STATS Group provides pressurised isolation of trunkline
STATS Group was recently retained by a major oil producer in Saudi Arabia to provide the pressurised isolation of a 36 inch trunkline, which was the first piggable isolation of its type completed in the region.
The operator had identified a requirement to replace the pig-trap launch valve to maintain the integrity of the pipeline, and to ensure routine cleaning and inspection operations could continue. STATS utilised its non-intrusive inline-isolation tool, which allowed a double-block-and-bleed isolation, facilitating safe valve replacement and maintenance activities to be successfully carried out.
The 29 km pipeline had no valves, or means of isolating the pipeline, between the pig-trap launch valve – which was to be replaced – and the production manifold. STATS Group decided to utilise its Remote Tecno Plug, which allowed a short section of pipeline to be isolated and prevented a shutdown of the production facilities, as well as the timely and costly process of de-oiling and flushing the entire pipeline.
The approach also had a positive impact on the environment by preventing extensive flushing, cleaning and the disposal of oil from the pipeline. Conventional isolations of this type would usually involve a traditional hot-tap line-stop and vents to achieve an isolation, whose sealing integrity is neither guaranteed to be leak-free, nor does the line-stop provide a verified double-block-and-bleed isolation.
The Remote Tecno Plug system provides a verified, fully tested, and monitored isolation while in the pipeline system, and avoids the need for additional tie-in weldments for the isolation tool or vent fittings. It is fully certified by DNV GL to verify that the design criteria satisfy the requirements for pipeline-isolation plugs: to provide dual seal and isolation in accordance with Offshore Standard DNV-OS-F101 (Submarine Pipeline Systems) and recommended practices DNV-RP-F113 (Subsea Pipeline Repair). It is also in compliant with ASME BPVC Section VIII, Division 2.
The client had the replacement pig-trap valve on hand and required the Remote Tecno Plug delivered within a four-week window. The project was fast-tracked and included a site survey to verify the client’s pipeline data, ahead of engineering, risk assessments, and a factory-acceptance test prior to the delivery of the plug to site.
Once on site, the Remote Tecno Plug was loaded into the launcher, pigged through the pig-trap launch valve, and positioned in a short section of pipeline between the valve and production tee. The location provided the option for the client to restart production during the valve-replacement activities.
During pigging operations, the plug was tracked and accurately positioned using through-wall communication. It was monitored throughout the isolation by an extremely-low-frequency (ELF) radio control system.
The plug was then hydraulically set, providing fail-safe and fully-tested double-block isolation against 15–20 bar pressure and the pipeline’s toxic contents. As is typical in the region, the pipeline had a high H2S sour content (11 per cent), so it was vital for the safety of the worksite and personnel that the plug provided a safe and reliable barrier prior to breaking containment.
Independent testing of each seal, with full pipeline pressure, confirmed leak-tight isolation and the pipeline was bled-down to ambient from the pig-trap launcher to the rear of the plug; the annulus void between the plug’s seals was vented to ambient to create a zero-energy zone.
The sealing plug features a fail-safe design which uses differential pressure acting on the tool to energise the lock grips and seals, which is referred to as self-energisation. When the isolation plug is self-energised, the isolation is maintained independent of the remote-control system. However, it is backed-up by the hydraulic control system which maintains the isolation when the differential pressure is below the self-energisation threshold.
Once the plug is activated the hydraulic circuits are locked-in by pilot-operated check valves and fail-safe solenoid valves. The lock grips provide twice the required lock contact area providing 100 per cent contingency.
In the event that the hydraulic control system is compromised, the tool-actuation mechanism will unset when differential pressure is equalised. The feature ensures pipeline integrity is maintained and the plug is always recoverable once the job has been completed.
After the isolation stability hold period the ‘Isolation Certificate’ was issued and the Tecno Plug was confirmed as providing double-block isolation, allowing the valve maintenance to commence. The tool was constantly monitored to confirm the integrity of the seals and remained set in place for three days while the valve was replaced. During the valve replacement, the operator conducted additional maintenance, including replacing the 12 inch kicker line valve and 4 inch drain valve.
With maintenance work successfully completed, the Tecno Plug was used as a test boundary to perform a reinstatement pressure test. This was achieved by raising the pipeline pressure from the pig-trap launcher side while the plug remained in a fully ‘set’ condition.
The reverse pressure-test operation created a test boundary to confirm the newly installed valve. Finally, the plug was unset and reverse pigged back to the launcher for demobilisation.
This article was featured in the June edition of Pipelines International. To view the magazine on your PC, Mac, tablet, or mobile device, click here.
For more information visit the STATS Group website.
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