Maximum tank pressure from a gas blow-by

[SpacelySprokets]

Hello to All.
An abnormal condition causes natural gas to blow through a liquid level control valve [LCV] to an atmospheric tank [p design is 15.7 psia]. I can show that the tank's relief valve has sufficient capacity to handle the gas flow rate, but I do not know how to determine the maximum pressure that can occur inside the tank during this blow by...
In this case, 1489 psia gas from a separator vessel flows through a 2" LCV that fails open [Max. valve Cv = 23.0], through 200 feet of 3" piping into a dip-tube to the bottom of the tank. The tank relief is a weighted 24" Varec relief manway.
...From my calculations, I see that at the exit of the dip-tube, the pressure is well above 15.7 psia; However, I envision the pressure dissipating very quickly as the gas exits the dip-tube. The problem is that I do not know how to calculate this, nor do I know whether this release of gas can damage the tank.
Your suggestions would be greatly appreciated! Thanks!

 

[TD2K]

If the Varec relief manway is akin to a pressure vent valve, you'll need to look at the pressure/capacity curve. You know the calculated blowby rate, the capacity curve will tell you how much pressure in the tank is needed to get the required flow.

If the Varec is one of the emergency overpressure devices that blows off the man-way, then you need to calculate how much pressure in the tank is needed to flow the blowby case through a 24" orifice (essentially, that is what you have once the cap if off the manway)

 

[SpacelySprokets]

Thanks, TD2K.
The Varec 221P will open at ~ 15.0 psia at ~650,000 scfh blow by rate.
However, in relation to vast pressure difference between the pipe exit and tank pressures, I suspect that expansion waves will occur near the pipe exit and give significant rise to the local pressure near the pipe. Can these local pressures be estimated simply using shock tables?
Do these pressures dissipate very close to the pipe exit, and thereby not affecting the global pressure in the tank?

 

[gerhardl]

How should expansion waves occur?

I know about shockvawes occuring by air sucked into pipes (for purpose airing downstream outlet of needle valves for water at high pressure differences over the valve). Critical speed of the air into the abrupt end of the airpipe intake will bring the air to swing, both high noise and considerable lesser air capacity is the result. Solution in this case for air intake: trumpet formed intake. Result: and air capacity increased (to more than double or triple) without noise and shockwaves.

If you fear somthing like this 'in reverse', perhaps a pipe-end with an 'expansion friendly form' - for instance a larger diameter pipe with a multitude of dissipating holes. I have not seen this done for this purpose, but thinking of mufflers and exhaust pipes.

But calculating or practical examples? And perhaps noise is more a problem than tank damage?