36” Tethered Tecno Plug | BP Sullom Voe Terminal, Shetland

STATS were approached to provide a double block isolation to facilitate the valve works and proposed the use of a 36” Tecno Plug, controlled using composite umbilical hydraulic lines to allow the valve change out to be carried out safely.

The compact design of the single module Tecno Plug allowed the plug to be set in the short section of pipework upstream of the production tee enabling export from the Brent pipeline to continue.

To allow deployment of a tethered Tecno Plug a temporary receiver door was used with a Stuffing Box arrangement allowing the umbilical (Hydraulic control and monitoring lines) to pass through the receiver door while the pipeline remained pressurised and operational.

With the Tecno Plug loaded into the receiver a leak test was performed to confirm the integrity of the temporary door and stuffing box. With the leak test successfully completed, the isolation plug was pigged with water to the set location. Accurate plug location was determined by markers on the umbilical to indicate the distance travelled into the pipeline,  additional positional verification was confirmed by an ultrasonic signaller from outside of the pipe at the desired isolation location. Accuracy of the isolation was crucial to ensure the Tecno Plug was positioned in the short pipe section between the valve to be replaced and the production tee. This ensured no shutdown of production during the valve changeout. 

The Tecno Plug was set at location using a hydraulic system via the umbilical and an annulus test was performed to verify the integrity of the primary and secondary seals. Both seals were independently tested with full pipeline pressure and monitored for 12 hours and once the verification period was completed, the isolation certificate was issued.

The STATS field team consisted of four isolation technicians as part of the workscope to provide constant 24 hour monitoring of the plug throughout the isolation duration.

With the receiver and valves depressurised and the Tecno Plug providing a verified isolation against the pipeline pressure, the receiver was rigged away, allowing the main umbilical to be disconnected and temporary control umbilicals were attached to ensure constant communication with the Tecno Plug, allowing the main umbilical to be removed through the valve. On completion of the valve maintenance, further umbilical management was carried out to allow the valve to be repositioned.