ABERDEEN, UK – STATS Group has completed an isolation project on a 16-in. subsea pipeline in the Dutch North Sea for Wintershall Noordzee.
The action enabled disconnection of a flexible gas export pipeline and replacement with a new rigid gas export pipeline.
STATS deployed its Tecno Plug tool for the isolation, which avoided the need for depressurization of the main trunk line, leading to reduced production losses.
A four-module 16-in. Remote Tecno Plug was pigged from the K5-A platform to the subsea isolation position 300 m (984 ft) from the platform. The tool was tracked and its location confirmed using the STATS through-wall communication system via a low frequency, monitored by technicians onboard the EDT Protea dive support vessel.
When set, the tool isolated a pressure of 70 bar (1,015 psi). On completion, primary and secondary seal tests were performed using full isolation pressure.
The pressure between the primary and secondary seals was monitored throughout the isolation, to ensure safe double block isolation. The section of flexible riser was then removed, allowing a new subsea valve to be added to the pipeline behind the isolating Tecno Plug.
Divers attached a temporary subsea receiver to the valve so that the tool could be remotely unset and reverse pigged into the receiver. The subsea valve was subsequently closed and tested before the temporary receiver was removed and retrieved to the Protea DVS. The new subsea valve then provided isolation while the permanent pipeline was tied in and re-commissioned.
STATS completed the project within six weeks. Design challenges included the need for bi-directional pigging through various 5D bends, and accommodating the layered helical winding on the internal surface of a flexible pipeline.