Contribution of finite element analyses to crack-like flaw assessments in a gas pipeline

When defects reach a critical size, failure occurs in engineering components. The criticality assessment of defects is hence a key aspect of the structural integrity of gas pipelines in service. Fitness-For-Service (FFS) assessments are generally employed for evaluating the criticality of a crack-like flaw in structures using simplified assumptions in relation to geometry and material proper-ties. Whilst the errors resulting from these modelling simplifications prove acceptable in many cases, there are situations where it will be necessary to take into account the nonlinearities in geometry and/or material behaviour. This can be either to avoid excess conservatism or, on the contrary, to ensure the results are safe. In such cases it becomes essential to develop a finite element model of the structure to account for such real-engineering complexity. Welding, the most prevalent technique to join pipe, often brings about a misalignment between two pipes and hence complex crack shape is formed. The aim of this study is to develop an elasto-plastic finite element model of a gas pipeline possessing a crack in a misaligned weld. The remaining life of the pipeline is deter-mined using a Failure Assessment Diagram (FAD) and the Paris law. The results obtained from the finite element method to determine the stress intensity factors are compared to results derived using the API-579 for stress intensity factors calculations.