Eliminating Dielectric Unions between Steel and Copper??
Eliminating Dielectric Unions between Steel and Copper??
(OP)
Hello All.
I'm working on an existing 6 story building hot water heating system. The client wants to eliminate all dielectric unions in the system because there are many that leak. The system consists of sch.40 steel pipe for the mains and risers and copper for the branches to the fintube. The steel and copper are separated by dielectric unions.
My question is can the dielectric union be replaced by a brass fitting? Does the brass act like a dielectric? Is this acceptable practice, or poor engineering? I don't feel comfortable with this setup and am looking for solid proof that this is a good or bad setup.
Any thoughts? Any links to hard facts about this?
Thanks in advance!
Ken
I'm working on an existing 6 story building hot water heating system. The client wants to eliminate all dielectric unions in the system because there are many that leak. The system consists of sch.40 steel pipe for the mains and risers and copper for the branches to the fintube. The steel and copper are separated by dielectric unions.
My question is can the dielectric union be replaced by a brass fitting? Does the brass act like a dielectric? Is this acceptable practice, or poor engineering? I don't feel comfortable with this setup and am looking for solid proof that this is a good or bad setup.
Any thoughts? Any links to hard facts about this?
Thanks in advance!
Ken





RE: Eliminating Dielectric Unions between Steel and Copper??
In other applications, I've run across the issue of corrosion from dissimilar metals. The problem is, everyone knows metal A will make metal B corrode, but no one seems to have a clue as to how fast, or if it's really a problem or not. So we find ourselves using insulators between epoxy coated steel and galvanized steel. Or one of my favorites, a real Dilbert candidate, is having two pieces of metal welded together at one end, then putting insulators between them at the other end.
You might check if the plumbing codes specify the insulation. Or see if you can get a higher quality fitting that doesn't leak.
RE: Eliminating Dielectric Unions between Steel and Copper??
So there definitely needs to be a dielectric fitting between the two?
RE: Eliminating Dielectric Unions between Steel and Copper??
The answers you are going to get are going to be "well it depends" If you think about it the cheapest thing to do is buy better dieletric unions and replace the old ones and be done. If you decide that you don't need them and eliminate them and then five years from now you have a ton of leaks that will be a lot more expensive then going the conservative route.
That being said we have copper pipes connected to carbon steel with just teflon tape on the pipes in a cooling water system. I have ohmed them out and they conduct across the transition. I have not seen any pipe failures close to these junctions and some of them are 15 years old or more. But if I was putting in new, I would go with the dielectric the cost is all in labor when you work it out anyway.
Good luck
Stone cold.
RE: Eliminating Dielectric Unions between Steel and Copper??
As far as I can tell, dielectric unions come in one grade - "double extra crappy" (XXC?). They are routinely chronic leakers, and the dissolved oxygen filled make up water, that is fed into the system to replace the leakage, is the source of more corrosion that the dissimilar metal issue ever caused. They seem to be a prime example of the cure being worse than the disease.
RE: Eliminating Dielectric Unions between Steel and Copper??
A probably more expensive, but reliable, alternate for your system might be to find some insulating flanges with sleeves for the bolts etc. Properly fitted the flanges should be much more reliable than unions, and will provide the electrical insulation you need. Same concept as the flanges we use at the ends of our cathodically protected pipelines.
jt
RE: Eliminating Dielectric Unions between Steel and Copper??