Corrosion has always been one of the most headache hazards of chemical equipment. A little carelessness can damage the equipment, or cause an accident or even a disaster.
According to relevant statistics, about 60% of the damage of chemical equipment is caused by corrosion. Therefore, when selecting a chemical pump, it is necessary to pay attention to the scientific nature of the material selection.
There is usually a misunderstanding that stainless steel is a “universal material”. It is very dangerous to take out stainless steel regardless of the medium and environmental conditions. The following EVP Vacuum talks about the key points of material selection for some common chemical media:
Sulfuric acid
As one of the strong corrosive media, sulfuric acid is an important industrial raw material with a wide range of uses.
The corrosion of sulfuric acid with different concentrations and temperatures is quite different. For concentrated sulfuric acid with a concentration of more than 80% and a temperature of less than 80℃, carbon steel and cast iron have good corrosion resistance, but it is not suitable for high-speed flowing sulfuric acid. It is not suitable for use as a material for pump valves; ordinary stainless steels such as 304 (0Cr18Ni9) and 316 (0Cr18Ni12Mo2Ti) have limited use for sulfuric acid media.
Therefore, when transporting sulfuric acid-containing steam, EVP liquid ring vacuum pumps usually choose all-titanium materials, and the seal chooses double-end mechanical seals.
Hydrochloric acid
Most metal materials are not resistant to hydrochloric acid corrosion (including various stainless steel materials), and high-silicon ferro-molybdenum can only be used for hydrochloric acid below 50°C and 30%.
Contrary to metal materials, most non-metal materials have good corrosion resistance to hydrochloric acid, so when transporting steam containing hydrochloric acid, some customers will choose to line rubber pumps and plastic pumps (such as engineering plastics, fluoroplastics, etc.) to save money cost. However, in the long run, titanium EVP liquid ring vacuum pumps and double mechanical seals are the best solution.
Nitric acid
Most metals are quickly corroded and destroyed in nitric acid. Stainless steel is the most widely used nitric acid resistant material. It has good corrosion resistance to all concentrations of nitric acid at room temperature. It is worth mentioning that stainless steels containing molybdenum (such as 316, 316L) ) The corrosion resistance to nitric acid is not only not better than ordinary stainless steel (such as 304, 321), and sometimes even worse. EVP VACUUM recommends directly choosing titanium material and a liquid ring vacuum pump solution with double mechanical seals.
Ammonia (Ammonia Hydroxide)
Most metals and non-metals have slight corrosion in alkali, liquid ammonia and ammonia (ammonium hydroxide). Only copper and copper alloys are not suitable for use. For example, vacuum pumps made of stainless steel SS304 and SS316 can be selected;
Brine (sea water)
Ordinary steel has a low corrosion rate in sodium chloride solution, sea water and salt water, and generally must be protected by paint; various types of stainless steel also have a very low uniform corrosion rate, but may cause local corrosion due to chloride ions, usually 316 stainless steel better.
For long-term considerations, EVP VACUUM recommends directly choosing titanium material and a liquid ring vacuum pump solution with double mechanical seals.
Alcohols, ketones, esters, ethers
Common alcohol media include methanol, ethanol, ethylene glycol, propanol, etc., ketone media include acetone, butanone, etc., ester media include various methyl and ethyl esters, and ether media include methyl ether, ethyl ether, etc. Butyl ether, etc., are basically not corrosive, so ordinary stainless steel can be used, and a reasonable choice should be made according to the properties of the medium and related requirements when selecting it. It is also worth noting that ketones, esters, and ethers are soluble in a variety of rubbers, so errors should be avoided when selecting sealing materials.
EVP oil-free dry screw vacuum pump /system is undoubtedly the best vacuum pump in the alcohol, ketone, ester, and ether industry applications. The flow parts are made of Harbin alloy nickel-plated and coated with nickel and phosphorus, which is clean and quiet, and has received unanimous praise from many customers.
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