Research on the Analysis Method of Coiled Tubing Fatigue Life

Coiled tubing (CT) and coiled tubing units (CTU) technology has been widely used in oil and gas field since World War II. Coiled tubing fatigue failure is one of the constraints on promoting used. CT bears complex loads, leading to multiple plastic deformations when operating. Then the fatigue damage cannot be ignored. Through the mechanics analysis of CT with finite element method (FEM) in working state at the wellhead, the results show that high stress and high strain are the main factors which cause CT failure. Based on the analysis, the fatigue life is predicted for CT without defects by using Manson-Coffin formula. The results of CT with different inner pressure show that simulations result is closer to the actual working conditions.