Double Block and Bleed is a term often used in the oil and gas industry to define a level of isolation sufficient to perform maintenance activities. The true definition relates to incumbent valves providing two proven levels of isolation against the outboard pressure to permit breaching of containment in the isolated pipe. This paper assesses how temporary isolation devices can provide equivalent isolation where incumbent valves do not exist at appropriate locations in the system. It reviews the different interpretations of Double Block and Bleed used within the industry and compares how different isolation devices are assessed in relation to the level of isolation they provide.

It will reference several examples from around the world of where temporary isolation devices have been used to replace valves and perform repairs in trunk pipelines without depressurising the whole pipeline. It will also cover examples of isolating live process pipe to perform maintenance activities outside plant shutdown.

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