Estimation of tensile strain capacity for thin-walled API X70 pipeline with corrosion defects using the fracture strain criteria

Various tensile strain capacity (TSC) prediction equations have recently been presented by many research organizations such as Pipeline Research Council International and ExxonMobil Corporation. The gas industry uses these equations to determine the allowable strain for the cracked pipe. However, these TSC prediction equations cannot be applied to pipes with other defects such as corrosion or mechanical damage. Corrosion defects are the most common type of defect in actual operating conditions, and thus, they are an essential element for evaluating pipe structural integrity as they are most frequently connected to accidents. Therefore, it is necessary to develop a TSC prediction equation for corroded pipes. In this paper, to propose a new TSC prediction equation for corroded pipes, we conducted parametric finite element (FE) analyses using fracture strain criteria. To determine the appropriate fracture strain criteria, we reviewed several methods to construct the fracture locus. Then, we conducted parametric FE analyses using this fracture locus by considering variables affecting structural integrity, such as corrosion depth, corrosion length, wrap angle, and pressure ratio. Lastly, we presented the TSC prediction equation using these analyses.