Test-based fracture criteria for pipeline steels

作为加拿大关键基础设施的钢管经常暴露在各种地质和环境条件下，导致管壁出现裂缝、凹痕和凿痕等缺陷，这些缺陷可能导致管道断裂，影响管道的整体功能，并导致重大经济损失、环境问题甚至死亡。有几种方法来预测断裂能力，包括实验测试，分析方法和先进的数值方法。由于大应变的集中，在计算机程序中实现的固定断裂应变准则的应用可能不能适当地预测裂纹扩展路径。此外，断裂准则，忽略裂纹尖端的约束，并取决于用于获得断裂指数的试样的类型可能会导致不一致的预测。有必要开发和实施更有效和准确的断裂标准，具体到管道钢作为裂纹尖端约束的函数，独立于所使用的试样的类型和预裂纹的大小。本研究计画旨在发展一套可校正的数值断裂准则，以预测钢管内的裂纹扩展。本项目中制定的标准将考虑裂纹尖端特定于各种载荷条件的约束，并将适用于用于制造管道的各种钢级，为加拿大管道行业提供评估和设计管道的增强方法。

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.