I just replumbed the main pipe in my heating system because I was getting rust where many of the radiator branches joined the main pipe, and I when I tried to remove one of the rusted screwed-together elbows, it broke. The system was over 50 years old, so it’s not surprising that we are starting to have trouble.
Anyway, the original pipe was steel and I replaced it with copper. Each radiator branch begins as a copper pipe teed off the main, but then it is soldered (using tin allow solder) to radiator pipes, which are steel. Now that the project is complete (and works better than the original system) I’ve been reading up on Galvanic corrosion. Is this something I need to worry about? It is a closed loop hot water system. Temperature swings can be almost 100 degrees, though, but shouldn’t go about 160 F.
Apparently there are connectors available to connect dissimilar metals, but I’d rather not resolder 24 pipes if I can avoid it.
Would you rather re-solder 24 pipes now or have your pipes fall apart at any number of those 24 pipes at some unspecified point down the line?
It’s a matter of fix it now or fix it later. How long will you be at the house? They aren’t going to corrode instantaneously or anything, but if this one’s a keeper, “do it right or do it twice”.
At the plant the worked at they had to chemicaly neutalize the cooling and heating water and adjust it monthly. It saved the whole system from corroding away. Different metal have different expansion factors, but I don’t know if the one you just did will fail because of it. They do sell expansion couplings for copper to steel so you know it’s an issue.
How did you manage to solder copper to steel? I didn’t know such a fitting even existed.
What you need are called dielectric unions. They’re made of a copper or brass bushing that’s soldered to the copper tubing, a threaded bushing that screws onto the steel pipe, an electrically insulating washer that sits between the two and a big nut that holds it all together. Expansion isn’t part of the problem - it’s relative electrical activity of the two different metals.
You need to fix this fairly soon. Depending on the mineral content of the water, you could be looking at having things clog up with corrosion in a few months. Leaking will probably happen in a couple years.
As Harmonious Discord mentions, there are corrosion inhibitors that you can add to the system. Check with your local heating/boiler companies to see what they recommend.
Just a couple days ago, several apartments were flooded at an apartment building I’ve been doing some phone and computer work at. The culprit was a copper pipe in the circulating hot water heating system that was run alongside a steel wall stud. The pipe was not electrically insulated from the steel, so galvanic action did its thing, and over however many years, the pipe wall corroded away until it burst. It’s unknown whether the pipe was never protected, or if the insulation fell away, or if the pipe had been originally thought to be far enough away to not need protection, but over the years, a support may have sagged, bringing the pipe into contact with the steel. Whatever the cause, the end result was a mess.
So, the moral of the story is: Don’t mix copper and steel/iron pipe without using dielectric fittings, and be sure to insulate copper pipe from things like steel wall studs, structural steel and pipe hangers.