the specific selection should also be based on the media properties and related requirements to make a reasonable choice. It is also noteworthy that ketones, esters, ethers are soluble in a wide variety of rubbers and avoid mistakes when selecting sealing materials. 9. Saline (seawater) Ordinary steel in sodium chloride solution and seawater, salt water corrosion rate is not too high, the general need to use paint protection; various types of stainless steel also have a low uniform corrosion rate, but may be due to chloride ions caused by the local Corrosion, usually 316 stainless steel is better.
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