Selection of Anti-corrosion Materials for Valves (Part Two)
5. Alkali (NaOH)
Steel is widely applied to sodium hydroxide (NaOH) solution below 80℃ (concentrations under 30%). Many petrochemical plants still apply ordinary steel to sodium hydroxide solution at 100℃ (concentrations under 75%). Although the corrosion rate increases, it is economical to use ordinary steel. Compared with cast iron, the corrosion resistance of ordinary stainless steel to alkaline liquor has no obvious advantages. Stainless steel is not recommended as long as a small amount of iron powder is allowed to be mixed in the medium. Titanium, titanium alloys or high alloy stainless steel is mostly used for high temperature lye.
6. Sulphuric acid
As one of the strong corrosive media, sulfuric acid is an important industrial raw material with wide application. The corrosion of valve materials by sulfuric acid with different concentrations and temperatures is quite different. For concentrated sulfuric acid with concentrations above 80% and temperatures below 80℃, carbon steel and cast iron have better corrosion resistance, but they are not suitable for use as materials of pump valves and for sulfuric acid with high speed flow. The pump valves for transporting sulfuric acid are usually made from high silicon cast iron (It is difficult to cast and process) and high alloy stainless steel (Alloy 20). Fluoroplastics have good resistance to sulfuric acid, and it is more economical to use fluorine-lined pump valves (F46).
7. Salt water (Seawater)
The corrosion rate of ordinary steel in sodium chloride solutions and salt water is not too high, so it is generally necessary to protect the steel with paint. All kinds of stainless steel also have low uniform corrosion rate, but local corrosion may be caused by chloride ions. 316 stainless steel is usually the better choice.
8. Alcohols, ketones, esters and ethers
Common alcohols are methanol, ethanol, ethylene glycol, etc. Ketones include acetone, butanone and so on. Esters contain various methyl esters, ethyl esters, etc. Ethers are methyl ether, butyl ether, etc. They are almost non-corrosive, and common materials are applicable. Reasonable selection should be made according to the properties of media and relevant requirements. In addition, it is worth noting that ketones, esters and ethers have solubility to various rubbers, so attention should be paid to the selection of sealing materials.
In short, don't choose valve materials at will, but look up more relevant sources or draw on some ripe experience.
Steel is widely applied to sodium hydroxide (NaOH) solution below 80℃ (concentrations under 30%). Many petrochemical plants still apply ordinary steel to sodium hydroxide solution at 100℃ (concentrations under 75%). Although the corrosion rate increases, it is economical to use ordinary steel. Compared with cast iron, the corrosion resistance of ordinary stainless steel to alkaline liquor has no obvious advantages. Stainless steel is not recommended as long as a small amount of iron powder is allowed to be mixed in the medium. Titanium, titanium alloys or high alloy stainless steel is mostly used for high temperature lye.
6. Sulphuric acid
As one of the strong corrosive media, sulfuric acid is an important industrial raw material with wide application. The corrosion of valve materials by sulfuric acid with different concentrations and temperatures is quite different. For concentrated sulfuric acid with concentrations above 80% and temperatures below 80℃, carbon steel and cast iron have better corrosion resistance, but they are not suitable for use as materials of pump valves and for sulfuric acid with high speed flow. The pump valves for transporting sulfuric acid are usually made from high silicon cast iron (It is difficult to cast and process) and high alloy stainless steel (Alloy 20). Fluoroplastics have good resistance to sulfuric acid, and it is more economical to use fluorine-lined pump valves (F46).
7. Salt water (Seawater)
The corrosion rate of ordinary steel in sodium chloride solutions and salt water is not too high, so it is generally necessary to protect the steel with paint. All kinds of stainless steel also have low uniform corrosion rate, but local corrosion may be caused by chloride ions. 316 stainless steel is usually the better choice.
8. Alcohols, ketones, esters and ethers
Common alcohols are methanol, ethanol, ethylene glycol, etc. Ketones include acetone, butanone and so on. Esters contain various methyl esters, ethyl esters, etc. Ethers are methyl ether, butyl ether, etc. They are almost non-corrosive, and common materials are applicable. Reasonable selection should be made according to the properties of media and relevant requirements. In addition, it is worth noting that ketones, esters and ethers have solubility to various rubbers, so attention should be paid to the selection of sealing materials.
In short, don't choose valve materials at will, but look up more relevant sources or draw on some ripe experience.
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