Is it necessary to have Isolation and bypass valves for all Instrumentation control valves?

Is there any standard to refer the requirement of Isolation and bypass valves for various applications?

 

First I am not aware of any standard that says you must have isolation and bypass valves around control valves. The are some key issues that have to deal with onstream time, process upsets, engineering errors, and safety items. In my opinion I feel it is best engineering pratice to be able to isolate and bypass a control valve in most process streams. This will assist operations in keeping the operation producing product and help identify process upsets.

However if valve is not critical and line can be safely isolated and shutdown without causing an upset then you could install without bypass and isolation valves.

This question really requires an economic, safety, and enviormental analysis. The engineer in conjucntion with operations, management, and fiscal personnel need to determine how critical each valve.

Mark

 

I work on Ammonia/Urea plant. Almost all the instrumentation control valves has bypass valves except for control valves on main urea solution at urea plant. The bypass of these valves are not provided as when the plant shuts down, the urea has tendency to freeze and turn into solid. The bypass valves in this condition will become major dead end and will block any way.

Point that I am making is that process condition should also be taken into account before deciding to have bypass valve or not.