The corrosion of stainless steel by a mixture of HCl and water vapor
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This post was last edited by Wang Genrong on 2015-8-19 09:50. Experts, during the early stage of the distillation process, a large amount of steam is mixed with a small amount of HCl. How does water vapor corrode stainless steel when it passes through a stainless steel heat exchanger (assuming no liquid phase is present)?
This post was last edited by Wang Genrong on 2015-8-19 09:47. This type of process typically involves reboilers or condensers: a reboiler is used to heat liquid material and cause it to evaporate, while a condenser is used to cool gaseous material and convert it back into a liquid state. The situation you described, in which there is no liquid phase, hardly exists; even though there is no visible liquid flow, the possibility of the existence of a film-like layer of liquid cannot be ruled out. Therefore, stainless steel heat exchangers cannot be used in process systems that contain water, hydrogen chloride, organic solvents, etc.; graphite heat exchangers are recommended.
A small amount of HCL shouldn’t cause stress corrosion; I think it can be used
You’ll know once you use it – the corrosion is extremely severe! If you are the boss, you can try using one to determine the severity of corrosion; if you’re not the boss, definitely don’t try it, or else the boss will spank you.
If austenitic stainless steel is used, pitting corrosion can occur under these conditions, as well as stress corrosion. I’ve seen several cases like that.
Steam implies high temperatures, and in such high temperatures, the presence of HCL, or chloride ions, causes stainless steel to rust very easily! ! ! The corrosion resistance of stainless steel can be tested using neutral salt spray, which helps to illustrate the destructive effect of chloride ions on the corrosion-resistant film of stainless steel. It is recommended not to use ordinary stainless steel.
Hastelloy: Hastelloy C-276 is a nickel-chromium-molybdenum alloy containing tungsten, with very low levels of silicon and carbon. It is generally considered a universal corrosion-resistant alloy. This alloy possesses the following properties: 1) It exhibits excellent corrosion resistance to most corrosive media in both oxidized and reduced states. 2) It exhibits excellent resistance to pitting, crevice corrosion, and stress cracking corrosion. C276 alloy is widely used in the chemical and petrochemical industries, such as in components containing chlorinated organic compounds and in catalytic systems. This material is particularly suitable for use in high-temperature environments, as well as in corrosive environments involving impure inorganic and organic acids (such as formic acid and acetic acid) and seawater. Other application areas: 1) Pulp and paper industry, such as pulping and bleaching units. 2) Wash towers in FGD systems, as well as heaters and moisture fans. 3) Equipment and components used in acidic gas environments. 4) Reactors for acetic acid and acidic products; sulfuric acid condensers; methylenediphenyl isocyanate (MDI); production and processing of impure phosphoric acid
It will definitely corrode stainless steel. Coating is required for corrosion protection
Prolonged exposure to HCL will definitely cause a chemical reaction with stainless steel; this reaction is known as stress corrosion. I recommend using distilled water in a circulating system, as even the presence of water vapor will not cause corrosion of the stainless steel. This can help save costs. Another option is to apply an anti-corrosion coating to the stainless steel heat exchangers, which will also ensure their longevity. If you have any technical questions, feel free to reach out at any time
I know very little about graphite heat exchangers. What are the requirements regarding temperature, pressure, and other conditions when using graphite heat exchangers?