The Impact of the Second Order Vessel Motion on the Fatigue Life of Steel Catenary Risers Available to Purchase

Fatigue is a primary factor in assessing the feasibility of a steel catenary riser solution for production and export of offshore hydrocarbons from floating production systems. The first and second order vessel motion due to wave and wind loading is a major source of fatigue. While the first order motion fatigue can be readily estimated through the vessel response amplitude operators, assessing the impact of the second order motion is time and effort consuming especially in generating the vessel motion time traces, more so for coupled analysis. However, inclusion of the second order motion at early stages of the riser feasibility assessment, when the mooring system design is far from final, is essential in predicting the riser fatigue life. In this article, a simplified approach for estimating the impact of the second order motion at an early stage in the design is presented based on the first order motion analysis and the vessel mean static offsets as obtained from frequency domain analysis.