please school me on electrolysis

warno

I'm getting ready to replumb my hydronic heating system. I was talking to a friend of mine and he reminded me to be aware of copper and dissimilar metals not getting along. I thought it was just on threaded fittings but he said even sweating copper to carbon or stainless steel I would get electrolysis going on. I have stainless and copper sweat together in my system already and now I'm concerned I should take those pieces out and go with brass to copper transitions. I will be plumbing in mainly copper and butt weld carbon steel fittings. My circulator flanges are threaded cast iron. I'm attaching a picture of my stainless to copper sweats. They were done with 50% silver.

So my questions are:

Will dissimilar sweat pieces still have this issue?

Should I change out my current pieces that are sweat?

warno

Hopefully the pics will work here

Gordy

Schools in session. Pull up a couch.

https://heatinghelp.com/systems-help-center/dissimilar-metals-and-electrolysis-corrosion/

warno

Well based on that reading I should be ok with my sweat fittings. Do we have any other articles here on the subject? I'm going back in now to read through the idronics article linked in there also.

EDIT: but according the idronics article it seems it's still a good idea to use brass in between cast iron/steel and copper.

warno

I've been reading a bunch of articles last night and this morning on this subject and I'm getting very conflicting ideas. Some say dieletric unions is the only way to go, some say the are junk. Some say use brass between the copper and other material. Some say make sure the piping is grounded well. So I ask everyone here, what is the best route to go from copper to cast iron/steel or copper to stainless steel?

hot_rod

In closed loop hydronic systems I don't recommend dialectic unions.

Yours is unique in that you have an open system, but not the same as a DHW system that see continuous fresh water with O2 constantly being introduces.

One guide is the galvanic chart the CDA has a good one related to copper and brass, or find them online.

The closer the metals the less potential for electrolysis corrosion.

The Garn open system steel boilers use anode rods for additional protection, you may consider that.

Also the better the fill water, low conductivity, the better.

warno

Based on that knowledge with brass being just below copper it would make sense to transition from copper to iron or stainless through a brass fitting. My other question now is, if a system had dissimilar metals throughout it wouldn't this problem be found elsewhere also? Or does it seem to just be around the transition joint itself?

Gsmith

So what would be the explanation for pin hole leaks in copper hot water piping downstream of an electric water heater. Water heater copper inlet and outlet pipes were bonded together properly; aluminum anode probably never changed for over 12 years. 6 to 7 pin hole leaks in copper pipe downstream of the water heater. A quick google search indicated that failing hot water heater inside coatings and loss of the anode would contribute to these leaks. But, copper is more noble than steel (the tank shell) so why would the copper pipe get the hole?

Gordy

Aggressive water. To much flux. Hottest water in the pipes.

pecmsg

Type and age of Copper!

Gsmith

All leaks so far ( 6 or 7) have been mid-pipe, not near joints or couplings. Original (then new) copper piping in new house, now about 36 years old. From neighbors and other input does not seem to be a very common local occurence (not a wave of complaints) like would be the case if the city water was the cause. @Gordy, yes, hottest water will give greatest corrosion, no leaks yet in any cold water piping. But, why the copper holes and not holes in the water heater tank? I thought if the lining was compromised, the tank would leak first (give up steel to the water, much like the aluminum anode, less noble than steel, corrodes first).

SuperTech

In my experience I have seen what hot rod states to be true. I live in an area where the water has a high mineral content and on older boilers that have a copper to steel connection it is common to see corrosion.
On the same boilers sometimes I will see a copper to brass to steel transition and it will be free of corrosion.

hot_rod

warno said:

Based on that knowledge with brass being just below copper it would make sense to transition from copper to iron or stainless through a brass fitting. My other question now is, if a system had dissimilar metals throughout it wouldn't this problem be found elsewhere also? Or does it seem to just be around the transition joint itself?

Better to eliminate the biggest variable which would be the water quality. With low or no conductivity demineralized water, electrolysis is all but eliminated.

Notice at the top of the chart aluminum and magnesium are the two metals used to make anode rods, low nobility. Adding some rod might be the cheapest way to assure you have protection.

Even copper to copper, new copper against old copper for example can experience electrolysis, galvanic corrosion, given the right water or fluid condition.

Then there is the relative area effect, a copper nail in a large sheet of iron, or an iron nail in a large sheet of copper. The anode to cathode area. So a large anode area, your steel boiler, with a small cathode, you 1" pipe connection is a small potential

Modern hydronic systems can have steel, iron, aluminum and stainless alloy, brass bronze, low lead alloys, etc. It is rare to see a lot of failures related to electrolysis. Potable water systems are the most prone. Although softened water in a system greatly increases the conductive and increases the potential for galvanic corrosion.

I'd put this low on the list of concerns for your system, your multi metal connections should be fine.

Larry Weingarten

Hello, Regarding the copper pin-holing, is the water softened? That can strip off the protective hardness layer that you want inside of the pipe. Excessive flow can be a problem too. Might be fun to save a piece of the damaged pipe and slice it length-wise to see what's there.

Yours, Larry

Gsmith

Domestic hot and cold water is not softened, below is a picture:

Not really sure how to attach picture

Gsmith

Green spot is where the pin hole is/as

hot_rod

That is pretty localized, almost like flux or stray electrical current. The rest of the tube looks healthy.
There is a way to use a VOM to see if you have current traveling in the line. Is the home electrical service grounded to the copper piping?

lots of data on copper failure and causes here, probably more than you want to know

https://www.copper.org/resources/

Gsmith

Yes, electrical service is grounded to water piping and to copper ground rods near service entrance

warno

@hot rod my boiler has a magnesium anode in the water jacket. It probably needs replaced by now. It was looking pretty rough when i checked it after season 2. I'm on season 3 with the boiler now. It's a pretty short anode i bought on eBay.

I guess I'll leave my current stainless to copper sweats alone and if/when they start leaking I'll address it then.