8 replies to this topic

[syn23]

on the relief valve bypass, there is a spectacle blind. Is there a code which states the position (open or close) of the spectacle blind.

Thank you.

 

  

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[fallah]

syn23,

 

As far as i know there is no need to consider spectacle blind in PSV by pass line, because the PSV set including PSVs, isolation valves, by pass line and valve are to be isolated positively from upstream vessel by a spool piece. The spool piece will be used instead of spectacle blind due to safety issue... 

[Ikka]

Syn23,

 

Agree with Fallah, spec blind is not required if the valve holds good. So I think this spec blind is provided for positive isolation and to have PSV in service all the time. Therefore the spec shall be in closed position all the time.

[shan]

The PSV by-pass line servers as vent line for empting vapor prior to the vessel maintenance. The spectacle blind function is lieu of LC (lock close) device to prevent accidentally releasing of vessel content during operation. Therefore, as shown in your drawing, the spectacle blind should be in close position during normal operation.

[syn23]

Thank you all for your response,

 

I agree that it should be left in CLOSE position.

I just found out the client preference, is to leave the blind in OPEN position. I was looking to see if there is any API code to dictate the requirement so that it will be a valid argument. Otherwise, its just "we want it this way".

[fallah]

syn23,

 

Client preference, to leave the blind in OPEN position, shows there might be a case he needs using the by pass line durnig normal operation. Suppose for the PSV configuration, appears to be for only fire case (because of single PSV), there would be a situation that the PSV should be taken out of service in order to be repaired or inspected and puting the spare might take a lot of time. Then the operator have to rely on by pass line during the time the PSV is out of service and a safety issue might be probable during the time between taking PSV and puting the spare. For your information there is a procedure well defined in ASME sec VIII by which it might possible taking a single PSV out of service for a short time in normal operation.  

Therefore IMO if you have to use spectacle blind there, i agree with your client to keep it in open position during normal operation... 

[Vmm]

Before posting my very first view on the above topic Iwould like to thank CHERESOURCE FORUM for its great work towards provide technical talk on many industrial issues, I found it very much helpful in many occasions.
Coming to the topic I agree with Mr Shane response , from my view the bypass line is Manual Depressurization line which shall be used to depressurize the vessel inventory before going for planned maintenance, therefore during normal normal operating cobditions

[Vmm]

Before posting my very first view on the above topic I would like to thank CHERESOURCE FORUM for its great work towards providing technical talk and knowledge sharing activity on many industrial issues, I found it very much helpful in many occasions.
Coming to the topic I agree with Mr Shan response , from my view the bypass line is meant for Manual Depressurization line which shall be used to depressurize the vessel inventory before going for planned maintenance, therefore during normal operating condition it is advised to keep spectacle blind closed along with lock close upstream and downstream isolation valves
If at all sp blind is kept open, additional precautions to be taken care to avoid valve passing.

[Shahnawaz Makroo]

Bypass line  is not mandatory for all PSVs were there is a line routed to flare or ATM from top of the vessel or column. Like  with  pressure control adustment to falre/ATM or gas blanketing facility (In-breathing and out  breathing).This line can be used for depressurisation bebore planned maitenanace.