Research on Application of Fatigue Life Prediction Model to Pipe-end Upset Taper Section

Studied in the article are the effects by the internal upset taper section length M_iu and the arc radius R of the Φ127 mm drill pipe on the SCF and fatigue life with the FEA and the fatigue life model. The analysis shows that the longer internal-taper length and the larger radius are, the smaller SCF and the higher fatigue life will be, nevertheless the fatigue life is still lower than that of the pipe body. When the radius R≥300 mm, and the influence of the length of the internal-taper on the SCF is reduced. When the radius R≥300 mm, and the internal-taper length M_iu ≥200 mm, the influence of the M_iu and the R as combined to each other on the SCF and the fatigue life gets gradually decreased, and the change amplitude is small. In case of predicting the fatigue life of the drill pipe internal taper section combination, both the Morrow and the Paris prediction models have obvious advantages.