Development of a Physics-based Approach For the Prediction of Strain Capacity of Welded Pipelines

Various industry efforts are underway to develop or improve methods to address design of pipelines for harsh arctic or seismically active regions. The design challenges associated with these regions involve multiple limit states that require characterization of load from large ground deformations, as well as material capacity. The focus of this paper is the development of a physics-based approach to characterize the strain capacity of a welded pipeline for the tensile limit state. Fullscale pressurized pipe tests and three dimensional (3D) finite element analyses (FEA) were conducted to develop the limit states. An experimental program was conducted to measure the strain capacity of full-scale pressurized pipes and provide validation to the physics-based approach. In addition to full-scale tests, round bar tensile and single edge notched tension (SENT) specimens were employed in the experimental program to characterize the weld properties. Multiple measures were taken to account for the influence of natural material variability on the full-scale test results to facilitate validation of the physics based approach. The measures included the use of gas metal arc welding (GMAW) mechanized welding procedure and the production of additional welds to characterize material variability around the circumference of the welded pipes and across multiple welds. Finite element analysis (FEA) based parametric study was conducted to model both fracture and plastic collapse failure mechanisms observed in full-scale tests. The parametric study shows that in addition to fracture toughness and overmatch, misalignment may also significantly affect strain capacity due to transition in failure mode from plastic collapse to ductile tearing. The study illustrates a need to incorporate the observed effect of these parameters in experimental programs designed to characterize strain capacity for development of next generation fracture assessment procedures.