Dynamic Plastic Deformation of Deepwater Steel Catenary Risers under Extreme Cyclic Compressive Loading

摘要

Steel catenary risers (SCR) on a large heave motion vessel are susceptible to compression in the risertouch down zone (TDZ). Dynamic compression can lead to over stress under extreme or abnormal weatherconditions. The response of an SCR under compression is highly nonlinear and sensitive to variousfactors. However, the current available industry design codes and practices do not provide a clear guidanceto address the acceptability of compression, over stress and the resulting plastic strains. In addition, thecurrent analysis method used in industry common practice cannot accurately capture the nonlinearbehavior of SCR involving accumulated plastic deformation, hysteresis effects and local buckling.In this paper, a finite element analysis (FEA) modeling method using combined beam and solidelements is presented that enables simulation of large plastic deformation, pipe ovality and local pipebuckling in the TDZ of a deepwater SCR. The model is developed using ABAQUS. The SCR nonlinearresponse is examined through dynamic analysis of a deepwater SCR hung-off a semi-submersible. Thekey analysis results are compared with a nonlinear beam element model. Moreover, dynamic ratchetinganalysis under multiple plastic strain cycles using the proposed solid riser model is conducted tounderstand the plastic strain accumulation and to check the acceptability of survival response of deepwaterSCR under a series of severe Hurricanes in its service life.This paper presents the methodology of evaluating the compression and plastic deformation that couldbe experienced by deepwater SCRs, including modeling approach, analysis results, possible failuremodes, and conclusions. The impact of the study findings on the robustness and suitability of SCRs fordeepwater application are discussed.