This question has been asked before but the answer wasn't exactly what I was looking for. What specs (Api etc..) dictate the operation of double block and bleed valves in a mutli product tank storage/ manifold? The previous answer was API 6D but I beleive that is the valve spec. I would like to know the tank storage spec if there is one.There is no standard or code mandating the use of DB&B valves in any particular service, apart of safety application in the ASME I, to prevent the steam pressure reaching the isolated boiler during the maintenance work.I have seen many specifications requesting the use of these valves, as prove of positive isolation of two incompatible systems (between tanks, between the pressurised equipment and associated instruments-pressure, temperature, etc, including the bleed on the ambient side). I have seen large DB&B valve between the potable water line and the fire water system;- Double block valves are mentioned in API RP 1595 for aviation airfield storage, Publication 346 for underground pipe leak detection, API RP 2023 for heated petroleum, API Soec 11N for LACT unit custody transfer, STD 2015 for sefe entry of storage tanks, STD 2610 for terminal and tank facilities, ...

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