When a multinational energy and services company planned to decommission an onshore gas terminal in northwest England, it required a fast total solution that would avoid depressurising and blowing down a 40 km, 36 inch (914 mm) gas pipeline.
The pipeline runs from an offshore field through north and south sub-terminals, before feeding into the UK’s gas transmission network.
A key concern was completing the line decommissioning safely and quickly in order to minimise potential disruptions to the supply schedule; the solution decided on was the TDW SmartPlug inline isolation tool.
The tool is a remotely controlled pressure isolation device that allows piggable pipeline sections to be isolated at, or close to, their operating pressure.
This reduces downtime during both planned maintenance and unexpected repairs, while also keeping pipeline inventory in place.
The operator initially contracted TDW to provide isolation services using a 36 inch SmartPlug to provide a double-block isolation against the gas pressure in the pipeline, enabling 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 with the goal of providing a safe vapour barrier behind cutting and welding taking place near an adjacent 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, which was configured to provide a single-block isolation as a risk mitigation measure.
The single module 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 a designed, assembled and tested second tool on site within three days.
The operation at the south sub-terminal began by launching, pigging and setting the first SmartPlug to create double-block isolation against the 16 bar gas pressure in the pipeline, setting it against full line pressure, and depressurising the line.
The second tool was then launched and pigged to the designated location approximately 40 m upstream of the primary isolation tool; the tool acted as a vapour barrier to the pipeline from the north terminal.
Both tools were tracked and remotely activated by the 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 tools were pigged back to the receiver using residual gas pressure from the pipeline.
TDW Senior Manager of Operations Offshore Thomas Idland said that, TDW Senior Manager, Operations Offshore, the nature of the operation required careful design, attention to detail, and risk mitigation during tool launch, set and retrieval.
“TDW engineers were available on site at all times during the operation to provide any additional support to the client and TDW operating crew,” Mr Idland said.
“The out-of-box solution engineered by TDW and the high quality of execution in the field were recognised and well-appreciated by the client.”
For more information visit the TDW website.
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Image supplied by T.D. Williamson