In the corrosive media conditions of the valve, anti-corrosion is the most damaging chemical equipment, local, if you can not properly select the chemical valve metal material, a little careless, ranging from damage to equipment, weight, but the event even lead to disaster. According to the calculation, about 60% of chemical equipment damage is caused by corrosion, so the selection of chemical equipment, the first to pay attention to the scientific selection. There is a general misunderstanding that stainless steel is "all-round material", no matter what the media and environmental conditions are out of stainless steel, which is not correct, but also very dangerous. The following for some common chemical media to talk about the key ingredients: 1. Sulfuric acid medium: As a strong corrosive medium, sulfuric acid is a very broad use of important industrial raw materials. Different concentration and temperature of sulfuric acid on the corrosion of different materials, the concentration of more than 80%, the temperature is less than 80 ℃ concentrated sulfuric acid, carbon steel and cast iron has better corrosion resistance, but it is not suitable for high-speed flow of sulfuric acid , Does not apply as a valve material; general stainless steel, such as 304 (0Cr18Ni9), 316 (0Cr18Ni12Mo2Ti) sulfuric acid medium is also limited use. Therefore, the delivery of sulfuric acid pump valve generally use high-silicon cast iron (forging and machining difficult), high alloy stainless steel (20 alloy) production. Fluorine plastic has better resistance to sulfuric acid function, the selection of fluorine valve (F46) is a more economical choice. 2. Hydrochloric acid medium: Most of the metal materials are not resistant to hydrochloric acid corrosion (including a variety of stainless steel), molybdenum high ferrosilicon can only be used at 50 ℃, 30% hydrochloric acid. In contrast to metallic materials, most non-metallic materials have excellent corrosion resistance to hydrochloric acid, so lined rubber pumps and plastic pumps (such as polypropylene, fluoroplastic, etc.) are the best picks for transporting hydrochloric acid. 3. Nitric acid medium: most of the common metals are agile nitric acid corrosion damage, stainless steel is the most widely used nitric acid materials, all concentrations of nitric acid at room temperature have excellent corrosion resistance, it is worth mentioning that the stainless steel containing molybdenum (Such as 316,316 L) nitric acid corrosion resistance not only not better than the average stainless steel (such as 304,321), sometimes even worse. For high-temperature nitric acid, titanium and titanium alloy materials are generally used.
4. Acetic acid medium: It is one of the most corrosive substances in organic acids. Generally, 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 Wen dilute acetic acid steam. For high temperature and high concentration of acetic acid or rich in other corrosive media and other demanding 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 plants at 100 ℃, 75% below the general use of steel is still selected, although the addition of corrosion, but the economy Good sex. General corrosion resistance of stainless steel lye and cast iron compared with no obvious strengths, as long as the medium allows a small number of iron incorporation, stainless steel is not recommended. On the choice of high temperature lye titanium and titanium alloy or perhaps high alloy stainless steel. 6. Ammonia (ammonia hydroxide): Most metals and non-metals in liquid ammonia and ammonia (ammonia hydroxide) corrosion are subtle, as long as copper and copper alloy should not be used. 7. Saline (seawater): The general steel corrosion rate in sodium chloride solution and seawater, salt water is not too high, generally need to use paint maintenance; all kinds of stainless steel also have a low uniform corrosion rate, but may be due to chloride ions and lead to local Sexual corrosion, the general selection of 316 stainless steel is better. 8. alcohols, ketones, esters, ethers: more common alcohol medium with methanol, ethanol, ethylene glycol, propanol, ketones have acetone, butanone and so on, there are a variety of ester media Esters, ethyl esters ethers, ethers medium ether, ether, butyl ether, etc., they basically no corrosive, commonly used materials are applicable, the specific selection should be based on the characteristics of the media and the request to make a reasonable choice. It is also noteworthy that ketones, esters, ethers are soluble in a wide variety of rubbers and are safeguards against mistakes when selecting sealing materials. There are many other media can not be introduced one by one in this article, in short, should not be arbitrary and blind selection of materials, should consult the materials or more mature learning experience.
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