29 replies to this topic

[JoeWong]

I guess whenever the manual blowdown is inadvertently opened, the system will depressurized. Low pressure alarm and/or trip will be initiated. Your operator would have been aware of it and take necessary checking and rectify problem immediately. Depressused vessel sitting on same pressure as flare header. Don't see how backflow is possible by differential pressure (diffusion may be).

Anyway, this thread is a bit draged. As i mentioned earlier, there is not YES or NO for LC/CSC the blowdown line in general but specific case may be. Hope this can call it a stop.

[jeffreyfrog]

An example might be at the inlet to a PSV. The inlet and outlet valves could be locked open so that the operation of the PSV is not erroneously defeated. The valves could still be closed, but administrative procedures should be in place to ensure that the unit's safety was not compromised by this unusual valve operation.
az locksmith

[Qalander (Chem)]

Dear jeffreyfrog:

Hello/Good Afternoon,

May I humbly suggest to open a new thread;since otherwise we are in a way might be going back to square one again.

Hope you do realize/appreciate.

Best regards
Qalander

[jrlaw]

It is very dangerous to allow parallel, fully-rated, relief valves open to the process. If the valves are not mounted on a selector type mechanism, one or the other inlet and outlet block valves must be locked or sealed. As stated, operators hate this and in a disturbing trend at some facilities, both sets of block valves are being left open. Google "parallel relief valves" for more information.

[totallockout]

When you've established the most appropriate process method for your application, you may need assistance selecting locking products for manual valves.

 

The right valve lock device depends on the nature of the service and the criticality of the valve isolation. A car seal, as the name suggests will seal the valve in a set position. But once you cut the cable to remove it, it's destroyed. If you need a reusable device a valve lockoff might be more suitable, fixed in place with a padlock.

 

And if valve control, especially when isolating safety relief valves is super-critical, a valve interlock could well be the way forward.