SylvanLMP
In reply to message posted by Douglas Tedeschi:
I am repairing broken hot water heating system pipes (usually cracked elbows or tees). Is it usually permissable to replace cast iron elbows or tees with copper? The reason for doing this is to avoid replacing an entire run of pipe, or sometimes because I am working in very tight spaces – sometimes there is barely room to turn an elbow.If it is permissable, are there special fittings I should use going from black pipe to copper and back to black pipe (I am familiar with male/female adapters & transition fittings) but I have heard there may be corrosion problems caused by using dissimilar types of metal pipe.
Thanks.
Wow, YOU heard there is a problem using dissimilar types of metals.
OK let me think about this one
A radiator valve is BRASS and connected to a black steel pipe and a Cast Iron or steel convector for 50 years yet nothing seems to leak AMAZING?
How about a black Gas line with a BRASS gas cock Again no leaks HUH?
Lets keep looking at all these problems that YOU HEARD about dissimilar metals
Black steel for fire suppression systems YET the sprinkler heads are brass AMAZING how folks have no clue to mixing these metals and the harm they are doing
Thank you for enlightening me as to the possibilities of what I thought was possible with a little knowledge of “basic” piping designs.
You know here is a little secrete between us, to be a REAL “plumber” takes 5 years of formal education 10,000 hours.
To be a “Master” takes a few more years plus many, many more tests and lots of education.
I think it would be very wise for you to hire a licensed PROFESSIONAL before you end up hurting yourself or some poor innocent who hired you.
Not for nothing but the questions you posted above a 1st year apprentice knows the answers to.
By you asking these questions means your may be over your head in this job.
Good luck sounds like your going to need it.. 
