Offshore staff
ABERDEEN, UK – STATS Group, has completed an isolation project on BG’s North Everest platform to facilitate a maintenance/replacement works program.
This covered three maintenance valves and one emergency shutdown valve (ESD) on a 20-in. (51-cm) gas import line onboard the platform.
Following a detailed site survey and piggability study, STATS opted to employ a tethered Tecno Plug pushed by stem bar to location from a temporary launcher.
The pipeline had not been pigged previously, but this technique was presumed to carry less of a risk than pigging a remotely operated plug from the pig trap.
Prior to performing the isolation the pipeline pressure was reduced to 6 barg, with the ESD closed and sealant injected.
The maintenance valve was then closed to provide temporary pipeline isolation. This allowed the temporary launcher to be installed inboard of the ESD valve, with STATS breaking out the piping.
STATS’ team also provided gas bags to act as a vapor barrier while a new 1500# flange was welded into the line. This was then pressure tested using a flanged weld test tool before reinstating the new bend and launcher valves.
With the temporary launcher now in place and fully pressure tested, the valves were opened and the Tecno Plug deployed into position outboard of the valves and hydraulically set to provide pipeline isolation.
Once set and monitored the stem bar was disconnected and the valves replaced. The Tecno Plug was installed in the reverse direction, providing full isolation and a test boundary to pressure test the integrity of the reinstalled valves.
A full pressure test at 208 Barg was conducted between the temporary launcher and the Tecno Plug before the plug was unset and recovered back into the launcher. The valves were then closed and the temporary launcher removed, allowing the pipeline to be reinstalled and restored to operation.
01/04/2012
