Friction, Contact Pressure, and Nonlinear Behavior of Steel Tubes in Subsea Umbilicals

This paper focuses on evaluating the impact of friction and contact pressure on helical steel tubes. The initial gaps between steel tubes and adjacent layers, friction coefficients and the contact stiffness are the main factors that affect such investigation. A novel methodology by using UFLEX2D (a MARINTEK product) has been applied for modeling complex umbilical cross sections and for the study of these parameters. Two cross sections for the same subsea application but with different designs have been investigated in the study. It has been shown how fatigue damage can be significantly impacted by different cross-sectional design. For this study, nonlinear moment/curvature relationship has been included in the analyses. Based on the findings of this study, more realistic results can be achieved by including the nonlinear behavior in global analysis for fatigue damage calculations instead of using nominal bending stiffness supplied by umbilical manufacturer.