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Offshore wind substations are subjected to uncertain loads from waves, wind and currents. Sea states are composed of irregular waves which statistics are usually characterized. Irregular loads may induce fatigue failure of some structural components of the structures. By combining fatigue damage computed through numerical simulations for each sea state endured by the structure, it is possible to assess fatigue failure of the structure over the whole deployment duration. Yet, the influence of the discretization error on the fatigue damage is rarely adressed. It is possible to estimate the discretization error on the quantity of interest computed at the structural detail suspected to fail. However, the relation between this local quantity of interest and the fatigue damage is complex. In this paper, a method that allows propagating error bounds towards fatigue damage is proposed. While increasing computational burden, computing discretization error bounds is an useful output of finite element analysis. It can be utilized to either validate mesh choice or guide remeshing in case where potential error on the fatigue damage is too large. This method is applied to an offshore wind substation developped by Chantiers de l'Atlantique using two discretization error estimators in a single sea state.