Understanding Operating Pressure
 

I've read several threads and the User's Guide on operating pressure and am very confused. I want to use basic examples to clear my confusion.

Based on my understanding, operating pressure is environment pressure? For example, if operating pressure is 2MPa, and I have a tank with 3MPa abs pressure inside, does that mean 1MPa gauge pressure inside?

Furthermore, if I have standard atmospheric pressure environment and a pipe with inlet 2MPa and outlet to atmosphere, could I set operating pressure to 2MPa, set velocity inlet BC with initial gauge pressure as 0, and pressure outlet BC with gauge pressure as -1.9MPa?

Thank you!

Yes. The operating pressure is arbitrary but it's generally taken to be some sort of environment temperature, but it can also used as any reference pressure as long as you keep track of the gauge pressures.

Correct.

Also correct.

Thank you Mr. Lucky.

operating pressure=gauge pressure.
So gauge pressure is 2 MPa. If the gauge is at atmospheric pressure, it would say 0, in vacuum - something.
Do you vent 2MPa straight to atmospheric? You will have gigantic velocities.