7 replies to this topic

[Hossein Deldari]

dear ALL
I have a question about sparing philosophy for pressure safety valves
based on some local design criteria, it is not necessary to provide sparing for PSVs unless its requirement is raised by basic designer / licensor.
I have heared that spare for those PSVs that govening scenario is fire case will be mandatory. is there any standard which compel basic designer / licensor to provide spare for PSVs
any reply in this regard will be appreciated

[fallah]

Spare PSV for fire case is mandatory but usually stored in warehouse.

[Hossein Deldari]

dear Mr. Fallah
I would be gratefull if you give me whcih standrad compels us to provide spare for the PSVs sized based on fire case

[fallah]

dear Mr. Fallah
I would be gratefull if you give me whcih standrad compels us to provide spare for the PSVs sized based on fire case

Dear Hossein,

It is not uncommon considering spare PSV for pressure safety valves in general.

But if the installed PSV is only for fire case,spare wouldn't be installed and as i mentioned before is stored in the warehouse.

"Process Sizing Criteria" by TOTAL Co. included a.m. point,as an example.

Hope above helps out

[Art Montemayor]

Hossein:

I believe what Fallah is referring to is that there are various ways to identify what a "spare" PSV constitutes:

1) A duplicate PSV is installed alongside the existing one and is valved off and kept as an installed, "standby spare".
2) A duplicate PSV is installed alongside the existing one and is always connected to the same system as a redundent, spare PSV in the event that the original PSV fails to relieve for whatever reason.
3) A duplicate PSV is purchased and kept in stock as a spare part in the normal stock room. It will be used as a replacement for the existing, installed PSV when this is being maintained, calibrated, or checked.

I have never heard of a mandatory legal requirement for having any of the above "spare" cases operating. However, this may be the case for some local jurisdictions - which are the top ruling authorities in any case.

Which of the above "spare" definitions are you referring to? Case (2) actually is nothing more than an over-design for relieving capacity and may, in some instances, be more dangerous than only one PSV due to the fact that chattering (in normal relieving) could damage the PSVs and render them inoperative.

[fallah]

2) A duplicate PSV is installed alongside the existing one and is always connected to the same system as a redundent, spare PSV in the event that the original PSV fails to relieve for whatever reason.
Case (2) actually is nothing more than an over-design for relieving capacity and may, in some instances, be more dangerous than only one PSV due to the fact that chattering (in normal relieving) could damage the PSVs and render them inoperative. [/font][/size]

Dear Art,

Operation of spare PSV in the case 2 isn't very clear.It has different set point with respect to main PSV?Its upstream/downstream valves always would be on?

As far as i know in all cases in which more than one PSV with valves on are used (e.g high relief load with PSV size limitation) they have different set points and will sequentially pop open.

Thus ,based on above and also your own statement about chattering due to case 2 configuration,i think only cases 1,3 are applicable for PSV sparing.

[Hossein Deldari]

dear ART
I agree with Fallah about that case 2 which you mentioned is not related to sparing philosophy. in this case set pressure of PSVs will be different for opening sequentially. regarding to case 3, since I am working in a basic design project and there are not any requirement from client side to consider PSV in warehouse, so this case is not applicable for me as well. but for case 1, if there is any ctandard which force us to consider spare PSV for main one, we should show it during P&ID generation. up to know, I did'nt find any standard in this regard and I think client should insist about putting spare PSV for main one

[Qalander (Chem)]

dear ART
I agree with Fallah about that case 2 which you mentioned is not related to sparing philosophy. in this case set pressure of PSVs will be different for opening sequentially. regarding to case 3, since I am working in a basic design project and there are not any requirement from client side to consider PSV in warehouse, so this case is not applicable for me as well. but for case 1, if there is any ctandard which force us to consider spare PSV for main one, we should show it during P&ID generation. up to know, I did'nt find any standard in this regard and I think client should insist about putting spare PSV for main one

Dear Hossein Deldari,As I gather from the discussions.The query in OP is somewhat inaccurately defined as 'spare PSV'

Which I understand(as analyzed and gathered from above post discussions) should have been a query about 'Capacity sharing multiple PSV's installation' and

their pop-up,re-seat pressure(s) Overall collective load sharing scheme.

Please do correct me if I am wrong!

Hope this should be helpful for further way forward.