Teach you how to choose a fluorine-lined valve under corrosive medium conditions. Anti-corrosion is the most critical part of chemical equipment. If the metal material of chemical valve cannot be selected correctly, a little carelessness will damage the equipment at light level, and cause serious damage to the equipment. cause accidents or even disasters. According to relevant statistics, about 60% of the damage of chemical equipment is caused by corrosion. Therefore, when selecting chemical equipment, we must first pay attention to the scientific nature of material selection. There is usually a misunderstanding that stainless steel is a 'universal materialLet’s talk about the main points of material selection for some commonly used chemical media: 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. 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 better corrosion resistance, but it is not suitable for high-speed flowing sulfuric acid. Not suitable for pump and valve materials; ordinary stainless steel such as 304 (0Cr18Ni9) and 316 (0Cr18Ni12Mo2Ti) are also limited in use for sulfuric acid media. Therefore, the pumps and valves for conveying sulfuric acid are usually made of high-silicon cast iron (difficult to cast and process) and high-alloy stainless steel (20# alloy). Fluoroplastics have better resistance to sulfuric acid, and the use of fluorine-lined pump valves (F46) is a more economical choice. If the pressure is too large and the temperature rises, the use point of the plastic valve will be impacted, and you can only choose a ceramic ball valve
that is much more expensive than it. 2. Hydrochloric acid medium Most metal materials are not resistant to hydrochloric acid corrosion (including various stainless steel materials), and molybdenum-containing ferrosilicon can only be used for hydrochloric acid below 50°C and 30%. Contrary to metal materials, most non-metallic materials have good corrosion resistance to hydrochloric acid, so lined rubber pumps and plastic pumps (such as polypropylene, fluoroplastics, etc.) are the best choices for delivering hydrochloric acid. However, if the temperature of such a medium exceeds 150 °C or the pressure is greater than 16 kg, any plastic (including polypropylene, fluoroplastic and even PTFE) will not be able to do it, and there is currently no ideal valve on the market. , but you can try the emerging ceramic ball valve. The advantages of this valve are self-lubrication, low torque, no aging, and a much longer life than ordinary valves. Its disadvantage is that the price is much higher than that of plastic valves. . 3. Nitric acid medium 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 molybdenum-containing stainless steel ( Such as 316, 316L) corrosion resistance to nitric acid is not only not better than ordinary stainless steel (such as 304, 321), sometimes even worse. For high-temperature nitric acid, titanium and titanium alloy materials are usually used. 4. Acetic acid medium It is one of the most corrosive substances in organic acids. Ordinary steel will be seriously 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 at high temperatures. and dilute acetic acid vapor. For severe requirements such as high temperature and high concentration of acetic acid or other corrosive media, high alloy stainless steel or fluoroplastic pumps can be selected. 5. Alkali (sodium hydroxide) Steel is widely used in sodium hydroxide solution below 80 °C and 30% concentration, and many petrochemical plants still use ordinary steel when it is below 100 °C and 75%. Although corrosion increases, it is economical. Okay. Compared with cast iron, the corrosion resistance of ordinary stainless steel to lye has no obvious advantages. As long as a small amount of iron is allowed to be mixed into the medium, stainless steel is not recommended. For high-temperature lye, titanium and titanium alloys or high-alloy stainless steel are mostly used. 6. Ammonia (ammonium hydroxide) Most metals and non-metals corrode slightly in liquid ammonia and ammonia water (ammonium hydroxide), only copper and copper alloys should not be used. 7. Chlorine gas (liquid chlorine) Most metal valves have limited resistance to chlorine gas corrosion, especially in the case of chlorine gas with water, including various alloy valves. In this case, tetrafluoro valve is a very good choice. However, chemical plants that produce chlor-alkali will find that the tetrafluoro valve takes a little longer, the torque increases, and the problem of tetrafluoro aging will become prominent, and the leakage that occurs in this case is fatal. It can be considered to replace the original ordinary PTFE lined valve with PTFE lined ceramic ball core, and the self-lubricating property of ceramics and the corrosion resistance of PTFE will have a perfect effect. 8. Salt water (sea water) The corrosion rate of ordinary steel in sodium chloride solution, seawater and salt water is not very high, and generally needs to be protected by paint; all kinds of stainless steel also have a low uniform corrosion rate, but localized corrosion may be caused by chloride ions. Corrosion, usually 316 stainless steel is better. 9. Alcohols, ketones, esters, ethers are common alcohol media such as methanol, ethanol, ethylene glycol, propanol, etc., ketone media include acetone, butanone, etc., ester media include various methyl esters, Ethyl ester, etc., ether-based media include methyl ether, ether, butyl ether, etc., which are basically non-corrosive, and commonly used materials can be applied. The specific selection should also be based on the properties of the medium and relevant requirements. Make a reasonable choice. It is also worth noting that ketones, esters, and ethers are soluble in many rubbers, so avoid mistakes when choosing sealing materials.
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