Influence of Cracks and Residual Stresses on the Limit Load of Thick-walled Cylinders

Development of “digital twins” to facilitate the design, operation, monitoring and overall, integrity assessment of structures is becoming hugely popular due to its promising benefit and in particular, huge cost savings. This study is aimed to address a particular aspect of structural integrity assessment in this context, i.e. the limit state or the collapse conditions. Accurate quantification of failure resistance of defect contained structures under loading histories allows reliable life-time predictions. Analytical approaches to integrity assessment procedures are accompanied by extensive numerical simulation-based studies. A simplified yet reliable approach to limit load estimations in damaged thick-walled pressurized cylindrical vessels is presented. Defects and residual stresses affect the limit load estimates in pressure vessels. Available design curves provide upper limit curves of global collapse. Defects and residual stresses reduce design curves from global to local collapse limits that require extensive detailed analyses covering a wide range of potential defects and residual stress fields to be accounted for. This study presents finite element-based exploration of limit loads in thick-walled cylinders containing defects and residual stresses. ABAQUS standard was used to conduct the analyses and obtain estimates of the limit state loads. A catalogue of crack configurations covering a range of axial and hoop cracks, shallow and deep, partial and extended, were considered and examined. Furthermore, a range of combined loading schemes and loading sequence scenarios for open-end and closed-end cylinders were simulated both with and without the presence of residual stresses that were induced as initial conditions. The results suggested that adjustments were necessary to reflect the role of material response, crack configuration and boundary conditions on the limit loads of defected thick-walled vessels. The findings, presented as normalized design curves, allow informed design decisions in dealing with the structural integrity of pipelines containing extended or part-through cracks and locked-in process-induced residual stress fields.