Di water and copper pipe compatibility 1

[centorr]

We were changing heat exchanger pipe material from c/s to s/s due to being advised that carbon steel will quickly contaminate the DI water. We now were asked to investigate making heat exchanger using copper pipe since the Induction power supply vendor rutinely runs DI water in copper manifold to cool their transformers.
- Is DI water flowing thru copper pipe compatible, or will there be a chemical reaction that will either significantly effect purity of DI water or attack the copper pipe walls?

 

[unclesyd]

I would not recommend Cu piping for DI water. DI water will cause copper to corrode, mainly pitting, and leak over time. It will definitely add Cu Ions to the water.
We use Al piping in several pure water streams.

 

[kenvlach]

centorr,
DI water will dissolve roughly 30 ppm Cu at ambient T and typical pH of 5, and more at higher T. Enough to visibly contaminate the water. Perforation is likely in the higher T portions of a closed system.
Of course, with enough Prestone, Peak, etc., you can use copper, brass, carbon steel, etc.

The only metals suitable for contact with pure DI wwater are noble metals (gold, platinum) and those with highly passive oxide films (304/316 SS, Ti, Zr). Aluminum 1100, 3003, 5052, etc. can be used to 100^oC if 0.04 ppm dissolved Al is tolerable [value for steam condensate tanks of Al 3003].

Pure DI hot water systems typically use 304/316 SS or Kynar (PVDF). Pyrex was also used in the past, but not so much anymore.

 

[moltenmetal]

DI water will be contaminated by trace levels of copper ions if you run it through copper pipe or tubing. But deoxygenated, neutral (i.e. properly deionized) water will not rapidly corrode copper. If this were not so, the millions of miles of copper steam tracing out there in the world would not survive, and it's clear that it does. Copper is routinely used for steam tracing, which has it in intimate contact with boiling, deoxygenated distilled water.

If the DI water is in contact with a source of oxygen, copper will fail rapidly.

 

[TBP]

Copper doesn't necessarily fail as steam tracing, but the condensate draining through the tracing can pull copper off the tubing. I've seen thermodyamic steam traps in this service fail because copper plated-out on the disc, allowing steam to blow through. Even worse is if the copper gets back to your boilers. It'll set up a galvanic cell, causing corrosion that looks very much like oxygen pitting. Bad news if that happens.

Copper in and of itself in condensate service doesn't normally cause problems. Some other factor has to be present before it becomes an issue. But if you've got copper, half of the equation is already in place. If I had copper tracing, I'd sewer the condensate rather than send it back to the boiler. It's not a corrosion issue that is so severe that it will affect the tubing - it's the potential for feedwater contamination.

 

[inductionexpert]

Induction power supplies use DI water between 50 micromo and 70 micro mo. The used of 0 micro mo Di is hungry and will attack copper or stainless. Put 30 % glycol mixture and it buffers the Di an it will stay in the 50-70 window for up to a year with no corrosion.
Fred Specht
Ajax Tocco Magnethermic

 

[EdStainless]

As I recall our X-ray tubes use 25megaohm (0.04micro mho) water for cooling. It must not conduct at 80kV. It has to be continously polished through a resin bed to maintain that resistance. And the copper tubing inside the xray tubes does not last forever.

= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[MJR2]

Does not a glycol mixture increase the conductivity and the risk of galvanic corrosion. The risk being present in transformers and hollow conductor electromagnetic coils.

 

[kenvlach]

inductionexpert,
Please provide info on the corrosion-inhibiting properties of glycol.
My understanding is that glycols primarily extend the liquid water temperature range. Corrosion inhibition comes from azoles [a few ppm of mercaptobenzothiazole (MBT), benzotriazole or tolytriazole; more if chlorine is present]* or sodium silicate.

*ASM Handbook, vol. 13, Corrosion p. 497.

I do recall that glycols can react with & neutralize dissolved CO₂ and some organic acids.