PRV discharge piping

[JoseMechEng]

I have a safety PRV on a flash tank.
I would like to connect the Safety PRV 1" discharge pipe to an existing vent pipe 3" diam.
the existing 3" diam. vent is connected to a back pressure regulator that acts as a pressure relief valve for the same flash tank.
In case of over pressure both the 1" Safety PRV and the 3" back pressure regulator will discharge into the same 3" vent.

Is this allowed by ASME code?
Where can I find manifold discharge piping sizing and reccomendations?

Thanks in advance

 

[psafety]

The vessel should be protected to no more than 10% over pressure unless fire conditions.

The the vent line delta P based on routing and worse-case conditions need to be verified.

 

[Sapphiron]

Maybe. It is usual practice to provide a dedicated vent for a Relief Valve. You may even tie several together to a common (larger) vent. The sizing is tricky and there isn't much guidance for it. The length of the line needs to be taken into account and the number of turns.

It may be possible in this case to do so provided the 3" valve can handle the expected load from both contributors. If you cannot guaranty that it is, then you must run a second line. Since the BP Reg is 3" ips I'd be concerned. I'm assuming the application is indoors and why you are considering this at all.

There is pathetically little on vent sizing. The outlet sizing comes from tested capacities at the manufacturer. Typically vent on a single valve is one pipe-size larger than the outlet due to a drip pan elbow being installed and the pipe on the outlet becomes one size bigger. So if your relief valve outlet is 1" then the DPE would be 1" x 1-1/4" or 1-1/2" and the leaving pipe would be the outlet size of the DPE. Use a DPE to make sure you don't blow water out of the vent when the valve discharges. If you use vent line sizing at 3000 fpm O psig then you get line sizes that are larger than they need to be. It's safe method and can be validated by the math. The other option is check the sizing of the BP regulator and make sure its adaquate (this should be size for the maximum capacity of the valve not the sized capacity) at 0 psig and then adding in the equivalent cross section of the relief valve vent and see if it comes out to 3" IPS. Just watch the elbows and the pitch of the vent if it isn't vertical A way to back into it.

If it were me, I'd just put in a dedicated line if at all possible.

 

[hacksaw]

the asme has quite a bit on vent header and vent stack sizing and bracing

 

[MJCronin]

Hey Jose...

You state that this is a flash tank. You also state:

"I would like to connect the Safety PRV 1" discharge pipe to an existing vent pipe 3" diam.

Is the 3" vent pipe on the flash tank or on another system ?

If the vent is on the flash tank (as would be expected), and the safety PRV is on the same tank, there is zero chance that the PRV will actuate.

Is this correct ? How about a sketch ....?????????

If this is correct, who cares about the vent on a PRV that cannot actuate ?

-MJC

 

[JoseMechEng]

MJCronin:
wrote
Is the 3" vent pipe on the flash tank or on another system ?
my response:
Yes it is

MJCronin:
wrote
If this is correct, who cares about the vent on a PRV that cannot actuate ?????

my response:
The safety relief valve is my last line of defense to protect the vessel and the personnel!
If the back pressure regulator malfunctions, the vent on the PRV better actuate!


I agree, I need to include a sketch! lawyers work with papers,Engineers shall all work with drawings to speak the same language, All acept my apologies!

Thanks in advance for the feedback

I was able to confirm that this allowed by ASME
and the sizing and connection details must be in compliance with

ASME section I PG 67-73
ASME section IV art.4, art.8
ASME section VIII, Div. 1 Appendix M
ASME B31.1 Appendix II

psafety,Sapphiron thank you for your postings, you added value to the thread

Best Regards
Saludos