4 replies to this topic

[JKM]

Dear All,

 

This topic has been discussed many times but I still have some doubts. I am sizing a PSV discharge line. I would like to know is there any criteria for sizing of PSVs which are discharging to the ATM. In our case as per calculation the mach no. is 0.92 and Rho.V²=123245 kg/m.s2. Fluid is Nitrogen; ; Set P: 40 barg. In the API code it is not specified for the PSV which are venting to ATM.

 

Looking forward to your reply.

 

Regards

JKM

 

 

 

 

[fallah]

 

This topic has been discussed many times but I still have some doubts. I am sizing a PSV discharge line. I would like to know is there any criteria for sizing of PSVs which are discharging to the ATM. In our case as per calculation the mach no. is 0.92 and Rho.V²=123245 kg/m.s2. Fluid is Nitrogen; ; Set P: 40 barg. In the API code it is not specified for the PSV which are venting to ATM.

 

 

JKM,

 

A well designed PSV tail pipe is specified with a Mach No. limitation of 0.7 to 0.85 at the end of the tail pipe. Because if the choked flow conditions happens along the tail pipe the PSV itself will no longer be the flow limiting component and the tail pipe will play the role of flow limiting component which will not be favorable at all.

 

In your case, it can be apparently thought the choked flow will not happen at the end of tail pipe but in real world the choked flow will be assumed to be happened beyond the Mach No. of around 0.85 (or even lower) hence you will be advised to increase the tail pipe size or decrease the length if it's possible...
 

Edited by fallah, 21 June 2016 - 02:54 AM.

[Bobby Strain]

You should consider noise, too.

 

Bobby

[JKM]

Dear Fallah and Bobby, thanks a lot for your prompt reply. I will increase size.

 

Regards

JKM

[latexman]

Don't forget to provide the thrust and moment arms to the structural and piping engineers.