Corrosion is always one of the most serious hazards for chemical pump, if you are careless, it will not only damage pump, but lead to huge disaster.According to relevant statistics, about 60% of the destruction of chemical equipment is caused by corrosion, so you should pay attention to the scientific selection of materials in the chemical pump selection.
There is usually a misunderstanding that stainless steel is "all-purpose material", no matter what medium and environmental conditions are holding out the stainless steel pump, this is very dangerous.The following are some common chemical liquid suggestions of materials selections:
1.Sulphuric acid as one of the highly corrosive media, and it is an important industrial raw material with a very wide range of usage. Corrosion of different concentration and temperature of sulfuric acid on the material difference is bigger, the concentration is above 80%, the temperature is less than 80 ℃ concentrated sulfuric acid, carbon steel and cast iron has good corrosion resistance, but it is not suitable for high-speed flow of sulfuric acid, is not used as a pump valve materials. Common stainless steel such as SS304 (0Cr18Ni9), SS316 (0Cr18Ni12Mo2Ti) for sulfuric acid medium also limited use.
Therefore, the delivery of sulfuric acid pump valve is usually made of high silicon cast iron (casting and processing difficult), high alloy stainless steel (no. 20 alloy).Fluoroplastic has better sulfuric acid resistance, using fluorine pump (F46) is a more economical choice.
2. General metal corrosion and damage, mostly in nitric acid was quickly is the most widely used nitric acid resistant stainless steel material, all to room temperature the concentration of nitric acid have good corrosion resistance, it is important to note that the molybdenum stainless steel (e.g., SS316, SS316L) of nitric acid corrosion resistance not only no better than ordinary stainless steel (e.g., SS304, SS321), sometimes even less. For high temperature nitric acid, usually titanium and titanium alloy materials.
3. Most general metal nitrate was rapidly in nitric acid corrosion damage, stainless steel is the most widely used of nitric acid resistant material, all the concentration of nitric acid for room temperature has good corrosion resistance, it is worth mentioning the molybdenum stainless steel (e.g., SS316, SS316L) of nitric acid corrosion resistance not only no better than ordinary stainless steel (e.g., SS304, SS321), sometimes even less. For high temperature nitric acid, usually titanium and titanium alloy materials.
4.Acetic acid is one of the most corrosive substances of organic acid, ordinary steel in all concentration and temperature of acetic acid will seriously corrosion, stainless steel is a good acetic acid resistant material, molybdenum-containing 316 stainless steel is also suitable for high temperature and dilute acetic acid vapor.
For high temperature high concentration acetic acid or contain other corrosive medium such as demanding, can choose high alloy stainless steel pump or fluoroplastic pump.
⒌ Alkali (sodium hydroxide) steel is widely used in under 80 ℃, 30% concentration of sodium hydroxide solution, there are also many factory under 100 ℃, 75% still USES the ordinary steel, while the corrosion increases, but the economy better.
The corrosion resistance of ordinary stainless steel to lye has no obvious advantages over cast iron, and stainless steel is not recommended as long as a small amount of iron is allowed in the medium. For the high temperature lye mostly titanium and titanium alloy or high alloy stainless steel.
6.Pictures of ammonia (ammonia hydroxide) most of the metal and non-metal in liquid ammonia and ammonia (ammonia hydroxide) corrosion is very small, only copper and copper alloy is not suitable for use.
7.Ordinary steel has not high corrosion rate in sodium chloride solution, sea water and salt water, so it must be protected by paint generally; All kinds of stainless steel also have very low uniform corrosion rate, but may cause local corrosion due to chloride ions, usually SS316 stainless steel is better.
⒏ alcohols, esters, ketones, ethers, common alcohol medium such as methanol, ethanol, ethylene glycol, propylene glycol, ketone medium such as acetone, butanone, there are all kinds of methyl esters medium, ethyl ester, ethers media such as methyl ether, ethyl ether, butyl ether, their basic no corrosive, commonly used materials are applicable, the specific selection should also according to the requirements of the dielectric properties and related make reasonable choice.
It is also worth noting that ketone, ester, ether on a variety of rubber solubility, to avoid errors in the selection of sealing materials.
