Conductor guide array replacement extends platform life by two decades

A recent Claxton fabrication contract for a replacement jacket guide assembly project called for a radical technical solution. The company’s involvement started in May 2011 with a survey of the existing guide assembly, which was reaching the end of its working life, at a North Sea platform. Detailed design work for a replacement then followed. With the field operator keen to make progress, Claxton’s rapid response saw design engineers going offshore in a matter of days to assess the condition of the existing structure.

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The 12 new guides will enable the operator to extend the working life of the platform by up to 20 years

The splash zones on offshore platforms are subjected to seawater exposure and high levels of lateral loading from the risers, and, in this case, it was clear that the entire splash-zone structure needed replacing. The solution Claxton proposed involved building the new assembly on top of the old guide using existing structural members for support before removing the old structure from underneath. This multistage process called for high-precision installation of uprights, beams and four rows of guides assembled with eight new guide sections. When complete, this would replace the splash deck of the platform, provide 12 new conductor guides and enable the field operator to extend the working life of the platform by up to 20 years.

The main challenges for Claxton involved restrictions on how the assembly could be installed; its modularity; and the flexibility required to deliver an appropriate engineering solution to a very tight timescale. Ann Vicens, project engineer, Claxton, explains, “This was a large-scale project that built on our experience in this sector and work we had already conducted for the operator, including maintenance and decommissioning services. In this case, we provided full project management and the close relationship we have with our suppliers meant that we were able to complete the fabrication phase in under 14 weeks.”

The project’s very tight schedule, with installation in May this year, presented some tricky challenges. The modular replacement structure had many small sections to be bolted together in situ. This required rope-access operations, which made it vital that the components fitted together easily without needing extensive manipulation.

To ensure this, Claxton conducted a complete full assembly test during fabrication before transporting the modules offshore. As part of its commitment to meeting the deadline, the company arranged with its suppliers to conduct the assembly test procedure using the various elements as they became available.

To meet the challenge of adverse weather conditions possibly interrupting the installation process, given the platform’s North Sea location, Claxton designed the new guide assembly so that the individual sections were secure and could self-support throughout the installation process.

Many of the production assets in the North Sea are operating beyond their original design lives and this is prompting field operators to find innovative engineering solutions that extend production and maintain asset integrity. The approach that Claxton devised for this guide replacement could have widespread application.

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