Copper branch piping in large system with iron risers?

Thor

I've had excellent luck with every question I've asked on the wall so far, so let me try this:



I'm in a large building complex, about 80 years old, where the hot water heating system was originally all iron pipe and rads (about 3/4 mile total (!) of horizontal main pipes in two loops, plus over 100 riser pairs per loop).



About 10 years ago the maintenance staff started to use copper for branch piping in the course of repairs. They do use bronze fittings at the junction of the two metals.



Now, of course, this is a building with about 1,000 80 year old cast iron rads in it and many of those are so full of crud they have perhaps 1/2 their design heat output. But it is my impression that problem has become much worse as more and more copper has been added to the system. Having just replaced a few of these (one of which came apart in very spectacular fashion as we "cleverly" tried to muscle it out of the ground floor apartment's window... oops) I know the crud is mostly iron oxide -- coal black when wet, perfect rust red once dry. Rust dust.



Could the increased amount of copper in the system be making more rust dust, from galvanic corrosion in the iron pipes and rads even though with bronze fittings, it's not obvious where the metals join? Or maybe this is a coincidence and those old rads are just old and the process of their gunking up hasn't really accellerated over the past 10 years.

LarryC

Lots of rust is because of lots of oxygen.

Lots of rust is because of lots of oxygen.  I am thinking the root cause of these problems is lots of oxygen is getting into your system. 

 

Do you need to add alot of make up water?  If so, WHY?

 

 Is there white smoke or steam in the boiler exhaust?

 

Are you familiar with the concept of PUMPING AWAY from the POINT of NO PRESSURE CHANGE ?  It could be that your are sucking air into the system at the pump(s) and consuming the oxygen in forming rust?