Effects of Girth Weld on the Local Buckling Response of Conventional Grade Pipelines

Pipeline structural integrity is a critical component of pipeline design in extreme environmental conditions. Severe loads may be an issue in pipeline design if differential ground movement is prevalent in the design region, e.g. ground faulting and permafrost heave and settlement. Iceberg or ice keel interaction and large seabed deformations interacting may also be a critical design integrity issue for offshore pipelines in ice environments. Numerical finite element modelling procedures have been developed to assess the bending moment and strain capacity of several pipelines over various typical pipeline parameters. This study looks at the effects of girth-weld imperfection on the bending response of welded pipelines. Limited guidance is provided by pipeline design standards, for example DNV OS-F101 and CSA Z662, as to how to account for girth weld effects on the local buckling response. This paper investigates girth weld effects across a range of practical design parameters. Calibration of the numerical analysis was performed using available data, from full-scale tests and finite element analysis, for girth welded pipes in order to obtain confidence in the numerical procedure. The significance of girth weld effects was to reduce the peak bending moment capacity by 10% whereas strain capacity was reduced by as much as 35% based on the degree of girth weld imperfection. Girth weld effects have been acknowledged in industry, however, further research and physical testing is required to fully understand the problem, as shown in this paper.