On the Wave and VIV Fatigue of Steel Catenary Risers Connected to Floating Structures

Abstract

The Steel Catenary Riser (SCR) concept has been considered as a vital option for most new deepwater field developments around the world. The use of an SCR, as a pipe connecting the export pipeline system and/or remote wells and infield flowline to a floating structure, has given more flexibility and potential to the oil exploration and transportation in water depths where other riser concepts would not tolerate the hydrostatic loads or would have become very costly. Major design concerns of the SCR pipes connected to a floating structure are the dynamic motion and the fatigue damage. The SCRs are very sensitive to the platform or vessel motion characteristics to which they would be attached as well to the environmental loads. The two main sources of fatigue are the random wave sea states and the associated platform motion and vortex induced vibration (VIV) due to current. The wave sea states are represented by wave spectra while the platform motions are applied as first order Response Amplitude Operators (RAOs) and second order slow drift motions. This paper gives a brief introduction about the development of the fatigue analysis methods that have been used to date. Results of parametric studies investigating several effects on the fatigue damage of the SCRs are presented. Some of these effects include flexible joint rotational stiffness, VIV analysis parameters, slow drift motion effects. The results will be for different size risers and fluid contents.