Loosening old black iron heating piping

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Plumber Jamie

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Vancouver, Canada

First post on this site, here. I have 77 old cast iron hot water radiators here that I need to remove the old bonnets on. I've done this on one before and it was a huge pain so I am checking to see if anyone has some tips or tricks for doing this efficiently.

On the previous one, I tried using a few different types of internal pipe wrenches which did not work. Next, I cut off the union nut and heated up the joint with a MAP gas torch, then used a 24-inch pipe wrench to try and loosen it, which just crushed the pipe. Finally, I ended up cutting grooves on the inside of the pipe so that I could hammer sections of the pipe threads from the radiator threads.

Does anyone have any ideas for making this process any easier? Would running an acetylene torch on the joint, rather than a MAP gas torch, have maybe helped un-seize the threads?


Licensed plumbing contractor
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San Francisco Bay Area
I doubt acetylene will make a difference.
No other tricks from me, sorry.
My favorite internal nipple wrench is the spiral type.
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