Corrosion has always been one of the most troublesome hazards of chemical equipment, the slightest inadvertence, light damage to equipment, serious accidents, or even lead to disaster. According to statistics, about 60% of the damage to chemical equipment is caused by corrosion. A large number of different equipment combinations are required each year globally in the manufacturing and handling process to address complex needs, and this includes pumps. Today we will discuss the selection of materials for chemical pumps
Chemical pumps are designed and manufactured from materials that can withstand varying degrees of viscosity, corrosiveness and abrasive substances. These substances require pumps that can handle them effectively without causing production downtime or pump failure. Before selecting a chemical pump, you need to have a firm grasp of the application requirements and chemical media properties and choose different materials based on the different media
Sulfuric acid is one of the strong corrosive media, sulfuric acid is a widely used and important industrial raw material. Different concentrations and temperatures of sulfuric acid on the corrosion of materials vary greatly, for concentrations of more than 80%, the temperature is less than 80 ℃ of concentrated sulfuric acid, carbon steel and cast iron have good corrosion resistance, but it is not suitable for high-speed flow of sulfuric acid, not suitable for pump and valve materials; ordinary stainless steel such as 304 (0Cr18Ni9), 316 (0Cr18Ni12Mo2Ti) for the use of sulfuric acid media is also very limited. Therefore, pump valves for conveying sulfuric acid are usually made of high silicon cast iron (casting and processing difficulties), and high alloy stainless steel (20 alloys). Fluorine plastic has good resistance to sulfuric acid, and the use of fluoroplastic centrifugal pumps is a more economical choice.
Hydrochloric acid most metal materials are not resistant to hydrochloric acid corrosion (including a variety of stainless steel), molybdenum high ferrosilicon can only be used for 50 ℃, hydrochloric acid below 30%. In contrast to metallic materials, the vast majority of non-metallic materials have good corrosion resistance to hydrochloric acid, so lined rubber pumps and plastic pumps (such as polypropylene, fluoroplastic, etc.) are the best choices for the delivery of hydrochloric acid.
Nitric acid Most metals are mostly corroded 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 ambient temperature. It is worth mentioning that stainless steel contains molybdenum (such as 316, 316L) The corrosion resistance of nitric acid is not only not superior to ordinary stainless steel (such as 304,321), but sometimes even worse. For high-temperature nitric acid, usually titanium and titanium alloy materials.
Acetic acid is one of the most corrosive substances in organic acids. Ordinary steel is 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 thinning Acetic acid steam. For high temperature and high concentration of acetic acid or other corrosive media and other harsh requirements, the choice of high alloy stainless steel pump or fluorine plastic pump.
Alkali (sodium hydroxide) steel is widely used in sodium hydroxide solution below 80 ℃, 30% concentration, there are many factories at 100 ℃, 75% below the ordinary steel is still used, although the corrosion increased, the economy is good. Ordinary stainless steel lye corrosion resistance and cast iron compared with no obvious advantages, as long as the medium allows a small amount of iron content is not recommended for incorporation of stainless steel. For high-temperature alkaline use titanium and titanium alloy or high alloy stainless steel.
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.
Brine (seawater) Common steel corrosion rate in sodium chloride solution and seawater, saltwater is not too high, the general shall be used paint protection; all kinds of stainless steel also have a low uniform corrosion rate, but maybe due to chloride ions caused by localized corrosion, Usually 316 stainless steel is better.
Alcohols, ketones, esters, and others are common alcohol mediums with methanol, ethanol, ethylene glycol, propanol, ketones have acetone, butanone, etc., ester medium has a variety of methyl ester, B Esters, ethers medium ether, ether, butyl ether, etc. They are basically non-corrosive, common materials are applicable, and the specific selection should be based on the media properties and related requirements to make a reasonable choice. It is also noteworthy that ketones, esters, and ethers are soluble in a wide variety of rubbers and avoid mistakes when selecting sealing materials.
