English Translation

Ceramic Valves

Ceramic valves are sintered mainly from silicon oxide, including zirconia, alumina, silicon nitride and other materials. They feature exceptional wear resistance, moisture resistance and thermal insulation, along with superior corrosion resistance. They resist hot concentrated nitric acid, sulfuric acid, hydrochloric acid, aqua regia, salt solutions and organic solvents, but are vulnerable to hydrofluoric acid, fluosilicic acid and strong alkalis. If other materials are adopted in such valves, their corrosion resistance shall be taken into account during selection.

Glass Valves

Manufactured by melting and sintering silicon dioxide as the main raw material, glass valves share identical corrosion resistance with ceramic valves.

Enamel Valves

Enamel valves are produced by coating and firing silicon dioxide-based enamel onto ferrous metal substrates, possessing the same corrosion resistance as ceramic valves.

Fiberglass Reinforced Plastic (FRP) Valves

The corrosion resistance of FRP varies with adhesive types. Epoxy FRP is applicable to hydrochloric acid, phosphoric acid, dilute sulfuric acid and certain organic acids. Phenolic FRP delivers favorable corrosion resistance. Furan FRP boasts excellent alkali resistance, acid resistance and comprehensive anti-corrosion performance.

Plastic Valves

Plastics generally have corrosion resistance, which differs greatly by material type.

Nylon (Polyamide)

A thermoplastic polymer with good corrosion resistance. It withstands dilute acids, salts, alkalis, hydrocarbons, ketones, ethers, esters and oils, yet fails to resist strong acids, oxidizing acids, phenol and formic acid.

Polyvinyl Chloride (PVC)

A thermoplastic material with outstanding corrosion resistance. It resists acids, alkalis, salts and organic substances, but is corroded by concentrated nitric acid, fuming sulfuric acid, acetic anhydride, ketones, halogenated compounds and aromatic hydrocarbons.

Polyethylene (PE)

It offers excellent corrosion resistance against non-oxidizing acids such as hydrochloric acid, dilute sulfuric acid and hydrofluoric acid, dilute nitric acid, alkaline salt solutions and room-temperature organic solvents. It cannot endure concentrated nitric acid, concentrated sulfuric acid and other strong oxidants.

Polypropylene (PP)

A thermoplastic polymer with corrosion resistance similar to and slightly superior to polyethylene. It resists most organic acids, inorganic acids, alkalis and salts, but has poor tolerance to oxidizing acids including concentrated nitric acid, fuming sulfuric acid and chlorosulfonic acid.

Phenolic Plastic

Resistant to non-oxidizing acids like hydrochloric acid, dilute sulfuric acid, phosphoric acid and salt solutions. It is susceptible to strong oxidizing acids such as nitric acid and chromic acid, alkalis and certain organic solvents.

Polyethersulfone (Chlorinated Polyether)

A linear highly crystalline thermoplastic plastic with remarkable corrosion resistance, second only to fluoroplastics. It withstands most acids (except concentrated sulfuric acid and concentrated nitric acid), alkalis, salts and organic solvents, but is corroded by liquid chlorine, fluorine and bromine.

Polychlorotrifluoroethylene (PCTFE)

Like other fluoroplastics, it has excellent comprehensive properties and corrosion resistance slightly lower than polytetrafluoroethylene. It performs well against organic acids, inorganic acids, alkalis, salts and various organic solvents. High-temperature halogen-containing and oxygen-containing solvents cause swelling. It cannot resist high-temperature fluorides, chlorides, molten alkalis, concentrated nitric acid, aromatic hydrocarbons, fuming nitric acid and molten alkali metals.

Polytetrafluoroethylene (PTFE)

It possesses supreme corrosion resistance. It withstands nearly all chemical media, excluding molten lithium, potassium, sodium, chlorine trifluoride, high-temperature oxygen trifluoride and high-velocity liquid fluorine.

Plastic-lined Valves

Given low mechanical strength of plastics, most valves adopt metal shells lined with plastic. Their corrosion resistance depends on lining materials, consistent with that of corresponding solid plastic valves. Corrosion resistance of auxiliary materials shall be evaluated in selection.

Rubber-lined Valves

Soft rubber linings enhance corrosion resistance and sealing performance of valves. Corrosion resistance varies by rubber category. Vulcanized natural rubber resists non-oxidizing acids, alkalis and salts, but is damaged by strong oxidants (nitric acid, chromic acid, concentrated sulfuric acid), petroleum products and specific organic solvents, and is gradually replaced by synthetic rubber.

Nitrile rubber has fine oil resistance but poor tolerance to oxidizing acids, aromatic hydrocarbons, esters, ketones and ethers. Fluororubber features superior corrosion resistance against acids, alkalis, salts, petroleum products and hydrocarbons, with weaker solvent resistance than fluoroplastics. Polyether rubber suits water, oil, ammonia and alkaline media.

Lead-lined Valves

Lead is an active soft metal commonly used as special valve lining. Its dense corrosion product film serves as a protective layer. Lead exhibits good resistance to sulfuric acid, phosphoric acid, chromic acid, carbonic acid, neutral solutions and seawater, while it is vulnerable to alkalis and hydrochloric acid, and unsuitable for service in corrosion byproducts.