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Using Deionized Water in Closed Loop Heating System


We have designed a closed loop heating system using carbon steel pipe. Our customer wishes to use Deionized Water for the first fill and make-up. We expect to add anti-freeze, anti-bacterial and rust inhibitors. What additives are used to reduce the aggressiveness of the deionized water on the carbon steel?

Willam Stewart


The corrosion inhibitors will protect the steel.

Lyle Kirman
consultant - Cleveland Heights, Ohio


I would not use DI Water in carbon steel pipe. I worked in an Aluminum Rolling Plant 25 years ago and they did the same thing and within 3 months it ate the carbon steel pipe fittings up and had to be changed out. They could just use the RO Water and have clean water, but I would not use DI Water.

Larry Dilda


We use the reject stream from our ultrafilters (which is still very high quality DI water) to top off the process cooling water system for our research facility. Corrosion inhibitors are added to protect the metal surfaces in the system. So far it has been very successful!


Timothy J Miller


Using research grade DI would not be wise and would be costly. I seriously doubt if 1 or 2 meg ohm water would cause any problem if inhibitors were used.
A tiny RO system would be optimal from my point of view.

James Watts
Navarre, Florida

April 2, 2011

I wanted to know if I could mix Corrosion inhibitor to a close loop DI water system. I have 15 Mohm-cm for resistivity, 7.74 micro S/cm conductivity and 7.7PH level. Answers are greatly appreciated. I have PECVD system that uses copper, brass fittings. Will this DI water leach the copper and brass. Thank you.

Amar Singh

April 6, 2011

DI water is corrosive to copper and brass, but a corrosion inhibitor may correct this. I recommend that you contact the inhibitor supplier for their advice on this.

Lyle Kirman
consultant - Cleveland Heights, Ohio

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