March 2018, Vol. 245, No. 3
TechNotes
Use of Pigging Tool Avoids Blowing Down 25-Mile Pipeline
When a multinational an energy and services company planned to decommission an onshore gas terminal in northwest England, it required a fast, total solution that would avoid depressurizing and blowing down a 25-mile (40-km), 36-inch gas pipeline that runs from an offshore field through north and south sub-terminals prior to feeding into the United Kingdom’s gas transmission network.
With the goal being to complete decommissioning safely and quickly, and minimize potential disruptions to the supply schedule, the solution taken was the SmartPlug inline isolation tool from T.D. Williamson (TDW).
The is a remotely controlled, piggable pipeline pressure isolation device that allows pipeline sections to be isolated close to 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-inch SmartPlug tool, providing double-block isolation against the gas pressure in the pipeline. This would enable the safe removal of a 36-inch 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 vapor barrier behind cutting and welding within 0.62 miles (1 km) of open, water-filled pipeline potentially containing a low content of dissolved hydrocarbons.
After considering the options, TDW delivered a second 36-inch 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. As time was of the essence, extreme focus and effort were required to deliver the designed, assembled, and tested second single module SmartPlug tool on site within three days.
The operation at the south sub-terminal began by launching, pigging and setting the first SmartPlug tool to create double-block isolation against the 16 bar (232 psi) gas pressure in the pipeline. Once the first tool was set against full line pressure, the line was depressurized. The second SmartPlug tool was then launched and pigged to the designated location 131 feet upstream (40 meters) of the primary isolation tool
This tool acted as a vapor barrier to the pipeline from the north terminal. Both SmartPlug tools were tracked and remotely activated by the proprietary TDW SmartTrack™ system, which uses extremely low-frequency signals from the built-in SmartPlug transponder.
After both tools were set, TDW monitored the integrity of each isolation during the full decommissioning work activity. Upon completion of the decommissioning activities, the SmartPlug tools were pigged back to the receiver using residual gas pressure from the pipeline. P&GJ
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