Actual VIV Fatigue Response of Full Scale Drilling Risers: With and Without Suppression Devices

Abstract

In an effort to more effectively understand and manage vortex-induced vibration (VIV) fatigue integrity of its drilling risers, BP has instrumented several of them on a number of mobile offshore drilling units (MODUs) and offshore production platforms worldwide. This paper presents several aspects of the findings from those monitoring campaigns, with particular emphasis on the relatively more densely populated MODU data sets. In-situ monitoring has practical use as a realtime quantifier of accrued VIV fatigue damage to both drilling riser and wellhead casing over the course of a given monitoring period, a fundamental indicator of structural integrity. At present, this can be very useful to operators given that the gap between predicted and measured VIV fatigue damage can be very large. In this paper, the measured data are used to expose some of the physical details of full-scale riser response whose omission from predictive design tools and methods may contribute to this wide gap. To characterize the size of the gap, the data are compared to calculations using the most commonly used industry VIV analysis software. This demonstrates the inherent level of analysis over conservatism with respect to full-scale, unsuppressed drilling risers in the field when typical analysis parameters are utilized. A means of adjusting the parameters to reduce the over conservatism is then implemented. Finally, the data are used to reveal some performance indicators for VIV suppression devices that are presently being utilized in drilling operations.

Reliability Based Factors of Safety for VIV Fatigue Using NDP Riser High Mode VIV Tests

“…A significant effort has been made over the last fifteen years by several prestigious universities worldwide to develop new VIV models or improve existing ones and to benchmark VIV software against experiments, see for example the blind predictions of laboratory measurements of VIV of a tensioned riser ( [1], [2]). Recent field experiments [3] as well as analyses of full scale data ( [4], [5]) have confirmed the complex nature of VIV that was previously observed in laboratory experiments [6] and emphasized the importance of in-line vibrations and super-upper harmonics, in addition to the well-known crossflow vibrations.…”

“…In other words, the FoS, γ, has to be calibrated such that multiplying the predicted damage rate by γ ensures that the associated target level of reliability is reached with respect to the limit state function provided in equation (5). From the reliability analysis, values of γ higher than 1 (γ > 1) are expected to be found.…”

Vortex-induced vibration (VIV) effects of a drilling riser due to vessel motion

“…Figure 3 shows the acceleration spectrum at a particular logger. The responses seen on the spectrum can also be due to sources other than VIV such as drill string rotation or wave-induced motion [13]. VIV occurs in a narrow range of low frequencies.…”

Numerical and Experimental Comparisons of Vortex-Induced Vibrations of Marine Risers in Uniform/Sheared Currents

“…Note that some recent riser experiments at high-mode VIV have observed travelling wave responses with regard to sheared flows [3]. Nevertheless, due to lack of relevant theoretical model and explanation, it is unclear whether the complexity in sheared-flow responses is due to the intrinsic behavior, the superimposition of individual standing-wave eigenmodes or both of them [19]. Therefore, our emphasis is placed on discussing the standing-wave responses due to uniform/sheared currents.…”