10 replies to this topic

[linda_pro]

Dear All members,

I have an issue with the liquid relief PSV.

The PSV are installed on pump discharge line for blocked outlet case and they are required a certification on capacity. PSVs type are conventional and also balance bellow.

Recently i got vendor quotation with two following issues:

1. PSV set pressure is 10barg. Pump discharge pressure is 8.5barg. Then Vendor has informed that for liquid relief PSV, they require 20% of set pressure for blowdown pressure. it means they ask us to change Operating pressure to 8barg. I cannot reduce operating pressure, and also cannot increase design pressure because this is an existing system. What is the solution in this case?

 

2. I have two vendors, one quotes API orifice size which gave less rated flowrate. Another one quotes ASME Orifice size which gave a very big rated flow. From process point of view, boths are fine. however, the Vendor who quotes ASME orifice explained us that because PSV is certified capacity, therefore they need to follow ASME VIII code. All projects that i did for this Client was API orifice, therefore the Client is not confident to go with ASME orifice (this vendor quotes a cheaper price)

I am abit confuse about API and ASME orifice. (i have read API520 and ASME but i still cant get the answer).

Do we have to follow ASME VIII all the time for the liquid PSV iwth certified capacity requirement? if yes, why some vendor still quote PSVs under API orifice type not ASME?

If anyone can explain me clearly about this.

 

I apprecite any help.

 

Thank you very much.

 

[fallah]

linda_pro,

 

1- The solution is using modulating pilot operated pressure safety valve...

 

2- Please clarify if from "API valve" you mean non certified valve?

[linda_pro]

Dear Fallah,

1. I cannot use pilot PSV type because the fluid very vicous i.e >2000 cSt. i am afraid the fluid in the tube inside the valve cannot move at ambient (it has heat tracing but to void the heat traciing fail) 

2. your question is also my question too. the datasheet that I gave to vendor says clearly that certified valve. Vendor send the quotation with

selected orifice area is API and confirmed that are certified valve. This made me confuse. Do you think it is Vendor mistake when they quote API for a certified valve?

 

Thanks,

[fallah]

linda_pro,

 

1- Please go through following link. You appears have to apply tubeless pilot operated safety relief valve as can be seen in Fig. 3:

 

http://www.hydrocarb...nt-upgrade.html

 

2- Please ask vendor API valves are certified by whom? Please upload vendor proposal for those valves if it's possible...

[linda_pro]

Dear Fallah,

Thanks for sharing the link. I will check with Client about the pilot-operated safety valve. But i guess they dont prefer this due to cost and the PSV is on transfer pump discharge in a tank farm, not a process unit.

 

I have attached 2 quotations that i got from Vendor. I hided the vendor and client information because it is confidential. you will find one is ASME orifice, another one is API. both are liquid relief PSV.

 

i have checked with the Vendor quoted API. They said they provide the capacity certification based on maximum flowrate calculated as per API (not ASME). so i guess it is by manufactuer.

 

Any advice is appreciated.

Thank you.

Attached Files

•  API PSV1.pdf   356.47KB   44 downloads
•  ASME PSV1.pdf   116.69KB   35 downloads

[fallah]

linda_pro,

 

API submits a preliminary sizing of PSV based on which you will get a preliminary size of PSV. But, the final sizing must be performed using the ASME actual orifice area and ASME actual coefficient of discharge. Then API and ASME don't provide separate methodology of PSV sizing and in fact they would complete each other in the way terminated to PSV final sizing...

 

Please ask two vendors to submit A_actual and K_actual  based on ASME values...

[oscarsender]

Hi,

 

If the PRV is protecting an equipment that is ASME stamped, you need to have your PRV to be ASME certified. In this case the PRV is protecting a pump discharge piping system which I think does not require stamp. You may stick with API sizing.

[domiBod]

Dear experts,

 

I have a question related to ASME orifice area. For a given orifice designation (the orifice letter), I understand that the ASME actual area depends on the manufacturer. In other words, Pentair and another competitor will provide different ASME actual areas for a PSV orifice L.

 

Am I correct ?

 

Thanks for your support

Dominique

[fallah]

Dear experts,

 

I have a question related to ASME orifice area. For a given orifice designation (the orifice letter), I understand that the ASME actual area depends on the manufacturer. In other words, Pentair and another competitor will provide different ASME actual areas for a PSV orifice L.

 

Am I correct ?

 

 

Dominique,

 

Yes, ASME orifice area is normally bigger than API one for not only "L" designation but also for all orifice designations...and also are different among the various manufacturers...

[domiBod]

Thank you Fallah,

 

my concern was to know if the ASME area is "manufacturer" dependent and you have clearly answered (YES it is).

 

Best Regards

 

Dominique

[fallah]

 

my concern was to know if the ASME area is "manufacturer" dependent and you have clearly answered (YES it is).

 

 

Dominique,

 

ASME area is manufacture dependent but the subsequent PSV characteristic i.e capacity should be certified by ASME...normally would be reported in red book  on NB....