Q & A > Question Details
Our HP sour gas header battery limit B/V is passing and leads to shut down other supplying unit to replace passing valve. To face this problem in future, maintenance is going to install 2nd block valve after removing originally installed NRV.
Q-1 Will it be successful?
Q-2 Why there are NRVs installed in battery limits for incoming lines?
 
Answers
19/02/2011 A: Sanjay Rajora, Essar Oil Ltd, srajora@essar.com
NRVs are installed at Battery Limits to contain the stream within B/L in case of any failure in the downstream in ISBL. For critical streams, block and bleeds are also provided at the B/L. To install 2nd block valve in your case will definitely be providing more safety in case of passing of either valve.
18/02/2011 A: keith bowers, B and B Consulting, kebowers47@gmail.com
In my year in Process Design and Project Management, I always insisted on positive isolation of each unit from off plot facilities , usually by double block and bleed or spectacle blinds. A single block valve is not 'positive isolation.' Too many deaths during unit maintenance activities have been caused by leaking single block valves. NEVER bet your life or those of others on any single valve holding. 'Leak Tight' is a specification, not an absolute--some leakage is permitted by that specification. 'Commercially tight' is much lower allowable leakage (under the test conditions), but very costly to achieve in larger sizes--AND the leak test conditions probably are not close to in-service conditions.