Environmental loads are the main source of dynamic excitation of offshore structures. Due to the random nature of these loads, one should consider statistical properties when designing such structures. Recent codes for the design of steel risers address the use of environmental contours or full long-term analysis to take into account the statistics of load effects. Moreover, sea states for fatigue design should also be carefully selected so as to include the region of the scatter diagram which most contributes to the total damage. This paper looks into fatigue and ultimate limit states of steel risers. The first part shows a comparative study of three design criteria for extreme statistical analysis. These criteria are based on design storm, environmental contour, and full long-term statistics. A joint probability distribution found in the literature for a Brazilian location was used to describe the correlation between the significant wave height and the zero crossing wave period. The second part deals with the analysis of the coefficient of contribution for fatigue and long-term extreme statistics. Several full time domain analyses were performed and the most important sea state region for each limit state is shown in two examples of steel catenary risers. A discussion about sea state selection is then presented.

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