Do mixing black pipe and galvanized piping cause pinhole leaks?

Dairon421

Been doing boiler pipe repairs and majority of the leaks  has galvanized mixed with  black pipe. If this the reason can you explain to me why? If not what else could cause pinhole leaks in boiler piping.

Jamie Hall

It can, and probably will. Galvanized pipe is steel with a zinc coating, more or less well applied, and black iron is just that. Black iron. Steel rusts, and the galvanizing tries to protect it from that by being eaten away itself. I'd almost be surprised if you didn't get leaks at threaded joints where the two join. For that matter, I've noted that galvanized often just develops leaks on it own.

ChrisJ

Jamie Hall said:

It can, and probably will. Galvanized pipe is steel with a zinc coating, more or less well applied, and black iron is just that. Black iron. Steel rusts, and the galvanizing tries to protect it from that by being eaten away itself. I'd almost be surprised if you didn't get leaks at threaded joints where the two join. For that matter, I've noted that galvanized often just develops leaks on it own.

Jamie,

As far as I'm aware modern "black iron" is steel pipe with a protective coating and galvanized pipe is the same exact pipe but galvanized.

Even if one were actual iron I don't see why galvanized pipe would have an issue with that.  Its not like mixing brass and aluminum or copper and steel.   They're very similar.

pecmsg

Once the threads are cut there both just steel pipe as far as any connection is concerned!

As far a quality the Chinese fittings and pipe were getting are garbage.

WMno57

Steam or Hot Water?

Cutting threads on a galvanized pipe compromises the galvanizing in the threaded area. So bare steel gets threaded into galv fittings all the time.

The mixing of galv and black that you see could be previous owners replacing the worst of the worse. I suspect the root cause of your pinholes is age and water quality, not mixing G and B.

How often is make up water added to your system?

Dairon421

@WMno57 Its a Steam System. 

hot_rod

It will be a steel to steel connection, so no issue there. Steamers like a bit of alkalinity, so if you raise ph or add a conditioner, that too will protect the pipings insides.
Check the water ph after it runs a few days, adjust as per the boiler manufacturers recommendations.

Some info from the Rhomar manual