A pipeline isolation and valve change out operation has been completed by STATS Group on Fairfield Energy’s Dunlin Alpha platform.

The workscope included the replacement of two 24” launcher valves on the oil export line from Dunlin to Cormorant Alpha in the North Sea and marks the company’s longest duration remote isolation to date.

Specialist isolation experts STATS used its in-house designed Remote Tecno Plug™ which provides double block and bleed isolation. The technology eliminates the need for communication tethers or specially modified pig trap doors and allowed the old valves to be removed without the requirement for tether management.

In preparation, STATS carried out a piggability study on the oil export line and trialled the Remote Tecno Plug™ onshore with a client witnessed factory acceptance test (FAT) with a purpose built test fixture simulating the offshore pipeline configuration.

The shutdown was scheduled for up to 80 days and as the Tecno Plug™ was the primary isolation on the export pipeline it had to be capable of meeting this scheduled duration.

Head of Intervention and Isolations at STATS Group, Dave Vernon, said: “This successful workscope has marked a new milestone for STATS and was the longest duration remote isolation we have performed to date. Our Remote Tecno Plug™ was constantly monitored and remained stable and in location for 72 days while maintenance operations were completed.”

On-site, the Remote Tecno Plug™ was loaded into the launcher before pigging to the set location with a mixture of water and nitrogen. The Plug was tracked and accurately positioned using through-wall communication. An Extremely Low Frequency (ELF) radio control system sets and then monitored the plug throughout the isolation prior to valve change-out and maintenance activities starting.

Once the new valves were installed STATS provided a bespoke 24” In-Line Weld Test Tool with an extended body and additional locking module to test the newly made-up flange joints. The extended body allowed the In-Line Weld Test Tool to straddle both flanges of the new valves.

As part of the planned maintenance scope the operator also replaced a 1.5” pig signaller which STATS pressure tested with a separate 1.5” Flanged Weld Test Tool. On successful testing of all valves and flanges the Remote Tecno Plug™ was unset and reverse-pigged back to the launcher for demobilisation.

Mr Vernon added: “We have developed a good relationship with Fairfield Energy Ltd and are currently discussing the use of STATS isolation technology for future maintenance activities.”

Tags: STATS Group