10" Subsea Hot Tapping and Line Stopping, Gulf of Mexico

In the Gulf of Mexico, at a water depth of around 25 metres, STATS was contracted to isolate and abandon a 10 inch oil pipeline as part of a decommissioning project.

The project required subsea hot tapping and line stopping at two locations to allow removal of a short section of pipework. Once isolated, purged and cut, one end of the remaining pipeline was terminated with a mechanical connector and blind flange; the other was fitted with a full bore valve and blind flange.

STATS BISEP was deployed through a mechanical hot tap clamp and slab valve, to provide leak-tight isolation of the pressurised pipeline through a single fitting. Hydraulically activated dual seals gave fully proven, monitored isolation of the pipeline's contents throughout the project - an advantage over traditional line stop technology.

Once equipment and personnel were mobilised to the vessel, the slab valve and hot tap machine were attached to the mechanical hot tap clamp and lowered into position. The clamp was bolted to the pipeline and leak-tested to confirm the fitting's integrity before cutting into the live line.

With both hot taps complete, the first BISEP was lowered into position, pressure-tested against the closed slab valve, then deployed into the pipeline toward the pressure threat and hydraulically activated to create the first isolation barrier. A second BISEP was installed and deployed to create a midline isolation of the pressurised pipeline. Each BISEP was independently tested on its primary and secondary seals to verify a zero-energy zone in the seal annulus, and an Isolation Certificate was issued once testing was complete.

STATS then used the BISEP launcher's integrated 2 inch port to attach a downline from the vessel to each launcher, upstream and downstream, flushing the isolated pipe section with seawater before it was cut. This is a feature exclusive to the BISEP design: it avoided additional hot tapping and reduced the number of fittings installed on the pipeline, saving the client time and money and reducing risk to the project.

Once the section was clean, it was cut behind each BISEP and recovered to the vessel. New pipe sections, including flushing ports, a barred flange and a 10 inch ball valve, were installed at both ends. With the BISEPs still isolating the pipeline, a leak test confirmed the new pipework before both BISEPs were unset, retracted and recovered to the surface. Completion plugs were installed in the hot tap clamps and the slab valves were removed.

The client then launched a single dewatering pig from the onshore processing facility to the newly installed 10 inch ball valve; de-oiling the pipeline took three days, confirmed complete when the pig was received at the barred flange. The valve was closed, flushing hoses installed, and the pipe flushed through the new 2 inch ports to verify every trace of oil had been removed before the flushing equipment was recovered. A blind flange was installed on one end of the connector, abandoning the section of pipeline running to the onshore facility, and another was fitted to the 10 inch ball valve, securing that section and leaving it ready for future tie-ins.