Allen Cain wrote:
As the volume (V) increases as the tank is emptied the pressure (P) must decrease proportionally creating a vacuum to balance the equation. This can and has collapsed many storage tanks. Not sure if a rail tank car is strong enough to avoid collapsing as a full tank is drained to empty?
You mean like the one shown below? This one was steam cleaned and the manway closed with the tank hot. As it cooled and the pressure inside decreased, voila!