Conventional models have been proven to be successful in predicting the mechanical fatigue life of coiled tubing (CT) without defects. However, defects of various types, including mechanical, manufacturing or corrosion defects, on CT are commonplace in the real world. The impact of such defects on CT fatigue life has been widely recognized. Today's common practice heavily relies on prove-up and manual measurement of defect dimensions, to assess the defect severity on tubing integrity issues, such as fatigue life. Such practice tends to be inefficient, user-dependent, and inconsistent in fatigue and severity assessment; sometimes it's even not feasible in the case of internal defects.

A novel defect severity analysis based on magnetic flux leakage (MFL) was used to quantitatively assess the CT fatigue life reduction due to mechanical defects. This new quantitative approach allows consistent, automated in-line fatigue analysis during operation, as it does not depend on a user's manual measurement of defect dimensions. The new model results compared well with experimental data. The analysis method was successfully used in fatigue assessment of realistic field defects.