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According to relevant statistics, approximately 60% of chemical equipment damage is caused by corrosion. Therefore, the scientific nature of material selection should be paid attention to in the selection of chemical equipment. People often misunderstand that stainless steel is invincible. No matter what medium or environmental conditions, stainless steel is held in their arms. This is both incorrect and dangerous.

The following talks about the selection points of some commonly used chemical media, such as sulfuric acid media, hydrochloric acid media, nitric acid media, acetic acid media, alkali (sodium hydroxide), ammonia (ammonium hydroxide), chlorine (liquid chlorine), brine (seawater), alcohol , Ketones, esters, ethers, etc.

One, sulfuric acid medium.

Sulfate is a strong corrosive medium, and sulfuric acid is an important industrial raw material that is widely used. The corrosiveness of sulfuric acid to materials at different concentrations and temperatures varies greatly. For concentrated sulfuric acid with a concentration above 80% and a temperature below 80°C, carbon steel and cast iron are more corrosive, but low temperature solenoid valves are not suitable for high-speed flow For sulfuric acid medium, general stainless steel such as 304 (0Cr18Ni9), 316 (0Cr18Ni12Mo2Ti), etc. are also limited in use. Therefore, the pump valve for transporting sulfuric acid generally uses high-silicon cast iron (difficult to cast and process) and high-alloy stainless steel (alloy 20). Fluoroplastic materials have good resistance to sulfuric acid, so it is more economical to use a fluorine-lined pump valve (F46). If the pressure is too high and the temperature is too high, the point of use of the plastic valve will be impacted, and the only choice is the ceramic ball valve, which is more expensive than the hydraulic solenoid valve.

The second is hydrochloric acid medium.

Most metal materials are not resistant to hydrochloric acid corrosion (including various stainless steels), and ferrosilicon containing molybdenum can only be used in hydrochloric acid at 50°C and less than 30%. Contrary to metal materials, most non-metal materials have good corrosion resistance to hydrochloric acid. Therefore, lined rubber pumps and plastic pumps (such as polypropylene and fluoroplastics) are the best choices for transporting hydrochloric acid. However, if the temperature of this medium exceeds 150°C, or the pressure is greater than 16 kg, any plastic (including polypropylene, fluoroplastics, and even polytetrafluoroethylene) cannot be used. There is currently no ideal valve on the market, but You can try the ceramic ball valve that appears now. The advantage of this valve is that it is self-lubricating, has low torque, does not age, and has a much longer life than ordinary valves. The disadvantage is that its price is much more expensive than plastic valves.

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