5 replies to this topic

[Ghasem.Bashiri]

Dear Process Expert
A process engineer claimed that Spectacle blind should be considered as "Block Outlet" Source for PSV.
I am sure it is not ture as very obvious issue.
But I share this point for more clarification.
Please put your points based on some facts and practice.
GB

[fallah]

Dear Ghasem,

If he/she means the spectacle blind in upstream/downstream of the PSV,he/she is right and for this reason,during maintenance in oppose to other nozzles of a vessel,PSV nozzle isolated with the vessel by removing a preinstalled spool piece of pipe and subsequent blinding.Other nozzles would be isolated by spectacle blinds.

Fallah

[paulhorth]

Ghasem,

Fallah is right, you should certainly use a removable spool and not a spectacle blind to isolate a vessel from a PSV.

For other spectacle blinds, it is difficult to imagine a case where there is a spectacle blind without a manual block valve in the same line. Therefore, the manual block valve can be closed and so cause blocked outlet, and the blind in the same line does not give rise to an additional relief case or a different relief case from that of the block valve.

Paul

[Ghasem.Bashiri]

No, Mis Understanding!
Assume a system without manual valve. Is it required and possible to consider Spectacle blind (Spade/Spacer) as source of overpressure (block outlet).
I think for such blockage we should shut down the system and change position of Spectacle or Spade/Spacer.

Or alternatively someone may forget to change position of Spectacle blind during startup from close to open and then system can be block!!!

Is it required to consider this issue as source of over pressure and block outlet.

GB

[paulhorth]

Ghasem,

To avoid any misunderstanding, please SEND US A DIAGRAM, showing exactly where this blind is and which equipment is in danger of overpressure.
Before you send a diagram, please note that the PID which you have just sent through on the Relief Devices Forum, which seems to be about the same set of problems which you have asked about, does NOT show where this blind is located.

Quote:
Or alternatively someone may forget to change position of Spectacle blind during startup from close to open and then system can be block!!!

This is quite correct, that is the time when you will get a mal-operation. So, do not use a spectacle blind, use a removable spool, which cannot cause a blocked system.

This series of posts from you, since February, is becoming a detailed PID review, free of charge, while you are being paid to resolve these problems. I don't think that is an appropriate use of this forum.

Paul

[fallah]

No, Mis Understanding!Assume a system without manual valve. Is it required and possible to consider Spectacle blind GB

Mentioned misunderstanding is the result of presenting your query without adequate information/explanation,supporting sketch,.....

Considering the above, you shouldn't expect the forum members to know what exactly is in your mind about the query!