8 replies to this topic

[kinetic123]

Hello all,

 

Once again, I am here with some more queries please.

 

1) I am calculating reaction forces for 12” bursting disc discharge pipe for two phase flow conditions for steam + water.

Release rate is about 80kg/sec and using various methods [e.g. ISO 4126 and Pentair/API], reaction forces are about 50,000N to 280,000N.

 

2) Also, for vapour release rate of 2kg/sec through 3"relief valve, reaction forces are in the range of 500 to 1500N.

 

3) Do you think such reaction forces are credible, especially for 12" bursting disc line?

 

4) I am sure there is a mistake in the unit on pages marked 6.24 and 6.25 of an attached Pentair handbook.

The unit for ‘W’, actual relieving capacity has been stated as kg/hr but it should be ‘kg/sec’ [for above calculations, I have used kg/sec for these equations]

 

Has anyone used these equations before?

 

Thanks

 

 

Attached Files

•  Pentair RV sizing book - Pages.PDF   93.44KB   77 downloads

Edited by kinetic123, 07 May 2014 - 08:58 AM.

[kinetic123]

Hello engineers!

 

Any idea on this one please?

Your reply would be greatly appreciated.

 

Thanks in advance.

[kinetic123]

Not sure, why no discussion on this topic.

Wondering if process engineers are not suppose to do such calculations?

Thanks

[PaoloPemi]

for two phase flow you may assume homogeneous flow and calculate average density,

there are simple formulations (based on momentum) in API and other standards,

these will differ for open and close discharge system (i.e. main difference is static contribute),

acceptable values depend from several factors, many engineering companies

provide guidelines for this.

[kinetic123]

PaoloPemi

 

Thanks for your reply.

Above calculations are for the closed system and are based on various formulas given in API and Pentair book etc but i have never done such calculations before and was not sure if above stated range are OK or not.

 

Thanks,

 

PS: I also want somebody to confirm if there is a mistake in the units for release rate W in the Pentair handbook.

[ChemEng01]

AS per API W should be kg/s. I agree wrong units have been used  in Pentair handbook

 

Reaction forces seem realistic to me . Did you use static pressure at tailpipe outlet for RV reaction force?

 

Normally Mechanical engineers with determine reaction forces based on data supplied by process engineer.

Edited by ChemEng01, 14 May 2014 - 02:00 AM.

[kinetic123]

ChemEng01

Thank you very much for your reply.

Yes, I have calculated static pressure. Please see attached files and comments below.

 

Attached File#1 : I have used formula for ‘Gas Service’ [Pentair page 6.24] for vapour release only for relief valve BUT again this equation is for open discharge while we have close discharge i.e. pipe away discharge to dump tank.

 

Query: Can I use this equation? If yes, how can I calculate static pressure,P2?

NOTE: API and Pentair use the same formula but the only difference is Pentair gives equation for calculation of static pressure [P2] while API does not.

 

Attached File#2: I have used formula for ‘Two phase flow’ [Pentair page 6.25] for two phase flow release only for bursting disc BUT again this equation is for open discharge while we have close discharge i.e. pipe away discharge to dump tank.

 

Query: Can I use this equation? If yes, what would be the pressure at pipe exit , PE? We have discharge line pressure drop of 0.2bar and bursting disc set pressure of 2.75barg.

 

If I consider, PE = 2.75-0.2 = 2.55barg = 3.55bara, reaction forces are in the range of 1,000,000N

If I consider, PE = 0.2barg = 1.2bara, reaction forces are in the range of 50,000

NOTE: Please ignore 280,000N which I quoted earlier.

 

Your input would be highly appreciated.

Thanks

Attached Files

•  File#1 gas-relief valve.PDF   486.6KB   52 downloads
•  File#2 two phase - bursting disc.PDF   402.33KB   66 downloads

[breizh]

Kinetic 123 and others ,

 

Regarding safety valves , let you try to get a copy of this book , very good , very clear :

 

"the safety relief valve handbook " by Marc Hellemans

 

Breizh

Edited by breizh, 14 May 2014 - 10:04 PM.

[kinetic123]

Hi Breizh

 

Thank you so much.

That attachment is really very useful..

 

PS: It looks like API needs to be updated big style ...