20p,
Not sure about cracking the pipe - though I would have expected cast iron to cope with heat OK.
But I would be surprised if you could get the cast iron hot enough to strip the paint - it being a good conductor.
a long time ago our firm restored a listed building, we had to take down Ci gutters and strip them. It came off easy and quite quickly with a blow lamp shavehook and wire brush We didnt crack any. Dont think its possible to crack it with heat, though we went gently at it ie didnt need to get it red hot. Watch you leave it to cool for a while naturally, drenching suddenly from hot may crack it. Like cylinder head in car. It takes some time to cool Stripper will work but it's messy and takes time and money.
Good luck
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