April Editorial Focus - Trelleborg

Slashing Downtime with Innovative Seal Welding Technology

By Henk-Willem Sanders, Technical Manager Oil & Gas, Trelleborg Sealing Solutions

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 that can be exhausted in a few years and do not necessitate the expense of installing a pipeline, maintaining those installations can often prove difficult and time consuming, especially as environments become more challenging.

With financial data suggesting that losses from an hour of downtime for an offshore production facility is among the highest of any industry, every moment saved in downtime means significant cost savings for the operator. This article considers why optimizing the design, operability, and safety of FPSOs has never been more important if downtime is to be combated and will focus on the development of new seal welding solutions that have been specifically designed to help operators do this.

While all oil platforms originally sat on the seabed, floating production systems were developed and introduced in the 1970s as exploration moved to deeper waters and more distant locations. A viable solution that brought with it significant advantages, including the ability to move production to a new location once the field became depleted, this technology quickly proved popular, and now over 200 vessels are currently deployed worldwide as FPSOs.

However, along with new benefits came new challenges—and it wasn’t long before the maintenance of these facilities became a hot topic and set the offshore agenda. Maintenance is an issue because with a number of component failures able to easily cause an FPSO to a shutdown that requires onshore maintenance, the cost and traveling time required to return an FPSO to shore quickly adds up.

As such, reliability, safety, and flexibility are of key importance when securing maximum up-time for an FPSO facility and offshore operators are continually on the lookout for ways to reduce the chance of FPSO shutdown, avoiding the downtime associated with maintenance.

A critical element on board an FPSO facility, the swivel stack is the heart of the turret, mooring, and fluid transfer system. The swivel stack ensures that all fluids (liquids and gas), controls, and power are transferred safely from the geo-stationary components (wells, flowlines, manifolds, and 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. Replacement of the seals in a swivel stack requires the FPSO to return 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 hundreds of millions of dollars.

With every second saved in downtime adding to the bottom line of the operator, cutting out the traveling time required to return an FPSO to shore for a seal replacement could provide operators with a huge financial savings.

The idea to solve this issue of offshore maintenance was an obvious one—remove and replace the seal in situ on the FPSO offshore. However, to actually do this and create a viable technique was not so simple.

It would require the development of a technique that would bond the ends of a cut seal offshore, something that would prove extremely difficult. Adding to the challenge, seal welding has to be possible when other swivels are still in production—this could be extremely high risk without special safety features incorporated into the welding equipment. Furthermore, the equipment would need to be portable so it can be transported to the FPSO and a committed and fully trained service team would need to be put together that could go out to the FPSOs to replace the seal in the field.

A commonly used technique for leading manufacturers of seals is billets welding. However, dedicated to meeting the wants and needs of the offshore operators through innovation, some manufacturers have been working to provide an enhanced solution. Investing significant time and resources, they have been able to develop a viable, fully tested portable system that will replace seals in situ by optimizing the billets welding technique for a seal profile.

The latest in seal welding technology has more than met the challenge and is set to revolutionize the FPSO market. An example of this innovation can be found in Trelleborg Sealing Solutions’ new seal.

Trelleborg has developed a new seal that, 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 that 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 that has been cut in one place using a specially designed tool. The product is then packaged so that it is well protected from any damage in transit.

Onboard the FPSO offshore, 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) that, 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 or requiring downtime of the FPSO.

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.

Safety on FPSOs is of paramount importance and in the harsh offshore oil and gas industry, operators must take every precaution to minimize risk at every turn. But at the same time, spiraling maintenance costs and project downtime have proven to be real issues for the offshore sector.

With seal welding, a requirement for the smooth running of the FPSO swivel stack, a critical element of operations—replacement involving a melting process—has always had to be conducted offshore, resulting in extremely costly and time-consuming downtime for the facility as the FPSO has to be disconnected.

As such, for many years there has been a desire for a safe and reliable alternative to this process that can be carried out in situ. However, after years of development, Trelleborg Sealing Solutions has created a fully tested, portable system that is not only set to make life for the offshore operator safer and easier, but also dramatically improves the bottom line for the oil company.