Two magma pipes!?! Save file plz?
It's probably a pipe and a pool. I don't think it's possible to have 2 pipes on the same region tile, unless someone has figured out a way to do that via modding or memory address hacking.
It is possible, but extremely rare, there was another case mentioned on the forum a while(Several months ago even?) back, and apparently the game only shows one of them at embark, even if there are more. My memory is a bit fuzzy, and I don't know the rest of what happened in the thread, but I think it may be possible to have a volcano with magma pipe at the same region tile. Technicly they are both magma pipes, but there is a small possibility the game mistakes it for something else.
Not that it really matters, the way we get our magma will change next version anyway, and I won't be surprised if there are several ways of getting (near)infinite magma.
As for the OP's question, which I'm not sure is answered as he intended the question, there are 2 things.
Magma does not drain off the map.
And Magma will only cool off if it's at 1/7 depth, 2/7 will not cool.
From this it can be concluded that if you use just enough magma it is possible to completely wipe the map of live, while allowing the magma to slowly cool. Note you can store magma in an aboveground reservoir while letting the pipe refill. I made a magma flooding device, success is easier at small maps.