Demineralised water - Effect on 304 Stainless Steel
Demineralised water - Effect on 304 Stainless Steel
(OP)
We have a customer who is requesting that we remove a 304 Stainless Steel ring main and replace for plastic due to corrosion issues associated with passing Demineralised water through the pipe work. I have always been of the thinking that Stainless should be fine for this application. Does anyone have any comments? The quality of the water will be in the region of 1 - 5 Microseimens. Many thanks





RE: Demineralised water - Effect on 304 Stainless Steel
RE: Demineralised water - Effect on 304 Stainless Steel
RE: Demineralised water - Effect on 304 Stainless Steel
RE: Demineralised water - Effect on 304 Stainless Steel
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RE: Demineralised water - Effect on 304 Stainless Steel
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RE: Demineralised water - Effect on 304 Stainless Steel
raw water (inland, river, lake, pond) - carbon steel;
raw water (brackish, estuary, sea) - 304/316/PP/PE
decationized water (after cation exchanger, strong, pH around 3-4) - PVC/PP/PE (temperature depending: PVC below 40C, PP/PE up to 80C, steel above - can be lined)
demineralized water (after cation-anion or RO, conductivity up to 5uS, pH 7-9.5) - as above, but if steel then 316
deionized water (conductivity up to 1uS, pH 6.5-8) - plastic or lined steel
last two of above, thermally degassed to oxygen content below 100ppb as micrograms of O2 - plastic, if temperature would allow.
In general, indoor pipelines with temperature below 40C - PVC, 40-80: PE/PP, above 80C - steel.
Last but not least:plastic is far cheaper, have 20years of lifetime, and is much cheaper and easier to modify or repair.
RE: Demineralised water - Effect on 304 Stainless Steel
RE: Demineralised water - Effect on 304 Stainless Steel
There will be no carbon dioxide in demineralized water. The anion will remove the carbon dioxide. The pH of demineralized water is normally a pH of 10 since the efflluent is in the form of sodium hydroxide.
Some power plants are successfully operating carbon steel boiler systems with demineralized water. The secret is the water must be oxygen free.
RE: Demineralised water - Effect on 304 Stainless Steel
Some power plants operate carbon steel piping systems with demineralized water. The reason that this works is that there is zero oxygen presnt.
RE: Demineralised water - Effect on 304 Stainless Steel
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RE: Demineralised water - Effect on 304 Stainless Steel
deionized water: water after one or two stages of RO, typically with conductivity around 5uS. Same is if the final stage is anion exchanger only, without mixed bed or EDI.
demineralized water: water after mixed bed ion exchanger or EDI, typically with direct conductivity below 1uS.
Same time, demineralized water pH would be around of 7. Deionized water ph will be alkaline ONLY after the anion exchanger, after RO it will be close to neutral.
Both water: in case of storage in tank which is not fit with carbon dioxide trap (e.g. with Sofnolime), it will absorb carbon dioxide from atmospheric air.
About the "oxygen free" water for use with boiler - especially for the low pressure sections - it is a simplest way to introduce flow accelerated corrosion in the system. Please refer for example to "Cycle Chemistry Guidelines for Fossil Plants: Oxygenated Treatment, EPRI, Palo Alto, CA:2005. 1004925."
From my practice, to avoid FAC in LP systems (both, in HRSG and "normal" coal boilers) it is necessary to introduce 2% Cr steel to exposed regions and/or to DOSE oxygen to keep it from 20-100ppb.
RE: Demineralised water - Effect on 304 Stainless Steel
With due respects, the post above was meant to correct some of the previous posts. Instead, additional further erroneous posts are added.
Water treatment professionals would not equate RO effluent and demineralized water. They are different.
RO effluent typically has a lower pH because carbon dioxide passes through the membrane.
For example, "Demineralisation" Any process used to remove minerals from water, however, commonly the term is restricted to ion exchange processes.
http://www.lenntech.com/applications/process/demin...
RO effluent is not considered to be demineralized water. There are too many ionic elements still present in the RO effluent since RO process are generally guaranteed to remove about 90% of the ionic elements whereas ion exchange systems remove about 100%. The effluent from a cation unit is also not demineralized water either, since you have removed just 50% of the ionic parameters.
Definition of demineralization from the Environmental Engineering Dictionary:
Water which has been passed through a mixed-bed ion exchanger to remove soluble ionic impurities. Nonelectrolytes and Colloids are not removed from water so treated. Also referred to as Deionized Water.
http://www.ecologydictionary.org/DEMINERALIZED_WAT...
Regarding absorption of Carbon Dioxide from air. If this is a concern, many facilities use nitrogen blanketing of storage tanks to prevent this from occuring. If carbon dioxide was present in demineralized water, one would assume that you have demineralized water that has been contaminanted.
In conventional all-volatile treatment (AVT) for boilers, the water quality is adjusted using ammonia to control pH and hydrazine as a deoxidant. Because dissolved oxygen is thought to be a corrosive component, its concentration is minimized and the boiler feed-water pH is adjusted to prevent
corrosion. Oxygenated treatment (OT), on the other hand, is based on the theory that slightly soluble oxides adhered to the surface of steel can prevent steel corrosion and elute corrosion products into water. OT includes neutral water treatment (NWT), in which dissolved oxygen is allowed to
coexist in neutral water, and CWT, in which dissolved oxygen is allowed to coexist in weak alkaline water adjusted to a range of pH 8.0 to 9.3 by ammonia. Boiler piping systems for these systems utilize carbon steel piping.
Finally, the effluent of a demineralizer is 10 (NOT pH 7) because the demineralized effluent is in the form of sodium hydroxide ionic species. Sodium leakage occurs from the cation unit and hydroxide leakage occurs from the anion unit.
RE: Demineralised water - Effect on 304 Stainless Steel
What is more, I know several organizations, which should now shut their water treatment down as they are using wrong equipment.
But, following the above, could you please explain me how are you obtaining the sodium hydroxide in the final effluent of mixed bed (typical in my, again: totally wrong, setups final stage of demineralization)?
I see only two alternatives:
1. to bypass mixed bed at all;
2. to regenerate the anion exchanger poorly (e.g. by not finishing the mixed bed final flushing in recirc mode).
Anyway, I'm happy that you discovered a way to avoid ammonia dosing in your installations, as you stated above: demin plant effluent pH value is 10, so please compare it with pH requirements for feedwater and cycle params.
It seems that most of Utilities are wasting ammonia and phosphate, huh? Instead, maybe they should start acid dosing to decrease pH of feed water from mentioned by you 10 to around 9?
Finally, "Oxygenated treatment (OT), on the other hand, is based on the theory that slightly soluble oxides adhered to the surface of steel can prevent steel corrosion and elute corrosion products into water." - it is wrong.
In AVT-R regime you have protective layer of magnetite (Fe3O4). In some systems, where two phases or single phase turbulent, directed flow occurs (e.g. in bends, header inlets etc) in specific pressure/temperature conditions (again: typically in LP systems), the mmagnetite layer is stripped out. In AVT-R regime, there is no conditions to restore protective layer, therefore lower pH and some oxygen injection is applied to promote oxides (mixture of hematite and magnetite) growth. In addition to that, many of HRSG owners have replaced the exposed locations to 2-3% Cr steels, as FAC occurs ONLY in carbon steel (of course: too much chromium would cause SCC in such chemical conditions, but this is another story).
To shorten, it seems that you (surprisingly) have not too much experience with professional generation utilities? I'd be curious if you could give the example of power station where the final stage of makeup water treatment is NOT the mixed bed or EDI, but to shorten the thread - please direct it as PM.
RE: Demineralised water - Effect on 304 Stainless Steel
Assume that the effluent from a demineralizer is less than 1 ppm. Would not that 1 ppm be sodium hydroxide? If not, what is it? Would also expect you to inderstand that there is essentially no buffering capacity in demineralized water.
Don't believe that I mentioned anything about condensate polishing in the ammonia cycle in any of the above comments either.
The original poster's enquiry was about corrosion of a piping system with demineralized water. The only thing that can be stated with the known information is that the corrosion is probably caused by oxygen.
RE: Demineralised water - Effect on 304 Stainless Steel
First, it can be everything, starting from the traces of chlorides from cation exchanger, via the slip of carbon dioxide, silica, ammonia or sodium.
But OK, lets follow your assumption that it is 1ppm of sodium.
Therefore, from the commonly known table, assuming that there is absence of other impurities, you will have: pH=9.4, conductivity of 6.2uS/cm.
Sorry, but it is NOT ultrapure water for whatever reason you'd like to use it.
Lets go further, pH of 10, you said? so again, lets assume, as you want, that all of it is caused by sodium only.
Therefore, the amount of sodium would be 4ppm, with the conductivity of 24.8uS/cm (the conductivity, contrary to pH, is directly proportional to sodium ions concentration).
If you could not find the tables, although commonly available, here is a set of graphs:
RE: Demineralised water - Effect on 304 Stainless Steel
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RE: Demineralised water - Effect on 304 Stainless Steel
RE: Demineralised water - Effect on 304 Stainless Steel
RE: Demineralised water - Effect on 304 Stainless Steel
As result, you were posting grammatically accurate descriptions, comments and replies, which were completely inaccurate from process point of view.
RE: Demineralised water - Effect on 304 Stainless Steel
mxmaciek posts "Same time, demineralized water pH would be around of 7"
then why mxmaciek do you post graphs that show that the pH will not be 7?:
mxmaciek posts "Carbon dioxide (if present) would cause corrosion as well (5uS is deionized water rather than demineralized one, so I'd expect some sodium which can mask the CO2 in pH reading)."
mxmaciek, deionized water and demineralized water are the same thing. In addition, carbon dioxide is never present in the effluent of deionized water and/or demineralized water production equipment.
mxmaciek posts "deionized water: water after one or two stages of RO, typically with conductivity around 5uS. Same is if the final stage is anion exchanger only, without mixed bed or EDI.
demineralized water: water after mixed bed ion exchanger or EDI, typically with direct conductivity below 1uS."
mxmaciek, deionized water and demineralized water are the same thing. For example, Lenntech's definition of demineralisation: Any process used to remove minerals from water, however, commonly the term is restricted to ion exchange processes.
http://www.lenntech.com/applications/process/demin...
No competent water treatment professional would consider RO effluent (without additional treatment) to be demineralized water. There are many ionic elements still present in the RO effluent since the RO process is typically guaranteed to remove only about 90% of the ionic elements whereas ion exchange systems remove about 100%. The effluent from a cation unit is also not considered to be demineralized water either, since you have removed just 50% of the ionic parameters in the cationic demineralizer unit.
mxmaciek states "after RO it will be close to neutral."
mxmaciek, a mid-career water treatment professional like yourself should know that RO effluent typically has a lower pH than neutral because carbon dioxide passes through the membrane and will depress the pH until the carbon dioxide is removed.
RE: Demineralised water - Effect on 304 Stainless Steel
When you'll be on that stage of career in water treatment, you'll discover such units like CO2 degassers added before RO to decrease the load, as a standard in developed installations designed not for home users.
Sorry, but you're contrary to yourself. I can provide several installations [working, not existing in Lenntech (there are many other companies, did you know that?) web page only] which RO effluent is on or slightly below 5uS. This stage is frequently (for me, because for you it seems to be something new) used without polishing for example to fill and maintain the district heating circuits, where use of polished below 1uS water would be waste of chemicals.
By the way, part of the stream usually is polished, in the amount needed to feed the steam cycle.
Anyway, it is entertaining to see some professional stating that "you have removed just 50% of the ionic parameters in the cationic demineralizer unit.", as during whole of my education some people were trying to convince me that on cation exchanger only I'm just replacing metal and other cations (like ammonia) with the hydrogen one (or sodium, depending from the regeneration media: brine or acid), and ionic load remains same.
Finally, about the pH of 7: as you can see on the graph, it starts with NaOH content of 0.1ppm, which gives pH of 8.4. I'm sure that having some knowledge what the pH is, you can calculate what would be the concentration of OH- ions for pH of 7.5, right? Alternatively, you could use software like the Visual Minteq.
Last but not least: carbon dioxide is a common problem in pure water applications. and for me it is a surprise that you do not know it... I'll disclose you a secret: you can have perfectly pure water leaving your EDI or mixed bed, and same time you can face CO2 problem in application. This is the effect of installation of (another surprise for you) equipment called: demin water storage tank (do not mix up with feed water tank), and mysterious phenomenons called air ingress and CO2 dissolution in the pure water. It will even speed up in the presence of sodium ions causing equilibrium movement due to the formation of sodium carbonate and bicarbonate.
I think that you must be a lucky man, if you did not experienced such issues yet.
If you'd be interested, I can provide you with more details, but I propose private messages exchange rather than this thread.
RE: Demineralised water - Effect on 304 Stainless Steel
Perhaps there is a simple difference of nomenclature. There are many levels of DI water, but the semiconductor industry only uses the purest level: http://tmasc.com/di%20water%20specs.htm
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RE: Demineralised water - Effect on 304 Stainless Steel
This posting started off with a simple question about demineralized water and corrosion. The original post stated demineralized water without any details about the application. Demineralized water is a very basic concept, but is limited by definition. (Some even want to argue about definition of demineralized water.)
What it has turned into is an off topic extraneous discussion about all sorts of assumptions where a oouple of people with some experience in water treatment are making all sorts of assumptions.
People are posting about degasifiers, condensate polishing, RO systems, carbon dioxide dissolution, water for processing ssemiconductor, storage tanks, power plant water treatment, mixed bed units, water quality and on and on. It is obvious that you have not worked long enough to have had the joke about the word ass/u/me cross your desks.
Demineralized water is not synonymous with condensate, or ultrapure water, or RO water, or decationized water, etc.
Would strongly suggest that you read:
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RE: Demineralised water - Effect on 304 Stainless Steel
That's, of course, your opinion, but you concede that the OP never specified his "demineralized water," so I fail to see why attempting to define the problem is off topic. Obviously, the OP is AWOL, but the fact that people continue to disagree about the definition suggests that this was never a "simple question."
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RE: Demineralised water - Effect on 304 Stainless Steel
RE: Demineralised water - Effect on 304 Stainless Steel
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RE: Demineralised water - Effect on 304 Stainless Steel
This is definition not related with water industry, but purely chemical. Please do not mix with distilled water or ultra pure water, this last would be with organics and non-ionic compounds removed as well (@IRStuff: I think you'll agree with that).
Regarding the demineralised water, and common use of ion exchange - the ionic impurities level can be reduced to (according the spec of existing plant after one year in service, so NO brand new resins):
- fluoride 0.1
- acetate 0.3
- formate 0.3
- chloride 0.7
- sulfate 0.7
- sodium 0.1
- ammonia 0.5
- magnesium 0.0(nd)
- calcium 0.6
all above values in ppb or ug/L, resulting with the conductivity of 0.058uS/cm
And again, not in water industry, but in power applications, these values are nothing unusual, as if you really need the pure output, you can look into the special resins with e.g. chloride leak below 30ppt (ng/L).
finally, I think that OP is not interested in this thread anymore, otherwise he would precise his specs...
RE: Demineralised water - Effect on 304 Stainless Steel
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