How should acid and alkali resistant pump models be selected based on the medium to be transported?

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Corrosive liquids commonly used in the chemical industry, such as sulfuric acid, nitric acid, hydrochloric acid, hydrobromic acid, and hydriodic acid, require pumps made of different materials for transporting various liquid media. If the appropriate chemical pump is not selected, corrosion can easily occur. Once a chemical pump is corroded, it can no longer be used. ZL Pump Industry has compiled a list of pump options suitable for common corrosive liquids; this should help people make the right choice when selecting acid- and alkali-resistant chemical pumps. 1. Analysis in hydrochloric acid medium: The selection of hydrochloric acid pumps depends on the type of hydrochloric acid, with pumps of different configurations being chosen accordingly. The common order of metal reactivity in terms of hydrochloric acid corrosion is: potassium, sodium, calcium, magnesium, aluminum, zinc, iron, tin, lead, (hydrogen), copper, mercury, silver, platinum, gold. The further forward, the more reactive they are; those in front of hydrogen are those that can react with hydrogen. Therefore, when choosing a hydrochloric acid pump, pumps made of metallic materials (iron-based) should not be used; austenitic stainless steels such as 304 and 316L can also suffer from intergranular corrosion in media containing chloride ions. Special metal materials are also used, such as Hastelloy, but they are extremely expensive; therefore, when choosing a hydrochloric acid pump, it is advisable to opt for ones whose flow-through components are made of fluoroplastic, as this offers both cost efficiency and safety. ①If there are hard particles in the hydrochloric acid (waste hydrochloric acid from the pickling process), filtration is necessary. When selecting a centrifugal pump, it is important to use a mechanical seal of the SIC-on-SIC type, which ensures proper operation of the mechanical seal even when the waste hydrochloric acid is not filtered thoroughly. ②For pure hydrochloric acid without particulates, a centrifugal pump or magnetic pump can be chosen. The vast majority of non-metallic materials exhibit good corrosion resistance to hydrochloric acid; therefore, rubber-lined pumps and plastic pumps (such as engineering plastics and fluoroplastics) are the best choices for transporting hydrochloric acid. The company’s applicable products include: CQB type fluoroplastic leak-proof acid-resistant pumps, CQF engineering plastic magnetic pumps (or fluoroplastic magnetic pumps), etc. 2. Analysis in nitric acid medium: Most metals are rapidly corroded and damaged in nitric acid. Stainless steel is the most widely used material resistant to nitric acid, exhibiting good corrosion resistance against nitric acid at all concentrations at room temperature. It is worth noting that stainless steels containing molybdenum (such as 316 and 316L) do not have better corrosion resistance to nitric acid than ordinary stainless steels (such as 304 and 321); in some cases, their resistance is even lower. For high-temperature nitric acid, titanium and titanium alloy materials are typically used. Concentrated nitric acid contains approximately 65% HNO3, has a density of 1.4 g/cm3, and possesses a strong pungent odor as well as corrosive properties. It is a strong oxidizing agent that can react with almost all metals, but not with fluoroplastic materials. Therefore, using fluoroplastic pumps for transporting nitric acid is both economical and durable. The nitric acid transfer pumps we recommend are suitable in the following situations: 1) For 98% concentrated nitric acid, the IHF type fluoroplastic centrifugal pump can be chosen. The flow-through components of this series of pumps are all made of fluoroplastic (perfluoroethylene propylene), and the mechanical seal is a bell-type mechanical seal with a fill material of tetrafluoride installed on the outside, which effectively prevents leaks of concentrated nitric acid. The power of the motor required should be slightly increased; this value can be determined by calculating the shaft power needed for transporting concentrated nitric acid based on the pump’s rated shaft power. 2) For dilute nitric acid with a low concentration, a leak-free CQB (magnetic drive centrifugal pump), namely a fluoroplastic magnetic drive pump, can be chosen. These pumps utilize magnetic drive and are leak-free; they are designed specifically for transporting highly corrosive fluids such as nitric acid, sulfuric acid, and hydrochloric acid. 3. Sulfuric acid, as one of the strong corrosive agents, is an important industrial material with a very wide range of applications. Pump types used for transporting sulfuric acid include fluoroplastic centrifugal pumps, fluoroplastic magnetic pumps, and fluoroplastic self-priming pumps. Sulfuric acid of different concentrations and temperatures has varying degrees of corrosive effect on materials; for concentrated sulfuric acid with a concentration of over 80% and a temperature below 80°C, carbon steel and cast iron exhibit good corrosion resistance. However, they are not suitable for sulfuric acid flowing at high speeds, and thus cannot be used as materials for pumps and valves ； Common stainless steels such as 304 (0CR18NI9) and 316 (0CR18NI12MO2Ti) also have limited utility in sulfuric acid media. Therefore, pump valves for transporting sulfuric acid are usually made of high-silicon cast iron (which is difficult to cast and process) or highly alloyed stainless steel (grade 20 alloy), but their difficulty in processing and high cost render them less attractive. Fluoroplastic alloys exhibit excellent resistance to sulfuric acid; no chemical agents have been found to react with them within the applicable temperature range. Therefore, using fluorinated pump materials (F46) is a more economical choice. Applicable products include: CQB fluoroplastic magnetic pump, IMD fluoroplastic magnetic pump, IHF fluoroplastic centrifugal pump, FSB fluoropolymer alloy centrifugal pump, etc. 4. Acetic acid is one of the most corrosive organic acids; ordinary steel suffers severe corrosion in acetic acid at all concentrations and temperatures. Stainless steel is an excellent material resistant to acetic acid, and 316 stainless steel containing molybdenum can also be used in high-temperature environments as well as with dilute acetic acid vapors. For demanding applications such as high-temperature, high-concentration acetic acid or environments containing other corrosive substances, high-alloy stainless steel or fluoroplastic pumps can be used. Nitric acid and acetic acid have some similar properties, but it is not possible to make generalizations when selecting fluoroplastic pump types. Whether to choose a fluoroplastic centrifugal pump, a fluoroplastic magnetic pump, or a fluoroplastic self-priming pump, etc., it is still necessary to select the most suitable model based on the actual production environment of the enterprise. For example, in some environments a high head is required; in our cases the highest required head has been 300 meters. There are also situations where the pump is expected to have insulation capabilities. Therefore, the selection of fluoroplastic pumps must be done carefully and thoughtfully based on actual conditions. 5. Alkalis (sodium hydroxide): Steel is widely used in sodium hydroxide solutions at temperatures below 80°C and concentrations up to 30%. Many factories still use ordinary steel at temperatures of 100°C and concentrations below 75%; although corrosion increases, it remains cost-effective. Ordinary stainless steel does not have a significant advantage over cast iron in terms of corrosion resistance to alkaline solutions; it is not recommended to use stainless steel as long as a small amount of iron can be tolerated in the medium. For high-temperature alkaline solutions, titanium and titanium alloys or highly alloyed stainless steels are commonly used. 6. Ammonia (ammonium hydroxide): Most metals and non-metals suffer only mild corrosion in liquid ammonia and ammonia water (ammonium hydroxide); only copper and its alloys are not suitable for use. 7. Saltwater (seawater): Ordinary steel experiences a low rate of corrosion in sodium chloride solutions as well as in seawater and brackish water; coating protection is generally required ； Various types of stainless steel also have very low uniform corrosion rates, but local corrosion may occur due to chloride ions; therefore, 316 stainless steel is generally the better choice. 8. Common materials chosen for hydrogen fluoride transfer pumps: Magnesium (Mg): An ideal corrosion-resistant material for hydrogen fluoride, generally used only for containers ； Titanium: Suitable for concentrations of 60–100% (at room temperature); the corrosion rate increases at concentrations below 60% ； Monel alloy: It is an excellent material resistant to hydrofluoric acid, and it can withstand all temperatures and all concentrations (including the boiling point) ； Silver (Ag): Boiling hydrofluoric acid, commonly used in metering devices. 9. Alcohols, alkanes, esters, and ethers. Common alcohol-based media include methanol, ethanol, ethylene glycol, propanol, etc.; alkanes include propane, butane, etc.; ester-based media comprise various methyl esters, ethyl esters, etc.; ether-based media include methyl ether, ethyl ether, butyl ether, etc. These substances generally have no corrosive properties, and most common materials can be used with them. When making a selection, it is necessary to consider the properties of the medium as well as relevant requirements in order to make a proper choice. It is also worth noting that alcohols, esters, and ethers are soluble in various rubbers, which helps to avoid mistakes when selecting sealing materials. There are many other media that cannot be introduced one by one here.