RO/DI water more reactive towards metal than ionized water?

[Saltz Creep]

Originally posted by thrlride
RO water is agressive towards metal fittings? How so?
Originally posted by coastal
Because it is cleaned so well it is free of minerals and that causes it to act agressive towards metals
Originally posted by Saltz Creep
I disagree.
Any ions in water (seawater being an extreme example) act as a catalyst for oxidation or reduction reactions of metal.
Originally posted by coastal
ask any plumber or should I say a water treatment specialist and he will agree. We install hole house ro units and take care not to have any metal fittings. Ive seen it destroy faucets. But dont take my word for it I'm just an idiot with 20 years experience Originally posted by Saltz Creep
Don't take offense. I'm not inferring that your an idiot or doubting your experience. It's just in theory, it doesn't make any sense why the purest water would be more reactive than ionized water. Can anyone offer a chemistry explanation for coastal's experience? I might put this question in Randy' forum.
What's your expert opinion on this, Randy?

[thackray]

-An interesting piece of input-

The swimming pool industry has borrowed an equation from the water utility industry called the Saturation Index (SI). If the SI of water is less than zero, the water is corrosive, if it is zero (+/-.3) it is neutral and if it is positive it will scale (deposit Ca). The SI increases with higher pH, higher temperature, higher calcium hardness and higher alkalinity. RO/DI water calculates out as corrosive in this equation because it has no Ca or Alk. This means that RO/DI water will attack metal and also remove calcium from concrete structures (swimming pools, concrete storage pools, tiled storage pools etc).

Randy can provide the chemical insight as to why this happens.

I suspect that the “corrosive� nature of RO/DI is the reason some people recommend adding alkalinity or re-mineralizing agents to RO/DI water. Where RO/DI water might come in contact with metal or concrete containing structures such additions would be warranted. In the modern world of glass and plastic, such additions would not be necessary.

[coastal]

See I told you!

[Glenntessmer]

DI/RO water is more aggresive than less pure water. High purity water is often measured in MegaOhms of resistance. 5 stage RO DI systems can produce water in the 17 MOhm range. High purity water is an isulator not a conductor of electricity. The reason for this is that high purity water has very few ions in it to conduct electricity. *Never* drink* laboratory grade water is will tear you up. Truely pure water has a resistivity of about 18 Mohms.

RO/DI more aggresive than low purity water? How so? The water molecule is highly polar meaning the the 2 Hydrogen atoms are on one side and the O atom is on the other. The H atoms are about 105 degrees (angle) apart. Water molecules look more like
H
O< than H-O-H in structure
H

The elctrical charge of the water molecule is nuetral (not an ion but is locally polarized. Positive on the O side and negative on the H side because the electrons binding the H into the molecule spend more time on the H side.


So a water molecule has the electrons that hold the H are swung way out to one side. This leaves one side of the O atom "esposed" and able to react with anything it comes into contact. As you know O is very corrosive (rust for Fe iron) and does a great job in a protein skimmer where it oxidizes proteins.

Now in the case of impure water (tap, aquarium water) the resistivity is very low. This is due to the ions in the water. Many ions are generated by water molecules attacking impurities and oxidizing->ionizing them. These ions conduct electricity. Because there are so many ions in the water the polar nature of the water molecule is constantly attracted to the impurities and their resultant ions. Impure water is less reactive because there are so many reactions already taking place in it.

We want to start with pure water and chose the impurities we add for our tanks.

The higher the water purity the more reactive it is. However as it reacts the purity decreases and the reaction rates slow down.

bonus - truely pure water can be cooled below the freezing point of 32F = 0C because the phase change to a solid starts at an impurity site. As soon as an impurity hits the surface of supercooled water then entire body of water freezes very quickly.

Guess I didn't kill all the brain cells in college.
Glenn.

[Glenntessmer]

Rats the molecule diagram didn't post correctly. should be

............H
.......O<
............H
where the < are the bonds holding the H to the O and the ....... are just there for the diagram to post correctly

[Boomer]

Where did you guys get this nonsense from :D

When two different metals such as steel and brass, come in contact with a solution, which conducts electricity ( which pure water does not do ), a galvanic cell is formed. One of the metals will corrode in proportion to the electricity generated. If plumbing is installed using different metals (copper, steel, brass,etc.) corrosion will occur. Oxygen dissolved in water will also increase the process of corrosion. The pH and temperature of water are also a significant factors in the rate of corrosion. Above 140°F the rate of corrosion of steel doubles with every 20°F increase in temperature. And high and low pH's, such as Hydrochloric acid or sodium hydroxide. Pure water with little O2 and a neutral pH, at room temperature, is about the least corrosive water there is. Sounds like most of you are saying that pure water is more corrosive than seawater, not so at all. Soft water or pure water can be corrosive if it has a low or high pH and not because it is pure.

In general when ions are added to the water it becomes more corrosive and NOT less

Salt Creep is correct

Here is some acid base chemistry and water chemistry for you guys to read ;)

http://webhost.bridgew.edu/dlipp/Chemistry%20In%20Everyday%20LifeCH10.pdf

http://209.224.198.110/pdf/Nov_Dec_03/54-61.pdf

http://www.hc-sc.gc.ca/hecs-sesc/water/pdf/dwg/ph.pdf



You are are also misusing or interchanging terms that don't mean the same thing "corrosion", " agressive". " reactive"



Tacky

You need to watch when using the LSL, as it does not deal with corrosion /say of metals but the solubility of CaCO3 or the ability to produce scale deposits. Many don't' like it as it is a misleading corrosive indicator

*Never* drink* laboratory grade water is will tear you up

Wait till Randy or Habib sees this. We all had a long post on this subject and it is a myth

[coastal]

No one said it was more corrosive than sea water. All I was trying to say is that ro water is agressive towards metal fittings . Yes maybe at room temp with neutral ph your right but how often is ro water going to come out of a ro like that , Icant seem to get my ro to produce room temp water .maybe yours does

[Boomer]

Well, lets have it your way then :) At the same temperaure and pH tap water is more corrosive than RO/DI

[coastal]

you are saying that tap water is more aggresive to pipes than ro?

[Boomer]

Go read those links I posted ;)

[Randy Holmes-Farley]

In some cases, metals corrode more rapidly in RO/DI water. In other cases, they dissolve more rapidly in tap water. I do not think that one can make general statements about every metal.

Here's a copy and paste from an earlier thread on this topic:

http://archive.reefcentral.com/forums/showthread.php?s=&threadid=246207


OK, it looks like one should go with water that has the pH raised a bit. Pure water is not always more corrosive than drinking water (though people often say that it is, see the third article), but I presume that depends on exactly what is in the water (see the comments on stainless steel and copper in the second article).


Here are some articles:

Copper corrosion in highly purified water. Effertz, P. H.; Fichte, W. Allianz-Zent., Technik G.m.b.H., Munich, Fed. Rep. Ger. Vom Wasser (1974), 43 433-41.

Abstract

The release rate of corrosion products was studied by flowing deionized H2O at 40° through a Cu spiral in a circulatory system equipped with membrane- and cationic-exchange filters. Cu analyses were carried out by at. absorption spectroscopy, and surfaces were examd. by x-ray anal. Over 80% of the release was in the form of ions. At pH 8 adjusted with NH3, the release rate decreased and was independent of the O content. At pH 6 adjusted with CO2, high release rates were found. The O content was unimportant.


Corrosion studies in highly pure water. Marshakov, I. K.; Karavaeva, A. P.; Koroleva, T. A.; Mazo, A. A. Nauchno-Issled. Inst. Khim., Voronezh, USSR. Zavodskaya Laboratoriya (1972), 38(3), 309-10.

Abstract

Of the materials corrosion tested in a closed loop (at 69 m/hr) of deionized water with elec. resistivities of (1-10) ´ 106 ohm cm, Kh18N9T stainless steel was most resistant and is thus best suited for the construction of cooling equipment. The corrosion of St-3 steel decreased with increased water purity; it can be used as a construction material in the cooling of pure deaerated water. High-purity water caused a 50-fold increase in the corrosion of Pb; deaeration of water reduced the rate from 11 to 0.6 g/m2 day. Cu corrosion increased with heating rate and was highest in pipes carrying drinking water.

Tin corrosion induced by corrosive De-ionized (DI) water. Khandekar, Shekhar; Vedula, Lakshmi; Malshe, Vinod. Level One Communications Inc., Sacramento, CA, USA. ISTFA '99, Proceedings of the International Symposium for Testing and Faliure Analysis, 25th, Santa Clara, CA, United States, Nov. 14-18, 1999 (1999), 141-143.

Abstract

Very highly purified water such as De-ionized (DI) water tends to become very corrosive once exposed to the atm. This "Hungry Water" as known in the water purifn. world is known to be a major source of corrosion. The DI water was responsible for corrosion of tin during autoclave (pressure cooker) testing of Integrated Circuit (IC) devices assembled in plastic Quad Flat Package (QFP) with fine pitch leads. The copper leads of these packages are plated with solder. The copper leads of the packages are plated with solder composed of Lead and Tin. Due to the effect of corrosive water, Tin from solder corroded during the autoclave testing and formed thin whiskers of solder. These whiskers created a leakage path between the leads causing the devices to fail for pin to pin leakage.

[coastal]

ok here it is ro water is stipped of 98% or so of anything in the water. So that leaves you with low ph product water thus it is ready to be agressive toward pipes exspecialy copper pipes. so yes copper will leach (blue green stains) . Boomer I geuss you didnt read the first thread. RO is going to have low ph thus it will be more agressive towards metal pipes. My point is dont use metal fittings on your ro unit. Thats all

[Glenntessmer]

Hi Boomer and Randy,
The links you post and articles quoted are very good and correct. However they do not address high quality water. Great reply Randy. Note that the abstract states 106 Ohm water. Pure water is 18+meg ohm (18,000,000) Boomer, below is a quote from www.tmasc.com/cleaning_chemicals.htm about high purity water.

DE Ionized Water
De Ionized water is water that has had all of the minerals, particulates, and dissolved ions removed by a filtration process. It is extremely pure water. The level of purity is expressed in Meg Ohms [resistance to an electrical current DI water is extremely active. It will pull ions from any surrounding metal, including stainless steel. To heat DI water in a stainless steel vessel is possible though if it remains standing in the vessel it will eventually pick up ions and deteriorate. A better method is to heat the DI water only when it is needed.

Ultra pure DI water is rated at 18 Meg Ohms this is extremely pure water. Lesser grades of DI water are also used for cleaning. [10 meg ohm etc.] ***It is so clean that if you drank it would pull the ions from your body chemistry and would cause serious health problems. ***

The high purity DI/RO water spigots at work (semiconductor reasearch are all label as health hazards and "do not drink"

[jfinch]

RO is going to have low ph thus it will be more agressive towards metal pipes.

Why would RO water have a low pH? Pure water will by definition have a pH of 7.

My point is dont use metal fittings on your ro unit.

Very good advice. All water has the potential to pick up some ions from the metal. No reason to dump 'em into the tank.

***It is so clean that if you drank it would pull the ions from your body chemistry and would cause serious health problems. ***

Myth. I'd be dead by now if it were true :lol:

I think some RO/DI units have this warning because the resins used in the DI chamber are not NSF certified.

[jfinch]

Any of you work around steam systems? We have many boilers and miles of steam and condensate piping. The feed water for our steam system is very pure RO water. Admittedly not 18 megohm, but as pure as most home RO/DI units. The condensate from these systems is pretty corrosive. But the reason is not because it's been demineralized, it's because of the O2 and CO2 dissolved in the water feeding the boilers. We go through great lengths to degass this condensate. We have piping systems that are 30-40 yrs old and still have adequate pipe thickness.

IMO, the it's the O2 and CO2 that are the issue when it comes to fresh water corrosion. Seawater is completely different beast.

[Glenntessmer]

Hi jfinch,
Do you know the resistivity of the water you've been drinking? - just curious

[Randy Holmes-Farley]

Note that the abstract states 106 Ohm water.

Actually not. That is font error. It is purified water.

"(1-10) ´ 106 ohm cm" Is really 1-10 x 10^6 ohm cm (or something similar, I don't have the original at home).

RO is going to have low ph

It may, and should if it is only pure water plus CO2, but mine reads above pH 9. I do not know if that is real or artifact, however.

[Glenntessmer]

Thanks for the clarification Randy. I'll look into the drinking 18MOhm is bad or not.

[jfinch]

Do you know the resistivity of the water you've been drinking?

Not sure... all I know is that it's lab grade DI water. The unit is a series of very large AC and DI beds that Culligan services and maintains. I was introduced to drinking this stuff by a couple lab techs that I worked with a few year back. The first I ever heard that it could be unhealthy was right here at reefcentral.

[ab5ebdxer]

Drinking free water as a bad thing is not a myth. I agree it wont eat your stomach but it is not good to do. Just driking reqular water in large amounts is enough to drop your blood Sodium levels to the point of seizure and death. I would not recommend drinking lots of free water. As an IV free water is a complete no no.

If your waters ph is not 7 then it is not pure water. It has to have more or less hyrogen ions out of proportion to what a ph of 7 is.

[gillboy]

the 18 Mohm water used in the semiconductor industry is agessive but I think that the scale of impurities that the industry can tolerate is so low that unless you are working on the atomic or molecular scale (as semiconductors do) you would not be able to tell the difference - that salfert kit just won't do.

I think the reaction chemistry in high purity water (redox?) is different than the reactions discussed in salt water (electrochemistry?)

I gotta get my inorganic book out

and as the doc says pH is the inverse log of the H+ ion concentration

[Boomer]

As I said before the corrosiveness of water is dependant on its conductivity, the ions in solution, which produce a galvanic cell. The metals will corrode in proportion to the electricity generated. If plumbing is installed using different metals (copper, steel, brass,etc.) corrosion will occur. The corrosion effect is increased as temp rises and pH drops or rises above 7 for some metals. This is what started this tread go back and look at the first post.

It is not that RO/DI water is not corrosive, you guys are missing the point. Any water is/can be corrosive. Pure water at the same pH and temp is less corrosive than tap water at the same pH and temp. Lets throw in O2 also. It is only the lowering of the pH created, as RO/DI water reacts with CO2 and forms carbonic acid. In general RO/DI water does act with CO2, making it more corrosive. A FW solution with a pH of 5 will be more corrosive than a solution of pH of 7,same for RO/DI water


If you go back and look at Randy's abstracts there is nothing there that says pure water is more corrosive than FW water, at the same pH and temp......as pure water produces no or little galvanic effect. Some FW may have corrosive inhibitors and some may not. Some treatment plants use sodium hydroxide, which raise the pH up high in tap water, while others are low in pH. Many tap waters use Chorine, Chloramine or ozone all three are very strong oxidizers, which create corrosion.

Pure water has a higher activity than FW or SW, that dose not mean it is more corrosive. Activity means the wanting of an ion to stay in solution or leave solution and wanting to leave solution is a high activty which FWand pure water have. Seawater has a low activity, things like to stay in solution. And FW has a lower activity than pure water. Meaning, you can dissolve more NaCl in seawater than you can in pure water. Or more NaCl in FW than pure watrer.

Did any one read the PDF's' I posted, some remarks from them

Acids and Bases Vary in Strength

• Stronger acids donate more protons
– HCl
• Stronger bases accepts more protons
– NaOH
• Corrosiveness = Strength

How Does a Chemist
Measure Strength?

• Ability to conduct electricity
• Pure water does not conduct e-
– few ions
• Acetic acid conducts slightly
– more ions
• HCl is very conductive
– lots of ions!

Concentration and Corrosivity

• Small amount of strong acid in water?
• Large amount of weak acid in water?
• Compare strength at equal concentrations!

Corrosion


“Corrosion� is the loss and eventual failure of metals and
alloys from the electrochemical reaction between water
and the pipe material. It is separated into two basic types:
general and localized. General corrosion describes the potential
dissolution of pipe over its entire exposed surface.
Localized corrosion affects only a small area of the pipe
surface.


• General corrosion. This is a breakdown of the pipe
material at a uniform rate over its entire surface by direct
chemical attack. It is caused by the loss of the protective
passive film that forms on the surface of the
pipe coupled with a chemical reaction occurring between
the pipe material and the chemicals in the fluid.
Particular types of corrosion include the following:


“Galvanic corrosion� is a type of corrosion that occurs
in a liquid medium (called an electrolyte) when
a more active metal (anode) and a less active metal
(cathode) come in contact with one another and
form an electrode potential. When this occurs, the
more active (noble) metal will tend to dissolve in the
electrolyte and go into solution.





Metals used in distribution systems, such as cast
iron, steel and copper, tend to corrode in contact with
water because of their thermodynamic instability. The
deterioration of concrete, asbestos-cement and cementlined
cast iron pipe, all of which are commonly used in
distribution systems, may also occur. Natural waters
contain gases, colloidal matter and a variety of
electrolytes and non-electrolytes that, together with pH,
determine the extent to which corrosion is possible in a
given situation.(7) In general, the presence of anions that
form soluble compounds with a metal increases the
corrosiveness of the water with respect to that metal,
whereas the presence of anions that form insoluble
compounds may increase its passivity.

The role of pH in the corrosion of metals used in
water distribution has been summarized by Drane(7) as
follows:

1. Steel corrodes at approximately the same rate at
all pH levels commonly found in natural waters. The
form that the corrosion takes is, however, affected by
pH. At values between 7.5 and 9.0, there is a tendency
for the corrosion products to adhere in a hard, crusty
deposit. At lower pH values, adherent corrosion
products are not so evident, although a very hard form
of deposit is sometimes seen in pipes that have been in
service for some years. Loss of head, owing to scaling
of a pipe, is more commonly found in the higher pH
range; at lower pH values, “red water� complaints
arising from corrosion products in suspension are more
common. Cast iron behaves in a manner similar to steel
at alkaline pH values, but at lower pH values it is subject
to graphitization.

2. Copper is markedly affected by pH. In
aggressive waters, slight corrosion occurs, and the small
amount of copper in solution may cause staining of
fabrics and plumbing fixtures. In addition, redeposition
of copper on aluminum or galvanized surfaces sets up
electrochemical cells resulting in pitting of these metals.
In most waters, the critical pH value is about 7.0, but in
soft waters containing organic acids it may be higher.

3. Lead corrosion is affected by carbonate content,
pH and mineral constituents. The simplest method of
control is usually to increase the pH by adding alkali.
Few waters are plumbo-solvent if the pH is above 7.0.
Zinc coatings on iron and galvanized steel are
attacked in the same way as iron, but usually more
slowly. Very alkaline waters, above about pH 10.5, can
be aggressive to zinc(13) and will often remove
galvanized coatings.

Corrosion control may result from calcium
carbonate deposition. The factors affecting this process
are temperature, pH, total dissolved solids, hardness,
carbon dioxide and alkalinity. A rigorous treatment of
the calcium carbonate – bicarbonate equilibrium is
invariably impossible under practical conditions.
Accordingly, a number of semi-empirical and empirical
relationships using easily measured parameters have
been developed

Not to mention a 50 page chapter on the corrosiveness of water in my book Water and its Impurities. Almost any FW chemistry book discusses it in great detail. Lastly, you don't know what the pH of your RO/DI is, as a pH meter or test kit can't measure its pH, as there is noting in the water to measure. We just normally assume it is lower than 7. I posted info on this on a recent thread.

Finally, as Randy pointed out, it it may be hard to tell which one may be more corrosive, "Bobs RO/DDI or Jim's tap water", as there are to many unknowns about each sample but two samples at the same temp, O2 and pH ( nothing added to the water) the FW will be more corrosive than the pure water.

Doc

Drinking free water as a bad thing is not a myth. I agree it wont eat your stomach but it is not good to do. Just driking reqular water in large amounts is enough to drop your blood Sodium levels to the point of seizure and death. I would not recommend drinking lots of free water. As an IV free water is a complete no no.

If your waters ph is not 7 then it is not pure water. It has to have more or less hyrogen ions out of proportion to what a ph of 7 is

Yes, the myth was that it will eat your stomach away. Lots of "free water", didn't know than thanks. Also didnt' know lots of normal water may drop your Sodium levels and IV free water is a no-no :D Drinking a glass of "fee water", a day is then not an issue ?

Yes, pure water has a pH of 7 and a pOH of 7 and is just H3O+ and OH-.

[ab5ebdxer]

I dont think a glass of free water a day is an issue, as long is that is not all you drink. I thought the RO/DI water tasted bad anyways. Do people really drink this stuff?

[Boomer]

Y es Doc they do. And many home tap units use RO systems, although no DI so it is not that pure. There are a few lab chemists here that drink it all the time. We had a thread on drinking RO/DI water a few months ago. I don't like the taste of it etiher ;) I like my lake Superior water.

Some technical data from that thread, sounds like a doc, who disagrees with you on drinking RO or RO/DI water :D I completely forgot about this statement........getting old

There is nothing wrong with RO or RO/DI water for drinking. Your body is very adept at maintaining osmotic equilium in the setting of hypo and hypertonic fluids. The primary components that make up serum osmolality are sodium, glucose, and blood urea nitrogen (which can be roughly estimated by Na x 2 + BUN/2.8 + glucose/18). Serum oncotic pressure is also maintained by blood protein, primarily albumin. None of these things are found in great quantity in tap water or RO/DI. It just tastes different because of the lack of contaminants normally found in tap water. Most of the trace elements and ions you get from your diet, not drinking water.

You can cause electrolyte imbalance by drinking enough RO/DI or tap water alone (called psychologic polydipsia, which is rare but usually seen in schizophrenics and others with mental illness.) And I'm talking gallons of excess water a day. You simply overload your kidneys ability to get rid of the hypoosmolar solution and eventually your sodium drops too low and you seize (typically when it hits less than 120 MeQ/dl - normal is 135 -145). In contrast this can happen inadvertently in newborns just by giving them as little as 8-12oz of tap water a day for several days due to their relative body surface area (which is why newborns should only receive formula or breast milk.)

Ok, now that I have bored everyone silly with this long winded explanation, the bottom line is RO/DI is just as safe as tap water, as long as you drink it to match your daily requirements. Any ions, minerals, etc that have been removed you will easily replace by eating. The only thing that you might not be getting enough of is flouride, but as long as you brush your teeth you will be fine. Just be careful with the kids since flouride in municipal water has been shown to reduce cavities in children, and they don't brush like they should. So drink up!

and from WaterKeeper a lab/ water chemist

RO units have been used for years for drinking water purposes. From under the counter units to massive million gallon per day plants it is a method that is recognized by EPA, AWWA, NSF and a host of other American and World health organizations. The greatest use is for de-salinization but it is also used to treat difficult supplies that would otherwise be unfit to drink. The main reason it is not more widely used is that it is wasteful when used on a large scale. The reject water loss outweighs the benefits of the output quality.

DI is a grey area. There is no known harm from drinking DI but there is also no demand because of the cost of treatment. This means there has been almost no attempt in the water treatment industry to promote its use. Of course, in an off hand way millions of people drink its close cousin sodium exchanged (demineralized) treated water form either home units or municipal supplies. Except for the added sodium in such water, there have been no health related issues. Drinking DI would even eliminate the sodium problem, but again, cost is the factor and DI would cost more than sodium exchange as the sulfuric acid and sodium hydroxide used as the regenerants cost more than salt. Also, these regenerant's disposal is somewhat more involved

The full thread

Do you drink your RO water

http://archive.reefcentral.com/forums/showthread.php?s=&threadid=218154&highlight=drinking+Ro%2Fdi+water

[ab5ebdxer]

I dont think he disagrees with me. In large amounts water is bad for you which is what he says. Drinking large amounts of RO/DI is bad for you. I recently saw a 4 year old who had a sodium of 122 normal is around 135. This is just about low enough to cause seizures. He had a small bowel obstuction and was only give water. This was not only reason his Sodium was so low but if he had been drinking something like gatorade he most likely would have been fine with his sodium. It is hard to make general statements, there is usually always an exception.

[Boomer]

Ok thanks doc :thumbsup:

[ab5ebdxer]

Just on a side note I had a patient with what we believed was psychologic polydipsia. It was kind of weird because he also had TB meningitis which could have caused some of this. Any ways we had to get maintaince to come in and turn off all the water to his sink and his shower in his room so he would stop drinking water.

[Randy Holmes-Farley]

Any ways we had to get maintaince to come in and turn off all the water to his sink and his shower in his room so he would stop drinking water.

:D OK, there are some folks that shouldn't drink DI water.

[Boomer]

OK, there are some folks that shouldn't dring DI water

I see that glass in your hand, so put it down :D

[Randy Holmes-Farley]

Hey, that's Diet Pepsi. :D

[FlashPro]

I'm an hvac and utilities engineer that does work for biotech companies (like Pfizer, Bristol Myers Squibb, Wyeth, GSK) and obviously they use plenty of DI water for making drugs. A plant steam boiler will use treated city water and is piped with carbon steel. But clean steam (the stuff for making the drugs, not the hvac) uses DI water that's filtered (at a cost of about $10/gal) to around a few parts per billion of total disolved solids. The piping for clean steam and clean steam condensate ALWAYS uses stainless steel. I've seen first hand the difference between stainless steel and copper or steel piping used for clean steam condensate. Contractors sometimes make mistakes or try to save money by using copper in the condensate lines. The non-stainless steel piping erodes like crazy.

[jfinch]

This has gone off on a bit of a tangent, sorry...

A plant steam boiler will use treated city water and is piped with carbon steel.

Is that a steam generating boiler or a hot water HVAC system? Closed loop systems (like most HVAC boilers I've seen) are non corrosive because they are close-looped. The O2 and CO2 that are initially in the feed water are used up quickly (causing a small amount of corrosion) and since there is not make-up water needed the corrosion then stops.

If they are steam producing boilers then they should be using demineralized feed water and incorporate a condensate/steam treatment program (i.e. filmer amines and pH control).

But clean steam...

If this steam is used in making food or drugs then certainly it will incorporate stainless steel because a boiler feed water/steam treatment program could not be used. The chemicals used in these treatments would make the steam unusable for food or drugs. Any steam without some type of treatment will corrode like crazy, but it's due to the O2 and CO2. Even minute traces of these gasses can be problematic.

Believe me... if we had a cheap source of 18 megohm water for our boilers we'd use it :D