Trelleborg and Diamond Offshore develop enhanced design for riser operations
Trelleborg and Diamond Offshore, Inc. have met a major milestone as part of a joint development agreement by creating a design with enhanced performance for drilling riser operations in high current conditions.
Test results revealed that with the patented helically grooved buoyancy design vortex induced vibration (VIV) is effectively eliminated in high currents, while also reducing drag loading to a level comparable with fairings, when using the patented design.
In June 2017, tow tank testing on the design was performed at the SINTEF Ocean and Norwegian University of Science and Technology (NTNU) joint facility in Trondheim, Norway, allowing testing of the new buoyancy design in the supercritical flow regime representative of offshore current conditions.
“Based on the extensive modelling performed by both Diamond Offshore and ourselves, we were very confident that the design would be fully validated by testing,” Trelleborg Offshore Operation Business Group Director Antony Croston said.
“In reality, the results exceeded even our own expectations.
“For many years, fairings have been accepted as the best technical solution for drag and VIV reduction on drilling risers.
“Their use has come with an operational penalty in the form of increased running and retrieval time, as well as handling issues, especially in harsh weather.
“We now have an integral concept, which has been proven to match the performance of fairings, without any issues in drilling riser handling and running methodologies.”
The extensive test program provided valuable hydrodynamic data confirming the design’s drag reduction and VIV suppression performance.
Fixed and dynamic drag coefficients of the new design were recorded during separate fixed and free vibration tow testing.
Drag coefficients at an average of 0.65 were observed for relevant flow regimes, which is comparable to the performance of riser fairings.
This is achieved through the highly successful VIV suppression of the design, effectively eliminating VIV response and subsequent drag amplification in the high excitation response range of offshore drilling risers.
Forced motion testing of the helically grooved design was also performed to better understand excitation of the riser under high current conditions and for the development of lift coefficient data for use in analytical fatigue damage prediction programs.
The helical drag reduction and VIV suppression performance shows strong independence of current speed, which is consistent with the behaviour of an external helical strake; however, the underlying flow physics causing the suppression are quite different, leading to the suitability of the helically grooved design for large diameter drill riser buoyancy.
Trelleborg has manufactured and delivered two complete strings to Diamond Offshore that have been recently deployed in the Gulf of Mexico.
For more information visit the Trelleborg website.
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