Test-based fracture criteria for pipeline steels

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Steel pipelines, as key Canadian infrastructure, are often exposed to various geological and environmental conditions that cause defects such as cracks, dents, and gouges in the pipe wall, which can lead to pipe fracture in pipelines, compromising the entire functionality of pipelines and resulting in significant economic losses, environmental issues or even fatalities. There are several methods to predict the fracture capacity, including experimental testing, analytical approaches, and advanced numerical methods. The application of the fixed fracture strain criterion implemented in the computer programs may not appropriately predict the crack propagation path because of the concentration of large strains. Furthermore, fracture criteria that ignore the crack tip constraints and depend on the type of test specimens used to obtain fracture indices may lead to inconsistent predictions. There is a need to develop and implement more efficient and accurate fracture criteria specific to pipe steel as a function of crack tip constraints, independent of the type of specimens used and the size of pre-cracking. This research project aims at developing calibrated numerical-based fracture criteria for predicting the crack propagation in steel pipelines. The criteria developed in this project will take into consideration the constraints at the crack-tip specific to various loading conditions and will be applicable to various steel grades used to manufacture pipes, providing the pipeline industry in Canada with an enhanced method to assess and design pipelines.