In order to accurately evaluate the ultimate bearing capacity of the coiled tubing(CT)with defects,a theoretical model of the ultimate bearing capacity of CT with defects based on the plastic failure criterion was proposed.Based on the finite element results,the influence of different types of defects on the ultimate bearing capacity of CT was compared,and through the grey correlation method,it was concluded that the depth of defects and the cross-sectional area of defects are the sensitive factors affecting the ultimate bearing capacity of CT.Based on the ultimate bearing theory of complete CT,a nonlin-ear surface fitting method was used to fit the defect correction coefficient,and a theoretical model of the ultimate bearing capacity of CT with defects including the ultimate internal pressure,ultimate external pressure and ultimate tensile load was established.The results show that the error of this model is less than those of classical models,and the maximum error is only 4.56％,which can effectively evaluate the ultimate bearing capacity of CT with defects.The research results can provide ref-erence for the safe operation of CT.
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