2 replies to this topic

[usama.iqbal]

Hi fellows,

 

Hope you all are fine.

 

I seek your opinions on the following query:  I am procuring a 12" emergency shut down valve that should be a full port, ball valve and used for on/off service.  I have asked to vendor to provide me with a sizing sheet of this valve and he has turned down by saying  "There is no need for a sizing sheet on an emergency shut down valve ".

 

Kindly advise me if there is any need/significance for an ESDV sizing sheet for this specification.

[fallah]

Hi Usama.

 

When you have already sized the relevant line along with an full port ESDV is to be placed, appears vendor response is reasonable.  Among the main characteristics of an ESDV for which the relevant vendor should provide the info are: the stroke time (from full open to full close position and vice versa) and the maximum shut off pressure the valve can tolerate without considerable leakage both are related to relevant actuator design and sizing.

[Art Montemayor]

Usama:

 

As usual, Fallah is absolutely correct when sizing an emergency shutdown valve for routine, normal emergencies.  However, some of my personal experience indicates that you should also be advised that the important item to always bear in mind is - What is the Emergency you are expecting?  You have failed to tell us that significant point that is the heart of the total application for a total venting of process material.

 

For example, if you have a process involving a reaction or a possible spontaneous decomposition of material it is extremely important that you have your process lines (and valves) sized for the eventual flow rate expected from such an "emergency".  The emergency that I am assuming (and probably Fallah as well) that you mean is some process upset not related to such an event, but rather to something like a process over pressure or power failure that gives you reason to quickly shutdown your process and vent it immediately for safety precaution.  For that type of emergency Fallah is completely correct.  The size of the related piping (12") has already been determined or calculated correctly (I assume this has been done and documented), so the size of the correct ESDV has been fixed.  But if there is a possibility of any generation of vapors or matter in your process over and above those normally expected as noted in your documented calculations, than YOU need to furnish any valve vendor with that information in a Specification Sheet.

 

When I was a process engineer many years ago, I followed the rule that if the involved process was a Unit Operation, the flows did not change from that indicated in the calculated total mass balance.  However, if the operation involved a Unit Process, then there was cause to worry about excessive flow rates.  So it is important to define the type of expected emergency shutdown.