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In-situ billet welding to slash downtime on FPSO platforms

Trelleborg AB Group Head Office : 03 September, 2013  (Technical Article)
Trelleborg has launched a revolutionary new SealWelding technology which allows seals to be welded in-situ on an FPSO (floating production, storage and offloading) platform. This new technology will massively reduce the downtime and associated costs that come from maintaining a floating production, storage and offloading (FPSO) swivel stack. Currently, swivel stack maintenance requires a vessel to travel back to shore so that components can be completely disassembled and seals replaced.
The offshore oil and gas sector has been going strong since the late 1940s, however, as the industry continues to move toward even more demanding offshore applications in order to drill deeper and reach further, the use of floating production, storage and offloading (FPSO) vessels have become particularly popular. Eliminating the need to lay expensive long-distance pipelines from the processing facility to an onshore terminal, the FPSO is suitable for remote or deepwater locations where seabed pipelines are not cost effective.
But, while offshore facilities have opened the vast frontier of the world’s oceans to oil and gas exploration and production, they have also resulted in new and unique challenges. For example, while FPSOs can provide an economically attractive solution for smaller oil fields which can be exhausted in a few years and do not justify the expense of installing a pipeline, maintaining those installations can often prove difficult and time consuming, especially as environments become more challenging. 
A critical element onboard an FPSO facility, the swivel stack is the heart of the turret, mooring and fluid transfer system. The swivel ensures that all fluids (liquids and gas), controls, and power are transferred safely from the geo-stationary components (wells, flowlines, manifolds, risers) to the rotating vessel and its process plant, under any environmental conditions. 
Seals are vital when it comes to ensuring the continued efficient and safe operation of an FPSO swivel stack. As replacement of the seals in a swivel stack requires the FPSO to travel back to shore so that components can be completely disassembled and seals replaced. In fact, this whole operation is extremely time consuming and requires huge preparation time; typically the FPSO would be down for between 6 and 12 weeks and the cost of that could rise to 100s of millions of dollars. 
A commonly used technique for leading manufacturers of seals is billet welding. Trelleborg has developed a new seal which, manufactured from its established seal material, can be welded on the platform without the need to return to shore. By using a well-established and proven material as opposed to a modified substance, Trelleborg has been able to avoid integrating something which has not been fully tested into the new system to ensure full compliancy and reliability for the offshore operator. 
In a controlled manufacturing area, Trelleborg starts the process by producing a seal which has been cut in one place using a specially designed tool. The product is then packed so that it is well protected and avoids any damage in transit.
Offshore, onboard the FPSO, the seal is unpacked and installed onto the swivel by highly trained personnel from Trelleborg’s service team; the skilled engineer installs it in the Weld Head Enclosure (part of the welding machine) which, certified to ATEX zone 1, is then pressurized so that the welding can take place. Fully enclosed, production on other swivel stacks can continue without risk.
A Control Cabinet, which is purged and will also be certified to ATEX zone 1, ensures the smooth running of the process, as well as monitoring and logging all data. After the process is finished, the seal is safely removed from the Weld Head Enclosure before being polished and checked. If the values from the recorded data are satisfactory, the seal will be released for installation. 
Henk-Willem Sanders, Technical Manager Oil & Gas, Trelleborg Sealing Solutions
Offshore Technology Conference, Houston, Texas, US. May 2013.
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