black pipe/copper connection

Pipe dope seems to help this. The only ones I have see have been a male black pipe going into a cast fitting.

nrcrash said:

I see in some of the installs that people are connecting black pipe to copper pipes. Is there any reason to be concerned with electrolysis at the connection?

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if it is a closed system there will not be a problem mixing the two metals, it's done all the time. Some installers use a brass valve or nipple to make the transition.

You need O2 for corrosion to occur, the O2 in the initial fill water will allow some oxidization, once depleted corrosion is not possible, the water becomes what some refer to a "dead water".

If the system has a leak and takes on fresh water, or if non O2 barrier tubing is installed then it is possible to have corrosion, or rust problems, as the system has a fresh supply of O2.

hr

Yes electrolysis is a problem. You should not connect black pipe to copper. Best to use a brass fitting in between or a a special fitting that will electrically isolate the steel from the copper.

Use a brass coupling, valve, dielectric union.
With dis-similar metals its easier to use a brass fitting.

Tom

Certainly the copper tubing (the cathode) can eat away the steel pipe (the anode) if the water conditions (i.e. the electrolyte), are not right. I just took apart a 40 year old wood boiler system with copper-steel connections and there wasn't any major corrosion issues. I do deal with salt water cooling systems and the galvanic issues are tremendous. I do try to use a brass fitting between copper and steel since in the heirarchy of galvanic corrsion in metals they are more closely compatible and should result in less corrosion.

I just googled for a reference. Try this: http://en.wikipedia.org/wiki/Galvanic_corrosion

steam man said:

Certainly the copper tubing (the cathode) can eat away the steel pipe (the anode) if the water conditions (i.e. the electrolyte), are not right. I just took apart a 40 year old wood boiler system with copper-steel connections and there wasn't any major corrosion issues. I do deal with salt water cooling systems and the galvanic issues are tremendous. I do try to use a brass fitting between copper and steel since in the heirarchy of galvanic corrsion in metals they are more closely compatible and should result in less corrosion.

I just googled for a reference. Try this: http://en.wikipedia.org/wiki/Galvanic_corrosion

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Yes salt water makes a big difference.

Some info the CopperDevelopment Association sent me years ago when I researched dissimilar metals in piping.

"Salt water and acid are excellent electrolydes, ordianry fresh water is a weak electrolyte. The weaker the electrolyte the more limited the galvanic action. It should be emphasized that with fresh water, galvanic corrosion is not comon. Often any form of corrosion that is not clearly understood is wrongly labeled as electrolysis or galvanic action."

"Black steel is anodic with respect to copper tube, however the close proximity of the two metals in the galvanic series indicates corrosion potential is only moderate."

"The pipe dope or sealant tape further tends to increase the joints electrical resistance, further decreasing the corrosion potential."

The film that forms inside the piping in hydronic systems also offers protection from corrosion. This is one of the components in hydronic conditioner fluids, a film provider to lessen corrosion potential.

Fire protection sprinkler systems mix copper and steel connections also.

I agree a typical plumbing brass does add some additional protection, on the galvanic series it is right next to copper, so very little additional protection.

Remember regular, off the shelf dielectric unions are temperature rated to 180F, not a great fitting for boiler use, fine for water heaters, or any galvanized to copper connection.

There is always potential for corrosion even with copper to copper connections, an example in the studies shows a new piece of copper added into an older system pin holed.

You will not have any abnormal issues with steel/iron to copper. As Hot Rod said the incidence of corrosion only rears its ugly head when a constant supply of O2 is present in the system so the integrity of the piping is key. Once the O2 is purged from the system there can be no corrosion from that standpoint.

Dielectric unions are something I have never used on a boiler. Hot water heater, yes but a water heater is a completely different kind of system dealing with (usually) lower temperatures and constant fresh water.

Now........Open system OWB's are a whole 'nuther breed of cat.....they obviously can absorb water if chemical treatment levels get low or are neglected plus they are capable of easily exceeding the temps di-electric unions are rated for. I have over the years decided to not use di-electric unions on any boiler application. They invariably leak due to high water temps and this usually causes far more damage or other issues than corrosion. If the boiler owner/operator fails to monitor his water chemistry and keep it where it needs to be that's his business unless he's hired me to do it for him. Leaks are something that I always get the phone call about so I make sure that doesn't happen.

I asked this very question over on heating help last year and got the same answers as you have on here. Some said it's a no-no and to use only dielectric unions, some said brass between was ok, and some said to just thread them together and not worry about it. I do the latter, as there are so many old instally with copper threaded to iron with no problems.....in a closed loop system. The engeneering types like to specify dielectric unions, but the thought of plastic in a hydronic system is a leak waiting to happen.

My opinion is that I only thread copper or brass into iron/steel. I have found if you use copper FIP over iron it seems to leak after a few years, my theory is the softer copper/brass streaches and relaxes over the iron allowing a leak over time, not electrolisis. Useing male copper adapters into iron doesn't have this same problem as the copper is thicker and under compression. This is my theory based on what I've seen in the feild. I always use pink teflon tape and a thin painting of Gasoila dope on all threaded connections in a hydronic system.

TS