Research on damage assessment of buried pipelines with circular dent defects subjected to blast loading

In order to evaluate the damage characteristics of buried natural gas pipelines with circular dent defects subjected to blast loading, based on pressure–impulse damage theory, explosion experiment and numerical simulations were implemented to evaluate the damage of a natural gas with circular dent defects buried in soil under blast loading in this research. The ALE method was used to develop a coupled pipeline-soil simulation model using LS-DYNA software, and the validity of the established model was verified correctly compared with experimental results and empirical theory equations calculations. Furthermore, according to regulations in the Assessment and Management of Pipeline Dents (American Petroleum Institute Recommended Practice 1183), the effect with different circular dent defect diameter on the mechanical properties of natural gas was also investigated and analysed. The results showed that, under the blast loading, plastic deformation happened on the surfaces of the pipeline facing the explosive, and the high-stress zone appeared in the circumferential direction with 32.27°. The range of the high-stress zone firstly expanded along the axial direction of the pipelines and then along the circumferential direction. The larger diameter of the circular dent defects had, which resulted in a failure at the defects under the condition of the depth of the defects keeping constant. The effect of the size of defect diameter on the amount of pipeline deformation was further investigated, and the mathematical formula described the maximum plastic deformation with different defect diameter was established. Meanwhile, a finite element model of pipeline with a diameter of 457 mm was established for numerical analysis, which implied that the larger diameter of pipeline with the same defect had, the lower risk of pipeline in failure subjected to blast loading had. And through mathematical analysis and considering the feasibility of the actual situation, the curve described the maximum plastic deformation of the natural gas pipeline with three different defects varying in diameter were established respectively. In addition, a formula to express the relationship between pipeline defect diameter and maximum plastic deformation was established, which can effectively predict the critical plastic dent deformation of pipelines with different defect diameter subjected to blast loading. Besides, based on the pressure-pulse damage theory and with the damage assessment criterion of dent depth–dent length ratio of 0.072, the pressure–impulse diagrams of buried natural gas pipelines with defect diameters of 30 mm, 40 mm and 50 mm were defined, which can be used to predict the damage of pipelines with different defect diameters. Moreover, with the pressure–impulse damage evaluation curves, mathematical formula for the buried natural gas pipeline with the circular defects were established. Furthermore, the critical circular defect diameters with 30 mm was confirmed and the unique formula was also established, which could be effectively used to evaluate the safety of buried natural gas pipelines with the critical circular defects.