I myself have a very clear understanding of what happens.

I was questioning your understanding.

you state that the momentum moves the pipe , and you obviously are talking about the momentum of the air in the pipe , and then you state that at the same time the air
is stopping the pipe.

if the air is causing movement or supplying a force for movement then it must be supplying more force than the
resistance for movement that the air is also supplying
according to your assumption.

you cant have it both ways.

the air mass inside the pipe has moved from inside the tank
and distributed to the rest of the pipe.

some of the mass moved over 400 ft.
some moved over 300 ft -->
some moved over 200 ft -->
some moved over 100 ft -->

some small amount moved <--- between the pipe and the tank.

I cant understand your reasoning that the pipe will stop?

if you dont mind could you explain at which point the pipe
looses all momentum and stops?

3/4 inch of dust build up on the moon in 4.527 billion years,LOL and QM is fantasy science.