In actual projects, many media in the valve are corrosive to a certain extent; the same media, with the change of temperature, pressure and concentration, its corrosiveness is also different. Therefore, the valve suitable for the medium should be selected according to the corrosion resistance of the material. Small valves have mentioned in the valve selection series that buyers should choose valves according to the medium. However, there is no systematic introduction of what kind of medium is suitable for valves made of different materials. Today, the little valve will share this knowledge with you!
Gray cast iron valve
It is suitable for water, steam, petroleum products, ammonia and can work in most alcohols, aldehydes, ethers, ketones, fats and other less corrosive media. It is not suitable for hydrochloric acid, nitric acid and other media. But it can be used in concentrated sulfuric acid, because concentrated sulfuric acid can produce a passivation film on its metal surface. To prevent the corrosion of cast iron by concentrated sulfuric acid.
Ductile Iron Valves
Strong corrosion resistance, can work in a certain concentration of sulfuric acid, nitric acid, sulfuric acid, acid salt. But it is not resistant to the corrosion of hydrofluoric acid, strong alkali, hydrochloric acid and ferric chloride hot solution. Avoid sudden heat and sudden cold during use, otherwise it will burst.
Nickel cast iron valve
Alkali resistance is stronger than gray cast iron and ductile iron valves; nickel cast iron is an ideal valve material for dilute sulfuric acid, dilute hydrochloric acid and caustic alkali.
Carbon steel valve
The corrosion resistance of carbon steel valves is similar to that of gray cast iron, but slightly inferior to that of gray cast iron.
stainless steel valve
Stainless steel valves have excellent atmospheric resistance, can resist nitric acid and other oxidizing media, and can also resist corrosion by alkali, water, salt, organic acids and other organic compounds. However, it is not resistant to the corrosion of non-oxidizing acids such as sulfuric acid and hydrochloric acid, nor is it resistant to dry hydrogen chloride, oxidizing chlorides, and organic acids such as oxalic acid and lactic acid.
Stainless steel containing 2% to 4% molybdenum, such as Cr18Ni12Mo2Ti, etc., has better corrosion resistance than chromium-nickel stainless steel, and its acid resistance in non-oxidizing acids and hot organic acids and chlorides is better than chromium-nickel stainless steel. The pitting resistance is also good.
Stainless steels containing titanium or niobium are more resistant to intergranular corrosion.
Stainless steel containing high chromium and high nickel has higher corrosion resistance than ordinary stainless steel, and can be used to treat sulfuric acid, sulfuric acid, mixed acid, sulfurous acid, organic acid, alkali, salt solution, hydrogen sulfide, etc., even at certain concentrations high temperature occasions. But it is not resistant to the corrosion of concentrated or hot hydrochloric acid, wet fluorine, chlorine, bromine, iodine, aqua regia, etc.
Copper valves have 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. that do not contain oxygen or oxidants, and has good resistance to alkali. But it is not resistant to the corrosion of oxidizing acids such as nitric acid and concentrated sulfuric acid, nor the corrosion of molten metals, sulfur and sulfides. Avoid contact with ammonia, it can cause stress corrosion cracking of copper and copper alloys. When selecting, it should be noted that the grades of copper alloys are different, and their corrosion resistance has certain differences.
It has good corrosion resistance to strong oxidizing concentrated nitric acid, and can resist organic acids and solvents. But it is not corrosion-resistant in reducing medium, strong acid and strong alkali. The higher the purity of aluminum, the better the corrosion resistance, but the strength decreases accordingly, so it can only be used as a valve or valve lining with very low pressure.
Titanium is an active metal that can form an oxide film with good corrosion resistance at room temperature. It is resistant to seawater, various chlorides and hypochlorites, wet chlorine, oxidizing acids, organic acids, alkalis, etc. But it is not resistant to the corrosion of relatively pure reducing acids, such as sulfuric acid and hydrochloric acid, and it is not resistant to the corrosion of nitric acid containing oxidants. Titanium valves have good resistance to pitting corrosion. However, stress corrosion will occur in red fuming nitric acid, chloride, methanol and other media.
Zirconium is also an active metal. It can form a tight oxide film. It has good corrosion resistance to nitric acid, chromic acid, lye, melt, salt solution, urea, sea water, etc., but it is not resistant to hydrofluoric acid and concentrated sulfuric acid. , the corrosion of aqua regia, and it is also resistant to the corrosion of wet chlorine and oxidizing metal chlorides.
Valves made of silica-based melting and sintering, such as zirconia, alumina, silicon nitride, etc., have extremely high wear resistance and temperature resistance. In addition to heat insulation performance, it also has high corrosion resistance. In addition to being resistant to oxyfluoric acid, fluorosilicic acid and strong alkali, it can withstand heat-concentrated nitric acid, sulfuric acid, hydrochloric acid, aqua regia, salt solution and organic solvents. If other materials are used for this type of valve, the corrosion resistance of other materials should be considered when selecting.
Valves made of silica-based melting and sintering have the same corrosion resistance as ceramic valves.
Mainly silicon dioxide is melted and fired on ferrous metal products, and its corrosion resistance is the same as that of ceramic valves.
The corrosion resistance of FRP varies with its adhesive. Epoxy FRP can be used in hydrochloric acid, phosphoric acid, dilute sulfuric acid and some organic acids; phenolic FRP has better corrosion resistance; furan FRP has better alkali resistance, acid resistance and comprehensive corrosion resistance.
Also known as polyamide, it is a thermoplastic with good corrosion resistance. It can resist the corrosion of dilute acid, salt and alkali. It has good corrosion resistance to hydrocarbons, ketones, ethers, fats and oils. But it is not resistant to strong acid, oxidizing acid, phenol and formic acid.
Polyvinyl chloride is a thermoplastic with good corrosion resistance. Ability to acid, alkali, salt, organic matter. Not resistant to the corrosion of concentrated nitric acid, oleum, acetic anhydride, ketones, halogenated, aromatics, etc.
Polyethylene has excellent corrosion resistance. It has good corrosion resistance to non-oxidizing acids such as hydrochloric acid, dilute sulfuric acid, and hydrofluoric acid, dilute nitric acid, alkali, salt solutions, and organic solvents at room temperature. But it is not resistant to the corrosion of concentrated nitric acid, concentrated sulfuric acid and other strong oxidants.
Polypropylene is a thermoplastic, and its corrosion resistance is similar to that of polyethylene, slightly better than polyethylene. It is resistant to most organic acids, inorganic acids, alkalis, and salts. However, it has poor corrosion resistance to strong oxidizing acids such as concentrated nitric acid, oleum, and chlorosulfonic acid.
It can resist the corrosion of hydrochloric acid, dilute sulfuric acid, phosphoric acid and other non-oxidizing acids and salt solutions. However, it is not resistant to strong oxidizing acids such as nitric acid and chromic acid, alkalis and some organic solvents.
Chlorinated polyether valve
Polychloride, also known as polychloride, is a linear, high-crystallinity thermoplastic. It has excellent corrosion resistance, second only to fluoroplastics. It can resist the corrosion of various acids, alkalis, salts and most organic solvents except concentrated sulfuric acid and concentrated nitric acid, but it is not resistant to the corrosion of liquid chlorine, fluorine and bromine.
Like other fluoroplastics, it has excellent corrosion resistance and other properties, and its corrosion resistance is slightly lower than that of polytetrafluoroethylene. It has good corrosion resistance to organic acids, inorganic acids, alkalis, salts, and various organic solvents. Some solvents containing halogen and oxygen at high temperature can make it swell. It is not resistant to high temperature fluorine, fluoride, molten alkali, concentrated nitric acid, aromatic hydrocarbons, fuming nitric acid, molten alkali metal, etc.
PTFE has excellent corrosion resistance. It can resist corrosion of almost all chemical media except molten metal lithium, potassium, sodium, chlorine trifluoride, oxygen trifluoride at high temperature, and liquid oxygen at high flow rate.
Plastic Lined Valves
Due to the low strength of plastic, many valves use a metal liner as the outer shell and a plastic liner. Plastic lined valves, with different lining plastics, have different corrosion resistance. The corrosion resistance of the plastic lining is the same as the corresponding plastic in the above plastic valve. However, when selecting, the corrosion resistance of other materials used in plastic-lined valves should be considered.
Rubber Lined Valves
Rubber is soft, so many valves are lined with rubber to improve the corrosion resistance and sealing performance of the valve. With the different types of rubber, its corrosion resistance varies greatly. Vulcanized natural rubber is resistant to non-oxidizing acids, alkalis, and salts, but not to strong oxidants, such as nitric acid, chromic acid, concentrated sulfuric acid, or to petroleum products and certain organic solvents. Therefore, natural rubber is gradually replaced by synthetic rubber. Nitrile rubber in synthetic rubber has good oil resistance, but it is not resistant to corrosion by strong solvents such as oxidizing acids, aromatic hydrocarbons, fats, ketones, ethers; fluororubber has excellent corrosion resistance and can withstand various acids, alkalis, salts, petroleum products, Hydrocarbons, etc., but the solvent resistance is not as good as fluoroplastics; polyether rubber can be used in water, oil, ammonia, alkali and other media.
Lead Lined Valves
Lead is a reactive metal, but because of its soft material, it is often used as a lining for special valves. The corrosion product film of lead 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, but it is not resistant to alkali and hydrochloric acid. corrosion and are not suitable for working in their corrosion products.