It’s not the first time I read about the battery. I can only say that you have your brains. And in no case try to repeat at home: heating pipes, as a rule, are very well grounded. When you were a child, did you collect a detector receiver?
If you wrap the "zero" grandmother there, it’s obvious, nothing will be done. If "phase" - you are most likely to have automates. If they are good and correct. If not, you risk a fire.
Even if you assume that the heating pipes are not grounded - in order for the grandmother to hit the current, she must 1) touch the unpainted part of the pipe. 2) at the same time touch something grounded, or at least stand naked wet feet on the concrete floor. This is very unlikely, unlike the fire of wires in your apartment.
p.s : Bring it to the top, or physics is not taught and is led to all kinds of nonsense...