Material selection for common acid and alkali medium pumps

Thread Content

1. Sulfuric acid, as one of the highly corrosive substances, causes varying degrees of corrosion in materials depending on its concentration and temperature. 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, it is not suitable for sulfuric acid that flows at high speeds, and it cannot be used as material for pumps and valves； Ordinary stainless steels such as 304 and 316 have limited applicability in sulfuric acid environments; stainless steel multi-stage pumps used for transporting sulfuric acid are typically made of high-silicon cast iron (which is difficult to cast and process) or highly alloyed stainless steel (grade 20 alloy). Fluoroplastics exhibit good resistance to sulfuric acid, making the use of fluorinated-lined pumps (F46) a more economical option. 2. Hydrochloric acid: The vast majority of metal materials are not resistant to corrosion by hydrochloric acid (including various stainless steel materials); high-molybdenum high-silicon iron can only be used in hydrochloric acid at temperatures below 50°C and concentrations of 30% or less. Unlike metal materials, the vast majority of non-metallic materials exhibit good corrosion resistance to hydrochloric acid; rubber-lined pumps and plastic pumps (such as polypropylene, fluoroplastics, etc.) are excellent choices for transporting hydrochloric acid. 3. Nitric acid: Most metals are rapidly corroded and damaged by nitric acid. Stainless steel is a widely used material resistant to nitric acid; it exhibits good corrosion resistance to 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), and in some cases their resistance is even lower. For high-temperature nitric acid, titanium and titanium alloy materials are typically used. 4. Acetic acid: Ordinary steel is severely corroded in acetic acid at all concentrations and temperatures; stainless steel is a better 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 vapor. For demanding applications such as high-temperature, high-concentration acetic acid or environments containing other corrosive substances, high-alloy stainless steel pumps or fluoroplastic pumps can be used. 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 ammonium hydroxide; only copper and its alloys are not suitable for use. 7. Saltwater (seawater): Ordinary steel exhibits 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. Organic media (alcohols, similar compounds, esters, ethers): They are virtually non-corrosive, and most common materials can be used for them; however, a reasonable choice should be made based on the properties of the medium and relevant requirements. It is also worth noting that alcohols, esters, and ethers are soluble in various types of rubber; therefore, special attention must be paid to the selection of sealing materials for stainless steel multi-stage pumps.