We have been asked to identify the critical instruments in our plant. But we are struck up with the methodology to follow. Is there any clearly defined and widely accepted methodology to identify the critical instrument in plant? If yes..then please help.

 

perhaps whomever asked you to identify the critical instruments is the appropriate entity to define what the term "critical" means.

--
Bob
http://ilbob.blogspot.com/

 

Critical instruments are the ones that will cause down time in production if they should fail. If more than one instrument is installed doing the same job and you can swop the one for the other without production down time that is not a critical instrument. an Example will be where you measure the level of a vessel with a trip and a control transmitter. If one of them fails, the others signal can be used for both indications in the DCS and ESD. This is only done in emergencies but it will prevent down time and the plant can run like this until a new replacement transmitter arrives.

Hot spares should be kept for all critical instruments so that is the reason why you were asked to identify them.

The easiest way to identify a critical instrument is to create a scenario in your mind where the instrument have failed and you are tasked to get the plant up and running again. If it cannot be done without this instrument, mark it as critical and get a hot spare in the store for it. Make use of the Cause and Effects tables of your plant where you are unsure what the function of a instrument is or what the result will be should it fail.