Performing maintenance or repair on a live crude export pipeline can be a daunting task. The steps – from product removal and depressurising to flooding and then de-watering the line – can be risky, costly, and complicated.
During the recent replacement of two emergency shutdown valves (ESDVs) on one of its production platforms offshore West Africa, the operator, an independent Anglo-French oil and gas company, not only avoided those difficulties, but also maintained production and ensured increased safety through topside pipeline isolation for both valves. The operation on two 8 in. and 12 in. incoming risers integrated multiple isolation methods, including industry-standard double block and bleed technology.
To isolate the 8 in. riser, a single position STOPPLE® plugging system with bypass was set through a three-way spool. The 12 in. riser was similarly isolated via a three-way spool, complete with bypass, but this setup allowed for use of a STOPPLE Train system, which provided the additional safety of double block and bleed capability.
The double block and bleed technology provided by T.D. Williamson (TDW) allows two independent seals to enter the pipeline through a single hot tap opening, reducing the total number of fittings and hot taps required. A bleed port between the two seals then allows for pressure and product evacuation, which means workers performing welding or pipe cutting downstream are separated from the line’s pressurised contents.
“Although proper planning and coordination are requisite for all offshore operations,” says Fernando Pimenta, TDW Project Coordinator, “isolating topside on a production platform presents a number of unique logistical challenges.”
For example, due to the limited amount of workspace on the platform, the isolation equipment had to be positioned directly below the ESDVs through a complex network of scaffolding and lifting tools. The location of the valves meant that, ultimately, all equipment was operated while positioned horizontally near the surface of the water, just a few meters from the splash zone.
Throughout the four-week ESDV replacement, the operator successfully maintained production at a safe operating pressure of 15 bars (218 PSI) via bypass.
Adapted from a press release by David Bizley