STATS Group has successfully carried out inline isolation services to allow the replacement of an 18” bypass valve on an offshore platform in Australia’s Bass Strait. STATS were approached by an international oil and gas company to provide a fail-safe double block and bleed isolation to allow a bypass valve to be replaced during a planned shutdown.
STATS proposed the use of a tethered Tecno Plug® to provide a temporary fully proved, double block isolation of the 18” gas pipeline. The Tecno Plug was located in a short straight section of line beyond the launcher isolation valve and pipeline tee. The use of the Tecno Plug ensured that only a small section of pipework was required to be vented and purged while the valve replacement activities took place. This provided the operator with considerable time and cost savings while ensuring the safety of the worksite.
The offshore platform launcher was vertical and featured a quick opening closure door. 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. 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.
Gareth Campbell, Regional Sales Manager for Asia Pacific, said: “There is great demand for STATS double block isolation technologies throughout Australia and this workscope is now one of many safety critical isolation projects recently completed in the region.
“The Tecno Plug offers a high level of safety while providing a cost-effective solution for the operator, this successful isolation prevented the operator from depressurising and purging the entire gas pipeline required to ensure the pipeline was hydrocarbon-free prior to maintenance activities.”