Handling The Tension

Claxton's new tilting tensioning system pushes the boundaries of what can be done to help drillers in the North Sea.

Although from a production perspective the North Sea’s best days may now be in the past, the province still generates great examples of offshore engineering innovation, as this drilling riser project for BG Group plc illustrates.

About two years ago, BG Group plc approached Claxton to provide a conductor tensioning system to meet some unusually demanding requirements. The company wanted to drill in water depths of 78 m in the Jackdaw field using the Rowan Gorilla VI jackup drilling rig – nothing too out of the ordinary so far. However, as Chris Kyson, project engineering team leader, explains: “A combination of the way the rig was configured, the environmental conditions in the area and the fact that BG Group wanted the system to be capable of withstanding the sort of seas normally associated with a 50-year storm resulted in the need for a conductor tensioning system that could generate up to 400 t of load.”

A more common rating for conductor tensioning systems in the North Sea is 300 t, which can easily be achieved using Claxton’s positive-grip tension-ring systems. Presented with this challenge, Claxton went back to the drawing board and came up with a new tensioning system: one that would not only provide the required tensile loads but also tilt to reduce the bending stresses and wave-shock loading affecting the conductor.

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