Closed-loop Water Aggression/Copper 1

[BradV]

I need an explanation and clarification regarding the aggressiveness of water in a closed-loop (steam-water shell&tube heat exchanger) system. I believe that water becomes more aggressive over time, especially when heated, and corrodes copper. What are the causes of this, and what steps can be taken to avoid the corrosion and damage to copper piping/tubing? A web-site/reference would be helpful.
Thank you.

 

[TBP]

I'd bet that you're suffering erosion, as opposed to corrosion. If you have a system that is over-pumped (big pressure drops & associated velocities) - that will do it. If you have a constant circulation with un-reamed copper pipe - that will do it. If you're lucky enough to have both - bummer. I've seen copper pipe fail in as little as 6 months in situations like that.

Corrosion will be a general wasting of pipe and fittings. (And that can happen.) Erosion will be most evident at joints and especially at 90* els. The high velocity water swirling around the elbow will literally scrub metal off the pipe and fitting walls, just like stones being smoothed by water flow in a steam. If un-reamed pipe is also a factor, you can see significant metal loss just downstream of the little ridge that the cutting wheel leaves, if it hasn't been reamed properly.

 

[kenvlach]

The other possibility is, of course, corrosion due to poor chemistry of the water.
What is the pH? In general, pH of 8 is best for Cu as it will form a stable hydroxide film.
Was it purified water plus an inhibitor package, or just tapwater? Any analyses, either pre- or post-use?
DI water w/o additives has high dissolving power.

With a closed loop system, sometimes the cheapest solution is to add an automotive antifreeze/coolant. Contains silicates to form protective film, acid neutralizers, etc.