Parametric interpolation method for probabilistic fatigue analysis of steel risers

•The traditional fatigue analysis of marine structures is very computer demanding (processing and data storage).•The Parametric Interpolation Method is proposed to efficiently perform the probabilistic fatigue assessment of steel risers.•The accuracy and computational cost of the Parametric Interpolation Method are compared with the direct integration method.•The methodology is applied to a SCR connected to a FPSO in a water depth of 2100 m and the results are very encouraging. Slender marine structures such as mooring lines and risers are susceptible to failures due to stress variations coming from environmental actions. Wave, wind and current are random phenomena, and consequently the most adequate methodology to estimate the fatigue damage accumulation on these structures is the probabilistic fatigue analysis. In practice, the estimation of fatigue life requires the numerical simulation of a huge number of loading cases to compute the multi-dimensional integral of the total fatigue damage. This paper presents an efficient approach to compute the long-term fatigue damage of marine structures. The proposed method needs only a few number of numerical simulations to estimate the structure fatigue life. It uses a parametric interpolation procedure to evaluate the fatigue damage for any individual short-term condition (sea state) required in the calculation of the multi-dimensional integral. In this way, the total number of short-term structural analyzes is considerably reduced. The effectiveness and accuracy of the proposed method is compared to the full direct integration by means of two comprehensive examples. The first studied case is an idealized theoretical model of a single-degree-of-freedom (SDOF) system under wave loading, and the second one is a Steel Catenary Riser (SCR) connected to a FPSO (Floating, Production, Storage and Offloading floating unit).