Abstract: In order to ensure safe operation of risers at sea, it is necessary to evaluate safety of those with defects so as to avoid crushing, leakage and fracture accidents. Based on elastic-plastic linear hardening model and Von Mises yield criterion, a three dimensional finite element calculation model of risers with volume defects was constructed considering influence of internal pressure load from stretch bending and geometric defect size. Then, mechanical characteristics of safety working range of these defected risers were analyzed under combined load, and their safety was assessed. The results show that the greater defect depth, the more likely these risers will yield, and along with increase of defect depth, its safety range decreases. Heavier internal pressure load would cause an obvious decrease in safety range which, however, will be slightly impacted by defect depth in case of lighter load. Moreover, when bending load is too heavy, limit axial load in riser safety zone decreases remarkably while limit internal load does not change much.

Key words: riser, volume defect, safe range, finite element, load