Gas line Depressurisation

[ProdEngxxl]

Gents,

Could any one advise a method to calculate the time depressurise a Gas line with following details:
1- Length = 65616.6 ft
2- inside Diameter (ID) = 10"
3- Pipe pressure =1200psa
4- Temp 60oF

we need to depressurise the line before starting some works on the system.

Thanks
KOKA11

 

[zdas04]

Your flow rate down to 1 atm (gauge) is pretty easy to calculate, your exhaust flow will be at sonic velocity. Since choked flow is only dependent on upstream pressure and pipe size, I have had good luck recalculating flow rate every 100 psi down to 1 atm (i.e., calculate the mass at 1,200 paig and at 1,100 psig, determine the difference, see how long it takes to pass that much mass flow rate at sonic velocity with 1,200 psig upstream pressure, repeat for every step down to around 14 psig).

After you get below 1 atm, the flow rate is no longer choked and the blowdown time is very difficult to determine. I always try, but I'm never very close. I can get the first chunk within seconds, but seldom get the second chunk within tens of minutes.

David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

The Plural of "anecdote" is not "data"

 

[MTPipeliner]

I've got a program that will calculate the time to blow down a line.

I made a few assumptions so the program will run as follows.

One 3" ID blow down stack
Lubricated plug valve in stack.

I came up with 133 minutes

Let me know if these are incorrect and I'll try it again for you.

Pat