Neersite Consultant Ltd. Ltd.

We have calculated the critical live load on structure for several positions – to achieve realistic loading.

The complex structure of derrick top has been modelled in detail, with several hinges, trusses and springed supports.

This showed several critical points, -which due to the strict dimensional limitations-, had to be examined in depth. We have checked the plastic capacity of the multispan vertical rails, and have found these parts to be satisfactory. Nevertheless some parts had to be reinforced, but in a limited number and region.

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When checking a Lower Guiding Arm, we have looked at the possible loading scenarios, and the results of a possible equipment failure. We have found that the previously used design loads are low, and the environmental loads could cause the LGA fold back (as the cylinders switch off at an overloaded case). This in turn would have resulted in a potential loss a Drill-pipe bottom guideance. The control cabin was nearby, therefore we had to take action, and re-design this equipment.

The telescopic arm of a Lower Guiding Arm had sliding pad connections between the inner and outer box section. Due to serviceablity – the pads were in the middle of the webs, thus creating a large hole on the box and furthermore severe bending moments. We have checked this situation both with hand calculation and FE modeling. As a result – both the main section and the details have been reinforced.

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The full setback conditions (loading) have been significantly increased for general DP/DC Fingerboard lockfingers. Nevertheless the original size and geometry had to be kept as close as possible in the new design.

Checking each part and consulting with equipment designer, resulted in a very different optimized shape. The corners had to be rounded, to avoid large peak stresses in this region. Finally a casted element, was the solution.

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The design of several Gantry Crane was checked: first evaluating the possible loading scenarios and finding the governing situations. The main beam model of the crane was checked in several positions.

Also the main SWL (safe working load) was applied in the most realistic way. The sling arrangement was taken into account.

All details have been checked, and some found to be critical. These have been reinforced and have found a possible solution together with the project designer.

More on Bridge Crane and Gantry Crane design

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The Drillfloor Manipulator Arm is placed on the drillfloor. There is a pedestal between drillfloor and DFMA. A slewing frame/gear is fixed on the pedestal, which is able to move rotate.

Support conditions are allways significant element of analysis, as these can alter final results greatly.

Connection between slewing frame and pedestal in reality

Our first results showed, peak stresses mainly at the slewing frame supports. At these points the connection between slewing frame and pedestal was modelled with a vertical beam (bolt). The pedestal was modelled with a 1250mm*1250mm 750mm long vertical beam which were connected to the bolts by non-structural beams

Connection between slewing frame and pedestal in 1st model

We tried to avoid unnecessary changes of a finished design, therefore we looked at the displacements. We have found that these were not reliable (16mm) hence we have changed support conditions by defining supports at bolt ends.  At bolt-beam top (at slewing plate) we have added horizontal supports to take shear forces, and on bottom we allowed all possible forces due to slewing frame and pedestal connection. Also we used the exact bolt length. To get real displacement at bolt end we definied a spring (acting in bolt axis) modeling the pedestal capability to take vertical force.

Connection between slewing frame and pedestal in 2nd model

Thanks to all these changes, the stresses have been reduced at the critical points, while we have kept the bolt end's displacement within reasonable range. Finally we did not need to ask for any changes of this detail.

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