Here is what you should do:

Research the chamber pressures of m/l black powder guns. Might surprise you what the averages are.

Find out what schedule the "steam pipe" is. In the US, it is likely schedule 40. Then research the allowable pressures for the pipe.

Then compare the two. My first guess without taking a look at my references is the black powder pressures will be at least 10 times the allowable pressure for the pipe.

This is how pipe bombs are made.

If your steam pipe has no identifying numbers on it, meaning it was cut from a longer length that had the proper identification, then you must assume it is common water pipe and will likely burst at 300 or 400 psi or so.