Raising the tension - without the stress
A UAE-based rig builder put Claxton’s flexibility to the test recently when it asked the company to provide modified riser tension systems for two new jackup drilling rigs at very short notice.
Whereas previous similar rigs had left the rig builders yard in Sharjah with 50-tonne tension systems built according to a standard specification, the two latest rigs were required to have systems capable of applying 150 tonnes of tension to the drilling riser. Not such a challenge in itself, it could be argued, until it is added that the new systems had to be fitted within the existing rig layout. Claxton’s project manager Will Robinson describes the project as a retro-fit into a newly-built rig.
Robinson says, “We were asked to design and supply a tension system that could be installed on the drive deck beneath the drill floor without any serious structural changes to the rig to withstand the higher loads.”
The system that Claxon devised uses four hydraulic jacks pushing upwards against one of the company’s proprietary slip-activated tension rings. This tension ring, which was of a larger diameter than usual and so required to be redesigned, was chosen over a positive-grip tension ring because of its ability to handle the asymmetrical loads that resulted from having to work within a prescribed jacking layout.
Claxton received the initial enquiry in 2010 and engineers began to think about the design of the system. The firm order came some considerable time later, however, by which time the first system of the two was needed very quickly. Claxton carried out detailed design work and manufactured and delivered the first system, comprising tension cylinders, tension ring, ATEX-approved hydraulic power unit and a pipe centralizer, in just 6 weeks, about half the time normally taken for such an order. The second system was not required within such a tight timescale; still, it was put together and delivered in around 9 weeks.
“The project illustrates perfectly what Claxton is all about,” says Robinson. “The client came to us with an enquiry that required not only a tailored solution, but one that had to be supplied against the sort of timescales more associated with an off-the-shelf order. We are proud of our ability to take these combined technical and schedule challenges in our stride.”