RO Water Used to Make Clean Steam - Appropriate Material for the Condensate Piping??

[BronYrAur]

I have an application where RO water is used to make clean steam for use in a surgical air handler humidifier. All steam piping and the humidifier manifold is stainless steel. Drip traps and condensate piping back to the steam generator are stainless steel.

My question is in regard to the drain piping underneath the steam duct manifold. There is a drip pan that collects any excess water from the steam dispersion tubes. The water would get to this pan by "free fall" through the air inside the duct. The discharge line from this pan has a P-trap to overcome duct static. Again, this is all stainless. The debate comes with the piping outside the ductwork.

There is concerns that this condensate will be highly corrosive to the point where dumping it into a cast iron drain/sewer pipe would be a bad idea. I'm trying to understand if this is really the case. Since this condensate is the result of water "falling out of the air stream", how is it any different than the water that condenses on cooling coils? Cooling coil condensate is essentially distilled water, isn't it? It would seem to me that cooling coil condensate would be highly corrosive as well, but those are routinely sent to the sewer drain.

So I am trying to understand the chemistry of water that exits the humidifier drip pan of a unit that uses RO water to make clean steam. Can I put it into a cast iron sewer drain?

 

[EdStainless]

If it will be mixing with other water, yes.
But if there is a section of line that is only this RO drain then you need to be careful.
I presume that this air is very well filtered.
This water will contain no minerals or metals, but it will contain dissolved O2 and CO2 from the air.
The CO2 will lower the pH of the drain water.
I have seen high purity water drains cut grooves into CI piping.
What is wrong with using plastic for this section of drain?

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P.E. Metallurgy, Plymouth Tube

 

[BronYrAur]

I could use plastic to get to the floor drain, but the underfloor sanitary piping is already in place and is cast iron. This would not be a drain for the RO itself. Just a drain of the condensate coming from the air handler humidifier dispersion tube pan.

 

[itsmoked]

There are several neutralizing systems for handling this kind of issue. They're cartridges that you plumb inline.

One example

Another

Different Style Allows recharging and checking at-a-glance

Youtube demonstration

Keith Cress
kcress -

http://www.flaminsystems.com

 

[BronYrAur]

Thank you. I use those neutralizing systems on condensing boilers. I'm just trying to understand from a chemistry standpoint if this steam condensate is really any different than a cooling coil condensate.

 

[EdStainless]

This water is so clean that there is a risk.

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P.E. Metallurgy, Plymouth Tube

 

[IRstuff]

Invariably, what starts out as "pure" water, as measured by our resistivity meter at 18 Mohm at the output of the RO system would "collect" things like CO2 and whatnot, and drop down into the 10-Mohm range.

There was a fascinating story when I was growing up about a scientist who discovered what he called "polymerized water," or "polywater," for short, that was actually purified water that had dissolved glass from the glassware it was stored in. Doh!

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

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[BronYrAur]

But isn't the water condensed on a cooling coil just as "pure" as this RO Steam condensate? Cooling coil condensate is water coming out of the air stream .... I would assume mineral free and therefore somewhat deionized. I never hear talk about the corrosive nature of cooling coil condensate, so I am trying to understand the difference. I see cooling coil drains with PVC, copper, galv, etc. all the time. and they always run to the closest floor drain, which may very well be cast iron.

 

[moltenmetal]

RO water isn't corrosive if it's deoxygenated and close enough to neutral in pH, which your steam condensate is likely to be. If it is oxygenated, since it has no buffering capacity it can drop in pH easily and become somewhat aggressive toward a variety of metallic materials.

If you're concerned about keeping RO or DI water completely pure and free of metal ions, that's a very different matter than being concerned about the material being aggressive toward the general corrosion of metallic materials- a very little bit of dissolution can render DI/RO water conductive and hence contaminated beyond the tolerance of its permitted use, but that same amount of dissolution may take a hundred years to corrode pipe noticeably. It is for THIS reason that DI/RO water is often conveyed in plastic piping- to keep it pure, not because it is particularly corrosive.