Comparison of analytical models with a numerical model estimating the stress concentration factor in dented steel pipes

Oil and gas transmission pipelines during their design, placement and service may experience local plastic deformation due to mechanical impacts, some of which may be in the shape of dent. This paper provides four analytical assessment models of the stress concentration factor for dented steel pipes under cyclic internal pressure. The predictions derived from these simulations will be contrasted with the outcomes of our analysis, which is based on a finite element model simulating a pipe within the linear elastic range. The numerical model is used for two separate and complimentary simulations. The first consists of generating the dent and the second one uses the deformed pipe as the initial geometry to calculate the stress around the defect. This will allow us to assess the stress concentration factor for three distinct dent shapes (longitudinal, transverse and spherical). The results obtained from the numerical model will allow us to conclude about the most accurate analytical model among those studied. These results have shown that the API 579 and EPRG 1995 algorithms provide good approximations of the stress concentration factor in the case of a dented pipe under cyclic internal pressure.