Demineralized Water Corrosion on Carbon Steel
Demineralized Water Corrosion on Carbon Steel
(OP)
Hi, I'm Xeros.
I heard that Stainless Steel shall be used on Demineralized water service because it is severe corrosive for carbon steel.
I want to know why Demineralized water is severe corrosive for carbon steel.
and i heard that the reason is that Demineralized water is very active with ion such as CO2, O2 because it is very pure and unstable.
is it right?
if above reason is right,
is Demineralized water corrosive on carbon steel when it blended with fresh water?
I heard that Stainless Steel shall be used on Demineralized water service because it is severe corrosive for carbon steel.
I want to know why Demineralized water is severe corrosive for carbon steel.
and i heard that the reason is that Demineralized water is very active with ion such as CO2, O2 because it is very pure and unstable.
is it right?
if above reason is right,
is Demineralized water corrosive on carbon steel when it blended with fresh water?





RE: Demineralized Water Corrosion on Carbon Steel
Steve Jones
Materials & Corrosion Engineer
http://www.pdo.co.om/pdoweb/
RE: Demineralized Water Corrosion on Carbon Steel
The corrosion rate of the demi-water depends also on the oxygen and CO2 content, if your water is a closed circuit and is not in contact with atmosphere the corrosion rate will be low.
If you blend the waters than i'll use the corrosion rate of fresh water on carbon steel as a reference.
"In distilled water, which cannot form a protective scale to reduce the access of oxygen to the zinc surface, the attack is more severe than in most types of domestic or river water, which do contain some scale-forming salts."
http://www.key-to-metals.com/Article40.htm
So this could be one reason someone state that demineralized water is more aggressive than fresh water.
S.
http://www.corrosionist.com
RE: Demineralized Water Corrosion on Carbon Steel
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Plymouth Tube
RE: Demineralized Water Corrosion on Carbon Steel
rmw
RE: Demineralized Water Corrosion on Carbon Steel
Thanks for your help!!!
RE: Demineralized Water Corrosion on Carbon Steel
Modern supercritical steam plants use carbon steel tubed feedwater heaters, and add 50-200 ppb O2 to the demin water to promote the formation of hematite ( at pH of 8.0-8.5)- this is a much more stable oxide scale that does not erode off the tubes, and will not form a corrosion cell as long as the water is flowing . However, stagnant oxygenated water will lead to rapid corrosion , so outages much be preceeded by altering the feedwater chemistry to traditional 4 ppb O2 with no trace hydrazine and pH to 9.2. The DA must be burped occasionally to remove noncondensables including CO2.
So, I think the stainless steel may need to be reserved for the applications , or sectionof the steam cycle, where the noncondensibles have not been removed yet.
RE: Demineralized Water Corrosion on Carbon Steel
Stainless Steel or plastics are used on demineralized water service because oxygen is normally present. If you deaerate the water to remove the oxygen, the demineralized water will not be severely corrosive for carbon steel service.
The absence of calcium and magnesium from demineralized water makes demineralized water more aggressive than fresh water. Most fresh waters contain calcium and magnesium. It is also true that a fresh water lacking calcium and magnesium will be aggressive.
The langelier index was created to predict corrosion resulting from a lack of calcium and magnesium in water.
There is no CO2 present in demineralized water, since the demineralized water has a pH of 8-10 pH units. That means demineralized water is basic not acidic.
It is impossible to predict whether demineralized water blended with fresh water will be corrosive on carbon steel service without knowing the water quality parameters and whether oxygen is present.