Fatigue life analysis of internal circumferential crack of tubular structures

In this paper, the fatigue life of cracked tubular structures subjected to remote cyclic tensile stress is studied by using the fracture mechanics and Paris’ law. To evaluate the flooded member detection, a reassessed leak-before-break approach is implemented, in which a more realistic crack development, by taking the partly through thickness crack stage into consideration, has been investigated, and that has never been reported in literature for tubular member with internal crack. Parametric study demonstrates that the time available to detect the presence of the crack in its flooded life depends particularly on the rate of accumulation of fatigue damage and on the initial length of surface crack presented. The results of the analysis have been applied by a case study of a particular offshore structure and loading situation, obtained to support inspection intervals of three years for flooded member detection. By comparing the current results with the conventional leak-before-break procedure in flooded member detection, it is found that for the situation studied in this paper, the flooded life predicted from conventional leak-before-break method for the crack is always on the safe side. Therefore, it is too conservative for setting up the inspection interval for flooded member detection.