Analysis on the Operation Fatigue of Deepwater Drilling Riser System

Abstract

Fatigue is one of main failure modes of deepwater drilling riser system. Analysis models of wave induced fatigue and vortex induced fatigue of deepwater drilling riser are established according to the riser connection, installation and hang-off operations. Characteristics of wave induced fatigue and vortex induced fatigue of riser system in different operation modes are studied. The influence of each operation fatigue on the combined fatigue is also identified. The results show that wave induced fatigue damage and vortex induced fatigue damage of upper riser are large in installation and hard hang-off modes. The fatigue damage of riser system in soft hang-off mode is less than that in hard hang-off mode. The combined fatigue damage of the upper and lower riser is large. The lower riser is under the influence of wave induced fatigue and vortex induced fatigue, while the upper riser is mainly under the influence of wave induced fatigue, especially that in installation and hang-off modes. The fatigue damages of riser in installation and hang-off modes have a great influence on the combined fatigue of riser and cannot be neglected in riser fatigue analysis.