Parametric analysis of steel catenary risers : Fatigue behavior near the touchdown point

Steel catenary risers are an attractive solution from an economical viewpoint. However they are not always feasible and their feasibility must be verified case by case, considering both extreme and long-term loads. One of the critical portions of the riser is the region near the touchdown point. There the maximum change in curvature occurs and so that region is more likely to present a fatigue failure. The pre-tension applied to the riser top during the installation governs its mechanical behavior. The designer can choose its value to guarantee the expected production life for the riser. However, several cases must be studied in a very time-consuming process. This paper presents a parametric analysis focusing the fatigue behavior of the riser near the touchdown point concerning the first and second order motions of the riser top. That analysis uses simplified models, linear approximations, asymptotic formulas and frequency domain solutions. The approach considered can be used in a pre-design phase to assess the fatigue life and compare alternative solutions.