Use of ESDV as DBB valve
Use of ESDV as DBB valve
(OP)
Would anybody like to comment on this: Is it OK to use an ESDV as one of the valves in a DBB arrangement?
Best regards
Morten
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RE: Use of ESDV as DBB valve
If the double block and bleed is a function of the emergency shutdown, then I would see no problems but I don't think that is what you are asking.
If you are wanting to use the ESDV for something other than the emergency event for which it is intended, then it would seem that you would have to defeat or bypass the control logic provided to control the valve. This opens the door for potential problems. Such safety logic would typically have a high level of supervisory control so that not just anyone could do that without proper authority. This would seem to make using it as a DBB for more "routine" operations quite burdensome and rightly so.
Are your safety systems following the newer Safety Integrity Level (SIL) guidelines? I'm only vaguely familiar with these guidelines but I wonder if what you propose would have an impact on the SIL determination for the ESD system. Maybe that could answer your question.
In some cases, I've seen that the desired SIL can be achieved by activating a normal process control valve along with an independent, designated ESDV. I mention this only because I've seen normal process control valves used as part of an ESD system but can't recall knowing an ESDV being used for "routine" operations.
Of course this is only opinion and I'm not an instrument engineer but I've had to review quite a few safety systems during HAZOPs. Also, I don't know the details of your particular system, but unless there was good argument otherwise, I think I would avoid it.
RE: Use of ESDV as DBB valve
In the gas industry, most shutdown valves are quarter turn line-class ball valves. The process application dictates the requirements. The valve does not define the application as emergency shutdown. Perhaps the valve is defined as a process shutdown valve applicable to a simple single-vessel/single pump system. High level stops inflow. Low level stops outflow. The same valve may also close in the event of a unit fire. In this case the process shutdown valve is the emergency shutdown valve.
Clarify your situation. Perhaps we can address your question if better understood.
John
RE: Use of ESDV as DBB valve
This is not to be confused with automatic DBB, which is basically two SDV and a BDV in between. Automatic DBB is normally used in fuel gas supply to combustion equipment like fire heaters. This is to be 99.999 % sure, fuel supply is positively isolated in the event of an upset in the combustion equipment. This is for observes reason of not to continue supply fuel to fire. In this case a ESDV can be used as one of the SDV. However, your vendor may prefer that the whole automatic DBB system to be intergreted to his control system as a whole. I prefered to provided a SDV at the source fuel supply and the other close to the fired equipment.
Hope this will help.
RE: Use of ESDV as DBB valve