Material selection for common chemical media in diaphragm pumps

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Corrosion is one of the biggest threats to chemical processing equipment; therefore, it is crucial for chemical companies to decide on the appropriate material for diaphragm pumps used to transport fluids. Hence, when selecting diaphragm pumps for use in chemical applications, attention must first be paid to the scientific choice of materials. 1. Sulfuric acid: The corrosion effect of sulfuric acid varies significantly depending on 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 is flowing at high speeds. Materials are not suitable for use in pumps and valves; common stainless steels such as 304 (OCr18Ni9) and 316 (OCr18Ni12M32Ti) also have limited applicability in sulfuric acid environments. 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). Fluoroplastics exhibit good resistance to sulfuric acid, so the use of fluoroplastic-lined diaphragm pumps represents an economical option. 2. Hydrochloric acid: The vast majority of metal materials are not resistant to corrosion by hydrochloric acid (including various stainless steel grades); even high-silicon iron can only be used with hydrochloric acid at temperatures below 500°C and concentrations of less than 30%. Unlike metal materials, the vast majority of non-metallic materials exhibit good corrosion resistance to hydrochloric acid; therefore, rubber-lined pumps and plastic pumps (such as polypropylene (PP), fluoroplastics, etc.) are the best choices for transporting hydrochloric acid. 3. Nitric acid: Most metals are rapidly corroded and damaged in slightly acidic environments, while stainless steel is the most widely used material resistant to acids, offering good corrosion resistance to nitric acid at all concentrations at room temperature. For high-temperature nitric acid, Qin and its alloy materials are commonly used. 4. Acetic acid: It 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, which contains certain phases, 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 diaphragm pumps or fluoroplastic diaphragm pumps can be used. 5. Alkalis (sodium nitrite): Steel is widely used in sodium nitrite solutions at temperatures below 80°C and with concentrations of up to 30%; for high-temperature alkaline solutions, titanium and titanium alloys or highly alloyed stainless steels are preferred. 6. Ammonia: Most metals and non-metals can be used, but copper and its alloys are not suitable. 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 a low rate of uniform corrosion, but local corrosion may occur due to chloride ions, so 316 stainless steel is usually the better choice. 8. Alcohols, ketones, acetates, and ethers. Common alcohol-based media include methanol, ethanol, ethylene glycol, propanol, etc.; ketone-based media include propionone, butyronone, etc.; acetate-based media include various methyl acetates, ethyl acetates, 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 and relevant requirements in order to make a suitable choice.