Probabilistic flaw assessment of a surface crack in a mooring chain using the first- and second-order reliability method

This study reports the results of a reliability-based flaw assessment for cracks in the mooring chain of a floating type offshore structure. The flaw assessment procedure of BS7910 was combined with the first- and second-order reliability method (FORM, SORM) so that the acceptance of a given flaw can be assessed considering the uncertainties of the parameters that play an important role in the flaw assessment. The failure probability was calculated using FORM and SORM considering the probabilistic nature of the crack size and the long-term distribution of stresses acting on the crack in the mooring chain. To check the validity of FORM and SORM, a Monte Carlo simulation was also carried out to derive the true limit state function and compared with the results of FORM and SORM.