What type of corrosion is desalinated water corrosion?
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This post was last edited by lovepds on 2017-1-23 at 13:50. For demineralized water pipelines in refineries, especially those with temperatures above 60°C, austenitic stainless steel is usually chosen. What are the main considerations behind this material selection? Oxygen corrosion? Is it the requirement to control iron ions, or something else?
It should be to control the iron ion content
Generally speaking, demineralized water is non-corrosive; therefore, stainless steel was not chosen due to corrosion concerns. It is likely that cleanliness was the factor taken into consideration.
I’ve seen that in the devices made by many design units, the pipes for supplying and removing desalinated water are also made of stainless steel; after all, when the temperature is high, corrosion still needs to be taken into consideration
I saw someone in the forum reply as follows: Since both desalinated water and alkalis are corrosive, it is recommended to use pipelines made of 316 or 304 stainless steel, as well as stainless steel valves and fittings; or alternatively, pipelines made of polymer materials such as PP/PFA or nylon. The principle of corrosion is that water contains high concentrations of oxygen; it is this oxygen that causes electrochemical reactions on the iron surface, leading to corrosion. There is also oxygen in deionized water, so it cannot reduce corrosion – therefore, corrosion inhibitors still need to be added. In addition, microbialicides must be used in deionized water systems, as the growth of microorganisms can also cause corrosion in the pipes
There are several advantages to using stainless steel pipelines: 1. Desalinated water does not contain absolutely no salt, which helps to extend its service life； 2. The temperature of demineralized water is generally not high, to prevent condensation on the pipe outer shell; moreover, the condensate absorbing acidic gases from the air can also cause corrosion ； 3. Coastal areas and factories that produce acidic gases will have acidic gas condensate of their own! This is my understanding: in particular, for projects or factory sites in coastal cities where acidic gases are present, special attention is needed~
Stainless steel is used to account for oxygen corrosion, which is a type of electrochemical corrosion. The corrosion of iron by dissolved oxygen in water is a type of electrochemical corrosion, as iron and oxygen form a corrosion cell. The electrode potential of iron is always lower than that of oxygen; therefore, in a ferro-oxidative corrosion cell, iron acts as the anode and is corroded. The reaction is as follows: Fe → Fe2+ + 2e-. Oxygen acts as the cathode where reduction occurs, with the reaction being: O2 + 2H2O + 4e- → 4OH-. Here, dissolved oxygen plays a role in cathodic polarization, and it is the factor that causes iron corrosion. This type of corrosion is known as oxygen corrosion.