Residual Stress in Oil and Gas Pipelines with Two Types of Dents during Different Lifecycle Stages

The residual stress at a dented area is critical to oil and gas pipelines’ integrity and safe operation. A three-dimensional (3D) finite element-based model was developed to investigate the residual stresses in two typical dented areas during the lifecycle stages (pipeline construction and pipeline operation stages). Use of this model enables study of the distribution of the maximum residual stress (σRS) in the dented area. The effects of indenter size, pipeline size, internal pressure and dent depth on the residual stress of two types of dented pipelines were analyzed. A nonlinear regression analysis was used to obtain multi-factor formulas for predicting the σRS for different dents during different lifecycle stages. The results show that the σRS distribution in the dented area changes with dent depth. With σRS for a transversal dent being almost always greater than that for a longitudinal dent. During the pipeline construction stage, the influence of indenter size or pipeline size on σRS is almost the same for the two types of dent, whereas, during the pipeline operation stage, the influences are distinct. The tendency for pipeline size to affect σRS differs slightly as the dent depth increases. Multivariate fitting formulas can provide a reference for estimating σRS.