Qualification of Reactive Flex Joint on a Offshore Drill Rig

The RFJ has been found to respond as expected, reducing well-head moments in line with the maximum predicted from global analysis simulations conducted beforehand and for all conditions experienced, i.e. for wave conditions varying from 1.3 – 6.5 m (Hs) and drill-pipe tension up to 150 T (Weight-on-Hook up to 200 T). It is in particular noted that even for chaotic response motions caused by near-quarter seas and wave spreading; the moment response in all directions is reduced by the RFJ which works equally effectively on all components. The efficiency is similar for drilling conditions tested (17 ½”, 12 ¾” & 8 ½”, without X-tree) and for completion (with X-tree). The recommended value of Efficiency of the RFJ to be used in assessment of its effect on fatigue, when using rain-flow analysis, as a function of Hs and drill-pipe tension, is given. These curves are ∼5 %points conservative (i.e. lower) compared to Efficiency based on standard deviation of response.