Study on Strain Response of X80 Pipelines with a Type I Dent Formed by Blocky Rock

During the operation of pipelines, the mutual squeezing effect between the pipeline and the surrounding blocky rock mass can lead to the formation of Type I dents with a width much greater than their length. These dents may cause a reduction in the diameter of the pipeline, resulting in concentrated stress and strain, which could potentially shorten the lifespan of the pipeline. To reduce the complexity of calculations, this study simplifies the modeling of the blocky rock mass’s squeezing effect on the pipeline into two different dent models to represent the Type I dents. Through comprehensive numerical simulations, this study investigates the effects of hoop stick indenter size (representing blocky rock), diameter-to-thickness ratio, dent depth, and operating internal pressure on the strain distribution of pipelines with Type I dents. The experimental findings indicate that, under the specified conditions, the equivalent plastic strain at the center of a dent with a concave angle is approximately three times greater than that observed at the center of a dent without a concave angle. As the radius of curvature increases from 1,000 to 2,800 mm, the equivalent plastic strain in dents with a concave angle decreases by 18.75%, while the equivalent plastic strain in dents without a concave angle experiences an increase of 138.09%. Additionally, when the loading depth is elevated from 2%D to 12%D, the equivalent plastic strains for dents with and without a concave angle rise by 193.33% and 490%, respectively. As the internal pressure during operation gradually escalates, the equivalent plastic strain for both types of dents exhibits a linear increase, transitioning to a nonlinear increase as it approaches the burst pressure. Moreover, under identical conditions, it is observed that a higher diameter-to-thickness ratio of the pipeline correlates with a lower maximum equivalent plastic strain value, as well as a reduced rate of change in strain with respect to depth.