Steel/Copper corrosion in hydronic heating system. 1

[hooknem]

All, Please forgive me as this is more of a plumbing system question but I have not found a suitable answer to this question in my efforts so any help you could offer is greatly appreciated.

I have a home hydronic baseboard heating system that is run with galvanized tubing and soldered directly to copper fittings at the heating elements. This system has been in place for 50 years with no apparent signs of corrosion at any of the joints. What is the reason that no electrolytic corrosion takes place? The system is a sealed hot water system running between 100 and 180 degrees.

Thank-you for any help you may offer.

 

[strider6]

if it's a sealed closed system without oxygen then this can explain why there is no corrosion. If you don't have oxygen or other oxydant then the corrosion process can't take places. another possibily is that at that temp a layer of carbonate precipitate on the internal surface of the tubes preventiing corrosion.

ADVANTAGES OF CLOSED SYSTEMS

http://www.gewater.com/handbook/cooling_water_systems/ch_32_closed.jsp#ADVANTAGES OF CLOSED SYSTEMS

S


Corrosion Prevention & Corrosion Control

 

[moltenmetal]

The answer is the lack of oxygen inside the piping system. Any oxygen you feed with a flush or re-fill leaves via de-gassing when the water is heated, and via corrosion of the zinc-plated or bulk carbon steel material. You also have dry conditions on the external of the fittings, because they're not leaking, and they're hot so no condensation occurs on them.

This is of course a good reason NOT to flush and re-fill your system periodically! The secret to keeping it in good shape is to keep it TIGHT and add as little fresh water (and hence fresh oxygen) as you possibly can.

 

[Slowzuki]

There are oxygen scavenging and corrosion inhibiting additives used in hydronic heating systems as well to prevent corrosion. Not always used in closed systems.

When inspecting a hydronic system, if lots of makeup water has being used over time say due to a collapsed pressure tank, you are almost guaranteed to find rotten pipes and or boiler on the inside.

 

[trevorvdv]

We are considering manufacturing & installing a solar water heating system. Inner, potable water tank, heated by a vented jacket water system. Jacket water or heat transfer water is occasionally replenished via vented overhead storage tank.
We anticipate daily jacket water to reach a minimum 60-70deg C. Altitude 2000m.
Intention is not to flush the jacket or transfer water.
Our debate is if this is warm enough to expel oxygen from this stagnant water heat transfer medium??
We are gauging the materials to use for manufacturing the system