9 replies to this topic

[Engineer87]

Hi Members,

 

 

I have little confusion, as I have NGL unloading truck connected to the metering skid. I have P&ID attached showing the relief valve. I think PSV is there for fire protection but there is no vessel connected.Is this really use for protecting pipe against fire or blocked flow?. Really appreciate your responses. Thansk

Edited by Engineer87, 10 May 2014 - 07:46 PM.

[fallah]

Is this really use for protecting pipe against fire or blocked flow?. Really appreciate your responses. Thansk

 

Engineer87,

 

Appears it is there for protecting the pipe against overpressure due to thermal expansion of blocked in NGL. The whole PID might clear the point better...

[Engineer87]

Thanks Fallah.

 

 I have attached P&ID showing 1" MNPT x 1" FNPT relief valve. Should TRV be like that size?.Since piping system is installed so I think Thermal expansion is caused by solar radiation not fire ( no vessel ). Should I need to take more margin between set pressure and operating pressure as PSV is connected to Flare system ( more blowdown required).

 

 

Attached Files

•  NGL PID.JPG   58.74KB   6 downloads

Edited by Engineer87, 10 May 2014 - 07:45 PM.

[fallah]

Engineer87,

 

Yes, the heat source appears to be sunshine and TRV can be 1"*1" size. Due to higher blowdown (even around 20% of the set pressure) for liquid relief, it's better having more margin between set pressure and maximum operating pressure, otherwise there is potential the TRV continues to be opened even after TRV goes to reseat folllowing to removing overpressure source...

[Engineer87]

Thanks Fallah. Is there any special consideration for sizing TRV based on solar radiations.What allowable overpressure to be set in this regard?.does it would be same as fire case 20% or 21%?.

 

Little help regarding flashing out of liquid please.I have got total vapor pressure about 65 psi of the NGL stream obtained which is more then atmospheric pressure.Should flashing out of condensate occurs in this regards. Any your post  related to flashing of liguids would highly be appreciate.Thanks

[fallah]

Engineer87,

 

The overpressure is normally 10% of the set pressure for liquid trim relief valves. The expected build up back pressure must be considered for evaluation of flashing possibility. Saturation curve of the media should be used for such evaluation.

[Engineer87]

Thanks Fallah for great explanation:

 

I dont know the operating pressure yet and I hope it must be far less than set pressure.I was reading your post                             (http://www.cheresources.com/invision/topic/3967-thermal-expansion-relief-valve/) and you said that for thermal radiation the maximum allowable over pressure would be 25%.Can you please justify it. Thanks again Fallah for your help:)

[fallah]

I was reading your post (http://www.cheresources.com/invision/topic/3967-thermal-expansion-relief-valve/) and you said that for thermal radiation the maximum allowable over pressure would be 25%.Can you please justify it. Thanks again Fallah for your help:)

 

Engineer87,

 

Yes, you are right, i did mention such statement there...

 

Actually maximum allowable overpressure of 25% relates to standard trim PRVs for ASME non certified liquid capacity. For applications installed after 1995, liquid trim PRVs for ASME certified capacity at 10% overpressure must be used in all liquid services which fall under the scope of the ASME code.

 

Standard PRVs did provide full lift and flow capacity at 25% overpressure, while in liquid trim PRVs with a modified huddling chamber design the full lift and flow capacity are provided at maximum 10% overpressure...

 

Hope my explanation did clarify the matter....

Edited by fallah, 11 May 2014 - 04:56 AM.

[Engineer87]

Thanks Fallah
I just want to mention Here that pur metering Unit is inside the building,So in this case PSV sizing basis still a Sunshine.Moreover can you plZ mention the ASME code section you reffered 10% For TRV.Thanks again Fallah

[fallah]

Engineer87,

 

You can find the matter in attached page of API 520 sec. 3.8.1.1....

Attached Files

•  10% overpressure for TRV.docx   250.49KB   38 downloads