Pump material selection principle

Update:15-06-2019
Summary:

How to choose and how to choose the pump material has b […]

How to choose and how to choose the pump material has become the most important issue in the chemical industry. There is usually a misunderstanding that stainless steel is a versatile material, and stainless steel can be used regardless of the medium and environmental conditions. It is very risky to do so, but it will cause transaction disputes and serious accidents. Listed below are several common chemical media and their selection
1. Hydrochloric acid. Most metal materials are not resistant to hydrochloric acid corrosion. When the concentration of hydrochloric acid is relatively high, all kinds of stainless steel materials can not withstand corrosion. The high-silicon iron containing molybdenum can only be used for hydrochloric acid at 50 ° C and 30%. Contrary to metal materials, most non-metallic materials have good corrosion resistance to hydrochloric acid, so rubber pumps and plastic pumps (such as polypropylene, fluoroplastics, etc.) are the best choice for transporting hydrochloric acid.
2. Sulfuric acid. As one of the strong corrosive media, sulfuric acid is an important industrial raw material with a wide range of uses. Different concentrations and temperatures of sulfuric acid have a great difference in corrosion of materials. For concentrated sulfuric acid with a concentration above 80% and temperature less than 80 °C, carbon steel and cast iron have good corrosion resistance, but it is not suitable for high-speed flowing sulfuric acid. Therefore, pump steel materials are not suitable for carbon steel and cast iron; even ordinary stainless steels such as 304 and 316 have limited use of sulfuric acid media. Therefore, pump valves for transporting sulfuric acid are usually made of high-silicon cast iron or high-alloy stainless steel, No. 20 alloy, but they are difficult to cast and process. Fluoroplastics have better sulfuric acid resistance, and the use of a fluorine-lined pump is a more economical option.
3. Nitric acid. As a kind of acid with strong oxidizing property, most metals are mostly destroyed by rapid corrosion in nitric acid. At room temperature, fluoroplastics and stainless steel materials have strong corrosion resistance to nitric acid. It is worth noting that stainless steel containing molybdenum (such as 316, 316L) The corrosion resistance to nitric acid is not only not superior to ordinary stainless steel (such as 304, 321), and sometimes even worse. For high temperature nitric acid, titanium and titanium alloy materials are usually used.
4. Acetic acid It is one of the most corrosive substances in organic acids. Ordinary steel is severely corroded in acetic acid of all concentrations and temperatures. Stainless steel is an excellent acetic acid resistant material. Molybdenum-containing 316 stainless steel can also be used for high temperature and Dilute acetic acid vapor. High-alloy stainless steel or fluoroplastic pumps are available for demanding requirements such as high temperature, high concentration acetic acid or other corrosive media.
5. Alkali. A common chemical base is sodium hydroxide. Sodium hydroxide solution below 80 ° C and 30% concentration can be made of steel. Many factories still use ordinary steel at 100 ° C and below 75%. Although the corrosion is increased, the economy is good. The corrosion resistance of ordinary stainless steel to lye has no obvious advantages compared with cast iron. Stainless steel is not recommended as long as a small amount of iron is allowed in the medium. For high-temperature alkaline liquids, titanium and titanium alloys or high-alloy stainless steels are often used. Generally, cast iron pumps can be used for low temperature alkali liquor at normal temperature. For special requirements, various chemical glass steel pumps, chemical plastic pumps, PTFE magnetic pump stainless steel magnetic pumps, fluorine plastic magnetic pumps, high temperature magnetic pumps, etc. can be used.
6. Ammonia (ammonium hydroxide) Most metals and non-metals are slightly corrosive in liquid ammonia and ammonia (ammonium hydroxide). Only copper and copper alloys should not be used.
7. Alcohols, ketones, esters, etc. Common alcohols such as methanol, ethanol, ethylene glycol, propanol, etc.; ketones such as acetone, methyl ethyl ketone, etc.; esters such as methyl esters, ethyl esters, etc., which are basically non-corrosive, generally common materials, but It is best to use stainless steel for cleaning; it is also worth noting that ketones and esters have solubility in a variety of rubbers, and should be noted when selecting machine sealing materials.
8. Salt water and sea water. For mediums such as seawater, the corrosion rate of ordinary steel in sodium chloride solution and seawater and salt water is not too high, and it is generally required to be protected by paint; all kinds of stainless steel also have a low uniform corrosion rate, but may cause locality due to chloride ions. Corrosion, usually 316 stainless steel material is better.

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