ESDV or SDV on a Produced Water line of an HP Separator

[Sesquipedalianist]

Our current design has consideration of an ESDV being placed on a produced water line from an HP separator of an oil processing train. Personally I find this strange since the fluid here is water(almost),not flammable, not explosive and not hazardous. The SDV would be sufficient. Although an argument can be made that there is a large hydrocarbon inventory upstream of this valve, and the holdup time in the separator is not that long I still believe the qualification of this line as prominently water doesn't call for an ESDV consideration. What is your thought?

 

[georgeverghese]

You mean both an SDV and an ESDV on the PW exit line? SDV for process shutdowns and the ESDV for process shutdown and blowdown sequence? Are trip logics for both SDV and ESDV housed in a common dedicated PLC or similar?

 

[Sesquipedalianist]

What i meant is that the actual valve is specified as an ESDV. Yet I think having it as an SDV is sufficient.

 

[EmmanuelTop]

It's just terminology, meaning that the valve is supposed to close upon initiation of an EMERGENCY scenario on the produced water line. Carrying less hazardous fluid than hydrocarbons does not necessarily mean that emergency scenarios are not possible/credible. There might be something you have overlooked. It could be a scenario involving significant environmental spill (if undetected for long time), or gas blow-by from upstream HP separator, or something else. Also look at C&E Diagram to see what closes this particular valve, and if any of these events/scenarios classify as emergency.

There is no such thing as "common sense" - Apollo RCA

 

[Sesquipedalianist]

Hello Emmanuel, thanks for the response

My understanding is that an SDV refers to an actuated valve which is closed during partial or total process shutdown of system to which the valve protects whereas the ESDV is an actuated valve which is closed when triggered by a signal from an ESD level signal during emergency conditions. That has been at least the opinion I have held with a few others.

It is against that background that I enquired.

 

[EmmanuelTop]

SDV and ESDV valve look exactly the same - being in the same physical location of course. The only thing that differentiates them, is whether they are a part of emergency shutdown logic or not. If the subject valve is a part of any emergency scenario, then it will remain "ESDV". If it's not, you can rename it to "SDV". For majority of systems out there, both PSD and ESD are a part of SIS, hence it really makes little difference in real life.

There is no such thing as "common sense" - Apollo RCA

 

[Sesquipedalianist]

Great we hold a similar view.

Thus goes the question, for a line that is predominantly water, why make it part of an emergency shutdown logic especially since it is not hazardous in any way!

 

[georgeverghese]

The PW line SDV should auto close when interface level is low, and also when total level is low. There is no guarantee interface level will always work. In many plants, L-L interface control is a difficult task, and many interface detectors dont work well, if they do at all.

 

[EmmanuelTop]

If there is an emergency scenario involving PW line - and some of those scenarios are mentioned by George and myself in previous posts - the valve on the PW line is qualified for title ESDV.

There is no such thing as "common sense" - Apollo RCA

 

[MortenA]

You concern should be gas breakthrough to whereever the water is going - this would of course require than the vessel is completely drained - this could happen how? If your level control fails

So what do you need to prevent gas breakthrough? An independant low level switch and an independant valve (because in fact the valve is the most likely thing to fail). I dont really know what you definition of a SVD contra an ESDV but you should have an independant valve to shut down in case of a low level. This could be either if the water level becomes to low (if whereever your water go is NOT OK with oil) or ultimately if you liquid level becomes too low (but then you could get oil downstream)!

WO mere knowledge of your system its hard to put a double line under the answer but a through HAZOP should clarify this!

Best regards, Morten