Mixed bed resin canister failure in DI water unit.

[MTV]

I was using NRW37-SC resin on 13X54 canisters at 125-135 degrees farenheit to create DI water on a recyclable water system, with initial water conductivity of 20-36 microSiemmens. I have 4 carbon bed canisters, one 1 micron filter and one 5 micron filter, along with a UV light to get rid of organic components before the water goes into the mixed bed canisters, with the assumption that these components are good and no organics are going into the resin. The time water passes through carbon is 6 minutes contact time. The conductivity of my DI water was held at 16-17 megaohms for about 100,000 gallons before it started to fade into 8 megaohms, and at that time I had to change the resins. I figured I needed to change the resins because I was getting water spots on galvanized steel parts, which is not acceptable. By the way, there is no salt going into the system and I have 8 gallons per minute flow through the system.<br>
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But now I changed suppliers. I now have a resin, of &quot;proprietary content&quot;, in 10X40 canisters, with all the other assumptions the same. The results I'm getting is water spots after 35,000 gallons, but the conductivity of my canister is 17-18 megaohms. Can anyone tell me what could I possibly be doing wrong? I don't necessarily need to know the resin combination, but a rule of thumb as to what kinds of resins would most likely get me these kind of results or change their properties at the temperatures and flows I'm using, so I can avoid them. Thank you for your responses.

 

[willd]

What is the pH of the finished polished water?

 

[cub3bead]

pH at a resistivity of 17-18 Mohm is meaningless. There is nothing in the water to cause it to be either acidic or basic.

If this water is exposed to the atmosphere it will rapidly absorb CO2 which will form H2CO3 which will cause both the conductivity and pH to drop.

 

[aspearin1]

I once had a similar issue where 18M-ohm water was leaving water spots on parts. Our quick fix was to give the parts a rapid solvent drying step. This removed the remaining water and left solvent to evaporate. Perhaps not what you were looking for, but worked for us. There is a thread in here that discusses the misleadings of pH and conductivity readings. What I got out of it: water temperature can alter the pH and conductivity reading without necessarily giving bias to purity.

aspearin1