hot water system drained and open to air...rust?

R. Kalia_4

Yes, I have isolated what I could, but in an old (converted gravity) system, not much of that is possible.

Filling with N2 is not an option: if I could close it up I would fill it with water, but I am not ready to close it up.

My question is whether I am causing any major damage by leaving it open to air while I work on it a little bit each day.

R. Kalia_4

Is it a bad idea to have a hot water system open to air for a couple of weeks while I'm working on it on and off in the evenings? Or is rust more of a months-and-years kind of thing?

Brad White_9

Rust Happens

The key is that in a closed water system it can be managed. Once a system is filled, purged, vented and "boiled off" (heated to limit a few times for a final burp), the water should remain essentially Oxygen-Free forever. Ideally.

You ought not drain the system down unless absolutely necessary.

Personally, I prefer valves and valves... If I have to add a radiator, I have valves at the ready. If I have to move one or work on an area, I can isolate any part, drain it, work on it and get it back in operation without taxing the rest.

If you use products like Rhomar 922, it has an O2 scavenger among other good things which passivate the metal. But start with good, clean water, heat it to limit a few times, vent and top it off at least.

If I have spent a good deal of time and money on treating my water and system, I would save the water for re-introduction but the "dry" piping, if it had to be laid up, I would fill with dry nitrogen to about 5 psig for the duration. Purge of air, fill with nitrogen, bleed off a little then close it up to 5 psig. Carefully.

My $0.02

Brad

Brad White_9

I would be more concerned

with the repeated wetting and drying, that is where the damage is being done.

If you lay it up dry (used compressed air maybe if N2 is not an option), that would be best.

Laying up wet would be my next choice, second because 1) It is Water and 2) It has it's full compliment of free O2.