Evaporator manufacturers believe that there is no universal valve in the world. Only carefully selected valves can adapt to certain materials. The following is a brief introduction to the materials suitable for various common valves.
1. Cast iron valve: suitable for water, steam, petroleum products, ammonia and most of the less corrosive media such as alcohol, aldehyde, ether, ketone, ester and so on. It is not suitable for hydrochloric acid, nitric acid and other media, but it can be used in concentrated sulfuric acid, because the concentrated sulfuric acid produces a passivation film on its metal surface, which prevents the corrosion of concentrated sulfuric acid to cast iron.
Silicon cast iron valve has strong corrosion resistance and can work well in all concentrations of sulfuric acid, nitric acid, phosphoric acid and acid salt. However, it is not resistant to the corrosion of hydrofluoric acid, strong alkali, hydrochloric acid and hot solution of iron oxide. When using, avoid rapid heat and rapid cooling, otherwise it will explode.
Nickel cast iron valve, which has higher alkali resistance than ordinary cast iron, is used in dilute sulfuric acid, dilute hydrochloric acid and caustic alkali.
2. Carbon steel valve: The corrosion resistance of carbon steel valve is similar to that of gray cast iron, slightly inferior to that of gray cast iron.
3. Stainless steel valve: Stainless steel valve is resistant to nitric acid and other oxidizing media, as well as intestinal corrosion of alkali, water, salt, organic acid and other organic compounds. However, it is not resistant to corrosion by non-oxidizing acids such as sulfuric acid and hydrochloric acid, nor is it resistant to non-drying hydrogen hydride, oxidizing cyanides, and organic acids such as oxalic acid and lactic acid.
Stainless steel containing platinum has better corrosion resistance than grid nickel stainless steel. It has better corrosion resistance than chrome-nickel stainless steel in non-peony acid and hot organic acid and chloride, and has better pitting corrosion resistance.
Stainless steel containing high chromium and high nickel, such as chromium 20 nickel 22-30 stainless steel, has higher corrosion resistance than ordinary stainless steel, and can be used to treat sulfuric acid, phosphoric acid, sulfuric acid, sulfurous acid, organic acid, alkali, salt solution, Hydrogen sulfide, etc., can even be used in high temperature applications at certain concentrations. But it is not resistant to the corrosion of concentrated or hot hydrochloric acid, wet nitrogen, chlorine, Australian, iodine, aqua regia, etc.
4. Copper valve: Copper valve has good corrosion resistance to water, seawater, various salt solutions and organic matter. It has good corrosion resistance to sulfuric acid, phosphoric acid, acetic acid, dilute hydrochloric acid, etc. without oxygen or oxidant, and has good resistance to alkali. However, it is not resistant to corrosion by oxidizing acids such as nitric acid and concentrated sulfuric acid, nor is it resistant to corrosion by molten metals, sulfur and sulfides. Avoid contact with ammonia, which can cause stress corrosion cracking of copper and its alloys. In the selection, it should be noted that different grades of copper alloys have certain differences in corrosion resistance.
5. The aluminum valve has good corrosion resistance to strong oxidizing concentrated nitric acid, and is resistant to organic acids and solvents, but it is not corrosion-resistant in reducing media, strong acids, and strong alkalis. The higher the purity of aluminum, the better the corrosion resistance, but the strength decreases, and it can only be used for lining valves.
6. Iron valve: Qin is an active metal, which can form an oxide film with good corrosion resistance at room temperature. It is resistant to corrosion by seawater, various cyanides and hypochlorites, wet chlorine, oxidizing acids, organic acids, alkalis, etc. However, it is not resistant to the corrosion of relatively pure reducing acids, such as sulfuric acid and hydrochloric acid, but is resistant to the corrosion of nitric acid containing an oxidant. Chin valve has good resistance to pitting corrosion, but it produces stress corrosion in media such as red fuming nitric acid, nitric acid, and formazan.
7. Drilling valve: Orange is also an active metal, which can generate a tight oxide film. It has good corrosion resistance to nitric acid, lattice acid, lye, molten alkali, salt solution, urea, seawater, etc., but it is not resistant to the corrosion of hydrochloric acid, concentrated sulfuric acid, aqua regia, and it is not resistant to wet scratches and oxidizing metals. Corrosion of scratches.
8. Lead valve: Lead is also an active metal, and its corrosion product film is a strong protective layer. It is a well-known material resistant to sulfuric acid. It has high corrosion resistance in phosphoric acid, chromic acid, carbonic acid, neutral solution, seawater and other media. However, it is not resistant to the corrosion of glass and hydrochloric acid, and it is not suitable for working in their corrosion products. Lead is soft and suitable only for valve lining.
9. Ceramic, glass and enamel valves: ceramics, glass and enamel are melting or calcined products mainly made of silicon dioxide. They have high corrosion resistance. In addition to alkali, it is resistant to concentrated nitric acid, sulfuric acid and hydrochloric acid. , aqua regia, salt solutions and organic solvents. If other materials are used for this type of valve, the corrosion resistance of other materials should be considered when selecting the medium.
10. Rubber lined valve: Different types of rubber have different corrosion resistance. The vulcanized natural rubber is resistant to the corrosion of non-oxidizing acids, alkalis and salts, but it is not resistant to the corrosion of strong carrier agents, such as nitric acid, lattice acid and concentrated sulfuric acid, nor is it resistant to the corrosion of petroleum products and certain organic solvents. Therefore, natural rubber is gradually replaced by synthetic rubber. Good, but not resistant to the corrosion of strong solvents such as urbanizing acids, aromatic hydrocarbons, vinegars, ketones, ethers, acids, alkalis, salts, petroleum products, hydrocarbons, etc., but the solvent resistance is not as good as that of air plastics, and nitrile in synthetic rubber. Oil resistance of rubber The rubber has excellent corrosion resistance and can withstand various types of polyether rubber and can be used in water, oil, nitrogen, alkali and other media. Other synthetic rubbers are not listed one by one.
11. Glass fiber reinforced plastic valve: Boruili’s corrosion resistance varies with its glue. Epoxy FRP can be used in hydrochloric acid, phosphoric acid, dilute sulfuric acid and some organic acids. Phenolic FRP has good corrosion resistance, and FRP has good alkali resistance, acid resistance and comprehensive corrosion resistance.
12. Plastic valve. All plastics have certain corrosion resistance, and the corrosion resistance varies greatly with the different types of plastics.
Nylon: Also known as polyamine, it is a thermoplastic with good corrosion resistance. It can resist the corrosion of dilute acid, salt and alkali, and has good corrosion resistance to stove, ketone, ether, ester and oil. But it is not resistant to the corrosion of strong acid, phenolic acid, phenol and formic acid.
Polyvinyl chloride: Polyvinyl chloride is a thermoplastic with excellent corrosion resistance. Resistant to acid, alkali, salt, organic matter. But it is not resistant to the corrosion of concentrated nitric acid, fuming sulfuric acid, Minzhuan, ketones, halogenated, aromatic hydrocarbons, etc.
Polyethylene: Polyethylene has excellent corrosion resistance, and it has good corrosion resistance to hydrochloric acid, dilute sulfuric acid, hydrofluoric acid and other urbanized acids as well as dilute nitric acid, alkali, salt solution and organic solvents at room temperature. But it is not resistant to the corrosion of concentrated nitric acid, concentrated sulfuric acid and other strengthening agents.
Polypropylene: polypropylene is a thermoplastic, and its corrosion resistance is similar to that of polyethylene, but slightly better than that of polyethylene. It is resistant to most organic acids, inorganic acids, alkalis and salts, but has poor corrosion resistance to strong oxidizing acids such as concentrated nitric acid, oleum, and sulfonic acid.
Bakelite: Resistant to the turbidity of non-softening acids such as hydrochloric acid, dilute sulfuric acid, phosphoric acid, and salt solutions. However, it is not resistant to intestinal erosion of fortified acids, alkalis and some organic solvents such as nitric acid and lattice acid.