9 replies to this topic

[raisie]

Dear all,

 

I am designing (sizing) a PRV for a PIG Launching System placed in the discharge line of Positive Displacement pump (note that I am a junior and that I am doing this for the first time). The liquid is Crude Oil (16 deg API). The valve manufacturer sent a list of required information regarding the system in order to select an appropriate valve. However, I am not sure about some of the requirements. Some elaboration on the following topics would be much appreciated:

 

• First of all, the "Set Pressure" for the PRV is to be specified. Seeing as PD pumps have an "infinite shut-off pressure", to me it seemed correct to specify the set pressure as: Max. allowable line pressure (200 psi) minus % Allowable overpressure (10%); this equals 180 psi. Am I correct in doing so?
• Secondly, the Relieving Temperature is required. I have absolutely no idea on how to specify this; are there any guidelines/suggestions on how to do this?
• The Required Reliving Capacity is just the nominal operating capacity or is it the pump capacity at the max. allowable pressure?

 

See the attachment for the PFD of the system.

Any comment/clarification will be much appreciated.

Thanks in advance.

Attached Files

•  PFD PIG Launcher.png   23.08KB   2 downloads

[shan]

Single PRV Set Pressure = MAWP (Maximum Allowable Working Pressure, it is 200 psig in your case)

Reliving Temperature = Maximum Operating Temperature if the PRV is not sized for a fire case.

Required Reliving Capacity = pump capacity at the set pressure (Actually, I don't thing there is much capacity difference at either pressures for a PD pump)  

[fallah]

raisie,

 

1- PRV set pressure=Lower of 1)Maximum allowable working pressure of the PD pump; and 2)Maximum allowable pressure of pump's downstream facilities (usually till last isolation valve before next equipment) affected by PD pump as source of over pressure...

 

2- Relieving temperature=Maximum operating temperature of the pump

 

3- Pump's full/design capacity

Edited by fallah, 24 December 2014 - 08:28 AM.

[raisie]

Hi guys,

 

Thank you both for your responses.

 

 

Reliving Temperature = Maximum Operating Temperature if the PRV is not sized for a fire case.

Shan,

 

In my case, the Crude Oil is being pumped from the oil fields to the pump suction line.

So it is not clear how the max. operating temperature is to be determined.

 

 

2- Relieving temperature=Maximum operating pressure of the pump

Fallah,

 

I think you made a mistake in your statement?

 

 

After some thinking, I thought of specifying the max. operating temperature as 10-15% lower than the boiling point of the crude oil, because under all circumstances, the temperature of the crude oil will be kept lower than the boiling point in order to avoid pump damage due to cavitation.

What is your take on this?

[fallah]

raisie,

 

Yes, it was a typo error and i did correct it...

 

If the maximum operating temperature is a bit lower than the boiling point at relieving pressure, it could be considered as relieving temperature...

[raisie]

Thank you

[raisie]

Guys,

 

All the codes/standards I have come accross (API standards) are for sizing vessel PRV's. Are there specific standards for sizing pump PRV's such as in my case?

[fallah]

raisie,

 

API 520 part 1 is also applicable for sizing of pump's PRV...

Edited by fallah, 29 December 2014 - 12:36 PM.

[raisie]

Thanks Fallah!

 

I contacted a valve supplier and mentioned that the valve should be connected to the outlet of a Positive Displacement pump and redirected to the pump's suction line. The supplier then recommended using a Hydraulic Bypass Relief Valve or a Constant-Pressure Governor Actuator. 

I am starting to wonder which one will be more suitable for this application and why?

Any ideas?

 

[fallah]

raisie,

 

It's better the PRV outlet line redirected to pump's suction drum rather than the pump's suction line and specifying the destination point for redirection is normally out of supplier responsibility and scope. The PRV for the application you described is to be well specified in relevant data sheet based on which the vendors would submit their offers. You should select the best offer, with any title for the valve, which has the specifications as close as possible to those you has already reflected in relevant PRV data sheet...