1 reply to this topic

[vishvedeep]

On the Pilot operated relief valves in the unit we have observed that the block valve on the REMOTE SENSING LINE OF SPARE PORV ( NOT ONLINE) is kept locked open. The remote sense line is external type which means the  line begins upstream of the PORV inlet block valve and joins the pilot of the PORV. This means that the Dome of the spare PORV  is always pressurized..  I see both advantages and disadvantages of this arrangement

 

Advantages

1. Keeping the remote sense line of spare PORV open will keep the dome of PORV pressurized always and if the inlet block valve leaks the spare PORV will still stay in a closed position because the Dome is pressurized. Any unwanted relief will be avoided.
2. While taking the spare valve online opening the inlet block valve can cause the sudden lifting of PORV if the dome of PORV is not pressurized. Keeping the remote sensing line lock open will keep the dome pressurized and prevent operator error also.

Disadvantages

1. In case the remote sense line is kept lock open to the spare PORV and if the pressure in the vessel/line exceeds the set pressure the pilot valve of the PORV  will get lifted. In this scenario the spare valve pilot is getting lifted in addition to the online PORV and its pilot.  Since these small pilots are also  spring loaded valve any unwanted lifting might cause the valve to be not seated properly.

 

What is the API or Industrail philosophy on the spare PORV remote sense line valve?  In my opinion keeping it lock open is a better idea.

[fallah]

Hi,

 

As far as i know remote sense lines of POSV can be included inline valve or not included it, and i don't think API or industrial standards having any special recommendation in this regard.

 

The idea appears to be interesting at a glance but because the remote sense line can be as long as 30 m, keeping the isolation valve of this line in spare POSV at locked open position might lead to a hidden inventory escape due to probable line fracture in such very small size line...