Valve material selection and corrosion resistance analysis

The selection of the valve material and the analysis of its corrosion resistance are the key to ensure the stable operation of the valve in a specific working environment. The following is a detailed analysis of different valve materials and their corrosion resistance:

First, cast iron valves

Scope of application: water, steam, petroleum products, ammonia and can work in most alcohols, aldehydes, ethers, ketones, esters and other less corrosive media.

Corrosion resistance: Not suitable for hydrochloric acid, nitric acid and other media, but can be used in concentrated sulfuric acid, because concentrated sulfuric acid will produce a passivation film on its metal surface, preventing corrosion. Silicon cast iron valve corrosion resistance is very strong, can work well in all concentrations of sulfuric acid, nitric acid, phosphoric acid, acidic salts, but not resistant to fluoric acid, strong alkali, hydrochloric acid and ferric chloride hot solution corrosion. Nickel cast iron valve alkali resistance is higher than ordinary cast iron, can be used in dilute sulfuric acid, dilute hydrochloric acid and caustic soda.

Two, carbon steel valve

Corrosion resistance: similar to gray cast iron, slightly lower than gray cast iron.

Three, stainless steel valve

Scope of application: Resistant to nitric acid and other oxidizing media, but also resistant to alkali, water, salt, organic acids and other organic compounds.

Corrosion resistance: not resistant to sulfuric acid, hydrochloric acid and other non-oxidizing acid corrosion, not resistant to dry hydrogen chloride, oxidizing chloride and oxalic acid, lactic acid and other organic acids. Stainless steel containing 2%4% molybdenum, such as 1Cr18Ni12Mo2Ti, etc., its corrosion resistance is superior to chrome-nickel stainless steel. Stainless steel with high chromium and high nickel, such as stainless steel of chromium 20 nickel 2230, can be used to treat sulfuric acid, phosphoric acid, mixed acid, sulfite, organic acid, alkali, salt solution, hydrogen sulfide, etc., and even can be used in high temperature occasions at certain concentrations. But not resistant to concentrated or hot hydrochloric acid, wet fluorine, chlorine, bromine, iodine, aqua regia and other corrosion.

Four, copper valve

Scope of application: Good corrosion resistance to water, seawater, a variety of salt solutions, organic matter.

Corrosion resistance: It has good corrosion resistance to sulfuric acid, phosphoric acid, acetic acid, dilute hydrochloric acid, etc. which does not contain oxygen or oxidant, and has good resistance to alkali. However, it is not resistant to nitric acid, concentrated sulfuric acid and other oxidizing acids, nor to molten metal, sulfur and sulfide corrosion. Avoid contact with ammonia, which can cause stress corrosion cracking of copper and copper alloys. Different grades of copper alloys have certain differences in corrosion resistance.

Five, aluminum valve

Corrosion resistance: strong oxidizing concentrated nitric acid corrosion resistance is very good, can resist organic acids and solvents, but in reducing media, strong acids, strong alkali corrosion resistance. The higher the purity of aluminum, the better the corrosion resistance, but the strength decreases and can only be used as a valve or valve lining with very low pressure.

Six, titanium valve

Corrosion resistance: Titanium is an active metal that can generate an oxide film with good corrosion resistance at room temperature. It can resist the corrosion of seawater, various chlorides and hypochlorites, wet chlorine, oxidizing acids, organic acids, alkalis, etc. However, it is not resistant to more pure reducing acids, such as sulfuric acid, hydrochloric acid corrosion, but resistant to nitric acid containing oxidant corrosion. Titanium valve has good resistance to pitting, but it will produce stress corrosion in the media such as red fuming nitric acid, chloride and methanol.

Seven, other material valves

Ceramic, glass, enamel valve: has a high corrosion resistance, in addition to not resistant to oxygen atmosphere acid, fluorosilicic acid and strong alkali, can heat concentrated nitric acid, sulfuric acid, hydrochloric acid, aqua royal, salt solution and organic solvents and other media.

Rubber lined valve: vulcanized natural rubber, resistant to non-oxidizing acid, alkali, salt corrosion, but not resistant to strong oxidants, such as nitric acid, sulfuric acid, concentrated sulfuric acid corrosion, also not resistant to petroleum products and some organic solvents corrosion. Nitrile rubber in synthetic rubber has excellent oil resistance, and polyether rubber can be used in water, oil, nitrogen, alkali and other media.

FRP valves: Corrosion resistance varies with their gelling agent. 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.

Plastic valve: has a certain corrosion resistance, with the different types of plastics, its corrosion resistance is different. Such as nylon resistance to dilute acid, salt and alkali corrosion, ketones, ethers, esters, oils have good corrosion resistance, but not resistant to strong acids, oxidizing acids, phenols and formic acid corrosion. Polyvinyl chloride can resist acid, alkali, salt, organic matter, but not resistant to concentrated nitric acid, smoky sulfuric acid, alcohol, ketone, halogenated class, aromatic hydrocarbons and other corrosion.

The selection of valve material should be comprehensively considered according to the specific working environment, medium characteristics and cost. In terms of corrosion resistance, valves of different materials have advantages and disadvantages, and need to be selected according to actual needs.