Effective static stress range estimation for deepwater steel lazy-wave riser with vessel slow drift motion

Abstract

ABSTRACTAccording to the structural performance and economic benefits, steel lazy-wave risers (SLWRs) are developed to reduce deepwater riser’s top-end tension and decouple vessel motion from the touchdown zone (TDZ). In riser design, its fatigue life estimation is very essential. In this paper, a simplified solution is put forward to conduct an effective estimation on the static stress range of deepwater steel lazy-wave riser with vessel slow drift motion and ocean current. Considering the boundary-layer effect, SLWR configuration is artificially divided into three segments to investigate. Vessel slow draft motion is imposed on the riser hang-off point to gain its axial stress range on the condition that the riser overall length remains constant. An illustrative example analysis of a SLWR in a water depth of 1248 m is conducted to verify the accuracy and feasibility of the proposed approach by performing a comparison with the results calculated by the commercial package OrcaFlex.