Full-scale Burst Test and Finite Element Simulation of 32 Inch Oil Pipe with Girth Weld Defects

Recently several leak accidents occurred due to girth weld defects in long distance transmission pipelines of PetroChina. To avoid possible failure accidents, in-line inspections were performed on some certain pipelines. In some new built pipelines, a large quantity of girth weld defects were detected in the inspections. Many fitness-for-service (FFS) assessment methods have been proposed for various kinds of metal loss in pipeline, however, it is still difficult to obtain a confident assessment of girth weld defects. Several types of girth weld defects were manufactured on 32 inch oil pipe in this study and full-scale burst tests were performed combined with 3D finite element simulation to study the influence of girth-weld defect geometry on the failure pressure. These defects were manufactured with different opening width and orientation. After full-scale burst tests, the real morphology of the girth weld defects were examined by fracture analysis. The defect data and experimental results were obtained and used to FFS assessment, where FFS methods included API 579, BS 7910, Miller, Kastner etc. Error analysis results were illustrated by comparing the experimental data and the assessment results, and suggested that fracture failure should be considered for girth-weld defects assessment in a conservative view at last.