Abstract: To improve the accuracy of the method to assess pipeline dents, permission strain needs more adequate theoretical basis to formulate. Based on the ductile fracture model and damage mechanics, a damage assessment model was built for pipeline dents. With the help of the finite element method, the damage degrees of two typical dents (smooth dents and kinked dents) in different regions were studied. Critical failure strains are calculated for different pipe specifications and also under different internal pressures. Numerical simulation study shows that for different dent types, damage degrees are varying from regions to regions, and cracks are generated not always in the same way, that for different pipe specifications, critical failure strains are almost the same, that due to the effect of springback, critical failure strains vary under different internal pressures,that a fitting relationship of critical failure strains under different pressures is obtained, and that when assessing the dent by using the strain method, the type of the dent should be determined before selecting the corresponding strain standards.

Key words: pipeline dent, damage degree, critical failure strain, dent springback, strain assessment