Isolation valves for PSV 5

[wartono]

Should I put isolation valves before and after PSV for maintenance proposes or during PSV calibration?

I don't find this kind of rule in the API RP 520 part I and II. Maybe you guys have this experiences please share.
Thanks

 

[radomir]

Sir CHD01 (I do apologize if you are a Lady),

Anfortunately your motto is very true and I do like it. That's why ignorance is a bliss.

 

[CHD01]

No lady am I, just an engineer who's getting easier to live with as he ages. Glad you like the motto; I'll be honest with you - I don't know if I made it up or I heard it some time ago. But I do think it has a lot of truth. The other motto I would use is to not trust everything you read! The more you learn, the less you are certain of.

 

[aliansari]

API-RP 520 part II does address the installation of a "CSO" type valve between the PSV and the vessel.

ASME Sec VIII Div I Appendix M covers the matter in detail, Please refer.

Mohammad Ali Ansari

 

[CHD01]

ALIANSARI:

I STAND BY MY 10/9 MEMO IN THIS THREAD! The more you learn, the less you are certain of.

 

[TrevorP]

As an addendum to the above - for those who must be able to maintain and inspect a relief valve while the process is online - relief valve manufacturers (eg Crosby {Tyco}) can supply bespoke units that overcome some of the problems indicated above by using linked 3-way, 100% open valves either side of two relief valves. Crosby have a brochure on what they call 'safety selector valves', which may be worth a look. I am not sure how the costs compare with a conventional set-up.

I have not personally used one of these systems before, but am considering doing so for a future project, so would be interested in any feedback from anyone who has used this system before...

 

[hacksaw]

Isolation valves are permitted, but only in very special circumstances.

The isolation valves must be mechanically linked to prevent simultaneous shut-off.

The old rules simply relied on administrative control of lockable valves, but this was determined to be un-safe.

There are special valves available from safety valve manufactuers (described above). They are not cheap, but less expensive than separately mounted isolation valves, and certainly much safer.


Good luck,

 

[fufu]

Dear,
you can have 2 PSVs with a 3 way diverter valve before the PSVs, this way ,you can allways have the needed protection while calibrating one of the PSVs.
Regards