Corrosion issues between Glycol?Zinc/Copper

[fx57]

Can anybody advice me to if there any issues when using a 40% Glycol water mix in a system that has both Galvanised steel and copper components? is there any chemical reaction voltage difference taht would lead to attack on the copper? the system is used to cool water glycol from a boiler cooling application through and Air cooled Condenser.
Any Advice/Comment greatly appreciated.

[Victor Poole]

The water as a weak electrolyte will cause the zinc (galvanizing) to be sacrificed, but the copper being more noble will not suffer corrosion. When the zinc has been removed, the the steel will start to corrode, but again the copper will not. To get a feel for this issue, you might compare it to water cooling in a car engine. Here you also have dissimilar metals that may include steel, copper or aluminium. In your case, if the corrosion of the steel is a problem you can reduce it by using distilled water and minimise aeration of the coolant. You might consider the use of inhibitors such are used in car coolants and antifreezes, which also use glycols.

[BerndSehrer]

When you have a closed circuit system you have no problems with steel an copper. You have to reduce the oxigen inside the system, reduce the conductibility of the water (destilled water), adjust the pH-value of the water up to 9 and everything is all right.
Take special care for your expansion system and the minimum filling pressure of your system.
But you have one big problem because the glycol dissolves the zinc. So you will get some kind of zinc-salt in your system which can reduce the capacity of heat exchangers ....
It will be better to use black steel and copper!

[Victor Poole]

Zinc is considered to be fairly resistant to most glycols, with a corrosion rate < 12.5 micrometres/year in static exposure. However, if it is oxidised to acids, I agree with Bernd, that you will get corrosion of zinc using glycol. Certainly increasing the pH will assist. It is not clear to me what the temperature range is, or what parts are galvanised. You may want to check out an industrial inhibitor at the following site:

[link Point to another website Only the registered members can access]

[fx57]

Hi Victor,
Thanks for taking the time to reply, answers my questions fully.
We do use Glycol but the level had dropped so far it did not prevent freezing and it appears then this was fully the failure mode.
My question was raised as when looking at the copper around the failure line it had an almost shiny crystalline appearance and hence my question was it an electrolytic attack on the copper.
Your reply was a great help.
Best Regards
IAn