Safety Critical Inline Isolation For 18" Valve Replacement Offshore

To provide a temporary fully proven, double block isolation of the 18” gas pipeline, STATS proposed the use of a tethered Tecno Plug® which would be deployed vertically into the platform launcher. 

STATS tethered Tecno Plug is a single module mechanical isolation tool, comprising dual elastomer seals and an array of taper lock grips. Hydraulic steel tubes which activate and monitor the Tecno Plug are housed in interconnecting stem bars. The stem bar sections are assembled together to deploy the plug to the required location within the pipeline.

Temporary Enhancement To Quick-Open Launcher Door

To allow deployment of a tethered Tecno Plug, a temporary quick opening door with a stuffing box arrangement was installed onto the launcher, this allowed the stem bars (containing the hydraulic hoses) to pass through into the pipeline, to position and control the Tecno Plug, while the pipeline remained pressurised.

Once the Tecno Plug was installed into the launcher, a leak test was performed on the launcher’s temporary quick opening door and the stuffing box assembly. After the successful test, the launcher valve was opened, and the plug was hydraulically lowered 6 metres in a controlled operation to accurately position the Tecno Plug at the set location.

The compact design of the single module Tecno Plug allowed the tool to be set in the short section of pipework before a 5D bend. At the isolation location the Tecno Plug was hydraulically set. As the plug is set it compresses in length, this engages the taper locks with the pipe wall, securing the plug in place and radially expands the dual elastomer seals against the pipe wall to form the high pressure seals.

The dual seals of the plug were each then independently tested with full pipeline pressure in the correct direction to confirm leak-tight isolation. This allowed the pipeline to be vented to ambient from the platform launcher to the rear of the plug. The annulus void between the seals was then vented to ambient to create a zero-energy zone, and subject to an 8 hour isolation stability hold period before the Isolation Certificate was issued.

With the launcher and bypass valve depressurised and the Tecno Plug providing a verified double block isolation against the pipeline pressure, the valve replacement activities were conducted. The isolation plug was constantly monitored and remained stable throughout the entire isolation period.

Once the valve replacement was successfully completed and tested the Tecno Plug was unset and recovered fully into the launcher. The launcher valve was closed allowing the launcher to be depressurised and purged enabling the plug to be recovered and the temporary door replaced with the permanent quick opening closure door.