Fatigue Analysis of Flexible Riser - Effect of Mean Stress Correction Procedures

Abstract

As the critical part of the oil product system, flexible riser?s fatigue life during the normal operating service is more and more significant. Finding the most dangerous point in the flexible riser and using the accurate enough method to do the fatigue analysis are both critical for the safety of the whole riser system. In order to find the critical point?s position and lifetime, we execute the dynamic analysis and fatigue analysis on the flexible riser, utilizing the finite element analysis software RIFLEX and BFLEX2010, developed by MARINTEK, in this master thesis.Chapter 1 shows the literature study on the riser?s structure and method?s background introduction including the static analysis, dynamic analysis, fatigue analysis, effect of the mean stress and bending curvature. Chapter 2 introduce the mainly structure of the software RFLEX and BFLEX2010. It tells the function and responsibility in this thesis. Chapter 3 has defined the case situation and method to do the whole analytical process. Chapter 4 shows the curvature time series result of the static and dynamic analysis with the RFLEX. The result of rain flow counting process and the fatigue analysis with the BFLEX2010 has been got in Chapter 5. The fatigue damage is given with the formulation as Miner Sum. Chapter 7 has showing the conclusion for the whole thesis. It tells the different methods to do the fatigue analysis with both linear and nonlinear material by comparing the fatigue damage or lifetime. The thesis focuses on the process to finding the dangerous point in the special layer of the flexible riser and the different mean stress correction procedures? influence on calculating the fatigue damage for this dangerous point.