Inline isolation provides safe decommissioning benefits at UK gas terminal

STAVANGER, Norway — When a multinational Energy and Services company planned to decommission an onshore gas terminal in northwest England, they required a solution that would avoid depressurizing and blowing down a 25 mi, 36-in. gas pipeline. The pipeline runs from an offshore field through north and south sub-terminals prior to feeding into the United Kingdom’s gas transmission network. A key concern was to complete the line decommissioning safely and quickly, to minimize potential disruptions to the supply schedule.

The solution was the proprietary SmartPlug inline isolation tool from T.D. Williamson (TDW). The SmartPlug tool is a remotely controlled, piggable pipeline pressure isolation device that allows pipeline sections to be isolated at or close to their operating pressure. Not only does this reduce downtime during both planned maintenance and unexpected repairs, it also keeps pipeline inventory in place.

The operator initially contracted TDW to provide isolation services using a 36-in. SmartPlug tool, providing double-block isolation against the gas pressure in the pipeline. This would enable the safe removal of a 36-in. full bore tee as part of the decommissioning process. During operational discussions, however, the operator requested a pipe end barrier. The goal was to provide a safe vapor barrier behind cutting and welding near 0.62 mi of open, water-filled pipeline potentially containing a low content of dissolved hydrocarbons.

After considering the options, TDW delivered a second 36-in. SmartPlug tool configured to provide a single block isolation as a risk mitigation measure. The single module SmartPlug tool acted as a pipe end barrier to contain the pipeline contents once the pipeline was cut.

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