Residual ultimate strength of damaged seamless metallic pipelines with combined dent and metal loss

The combination damage induced by mechanical interference, in reality, is more likely to happen. In this paper, numerical models on pipes with combined dent and metal loss in terms of a notch are developed and validated through tests (diameter-to-thickness ratio D/ t of test pipes around 21), capable of predicting the residual ultimate strength of pipes in terms of bending moment (M-cr) and critical curvature (K-cr). The effect of residual stress is explored, assuming a linear distribution in the pipe hoop direction. Investigations of damaged pipes with different D/t (15-50) are carried out. Through changing damage parameters in the combinations, i.e. dent depth (d(d)) or metal loss depth (d(m)), the corresponding effects of damage are clarified. Results show that the combined dent and notch damage is a more severe type of damage on pipe strength compared with other damage types (excluding fracture). The dent in combined damage plays a more dominant role on the pipe residual strength. Empirical formulas are proposed to predict residual ultimate strength of damaged metallic pipes (D/t around 21) with combined dent and metal loss under bending moment, which can be used for practical purposes. The application domain can be expanded to pipes with D/t up to 30 based on simulations.