I have discovered a leak in an 80 year old steam radiator system. The pipe shown is 4" diameter cast iron that holds steam. It is below the floor and there is dirt below the pipe. It leaks at the seams where the old is attached to the new.

It looks to me like someone cut out a section of the cast iron and attempted to patch this a few years and did not do a good job. If I dig around this and pack a ton of bondo around the seams, will that solve the steam leak?

If not and I have to cut the cast iron, how do I attach the middle section to the old pipe? Do you weld it? If I have to weld it, how do I weld beneath the pipe?

Thanks for the help.

Your system is probably low pressure steam but I would check that to be sure. It is leaking for a reason and bondo will only hold for awhile until it rusts next to it.

The pipe should actually be replaced with black iron screw pipe unless you can find one of the adapters from years ago or you can try to piece and weld but good luck with that one.

We only replaced the pipe at our shop because we could never guarantee a weld on this cast iron.

I agree this is a tough problem. Maybe repost to plumbing. Some of them may have a trick. Otherwise, I am afraid the only long term fix may be to dig out enough room to weld in a new piece of cast with rod meant for cast.

Thanks for the replies. I agree that unscrewing and replacing the piece would be best, but the piping is so old that unscrewing the pipe is near impossible. I will repost to plumbing to see if they have any ideas.